{"id":4690,"date":"2019-06-24T14:22:08","date_gmt":"2019-06-24T14:22:08","guid":{"rendered":"https:\/\/pressbooks.ccconline.org\/acchumanbio\/chapter\/9-2-3\/"},"modified":"2023-11-30T18:48:11","modified_gmt":"2023-11-30T18:48:11","slug":"9-2-3","status":"publish","type":"chapter","link":"https:\/\/pressbooks.ccconline.org\/acchumanbio\/chapter\/9-2-3\/","title":{"raw":"7.2 Organization of the Body","rendered":"7.2 Organization of the Body"},"content":{"raw":"&nbsp;\r\n\r\n[h5p id=\"530\"]\r\n\r\n<em>Figure 7.2.1 Complex machines.<\/em>\r\n<h1>A Fantastic Machine<\/h1>\r\nThese robots were created for research or to do complex tasks, but they look like they might be fun to play with too! They are all complex machines. Think about some other, more familiar machines, such as power drills, washing machines, and lawn mowers. Each machine consists of many parts, and each part does a specific job, yet all the parts work together to perform certain functions. Many people have compared the human body to a machine, albeit an extremely complex one. Like real machines, the human body also consists of many parts that work together to perform certain functions. In this case, these parts and functions keep the organism alive. The human body may be the most fantastic machine on Earth, as you will discover when you learn more about it in this concept.\r\n<div>\r\n<h1>What the Human Machine Can Do<\/h1>\r\n<\/div>\r\nImagine a machine that has all of the following attributes:\r\n<ul>\r\n \t<li>It can generate a \u201cwind\u201d of 166 km\/hr (100 mi\/hr).<\/li>\r\n \t<li>It can relay messages faster than 400 km\/hr (249 mi\/hr).<\/li>\r\n \t<li>It contains a pump that moves about a million barrels of fluid over its lifetime.<\/li>\r\n \t<li>It has a control center that contains billions of individual components.<\/li>\r\n \t<li>It can\u00a0repair itself, if necessary.<\/li>\r\n \t<li>It may\u00a0not wear out for up to a century or more.<\/li>\r\n<\/ul>\r\nThis machine\u00a0has all of these abilities, and yet it consists mainly of\u00a0water. What is it? It is the human body.\r\n<div>\r\n<h1>Organization of the Human Body<\/h1>\r\n<\/div>\r\nThe human body is a complicated, highly organized structure that consists of trillions of parts that function together to achieve all the functions needed to maintain life. The biology of the human body incorporates:\r\n<ul>\r\n \t<li>The body\u2019s structure, the study of which is called <strong>anatomy<\/strong>.<\/li>\r\n \t<li>The body\u2019s functioning, the study of which is called <strong>physiology<\/strong>.<\/li>\r\n<\/ul>\r\nThe organization of the human body can be seen as a hierarchy of increasing size and complexity, starting at the level of\u00a0atoms and molecules, and ending at the level of the entire\u00a0<strong>organism,<\/strong> which is an individual living thing. You can see the intervening levels of organization in Figure 7.2.2. Read about the levels in the sections that follow.\r\n\r\n&nbsp;\r\n\r\n[caption id=\"attachment_2798\" align=\"aligncenter\" width=\"915\"]<img class=\" wp-image-2798\" src=\"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-content\/uploads\/sites\/152\/2019\/06\/101_Levels_of_Org_in_Body-2.jpg\" alt=\"\" width=\"915\" height=\"1081\" \/> <em>Figure 7.2.2 This diagram shows the levels of organization of the human body, from atoms to the whole organism.<\/em>[\/caption]\r\n<h2>Cells<\/h2>\r\nThe basic units of structure and function of the human body \u2014 as in all living things \u2014 are [pb_glossary id=\"5665\"]cells[\/pb_glossary]. By the time the average person reaches adulthood, their body has an amazing 37 trillion of them! Each cell carries out basic life processes that allow the body to survive. In addition, most human cells are specialized in structure and function to carry out other specific roles. In fact, the human body may consist of as many as 200 different types of cells, each of which has a special job to do. Just a few of these different human cell types are pictured in Figure 7.2.3. These cells have obvious differences in structure that reflect their different functions. For example, nerve cells have long projections sticking out from the body of the cell. These projections help them carry electrical messages to other cells.\r\n\r\n[caption id=\"attachment_2800\" align=\"alignnone\" width=\"1043\"]<img class=\"wp-image-2800 size-full\" src=\"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-content\/uploads\/sites\/152\/2023\/10\/Feature_Stem_Cell_new-e1589225900314-2.png\" alt=\"\" width=\"1043\" height=\"224\" \/> <em>Figure 7.2.3 A few of the many different types of cells in the human body are illustrated here. Each type of cell is specialized for a particular role in the body.<\/em>[\/caption]\r\n<h2>Tissues<\/h2>\r\nThe next level of organization in the human body is tissues. A\u00a0<strong>[pb_glossary id=\"2801\"]tissue[\/pb_glossary]<\/strong> is a group of connected cells that have a similar function. There are four basic types of human tissues: epithelial, muscle, nervous, and connective tissues. These four tissue types (shown in Figure 7.2.4) make up all the organs of the human body.\r\n\r\n[caption id=\"attachment_2802\" align=\"aligncenter\" width=\"500\"]<img class=\"size-full wp-image-2802\" src=\"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-content\/uploads\/sites\/152\/2023\/10\/Four-types-of-tissues-2.png\" alt=\"\" width=\"500\" height=\"412\" \/> <em>Figure 7.2.4 The human body contains these four types of tissues.<\/em>[\/caption]\r\n\r\n<div>\r\n\r\n<span style=\"font-size: 1.424em; font-weight: bold;\">Organs and Organ Systems<\/span>\r\n\r\n<\/div>\r\nOrgans are the next level of organization of the human body. An\u00a0<strong>[pb_glossary id=\"2803\"]organ[\/pb_glossary]<\/strong> is a structure that consists of two or more types of tissues that work together to do the same job. Examples of human organs include the heart, brain, lungs, skin, and kidneys. Human organs are organized into organ systems, which are shown in Figure 7.2.5. An <strong>[pb_glossary id=\"2804\"]organ system[\/pb_glossary]<\/strong>\u00a0is a group of organs that work together to carry out a complex overall function. Each organ of the system does part of the larger job.\r\n\r\n[h5p id=\"531\"]\r\n\r\n<em>Figure 7.2.5 The Human Organ Systems. Some of the system names shown in this illustration differ from the terminology used in this book, but the systems are the same.<\/em>\r\n\r\n&nbsp;\r\n<div>\r\n\r\n<span style=\"font-size: 1.602em; font-weight: bold;\">A Well-Oiled Machine<\/span>\r\n\r\n<\/div>\r\nAll of the organs and organ systems of the human body normally work together like a well-oiled machine, because they are closely regulated by the nervous and endocrine systems. The\u00a0nervous system\u00a0controls virtually all body activities, and the\u00a0endocrine system\u00a0secretes hormones that help to regulate these activities. Functioning together, the organ systems supply\u00a0body cells\u00a0with all the substances they need and eliminate their wastes. They also keep\u00a0temperature,\u00a0pH, and other conditions at just the right levels to support life.\r\n<div class=\"textbox textbox--key-takeaways\"><header class=\"textbox__header\">\r\n<h1 class=\"textbox__title\"><span style=\"color: #ffffff;\">7.2 Summary<\/span><\/h1>\r\n<\/header>\r\n<div class=\"textbox__content\">\r\n<ul>\r\n \t<li>The human body is like an extremely complex machine. It consists of multiple parts that function together to maintain life. The biology of the human body incorporates the body\u2019s structure (or anatomy) and the body\u2019s functioning (or physiology).<\/li>\r\n \t<li>The organization of the human body is a hierarchy of increasing size and complexity, starting at the level of\u00a0[pb_glossary id=\"5711\"]atoms[\/pb_glossary]\u00a0and [pb_glossary id=\"5779\"]molecules[\/pb_glossary], and ending at the level of the entire organism.<\/li>\r\n \t<li>[pb_glossary id=\"5665\"]Cells[\/pb_glossary]\u00a0are the level of organization above\u00a0atoms and molecules, and they are the basic units of structure and function of the human body. Each cell carries out basic life functions, as well as other specific roles. Variations in cell function are generally reflected in variations in\u00a0cell structure.<\/li>\r\n \t<li>The next level of organization above cells is the [pb_glossary id=\"2801\"]tissue[\/pb_glossary]. A tissue is a group of connected cells that have a similar function. There are four basic types of human tissues: epithelial, muscle, nervous, and connective tissues. These four types of tissues make up all the organs of the human body.<\/li>\r\n \t<li>The next level of organization above tissues is the [pb_glossary id=\"2803\"]organ[\/pb_glossary]. An organ is a structure that consists of two or more types of tissues that work together to do the same job. Examples include the brain and\u00a0heart.<\/li>\r\n \t<li>Human organs\u00a0are organized into organ systems. An [pb_glossary id=\"2804\"]organ system[\/pb_glossary] is a group of organs that work together to carry out a complex overall function. For example, the\u00a0skeletal system\u00a0provides structure to the body and protects internal organs.<\/li>\r\n \t<li>All of the organs and organ systems of the body normally work together like a well-oiled machine, because they are closely regulated by the nervous and endocrine systems.<\/li>\r\n<\/ul>\r\n<\/div>\r\n<\/div>\r\n<div class=\"textbox textbox--exercises\"><header class=\"textbox__header\">\r\n<h1 class=\"textbox__title\"><span style=\"color: #ffffff;\">7.2 Review Questions<\/span><\/h1>\r\n<\/header>\r\n<div class=\"textbox__content\">\r\n<ol>\r\n \t<li>How is the human body like a complex machine?<\/li>\r\n \t<li>Describe the difference between human anatomy and human physiology.<\/li>\r\n \t<li>[h5p id=\"532\"]<\/li>\r\n \t<li>Relate\u00a0cell structure to cell function, and give examples of specific cell types in the human body.<\/li>\r\n \t<li>Define tissue, and identify the four types of tissues that make up the human body.<\/li>\r\n \t<li>What is an organ? Give three examples of organs in the human body.<\/li>\r\n \t<li>Define organ systems. Name five examples in the human body.<\/li>\r\n \t<li>How is the human body regulated so all of its organs and organ systems work together?<\/li>\r\n \t<li>[h5p id=\"533\"]<\/li>\r\n \t<li>Which organ system\u2019s function is to provide structure to the body and protect internal organs?<\/li>\r\n \t<li>Give one example of how the respiratory and circulatory systems work together.<\/li>\r\n<\/ol>\r\n<\/div>\r\n<\/div>\r\n<div class=\"textbox textbox--examples\"><header class=\"textbox__header\">\r\n<h1 style=\"margin-top: 2.14286em; margin-bottom: 1.42857em; line-height: 1.28571em; color: #333333;\"><span style=\"color: #ffffff;\">7.2 Explore More<\/span><\/h1>\r\n<\/header>\r\n<div class=\"textbox__content\">\r\n\r\nhttps:\/\/www.youtube.com\/watch?v=i-icXZ2tMRM\r\n<p style=\"text-align: center;\">Rob Knight: How our microbes make us who we are, TED, 2015.<\/p>\r\nhttps:\/\/www.youtube.com\/watch?time_continue=202&amp;v=I43hq13MnYM&amp;feature=emb_logo\r\n<p style=\"text-align: center;\">Computers That Think Like Humans, Fw: Thinking, 2014.<\/p>\r\n\r\n<\/div>\r\n<\/div>\r\n&nbsp;\r\n<h2>Attributions<\/h2>\r\n<strong>Figure 7.2.1<\/strong>\r\n<ul>\r\n \t<li><a href=\"https:\/\/unsplash.com\/photos\/YKW0JjP7rlU\">White and brown human robot illustration<\/a> by <span class=\"_1JARO\"><a class=\"_3XzpS _1ByhS _4kjHg _1O9Y0 _3l__V _1CBrG xLon9\" href=\"https:\/\/unsplash.com\/@franckinjapan\">Franck V.<\/a><\/span> on <a href=\"http:\/\/unsplash.com\">Unsplash<\/a> is used under the <a class=\"ICezk _2GAZm _2WvKc\" href=\"https:\/\/unsplash.com\/license\">Unsplash License<\/a> (https:\/\/unsplash.com\/license).<\/li>\r\n \t<li><a href=\"https:\/\/unsplash.com\/photos\/1WBN-JKSmKI\">Mighty Mouse, a Robotic Vehicle Range (RVR)<\/a> by <a class=\"_3XzpS _1ByhS _4kjHg _1O9Y0 _3l__V _1CBrG xLon9\" href=\"https:\/\/unsplash.com\/@scienceinhd\">Science in HD<\/a>\u00a0on <a href=\"http:\/\/unsplash.com\">Unsplash<\/a> is used under the <a class=\"ICezk _2GAZm _2WvKc\" href=\"https:\/\/unsplash.com\/license\">Unsplash License<\/a> (https:\/\/unsplash.com\/license).<\/li>\r\n \t<li><a href=\"https:\/\/commons.wikimedia.org\/wiki\/File:Lauron4c_2009_FZI_Karlsruhe.jpg\">Lauron4c 2009 FZI Karlsruhe<\/a> from the FZI Research Center for Information Technology - Department IDS (Germany) on Wikimedia Commons is released for free use.<\/li>\r\n \t<li>NASA Mars Rover (artist's concept) by <a href=\"https:\/\/photojournal.jpl.nasa.gov\/catalog\/PIA04413\">NASA\/JPL\/Cornell University, Maas Digital LLC <\/a>(#PIA04413)\u00a0 on Wikimedia Commons is in the <a class=\"extiw\" title=\"w:public domain\" href=\"https:\/\/en.wikipedia.org\/wiki\/public_domain\">public domain<\/a>\u00a0(https:\/\/en.wikipedia.org\/wiki\/Public_domain).<\/li>\r\n<\/ul>\r\n<strong>Figure 7.2.2<\/strong>\r\n\r\n<a href=\"https:\/\/commons.wikimedia.org\/wiki\/File:101_Levels_of_Org_in_Body.jpg\" rel=\"cc:attributionURL\">101_Levels_of_Org_in_Body<\/a> by <a href=\"http:\/\/OpenStax.https:\/\/openstax.org\/books\/anatomy-and-physiology\/pages\/1-2-structural-organization-of-the-human-body\">OpenStax<\/a>\u00a0 on Wikimedia Commons is used under a <a href=\"https:\/\/creativecommons.org\/licenses\/by\/4.0\/deed.en\" rel=\"license\">CC BY 4.0 <\/a>(https:\/\/creativecommons.org\/licenses\/by\/4.0\/deed.en) licence.\r\n\r\n<strong>Figure 7.2.3<\/strong>\r\n\r\n<a href=\"https:\/\/commons.wikimedia.org\/wiki\/File:422_Feature_Stem_Cell_new.png\" rel=\"cc:attributionURL\">Feature_Stem_Cell_new<\/a>\u00a0by <a href=\"https:\/\/openstax.org\/books\/anatomy-and-physiology\/pages\/3-6-cellular-differentiation\">OpenStax College<\/a> on Wikimedia Commons is used under a <a href=\"https:\/\/creativecommons.org\/licenses\/by\/3.0\/deed.en\" rel=\"license\">CC BY 3.0<\/a> (https:\/\/creativecommons.org\/licenses\/by\/3.0\/deed.en) license.\r\n\r\n<strong>Figure 7.2.4<\/strong>\r\n\r\n<a href=\"https:\/\/www.ck12.org\/book\/ck-12-college-human-biology\/section\/9.2\/\" rel=\"cc:attributionURL\">Four types of tissues<\/a> by <a href=\"https:\/\/www.ck12.org\/book\/ck-12-college-human-biology\/section\/9.2\/\">CK-12 Foundation\/ Zachary Wilson<\/a> is used under a <a href=\"https:\/\/creativecommons.org\/licenses\/by-nc\/3.0\/\">CC BY-NC 3.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-nc\/3.0\/) license.\r\n<div><img src=\"https:\/\/www.ck12info.org\/wp-content\/uploads\/2016\/05\/logo_ck12.png\" alt=\"\" \/> <span style=\"font-size: 1em;\">\u00a9<\/span><a style=\"font-size: 1em;\" href=\"http:\/\/www.ck12.org\/\">CK-12 Foundation<\/a> <span style=\"font-size: 1em;\">Licensed under\u00a0<\/span><a style=\"font-size: 1em;\" href=\"http:\/\/creativecommons.org\/licenses\/by-nc\/3.0\/\"><img class=\"alignnone size-full wp-image-8217\" title=\"CK-12 Foundation is licensed under Creative Commons AttributionNonCommercial 3.0 Unported (CC BY-NC 3.0)\" src=\"https:\/\/www.ck12info.org\/wp-content\/uploads\/2016\/05\/icon_licence.png\" alt=\"CK-12 Foundation is licensed under Creative Commons AttributionNonCommercial 3.0 Unported (CC BY-NC 3.0)\" \/><\/a><span style=\"font-size: 1em;\">\u00a0\u2022\u00a0<\/span><a style=\"font-size: 1em;\" href=\"http:\/\/www.ck12.org\/about\/terms-of-use\/?_ga=2.193208365.186153724.1598904551-1392032960.1592870652\">Terms of Use<\/a><span style=\"font-size: 1em;\">\u00a0\u2022\u00a0<\/span><a style=\"font-size: 1em;\" href=\"http:\/\/www.ck12.org\/about\/attribution\/\">Attribution<\/a><\/div>\r\n<strong>Figure 7.2.5<\/strong>\r\n\r\n<a href=\"https:\/\/commons.wikimedia.org\/wiki\/File:Organ_Systems_I.jpg\">Organ Systems 1<\/a> by <a href=\"https:\/\/openstax.org\/books\/anatomy-and-physiology\/pages\/1-2-structural-organization-of-the-human-body\">Connexions\/ OpenStax<\/a> on Wikimedia Commons is used under a <a href=\"https:\/\/creativecommons.org\/licenses\/by\/3.0\/deed.en\">CC BY 3.0<\/a> (https:\/\/creativecommons.org\/licenses\/by\/3.0\/deed.en) license.\r\n\r\n&nbsp;\r\n\r\n<span style=\"font-size: 1.424em; font-weight: bold;\">References<\/span>\r\n<p class=\"hanging-indent\">Betts, J. G., Young, K.A., Wise, J.A., Johnson, E., Poe, B., Kruse, D.H., Korol, O., Johnson, J.E., Womble, M., DeSaix, P. (2013, April 25). <span class=\"os-title-label\">Figure\u00a0<\/span><span class=\"os-number\">1.3<\/span><span class=\"os-divider\">\u00a0<\/span><span id=\"42861\" class=\"os-title\" data-type=\"title\"><span class=\"search-highlight first text last\" data-timestamp=\"1594951484732\" data-highlight-id=\"6aeb8ede-949a-42a7-8c5b-539b9c5c7092\" data-highlighted=\"true\">Levels of<\/span>\u00a0Structural Organization of the Human Body<\/span> [digital image]. In <em>Anatomy and Physiology<\/em> (Section 1.2). OpenStax. https:\/\/openstax.org\/books\/anatomy-and-physiology\/pages\/1-2-structural-organization-of-the-human-body<\/p>\r\n<p class=\"hanging-indent\"><span class=\"os-title-label\">Betts, J. G., Young, K.A., Wise, J.A., Johnson, E., Poe, B., Kruse, D.H., Korol, O., Johnson, J.E., Womble, M., DeSaix, P. (2013, April 25). Figure\u00a0<\/span><span class=\"os-number\">1.4<\/span><span class=\"os-divider\">\u00a0<\/span><span id=\"7375\" class=\"os-title\" data-type=\"title\"><span class=\"search-highlight first text last\" data-timestamp=\"1594955809917\" data-highlight-id=\"528f84b2-6176-4d78-a9ff-058c8cf1e4df\" data-highlighted=\"true\">Organ Systems<\/span> of the Human Body [digital image]. In <em>Anatomy and Physiology<\/em> (Section 1.2). OpenStax. https:\/\/openstax.org\/books\/anatomy-and-physiology\/pages\/1-2-structural-organization-of-the-human-body\u00a0<\/span><\/p>\r\n<p class=\"hanging-indent\"><span class=\"os-title-label\">Betts, J. G., Young, K.A., Wise, J.A., Johnson, E., Poe, B., Kruse, D.H., Korol, O., Johnson, J.E., Womble, M., DeSaix, P. (2013, April 25). Figure\u00a0<\/span><span class=\"os-number\">3.36<\/span><span class=\"os-divider\">\u00a0<\/span><span id=\"16759\" class=\"os-title\" data-type=\"title\">Stem Cells<\/span><span class=\"os-divider\"> [digital image]. In <em>Anatomy and Physiology<\/em> (Section 3.6). OpenStax. https:\/\/openstax.org\/books\/anatomy-and-physiology\/pages\/3-6-cellular-differentiation<\/span><\/p>\r\n<p class=\"hanging-indent\">Brainard, J\/ CK-12 Foundation. (2016). Figure 4 The human body contains these four types of tissues [digital image]. In <em>CK-12 College Human Biology<\/em> (Section 9.12) [online Flexbook]. CK12.org. https:\/\/www.ck12.org\/book\/ck-12-college-human-biology\/section\/9.2\/<\/p>\r\n<p class=\"hanging-indent\">Fw: Thinking. (2014, May 14). Computers that think like humans. YouTube. https:\/\/www.youtube.com\/watch?v=I43hq13MnYM&amp;feature=youtu.be<\/p>\r\n<p class=\"hanging-indent\">TED. (2015, Febuary 23). Rob Knight: How our microbes make us who we are. YouTube. https:\/\/www.youtube.com\/watch?v=i-icXZ2tMRM&amp;feature=youtu.be<\/p>\r\n&nbsp;","rendered":"<p>&nbsp;<\/p>\n<div id=\"h5p-530\">\n<div class=\"h5p-content\" data-content-id=\"530\"><\/div>\n<\/div>\n<p><em>Figure 7.2.1 Complex machines.<\/em><\/p>\n<h1>A Fantastic Machine<\/h1>\n<p>These robots were created for research or to do complex tasks, but they look like they might be fun to play with too! They are all complex machines. Think about some other, more familiar machines, such as power drills, washing machines, and lawn mowers. Each machine consists of many parts, and each part does a specific job, yet all the parts work together to perform certain functions. Many people have compared the human body to a machine, albeit an extremely complex one. Like real machines, the human body also consists of many parts that work together to perform certain functions. In this case, these parts and functions keep the organism alive. The human body may be the most fantastic machine on Earth, as you will discover when you learn more about it in this concept.<\/p>\n<div>\n<h1>What the Human Machine Can Do<\/h1>\n<\/div>\n<p>Imagine a machine that has all of the following attributes:<\/p>\n<ul>\n<li>It can generate a \u201cwind\u201d of 166 km\/hr (100 mi\/hr).<\/li>\n<li>It can relay messages faster than 400 km\/hr (249 mi\/hr).<\/li>\n<li>It contains a pump that moves about a million barrels of fluid over its lifetime.<\/li>\n<li>It has a control center that contains billions of individual components.<\/li>\n<li>It can\u00a0repair itself, if necessary.<\/li>\n<li>It may\u00a0not wear out for up to a century or more.<\/li>\n<\/ul>\n<p>This machine\u00a0has all of these abilities, and yet it consists mainly of\u00a0water. What is it? It is the human body.<\/p>\n<div>\n<h1>Organization of the Human Body<\/h1>\n<\/div>\n<p>The human body is a complicated, highly organized structure that consists of trillions of parts that function together to achieve all the functions needed to maintain life. The biology of the human body incorporates:<\/p>\n<ul>\n<li>The body\u2019s structure, the study of which is called <strong>anatomy<\/strong>.<\/li>\n<li>The body\u2019s functioning, the study of which is called <strong>physiology<\/strong>.<\/li>\n<\/ul>\n<p>The organization of the human body can be seen as a hierarchy of increasing size and complexity, starting at the level of\u00a0atoms and molecules, and ending at the level of the entire\u00a0<strong>organism,<\/strong> which is an individual living thing. You can see the intervening levels of organization in Figure 7.2.2. Read about the levels in the sections that follow.<\/p>\n<p>&nbsp;<\/p>\n<figure id=\"attachment_2798\" aria-describedby=\"caption-attachment-2798\" style=\"width: 915px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-2798\" src=\"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-content\/uploads\/sites\/152\/2019\/06\/101_Levels_of_Org_in_Body-2.jpg\" alt=\"\" width=\"915\" height=\"1081\" \/><figcaption id=\"caption-attachment-2798\" class=\"wp-caption-text\"><em>Figure 7.2.2 This diagram shows the levels of organization of the human body, from atoms to the whole organism.<\/em><\/figcaption><\/figure>\n<h2>Cells<\/h2>\n<p>The basic units of structure and function of the human body \u2014 as in all living things \u2014 are <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4690_5665\">cells<\/a>. By the time the average person reaches adulthood, their body has an amazing 37 trillion of them! Each cell carries out basic life processes that allow the body to survive. In addition, most human cells are specialized in structure and function to carry out other specific roles. In fact, the human body may consist of as many as 200 different types of cells, each of which has a special job to do. Just a few of these different human cell types are pictured in Figure 7.2.3. These cells have obvious differences in structure that reflect their different functions. For example, nerve cells have long projections sticking out from the body of the cell. These projections help them carry electrical messages to other cells.<\/p>\n<figure id=\"attachment_2800\" aria-describedby=\"caption-attachment-2800\" style=\"width: 1043px\" class=\"wp-caption alignnone\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-2800 size-full\" src=\"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-content\/uploads\/sites\/152\/2023\/10\/Feature_Stem_Cell_new-e1589225900314-2.png\" alt=\"\" width=\"1043\" height=\"224\" \/><figcaption id=\"caption-attachment-2800\" class=\"wp-caption-text\"><em>Figure 7.2.3 A few of the many different types of cells in the human body are illustrated here. Each type of cell is specialized for a particular role in the body.<\/em><\/figcaption><\/figure>\n<h2>Tissues<\/h2>\n<p>The next level of organization in the human body is tissues. A\u00a0<strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4690_2801\">tissue<\/a><\/strong> is a group of connected cells that have a similar function. There are four basic types of human tissues: epithelial, muscle, nervous, and connective tissues. These four tissue types (shown in Figure 7.2.4) make up all the organs of the human body.<\/p>\n<figure id=\"attachment_2802\" aria-describedby=\"caption-attachment-2802\" style=\"width: 500px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" class=\"size-full wp-image-2802\" src=\"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-content\/uploads\/sites\/152\/2023\/10\/Four-types-of-tissues-2.png\" alt=\"\" width=\"500\" height=\"412\" \/><figcaption id=\"caption-attachment-2802\" class=\"wp-caption-text\"><em>Figure 7.2.4 The human body contains these four types of tissues.<\/em><\/figcaption><\/figure>\n<div>\n<p><span style=\"font-size: 1.424em; font-weight: bold;\">Organs and Organ Systems<\/span><\/p>\n<\/div>\n<p>Organs are the next level of organization of the human body. An\u00a0<strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4690_2803\">organ<\/a><\/strong> is a structure that consists of two or more types of tissues that work together to do the same job. Examples of human organs include the heart, brain, lungs, skin, and kidneys. Human organs are organized into organ systems, which are shown in Figure 7.2.5. An <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4690_2804\">organ system<\/a><\/strong>\u00a0is a group of organs that work together to carry out a complex overall function. Each organ of the system does part of the larger job.<\/p>\n<div id=\"h5p-531\">\n<div class=\"h5p-content\" data-content-id=\"531\"><\/div>\n<\/div>\n<p><em>Figure 7.2.5 The Human Organ Systems. Some of the system names shown in this illustration differ from the terminology used in this book, but the systems are the same.<\/em><\/p>\n<p>&nbsp;<\/p>\n<div>\n<p><span style=\"font-size: 1.602em; font-weight: bold;\">A Well-Oiled Machine<\/span><\/p>\n<\/div>\n<p>All of the organs and organ systems of the human body normally work together like a well-oiled machine, because they are closely regulated by the nervous and endocrine systems. The\u00a0nervous system\u00a0controls virtually all body activities, and the\u00a0endocrine system\u00a0secretes hormones that help to regulate these activities. Functioning together, the organ systems supply\u00a0body cells\u00a0with all the substances they need and eliminate their wastes. They also keep\u00a0temperature,\u00a0pH, and other conditions at just the right levels to support life.<\/p>\n<div class=\"textbox textbox--key-takeaways\">\n<header class=\"textbox__header\">\n<h1 class=\"textbox__title\"><span style=\"color: #ffffff;\">7.2 Summary<\/span><\/h1>\n<\/header>\n<div class=\"textbox__content\">\n<ul>\n<li>The human body is like an extremely complex machine. It consists of multiple parts that function together to maintain life. The biology of the human body incorporates the body\u2019s structure (or anatomy) and the body\u2019s functioning (or physiology).<\/li>\n<li>The organization of the human body is a hierarchy of increasing size and complexity, starting at the level of\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4690_5711\">atoms<\/a>\u00a0and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4690_5779\">molecules<\/a>, and ending at the level of the entire organism.<\/li>\n<li><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4690_5665\">Cells<\/a>\u00a0are the level of organization above\u00a0atoms and molecules, and they are the basic units of structure and function of the human body. Each cell carries out basic life functions, as well as other specific roles. Variations in cell function are generally reflected in variations in\u00a0cell structure.<\/li>\n<li>The next level of organization above cells is the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4690_2801\">tissue<\/a>. A tissue is a group of connected cells that have a similar function. There are four basic types of human tissues: epithelial, muscle, nervous, and connective tissues. These four types of tissues make up all the organs of the human body.<\/li>\n<li>The next level of organization above tissues is the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4690_2803\">organ<\/a>. An organ is a structure that consists of two or more types of tissues that work together to do the same job. Examples include the brain and\u00a0heart.<\/li>\n<li>Human organs\u00a0are organized into organ systems. An <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4690_2804\">organ system<\/a> is a group of organs that work together to carry out a complex overall function. For example, the\u00a0skeletal system\u00a0provides structure to the body and protects internal organs.<\/li>\n<li>All of the organs and organ systems of the body normally work together like a well-oiled machine, because they are closely regulated by the nervous and endocrine systems.<\/li>\n<\/ul>\n<\/div>\n<\/div>\n<div class=\"textbox textbox--exercises\">\n<header class=\"textbox__header\">\n<h1 class=\"textbox__title\"><span style=\"color: #ffffff;\">7.2 Review Questions<\/span><\/h1>\n<\/header>\n<div class=\"textbox__content\">\n<ol>\n<li>How is the human body like a complex machine?<\/li>\n<li>Describe the difference between human anatomy and human physiology.<\/li>\n<li>\n<div id=\"h5p-532\">\n<div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-532\" class=\"h5p-iframe\" data-content-id=\"532\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"Level of organization in the human body\"><\/iframe><\/div>\n<\/div>\n<\/li>\n<li>Relate\u00a0cell structure to cell function, and give examples of specific cell types in the human body.<\/li>\n<li>Define tissue, and identify the four types of tissues that make up the human body.<\/li>\n<li>What is an organ? Give three examples of organs in the human body.<\/li>\n<li>Define organ systems. Name five examples in the human body.<\/li>\n<li>How is the human body regulated so all of its organs and organ systems work together?<\/li>\n<li>\n<div id=\"h5p-533\">\n<div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-533\" class=\"h5p-iframe\" data-content-id=\"533\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"6.2 review questions\"><\/iframe><\/div>\n<\/div>\n<\/li>\n<li>Which organ system\u2019s function is to provide structure to the body and protect internal organs?<\/li>\n<li>Give one example of how the respiratory and circulatory systems work together.<\/li>\n<\/ol>\n<\/div>\n<\/div>\n<div class=\"textbox textbox--examples\">\n<header class=\"textbox__header\">\n<h1 style=\"margin-top: 2.14286em; margin-bottom: 1.42857em; line-height: 1.28571em; color: #333333;\"><span style=\"color: #ffffff;\">7.2 Explore More<\/span><\/h1>\n<\/header>\n<div class=\"textbox__content\">\n<p><iframe loading=\"lazy\" id=\"oembed-1\" title=\"Rob Knight: How our microbes make us who we are\" width=\"500\" height=\"281\" src=\"https:\/\/www.youtube.com\/embed\/i-icXZ2tMRM?feature=oembed&#38;rel=0&#38;rel=0\" frameborder=\"0\" allowfullscreen=\"allowfullscreen\"><\/iframe><\/p>\n<p style=\"text-align: center;\">Rob Knight: How our microbes make us who we are, TED, 2015.<\/p>\n<p><iframe loading=\"lazy\" id=\"oembed-2\" title=\"Computers That Think Like Humans\" width=\"500\" height=\"281\" src=\"https:\/\/www.youtube.com\/embed\/I43hq13MnYM?start=202&#38;feature=oembed\" frameborder=\"0\" allowfullscreen=\"allowfullscreen\"><\/iframe><\/p>\n<p style=\"text-align: center;\">Computers That Think Like Humans, Fw: Thinking, 2014.<\/p>\n<\/div>\n<\/div>\n<p>&nbsp;<\/p>\n<h2>Attributions<\/h2>\n<p><strong>Figure 7.2.1<\/strong><\/p>\n<ul>\n<li><a href=\"https:\/\/unsplash.com\/photos\/YKW0JjP7rlU\">White and brown human robot illustration<\/a> by <span class=\"_1JARO\"><a class=\"_3XzpS _1ByhS _4kjHg _1O9Y0 _3l__V _1CBrG xLon9\" href=\"https:\/\/unsplash.com\/@franckinjapan\">Franck V.<\/a><\/span> on <a href=\"http:\/\/unsplash.com\">Unsplash<\/a> is used under the <a class=\"ICezk _2GAZm _2WvKc\" href=\"https:\/\/unsplash.com\/license\">Unsplash License<\/a> (https:\/\/unsplash.com\/license).<\/li>\n<li><a href=\"https:\/\/unsplash.com\/photos\/1WBN-JKSmKI\">Mighty Mouse, a Robotic Vehicle Range (RVR)<\/a> by <a class=\"_3XzpS _1ByhS _4kjHg _1O9Y0 _3l__V _1CBrG xLon9\" href=\"https:\/\/unsplash.com\/@scienceinhd\">Science in HD<\/a>\u00a0on <a href=\"http:\/\/unsplash.com\">Unsplash<\/a> is used under the <a class=\"ICezk _2GAZm _2WvKc\" href=\"https:\/\/unsplash.com\/license\">Unsplash License<\/a> (https:\/\/unsplash.com\/license).<\/li>\n<li><a href=\"https:\/\/commons.wikimedia.org\/wiki\/File:Lauron4c_2009_FZI_Karlsruhe.jpg\">Lauron4c 2009 FZI Karlsruhe<\/a> from the FZI Research Center for Information Technology &#8211; Department IDS (Germany) on Wikimedia Commons is released for free use.<\/li>\n<li>NASA Mars Rover (artist&#8217;s concept) by <a href=\"https:\/\/photojournal.jpl.nasa.gov\/catalog\/PIA04413\">NASA\/JPL\/Cornell University, Maas Digital LLC <\/a>(#PIA04413)\u00a0 on Wikimedia Commons is in the <a class=\"extiw\" title=\"w:public domain\" href=\"https:\/\/en.wikipedia.org\/wiki\/public_domain\">public domain<\/a>\u00a0(https:\/\/en.wikipedia.org\/wiki\/Public_domain).<\/li>\n<\/ul>\n<p><strong>Figure 7.2.2<\/strong><\/p>\n<p><a href=\"https:\/\/commons.wikimedia.org\/wiki\/File:101_Levels_of_Org_in_Body.jpg\" rel=\"cc:attributionURL\">101_Levels_of_Org_in_Body<\/a> by <a href=\"http:\/\/OpenStax.https:\/\/openstax.org\/books\/anatomy-and-physiology\/pages\/1-2-structural-organization-of-the-human-body\">OpenStax<\/a>\u00a0 on Wikimedia Commons is used under a <a href=\"https:\/\/creativecommons.org\/licenses\/by\/4.0\/deed.en\" rel=\"license\">CC BY 4.0 <\/a>(https:\/\/creativecommons.org\/licenses\/by\/4.0\/deed.en) licence.<\/p>\n<p><strong>Figure 7.2.3<\/strong><\/p>\n<p><a href=\"https:\/\/commons.wikimedia.org\/wiki\/File:422_Feature_Stem_Cell_new.png\" rel=\"cc:attributionURL\">Feature_Stem_Cell_new<\/a>\u00a0by <a href=\"https:\/\/openstax.org\/books\/anatomy-and-physiology\/pages\/3-6-cellular-differentiation\">OpenStax College<\/a> on Wikimedia Commons is used under a <a href=\"https:\/\/creativecommons.org\/licenses\/by\/3.0\/deed.en\" rel=\"license\">CC BY 3.0<\/a> (https:\/\/creativecommons.org\/licenses\/by\/3.0\/deed.en) license.<\/p>\n<p><strong>Figure 7.2.4<\/strong><\/p>\n<p><a href=\"https:\/\/www.ck12.org\/book\/ck-12-college-human-biology\/section\/9.2\/\" rel=\"cc:attributionURL\">Four types of tissues<\/a> by <a href=\"https:\/\/www.ck12.org\/book\/ck-12-college-human-biology\/section\/9.2\/\">CK-12 Foundation\/ Zachary Wilson<\/a> is used under a <a href=\"https:\/\/creativecommons.org\/licenses\/by-nc\/3.0\/\">CC BY-NC 3.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-nc\/3.0\/) license.<\/p>\n<div><img decoding=\"async\" src=\"https:\/\/www.ck12info.org\/wp-content\/uploads\/2016\/05\/logo_ck12.png\" alt=\"\" \/> <span style=\"font-size: 1em;\">\u00a9<\/span><a style=\"font-size: 1em;\" href=\"http:\/\/www.ck12.org\/\">CK-12 Foundation<\/a> <span style=\"font-size: 1em;\">Licensed under\u00a0<\/span><a style=\"font-size: 1em;\" href=\"http:\/\/creativecommons.org\/licenses\/by-nc\/3.0\/\"><img decoding=\"async\" class=\"alignnone size-full wp-image-8217\" title=\"CK-12 Foundation is licensed under Creative Commons AttributionNonCommercial 3.0 Unported (CC BY-NC 3.0)\" src=\"https:\/\/www.ck12info.org\/wp-content\/uploads\/2016\/05\/icon_licence.png\" alt=\"CK-12 Foundation is licensed under Creative Commons AttributionNonCommercial 3.0 Unported (CC BY-NC 3.0)\" \/><\/a><span style=\"font-size: 1em;\">\u00a0\u2022\u00a0<\/span><a style=\"font-size: 1em;\" href=\"http:\/\/www.ck12.org\/about\/terms-of-use\/?_ga=2.193208365.186153724.1598904551-1392032960.1592870652\">Terms of Use<\/a><span style=\"font-size: 1em;\">\u00a0\u2022\u00a0<\/span><a style=\"font-size: 1em;\" href=\"http:\/\/www.ck12.org\/about\/attribution\/\">Attribution<\/a><\/div>\n<p><strong>Figure 7.2.5<\/strong><\/p>\n<p><a href=\"https:\/\/commons.wikimedia.org\/wiki\/File:Organ_Systems_I.jpg\">Organ Systems 1<\/a> by <a href=\"https:\/\/openstax.org\/books\/anatomy-and-physiology\/pages\/1-2-structural-organization-of-the-human-body\">Connexions\/ OpenStax<\/a> on Wikimedia Commons is used under a <a href=\"https:\/\/creativecommons.org\/licenses\/by\/3.0\/deed.en\">CC BY 3.0<\/a> (https:\/\/creativecommons.org\/licenses\/by\/3.0\/deed.en) license.<\/p>\n<p>&nbsp;<\/p>\n<p><span style=\"font-size: 1.424em; font-weight: bold;\">References<\/span><\/p>\n<p class=\"hanging-indent\">Betts, J. G., Young, K.A., Wise, J.A., Johnson, E., Poe, B., Kruse, D.H., Korol, O., Johnson, J.E., Womble, M., DeSaix, P. (2013, April 25). <span class=\"os-title-label\">Figure\u00a0<\/span><span class=\"os-number\">1.3<\/span><span class=\"os-divider\">\u00a0<\/span><span id=\"42861\" class=\"os-title\" data-type=\"title\"><span class=\"search-highlight first text last\" data-timestamp=\"1594951484732\" data-highlight-id=\"6aeb8ede-949a-42a7-8c5b-539b9c5c7092\" data-highlighted=\"true\">Levels of<\/span>\u00a0Structural Organization of the Human Body<\/span> [digital image]. In <em>Anatomy and Physiology<\/em> (Section 1.2). OpenStax. https:\/\/openstax.org\/books\/anatomy-and-physiology\/pages\/1-2-structural-organization-of-the-human-body<\/p>\n<p class=\"hanging-indent\"><span class=\"os-title-label\">Betts, J. G., Young, K.A., Wise, J.A., Johnson, E., Poe, B., Kruse, D.H., Korol, O., Johnson, J.E., Womble, M., DeSaix, P. (2013, April 25). Figure\u00a0<\/span><span class=\"os-number\">1.4<\/span><span class=\"os-divider\">\u00a0<\/span><span id=\"7375\" class=\"os-title\" data-type=\"title\"><span class=\"search-highlight first text last\" data-timestamp=\"1594955809917\" data-highlight-id=\"528f84b2-6176-4d78-a9ff-058c8cf1e4df\" data-highlighted=\"true\">Organ Systems<\/span> of the Human Body [digital image]. In <em>Anatomy and Physiology<\/em> (Section 1.2). OpenStax. https:\/\/openstax.org\/books\/anatomy-and-physiology\/pages\/1-2-structural-organization-of-the-human-body\u00a0<\/span><\/p>\n<p class=\"hanging-indent\"><span class=\"os-title-label\">Betts, J. G., Young, K.A., Wise, J.A., Johnson, E., Poe, B., Kruse, D.H., Korol, O., Johnson, J.E., Womble, M., DeSaix, P. (2013, April 25). Figure\u00a0<\/span><span class=\"os-number\">3.36<\/span><span class=\"os-divider\">\u00a0<\/span><span id=\"16759\" class=\"os-title\" data-type=\"title\">Stem Cells<\/span><span class=\"os-divider\"> [digital image]. In <em>Anatomy and Physiology<\/em> (Section 3.6). OpenStax. https:\/\/openstax.org\/books\/anatomy-and-physiology\/pages\/3-6-cellular-differentiation<\/span><\/p>\n<p class=\"hanging-indent\">Brainard, J\/ CK-12 Foundation. (2016). Figure 4 The human body contains these four types of tissues [digital image]. In <em>CK-12 College Human Biology<\/em> (Section 9.12) [online Flexbook]. CK12.org. https:\/\/www.ck12.org\/book\/ck-12-college-human-biology\/section\/9.2\/<\/p>\n<p class=\"hanging-indent\">Fw: Thinking. (2014, May 14). Computers that think like humans. YouTube. https:\/\/www.youtube.com\/watch?v=I43hq13MnYM&amp;feature=youtu.be<\/p>\n<p class=\"hanging-indent\">TED. (2015, Febuary 23). Rob Knight: How our microbes make us who we are. YouTube. https:\/\/www.youtube.com\/watch?v=i-icXZ2tMRM&amp;feature=youtu.be<\/p>\n<p>&nbsp;<\/p>\n<div class=\"glossary\"><span class=\"screen-reader-text\" id=\"definition\">definition<\/span><template id=\"term_4690_5665\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_4690_5665\"><div tabindex=\"-1\"><p>The smallest unit of life, consisting of at least a membrane, cytoplasm, and genetic material.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_4690_2801\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_4690_2801\"><div tabindex=\"-1\"><p>Created by CK-12 Foundation\/Adapted by Christine Miller<\/p>\n<figure id=\"attachment_671\" aria-describedby=\"caption-attachment-671\" style=\"width: 400px\" class=\"wp-caption aligncenter\"><img class=\"wp-image-661\" src=\"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-content\/uploads\/sites\/152\/2019\/06\/Kids-piant-duet-by-PJMixer-on-Unsplash.jpg\" alt=\"\" width=\"400\" height=\"268\"><figcaption id=\"caption-attachment-671\" class=\"wp-caption-text\"><em>Figure 8.6.1 A duet with the peripheral nervous system.\u00a0<\/em><\/figcaption><\/figure>\n<h1>One Piano, Four Hands<\/h1>\n<p>Did you ever see two people play the same piano? How do they coordinate all the movements of their own fingers \u2014 let alone synchronize them with those of their partner? The peripheral nervous system plays an important part in this challenge.<\/p>\n<div>\n<h1>What Is the Peripheral Nervous System?<\/h1>\n<\/div>\n<p>The\u00a0<strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4690_3009\">peripheral nervous system<\/a> (PNS)<\/strong>\u00a0consists of all the nervous tissue that lies outside of the\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4690_2579\">central nervous system<\/a>\u00a0(CNS). The main function of the PNS is to connect the CNS to the rest of the organism. It serves as a\u00a0communication\u00a0relay, going back and forth between the CNS and\u00a0muscles, organs, and glands throughout the body.<\/p>\n<figure id=\"attachment_671\" aria-describedby=\"caption-attachment-671\" style=\"width: 421px\" class=\"wp-caption aligncenter\"><img class=\"size-full wp-image-663\" src=\"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-content\/uploads\/sites\/152\/2023\/10\/Nervous_system_diagram.png\" alt=\"Peripheral Nervous System\" width=\"421\" height=\"695\"><figcaption id=\"caption-attachment-671\" class=\"wp-caption-text\"><em>Figure 8.6.2 The nerves of the peripheral nervous system are shown in blue in this diagram.<\/em><\/figcaption><\/figure>\n<div><\/div>\n<div>\n<h1>Tissues of the Peripheral Nervous System<\/h1>\n<\/div>\n<p>The PNS is mostly made up of cable-like bundles of axons called\u00a0<strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4690_3011\">nerves<\/a><\/strong>,\u00a0as well as\u00a0clusters of neuronal cell bodies called\u00a0<strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4690_2699\">ganglia<\/a><\/strong>\u00a0(singular,\u00a0<strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4690_2701\">ganglion<\/a><\/strong>). Nerves are generally classified\u00a0as sensory, motor, or mixed nerves\u00a0based on\u00a0the direction in which they carry\u00a0nerve impulses.<\/p>\n<ul>\n<li><strong>Sensory nerves<\/strong>\u00a0transmit information from sensory receptors in the body to the CNS. Sensory nerves are also called afferent nerves. You can see an example in the figure\u00a0below.<\/li>\n<li><strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4690_3111\">Motor nerves<\/a><\/strong>\u00a0transmit information from the CNS to\u00a0muscles, organs, and glands. Motor nerves are also called efferent nerves. You can see one in the figure\u00a0below.<\/li>\n<li><strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4690_3112\">Mixed nerves<\/a><\/strong>\u00a0contain both sensory and motor neurons, so they can transmit information in both directions. They have both afferent and efferent functions.<\/li>\n<\/ul>\n<p>&nbsp;<\/p>\n<div>\n<figure id=\"attachment_665\" aria-describedby=\"caption-attachment-665\" style=\"width: 868px\" class=\"wp-caption aligncenter\"><img class=\" wp-image-665\" src=\"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-content\/uploads\/sites\/152\/2023\/10\/Afferent_and_efferent_neurons_en.svg_.png\" alt=\"Afferent and Efferent Neurons\" width=\"868\" height=\"533\"><figcaption id=\"caption-attachment-665\" class=\"wp-caption-text\"><em>Figure 8.6.3 In this diagram, each nerve is depicted as a single neuron for simplicity. This afferent neuron sends nerve impulses from sensory receptors in the skin to the CNS. The efferent neuron is a motor neuron that sends nerve impulses from the CNS to a muscle. The cell body of the afferent neuron is located in a ganglion (not pictured), while the cell body of the motor neuron is located in the spinal cord.<\/em><\/figcaption><\/figure>\n<\/div>\n<div>\n<h1>Divisions of the Peripheral Nervous System<\/h1>\n<\/div>\n<p>The PNS is divided into two major systems, called the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4690_2533\">autonomic nervous system<\/a> and the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4690_3014\">somatic nervous system<\/a>. In the diagram\u00a0below, the autonomic system is shown on the left, and the somatic system on the right. Both systems of the PNS interact with the CNS and include sensory and motor neurons, but they use different\u00a0circuits\u00a0of nerves and ganglia.<\/p>\n<figure id=\"attachment_671\" aria-describedby=\"caption-attachment-671\" style=\"width: 1075px\" class=\"wp-caption aligncenter\"><img class=\" wp-image-667\" src=\"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-content\/uploads\/sites\/152\/2023\/10\/Autonomic-and-Somatic-Nervous-System.png\" alt=\"Autonomic and Somatic Nervous System\" width=\"1075\" height=\"510\"><figcaption id=\"caption-attachment-671\" class=\"wp-caption-text\"><em>Figure 8.6.4 The two major divisions of the PNS are the autonomic and sensory nervous systems.<\/em><\/figcaption><\/figure>\n<h2>Somatic Nervous System<\/h2>\n<p>The\u00a0<strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4690_3014\">somatic nervous system<\/a><\/strong>\u00a0primarily\u00a0senses\u00a0the external environment and controls voluntary activities about which decisions and commands come from the cerebral cortex of the brain. When you feel too warm, for example, you decide to turn on the air conditioner. As you walk across the room to the thermostat, you are using your somatic nervous system. In general, the somatic nervous system is responsible for all of your\u00a0<em>conscious<\/em>\u00a0perceptions of the outside world, as well as all of the voluntary motor activities you perform in response. Whether it\u2019s playing a piano, driving a car, or playing basketball, you can thank your somatic nervous system for making it possible.<\/p>\n<p>Somatic sensory and motor information is transmitted through\u00a012 pairs of cranial nerves and 31 pairs of spinal nerves. Cranial nerves are in the head and neck and connect directly to the brain. Sensory components of cranial nerves\u00a0transmit information about\u00a0smells, tastes, light, sounds, and body position. Motor components of cranial nerves control\u00a0skeletal muscles\u00a0of the face, tongue, eyeballs, throat, head, and shoulders. Motor components of cranial nerves also control the salivary glands and swallowing. Four of the 12 cranial nerves participate in both sensory and motor functions as mixed nerves, having both sensory and motor neurons.<\/p>\n<p>Spinal nerves emanate from the spinal column between vertebrae. All of the spinal nerves are mixed nerves, containing both sensory and motor neurons. The areas of skin innervated by the 31 pairs of spinal nerves are shown in the figure\u00a0below. These include sensory nerves in the skin that sense pressure,\u00a0temperature, vibrations, and pain. Other sensory nerves are in the\u00a0muscles, and they sense stretching and tension. Spinal nerves also include motor nerves that stimulate\u00a0skeletal muscles\u00a0to contract, allowing for voluntary body movements.<\/p>\n<figure id=\"attachment_671\" aria-describedby=\"caption-attachment-671\" style=\"width: 550px\" class=\"wp-caption aligncenter\"><img class=\" wp-image-669\" src=\"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-content\/uploads\/sites\/152\/2023\/10\/Dermatoms.svg_.png\" alt=\"Nerves\" width=\"550\" height=\"778\"><figcaption id=\"caption-attachment-671\" class=\"wp-caption-text\"><em>Figure 8.6.5 This drawing shows the areas of the skin innervated by sensory spinal nerves of the somatic nervous system. The left half of the figure shows the nerves in the front of the body, and the right half shows the nerves in the back of the body. The area that each spinal nerve innervates is shown in a different colour.<\/em><\/figcaption><\/figure>\n<h2>Autonomic Nervous System<\/h2>\n<p>The\u00a0<strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4690_2533\">autonomic nervous system<\/a><\/strong>\u00a0primarily\u00a0senses\u00a0the internal environment and controls involuntary activities. It is responsible for monitoring conditions in the internal environment and bringing about appropriate changes in them. In general, the\u00a0autonomic\u00a0nervous system is responsible for all the activities that go on inside your body\u00a0<em>without<\/em>\u00a0your conscious awareness or voluntary participation.<\/p>\n<p>Structurally, the autonomic nervous system consists of sensory and motor nerves that run between the CNS (especially the hypothalamus in the brain), internal organs (such as the\u00a0heart, lungs, and digestive organs), and glands (such as the\u00a0pancreas\u00a0and sweat glands). <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4690_3030\">Sensory neurons<\/a> in the autonomic system detect internal body conditions and send messages to the brain. Motor nerves in the autonomic system affect appropriate responses by controlling contractions of smooth or cardiac muscle, or glandular tissue. For example, when sensory nerves of the autonomic system detect a rise in body\u00a0temperature, motor nerves signal smooth muscles in\u00a0blood vessels\u00a0near the body surface to undergo vasodilation, and the sweat glands in the skin to secrete more sweat to cool the body.<\/p>\n<p>The autonomic nervous system, in turn, has three subdivisions: the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4690_3015\">sympathetic division<\/a>, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4690_3016\">parasympathetic division<\/a>, and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4690_2650\">enteric division<\/a>. The first two subdivisions of the autonomic system are summarized in the figure\u00a0below. Both affect the same organs and glands, but they generally do so in opposite ways.<\/p>\n<ul>\n<li>The\u00a0<strong>sympathetic division<\/strong>\u00a0controls the fight-or-flight response. Changes occur in organs and glands throughout the body that prepare the body to fight or flee in response to a perceived danger. For example, the\u00a0heart\u00a0rate speeds up, air passages in the lungs become wider, more\u00a0blood\u00a0flows to the\u00a0skeletal muscles, and the\u00a0digestive system temporarily shuts down.<\/li>\n<li>The\u00a0<strong>parasympathetic division<\/strong>\u00a0returns the body to normal after the fight-or-flight response has occurred. For example, it slows down the\u00a0heart\u00a0rate, narrows air passages in the lungs, reduces\u00a0blood\u00a0flow to the skeletal muscles, and stimulates the\u00a0digestive system\u00a0to start working again. The parasympathetic division also maintains internal\u00a0homeostasis\u00a0of the body at other times.<\/li>\n<li>The\u00a0<strong>enteric division<\/strong> is made up of nerve fibres that supply the organs of the digestive system. This division allows for the local control of many digestive functions.<\/li>\n<\/ul>\n<figure id=\"attachment_671\" aria-describedby=\"caption-attachment-671\" style=\"width: 597px\" class=\"wp-caption aligncenter\"><img class=\" wp-image-671\" src=\"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-content\/uploads\/sites\/152\/2023\/10\/The_Autonomic_Nervous_System.jpg\" alt=\"The autonomic nervous system\" width=\"597\" height=\"598\"><figcaption id=\"caption-attachment-671\" class=\"wp-caption-text\"><em>Figure 8.6.6 This diagram summarizes the structures and functions controlled by the parasympathetic and sympathetic divisions of the autonomic nervous system.<\/em><\/figcaption><\/figure>\n<p><span style=\"font-size: 1.602em;font-weight: bold\">Disorders of the Peripheral Nervous System<\/span><\/p>\n<p>Unlike the CNS \u2014 which is protected by\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4690_2552\">bone<\/a>s, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4690_2929\">meninges<\/a>, and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4690_2589\">cerebrospinal fluid<\/a> \u2014 the PNS has no such protections. The PNS also has no blood-brain barrier to protect it from toxins and pathogens in the\u00a0blood. Therefore, the PNS is more subject to injury and disease than is the CNS. Causes of nerve injury include\u00a0<a href=\"https:\/\/www.mayoclinic.org\/diseases-conditions\/diabetes\/symptoms-causes\/syc-20371444\">diabetes<\/a>,\u00a0infectious diseases\u00a0(such as <a href=\"https:\/\/www.mayoclinic.org\/diseases-conditions\/shingles\/symptoms-causes\/syc-20353054\">shingles<\/a>), and poisoning by toxins (such as heavy metals). PNS disorders often have symptoms\u00a0like\u00a0loss of feeling, tingling, burning sensations, or muscle weakness. If a traumatic injury results in a nerve being transected (cut all the way through), it may regenerate, but this is a very slow process and may take many months.<\/p>\n<p>Two other diseases of the PNS are Guillain-Barre syndrome and Charcot-Marie-Tooth disease.<\/p>\n<ul>\n<li><a href=\"https:\/\/www.mayoclinic.org\/diseases-conditions\/guillain-barre-syndrome\/symptoms-causes\/syc-20362793\">Guillain-Barre syndrome<\/a> is a rare disease in which the immune system attacks nerves of the PNS, leading to muscle weakness and even paralysis. The exact cause of Guillain-Barre syndrome is unknown, but it often occurs after a viral or bacterial infection. There is no known cure for the syndrome, but most people eventually make a full recovery. Recovery can be slow, however, lasting anywhere from several weeks to several years.<\/li>\n<li><a href=\"https:\/\/www.mayoclinic.org\/diseases-conditions\/charcot-marie-tooth-disease\/symptoms-causes\/syc-20350517\">Charcot-Marie-Tooth disease<\/a> is a hereditary disorder of the nerves, and one of the most common inherited neurological disorders. It affects predominantly the nerves in the feet and legs,\u00a0and often\u00a0in the hands and arms, as well. The disease is characterized by loss of muscle tissue and sense of touch. It is presently incurable.<\/li>\n<\/ul>\n<div>\n<h1>Feature: My\u00a0Human Body<\/h1>\n<\/div>\n<p>The autonomic nervous system is considered to be involuntary because it doesn't require conscious input. However, it\u00a0<em>is<\/em>\u00a0possible to exert some voluntary control over it. People who practice yoga or other so-called mind-body techniques, for example,\u00a0can\u00a0reduce their heart rate and certain other autonomic functions. Slowing down these otherwise involuntary responses is a good way to relieve stress and reduce the wear-and-tear that stress can place on the body. Such techniques may also be useful for controlling post-traumatic stress disorder and chronic pain. Three types of integrative practices for these purposes\u00a0are\u00a0breathing exercises, body-based tension modulation exercises, and mindfulness techniques.<\/p>\n<p>Breathing exercises can help control the rapid, shallow breathing that often occurs when you are anxious or under stress. These exercises can be learned quickly, and they provide immediate feelings of relief. Specific breathing exercises include paced breath, diaphragmatic breathing, and Breathe2Relax or Chill Zone on MindShift\u2122 CBT, which are downloadable breathing practice mobile applications, or \"Apps\". Try syncing your breathing with Eric Klassen's \"Triangle breathing, 1 minute\" video:<\/p>\n<p>https:\/\/www.youtube.com\/watch?v=u9Q8D6n-3qw<\/p>\n<p style=\"text-align: center\">Triangle breathing, 1 minute, Erin Klassen, 2015.<\/p>\n<p>Body-based tension modulation exercises include yoga postures (also known as \u201casanas\u201d) and tension manipulation exercises. The latter include the Trauma\/Tension Release\u00a0Exercise\u00a0(TRE) and the Trauma Resiliency Model (TRM). Watch this video for a brief \u2014 but informative \u2014 introduction to the TRE program:<\/p>\n<p>https:\/\/www.youtube.com\/watch?v=67R974D8swM&amp;feature=youtu.be<\/p>\n<p style=\"text-align: center\">TRE\u00ae : Tension and Trauma Releasing Exercises, an Introduction with Jessica Schaffer, Jessica Schaffer Nervous System RESET, 2015.<\/p>\n<p>Mindfulness techniques have been shown to reduce symptoms of depression, as well as those of anxiety and stress. They have also been shown to be useful for pain management and performance enhancement. Specific mindfulness programs include Mindfulness Based Stress Reduction (MBSR) and Mindfulness Mind-Fitness Training (MMFT). You can learn more about MBSR by watching the video below.<\/p>\n<p>https:\/\/www.youtube.com\/watch?v=0TA7P-iCCcY&amp;feature=youtu.be<\/p>\n<p style=\"text-align: center\">Mindfulness-Based Stress Reduction (UMass Medical School, Center for Mindfulness), Palouse Mindfulness, 2017.<\/p>\n<div class=\"textbox textbox--key-takeaways\">\n<header class=\"textbox__header\">\n<h1 class=\"textbox__title\"><span style=\"color: #ffffff\">8.6 Summary<\/span><\/h1>\n<\/header>\n<div class=\"textbox__content\">\n<ul>\n<li>The <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4690_3009\">peripheral nervous system<\/a> (PNS) consists of all the nervous tissue that lies outside the\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4690_2579\">central nervous system<\/a> (CNS). Its main function is to connect the CNS to the rest of the organism.<\/li>\n<li>The PNS is made up of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4690_3011\">nerves<\/a> and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4690_2699\">ganglia<\/a>. Nerves are bundles of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4690_2535\">axons<\/a>, and ganglia are groups of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4690_2576\">cell bodies<\/a>. Nerves are classified as sensory, motor, or a mix of the two.<\/li>\n<li>The PNS is divided into the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4690_3014\">somatic<\/a> and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4690_2533\">autonomic nervous systems<\/a>. The somatic system controls <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4690_3004\">voluntary<\/a> activities, whereas the autonomic system controls <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4690_3005\">involuntary<\/a> activities.<\/li>\n<li>The autonomic nervous system is further divided into <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4690_3015\">sympathetic<\/a>, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4690_3016\">parasympathetic<\/a>, and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4690_2650\">enteric divisions<\/a>. The sympathetic division controls <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4690_2682\">fight-or-flight responses<\/a>\u00a0during emergencies, the parasympathetic system controls routine body functions the rest of the time, and the enteric division provides local control over the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4690_2628\">digestive system<\/a>.<\/li>\n<li>The PNS is not as well protected physically or chemically as the CNS, so it is more prone to injury and disease. PNS problems include injury from\u00a0diabetes, shingles, and heavy metal poisoning. Two disorders of the PNS are Guillain-Barre syndrome and Charcot-Marie-Tooth disease.<\/li>\n<\/ul>\n<\/div>\n<\/div>\n<div class=\"textbox textbox--exercises\">\n<header class=\"textbox__header\">\n<h1 class=\"textbox__title\"><span style=\"color: #ffffff\">8.6 Review Questions<\/span><\/h1>\n<\/header>\n<div class=\"textbox__content\">\n<ol>\n<li>Describe the general structure of the peripheral nervous system. State its primary function.<\/li>\n<li>What are ganglia?<\/li>\n<li>Identify three types of nerves based on the direction in which they carry\u00a0nerve impulses.<\/li>\n<li>Outline all of the divisions of the peripheral nervous system.<\/li>\n<li>Compare and contrast the somatic and autonomic nervous systems.<\/li>\n<li>When and how does the sympathetic division of the autonomic nervous system affect the body?<\/li>\n<li>What is the function of the parasympathetic division of the autonomic nervous system?\u00a0Specifically, how does it affect the body?<\/li>\n<li>Name and describe two peripheral nervous system disorders.<\/li>\n<li>Give one example of how the CNS interacts with the PNS to control a function in the body.<\/li>\n<li>For each of the following types of information, identify whether the neuron carrying it is sensory or motor, and whether it is most likely in the somatic or autonomic nervous system:\n<ol type=\"a\">\n<li>Visual information<\/li>\n<li>Blood pressure information<\/li>\n<li>Information that causes muscle contraction in digestive organs after eating<\/li>\n<li>Information that causes muscle contraction in skeletal muscles based on the person\u2019s decision to make a movement<\/li>\n<\/ol>\n<\/li>\n<li>\n<div id=\"h5p-125\">\n<div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-125\" class=\"h5p-iframe\" data-content-id=\"125\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"8.2 Review Questions Introduction to the Nervous System\"><\/iframe><\/div>\n<\/div>\n<\/li>\n<\/ol>\n<\/div>\n<\/div>\n<div class=\"textbox textbox--examples\">\n<header class=\"textbox__header\">\n<h1 class=\"textbox__title\" style=\"text-align: left\"><span style=\"color: #ffffff\">8.6 Explore More<\/span><\/h1>\n<\/header>\n<div class=\"textbox__content\">\n<p>https:\/\/www.youtube.com\/watch?v=ySIDMU2cy0Y&amp;feature=emb_logo<\/p>\n<p style=\"text-align: center\">Phantom Limbs Explained, Plethrons, 2015.<\/p>\n<p>https:\/\/www.youtube.com\/watch?time_continue=1&amp;v=73yo5nJne6c&amp;feature=emb_logo<\/p>\n<p style=\"text-align: center\">Why Do Hot Peppers Cause Pain? Reactions, 2015.<\/p>\n<\/div>\n<\/div>\n<h2>Attributions<\/h2>\n<p><strong>Figure 8.6.1<\/strong><\/p>\n<p><a href=\"https:\/\/www.flickr.com\/photos\/pjmixer\/4460758776\" rel=\"cc:attributionURL\">Kid\u2019s piant duet<\/a> by\u00a0<a href=\"https:\/\/www.flickr.com\/photos\/pjmixer\/\" rel=\"dc:creator\">PJMixer<\/a> on <a href=\"http:\/\/flickr.com\">Flickr<\/a> is used under a <a href=\"https:\/\/creativecommons.org\/licenses\/by-nc-nd\/2.0\/\" rel=\"license\">CC BY-NC-ND 2.0<\/a>\u00a0(https:\/\/creativecommons.org\/licenses\/by-nc-nd\/2.0\/) license.<\/p>\n<p><strong>Figure 8.6.2<\/strong><\/p>\n<p><a href=\"https:\/\/commons.wikimedia.org\/wiki\/File:Nervous_system_diagram.png\" rel=\"cc:attributionURL\">Nervous_system_diagram<\/a> by <a class=\"extiw\" title=\"en:User:Persian Poet Gal\" href=\"https:\/\/en.wikipedia.org\/wiki\/User:Persian_Poet_Gal\"><span style=\"font-family: comic sans ms\"><span style=\"color: purple\">\u00a4~Persian Poet Gal<\/span><\/span><\/a>\u00a0 on Wikimedia Commons is released into the <a class=\"extiw\" title=\"w:en:public domain\" href=\"https:\/\/en.wikipedia.org\/wiki\/en:public_domain\">public domain<\/a> (https:\/\/en.wikipedia.org\/wiki\/Public_domain).<\/p>\n<p><strong style=\"text-align: initial;font-size: 1em\"><br \/>\nFigure 8.6.3<\/strong><\/p>\n<p><a href=\"https:\/\/commons.wikimedia.org\/wiki\/File:Afferent_and_efferent_neurons_en.svg\" rel=\"cc:attributionURL\">Afferent_and_efferent_neurons_en.svg<\/a> by <a title=\"User:Helixitta\" href=\"https:\/\/commons.wikimedia.org\/wiki\/User:Helixitta\">Helixitta<\/a> on Wikimedia Commons is used under a <a href=\"https:\/\/creativecommons.org\/licenses\/by-sa\/4.0\/\" rel=\"license\">CC BY-SA 4.0 <\/a>\u00a0 (https:\/\/creativecommons.org\/licenses\/by-sa\/4.0) license.<\/p>\n<p><strong>Figure 8.6.4<\/strong><\/p>\n<p><a href=\"https:\/\/commons.wikimedia.org\/wiki\/File:Autonomic_and_Somatic_Nervous_System.png\" rel=\"cc:attributionURL\">Autonomic and Somatic Nervous System<\/a> by <a title=\"User:Christinelmiller\" href=\"https:\/\/commons.wikimedia.org\/wiki\/User:Christinelmiller\">Christinelmiller<\/a> on Wikimedia Commons is used under a <a href=\"https:\/\/creativecommons.org\/licenses\/by-sa\/4.0\/\" rel=\"license\">CC BY-SA 4.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-sa\/4.0) license.<\/p>\n<p><strong>Figure 8.6.5<\/strong><\/p>\n<p><a href=\"https:\/\/commons.wikimedia.org\/wiki\/File:Dermatoms.svg\" rel=\"cc:attributionURL\">Dermatoms.svg<\/a> by Ralf Stephan (mailto:ralf@ark.in-berlin.de) on Wikimedia Commons is released into the <a class=\"extiw\" title=\"w:en:public domain\" href=\"https:\/\/en.wikipedia.org\/wiki\/en:public_domain\">public domain<\/a> (https:\/\/en.wikipedia.org\/wiki\/Public_domain).<\/p>\n<p><strong>Figure 8.6.6<\/strong><\/p>\n<p><a href=\"https:\/\/commons.wikimedia.org\/wiki\/File:The_Autonomic_Nervous_System.jpg\" rel=\"cc:attributionURL\">The_Autonomic_Nervous_System<\/a> by <a title=\"User:Geo-Science-International\" href=\"https:\/\/commons.wikimedia.org\/wiki\/User:Geo-Science-International\">Geo-Science-International<\/a> on Wikimedia Commons is used and adapted by Christine Miller under a\u00a0<a href=\"https:\/\/creativecommons.org\/publicdomain\/zero\/1.0\/\" rel=\"license\">CC0 1.0<\/a> Universal<br \/>\nPublic Domain Dedication license (https:\/\/creativecommons.org\/publicdomain\/zero\/1.0\/).<\/p>\n<h2>References<\/h2>\n<p class=\"hanging-indent\">Erin Klassen. (2015, December 15). Triangle breathing, 1 minute. YouTube. https:\/\/www.youtube.com\/watch?v=u9Q8D6n-3qw&amp;feature=youtu.be<\/p>\n<p class=\"hanging-indent\">Jessica Schaffer Nervous System RESET. (2015, January 15). TRE\u00ae : Tension and trauma releasing exercises, an Introduction with Jessica Schaffer. YouTube. https:\/\/www.youtube.com\/watch?v=67R974D8swM&amp;feature=youtu.be<\/p>\n<p class=\"hanging-indent\">Mayo Clinic Staff. (n.d.). Charcot-Marie-Tooth disease [online article]. MayoClinic.org. https:\/\/www.mayoclinic.org\/diseases-conditions\/charcot-marie-tooth-disease\/symptoms-causes\/syc-20350517<\/p>\n<p class=\"hanging-indent\">Mayo Clinic Staff. (n.d.). Diabetes [online article]. MayoClinic.org. https:\/\/www.mayoclinic.org\/diseases-conditions\/diabetes\/symptoms-causes\/syc-20371444<\/p>\n<p class=\"hanging-indent\">Mayo Clinic Staff. (n.d.). Guillain-Barre syndrome [online article]. MayoClinic.org. https:\/\/www.mayoclinic.org\/diseases-conditions\/guillain-barre-syndrome\/symptoms-causes\/syc-20362793<\/p>\n<p class=\"hanging-indent\">Mayo Clinic Staff. (n.d.). Shingles [online article]. MayoClinic.org. https:\/\/www.mayoclinic.org\/diseases-conditions\/shingles\/symptoms-causes\/syc-20353054<\/p>\n<p class=\"hanging-indent\">Mayo Clinic Staff. (n.d.). Stroke [online article]. MayoClinic.org. https:\/\/www.mayoclinic.org\/diseases-conditions\/stroke\/symptoms-causes\/syc-20350113<\/p>\n<p class=\"hanging-indent\">Palouse Mindfulness. (2017, March 25).\u00a0 Mindfulness-based stress reduction (UMass Medical School, Center for Mindfulness), YouTube. https:\/\/www.youtube.com\/watch?v=0TA7P-iCCcY&amp;feature=youtu.be<\/p>\n<p class=\"hanging-indent\">Plethrons, (2015, March 23). Phantom limbs explained. YouTube. https:\/\/www.youtube.com\/watch?v=ySIDMU2cy0Y&amp;feature=youtu.be<\/p>\n<p class=\"hanging-indent\">Reactions. (2015, December 1). Why do hot peppers cause pain? YouTube. https:\/\/www.youtube.com\/watch?v=73yo5nJne6c&amp;feature=youtu.be<\/p>\n<p>&nbsp;<\/p>\n<p>&nbsp;<\/p>\n<p>&nbsp;<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_4690_2803\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_4690_2803\"><div tabindex=\"-1\"><p>Created by CK-12 Foundation\/Adapted by Christine Miller<\/p>\n<figure id=\"attachment_713\" aria-describedby=\"caption-attachment-713\" style=\"width: 300px\" class=\"wp-caption aligncenter\"><img class=\"wp-image-3168\" src=\"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-content\/uploads\/sites\/152\/2019\/06\/Cappucino-Art-by-drew-coffman-tZKwLRO904E-unsplash-scaled-1.jpg\" alt=\"\" width=\"300\" height=\"169\"><figcaption id=\"caption-attachment-713\" class=\"wp-caption-text\"><em>Figure 8.8.1 A capaccino can affect your mental state, especially when it looks like this!<\/em><\/figcaption><\/figure>\n<p><span style=\"font-size: 1.602em;font-weight: bold\">Art in a Cup<\/span><\/p>\n<p>Who knew that a cup of coffee could also be a work of art? A talented barista can make coffee look as good as it tastes. If you are a coffee drinker, you probably know that coffee can also affect your mental state. It can make you more alert, and it may improve your concentration. That\u2019s because the caffeine in coffee is a psychoactive drug. In fact, caffeine is the most widely consumed psychoactive substance in the world. In North America, for example, 90 per cent of adults consume caffeine daily.<\/p>\n<div>\n<h1>What Are Psychoactive Drugs?<\/h1>\n<\/div>\n<p><strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4690_3169\">Psychoactive drugs<\/a><\/strong>\u00a0are substances that change the function of the brain and result in alterations of mood, thinking, perception, and\/or behavior. Psychoactive drugs may be used for many purposes, including therapeutic, ritual, or recreational purposes. Besides <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4690_2560\">caffeine<\/a>, other examples of psychoactive drugs include cocaine, LSD, alcohol, tobacco, codeine, and morphine. Psychoactive drugs may be legal prescription medications (codeine and morphine), legal nonprescription drugs (alcohol and tobacco), or illegal drugs (cocaine and LSD).<\/p>\n<p>Cannabis (or marijuana) is also a psychoactive drug that while illegal in many countries is legal for use in Canada by individuals over the age of 19 years. Legal prescription medications (such as opioids) are also used illegally by increasingly large numbers of people. Some legal drugs, such as alcohol and nicotine, are readily available almost everywhere, as illustrated by the images below.<\/p>\n<div id=\"h5p-129\">\n<div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-129\" class=\"h5p-iframe\" data-content-id=\"129\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"Scientific Method and &quot;Doing&quot; Science\"><\/iframe><\/div>\n<\/div>\n<p><em>Figure 8.8.2 These psychoactive drugs are legal and accessible almost anywhere.\u00a0\u00a0<\/em><\/p>\n<div>\n<p><span style=\"font-size: 1.602em;font-weight: bold\">Classes of Psychoactive Drugs<\/span><\/p>\n<\/div>\n<p>Psychoactive drugs are divided into different classes\u00a0based on\u00a0their pharmacological effects. Several classes are listed below, along with examples of commonly used drugs in each class.<\/p>\n<ul>\n<li><strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4690_3171\">Stimulants<\/a><\/strong>\u00a0are drugs that stimulate the brain and increase alertness and wakefulness. Examples of stimulants include caffeine, nicotine, cocaine, and amphetamines (such as Adderall).<\/li>\n<li><strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4690_3172\">Depressants<\/a><\/strong>\u00a0are drugs that calm the brain, reduce anxious feelings, and induce sleepiness. Examples of depressants include ethanol (in alcoholic beverages) and opioids, such as codeine and heroin.<\/li>\n<li><strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4690_3173\">Anxiolytics<\/a><\/strong>\u00a0are drugs that have a tranquilizing effect and inhibit anxiety. Examples of anxiolytic drugs include benzodiazepines (such as diazepam\/Valium), barbiturates (such as phenobarbital), opioids, and antidepressant drugs (such as sertraline\/Zoloft).<\/li>\n<li><strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4690_3174\">Euphoriants<\/a><\/strong>\u00a0are drugs that bring about a state of euphoria, or intense feelings of well-being and happiness. Examples of euphoriants include the so-called \"club drug\" MDMA (ecstasy), amphetamines, ethanol, and opioids (such as morphine).<\/li>\n<li><strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4690_3175\">Hallucinogens<\/a><\/strong>\u00a0are drugs that can cause hallucinations and other perceptual anomalies. They also cause subjective changes in thoughts, emotions, and consciousness. Examples of hallucinogens include LSD, mescaline, nitrous oxide, and psilocybin.<\/li>\n<li><strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4690_3176\">Empathogens<\/a><\/strong>\u00a0are drugs that produce feelings of empathy, or sympathy with other people. Examples of empathogens include amphetamines and MDMA.<\/li>\n<\/ul>\n<p>Many psychoactive drugs have multiple effects, so they may be placed in more than one class.\u00a0One\u00a0example is MDMA, pictured\u00a0below, which may act both as a euphoriant and as an empathogen. In some people, MDMA may also have stimulant or hallucinogenic effects. As of 2016, MDMA had no accepted medical uses, but it was undergoing testing for use in the treatment of post-traumatic stress disorder and certain other types of anxiety disorders.<\/p>\n<figure id=\"attachment_713\" aria-describedby=\"caption-attachment-713\" style=\"width: 434px\" class=\"wp-caption aligncenter\"><img class=\"size-full wp-image-708\" src=\"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-content\/uploads\/sites\/152\/2023\/10\/Ecstasy_monogram.jpg\" alt=\"\" width=\"434\" height=\"424\"><figcaption id=\"caption-attachment-713\" class=\"wp-caption-text\"><em>Figure 8.8.3 Ecstasy (MDMA) is most commonly taken in tablet form, like the tablets shown here.<\/em><\/figcaption><\/figure>\n<div>\n<p><span style=\"font-size: 1.602em;font-weight: bold\">Mechanisms of Action<\/span><\/p>\n<\/div>\n<p>Psychoactive drugs generally produce their effects by affecting brain chemistry, which in turn may cause changes in a person\u2019s mood, thinking, perception, and behavior. Each drug tends to have a specific action on one or more neurotransmitters or neurotransmitter receptors in the brain. Generally, they act as either agonists or antagonists.<\/p>\n<ul>\n<li><strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4690_3178\">Agonists<\/a><\/strong>\u00a0are drugs that increase the activity of particular <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4690_3056\">neurotransmitters<\/a>. They might act by promoting the synthesis of the neurotransmitters, reducing their reuptake from synapses, or mimicking their action by binding to receptors for the neurotransmitters.<\/li>\n<li><strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4690_3179\">Antagonists<\/a><\/strong>\u00a0are drugs that decrease the activity of particular neurotransmitters. They might act by interfering with the synthesis of the neurotransmitters or by blocking their receptors so the neurotransmitters cannot bind to them.<\/li>\n<\/ul>\n<p>Consider the example of the neurotransmitter <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4690_3062\">GABA<\/a>. This is one of the most common neurotransmitters in the brain, and it normally has an inhibitory effect on\u00a0cells. GABA agonists \u2014 which increase its activity \u2014 include ethanol, barbiturates, and benzodiazepines, among other psychoactive drugs. All of these drugs work by promoting the activity of GABA receptors in the brain.<\/p>\n<div>\n<h1>Uses of Psychoactive Drugs<\/h1>\n<\/div>\n<p>You may have been prescribed psychoactive drugs by your doctor. For example, your doctor may have prescribed you\u00a0an opioid drug, such as codeine for pain (most likely in the form of Tylenol with added codeine). Chances are you also use nonprescription psychoactive drugs (like caffeine) for mental alertness. These are just two of the many possible uses of psychoactive drugs.<\/p>\n<h2>Medical Uses<\/h2>\n<figure id=\"attachment_713\" aria-describedby=\"caption-attachment-713\" style=\"width: 372px\" class=\"wp-caption alignright\"><img class=\"wp-image-709\" src=\"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-content\/uploads\/sites\/152\/2023\/10\/US_Navy_030513-N-1577S-001_Lt._Cmdr._Joe_Casey_Ships_Anesthetist_trains_on_anesthetic_procedures_with_Hospital_Corpsman_3rd_Class_Eric_Wichman_aboard_USS_Nimitz_CVN_68.jpg\" alt=\"Anesthetic\" width=\"372\" height=\"567\"><figcaption id=\"caption-attachment-713\" class=\"wp-caption-text\"><em>Figure 8.8.4 This person is being prepared to receive a general anesthetic prior to surgery.<\/em><\/figcaption><\/figure>\n<p>General anesthesia is one use of psychoactive drugs in medicine. With general anesthesia, pain is blocked and unconsciousness is induced. General anesthetics are most often used during surgical procedures and may be administered in gaseous form, as in Figure 8.8.4. General anesthetics include the drugs halothane and ketamine. Other psychoactive drugs are used to manage pain without affecting consciousness. They may be prescribed either for acute pain in cases of trauma (such as broken bones) or for chronic pain caused by arthritis, cancer, or fibromyalgia. Most often, the drugs used for pain control are opioids, such as morphine and codeine.<\/p>\n<p>Many psychiatric disorders are also managed with psychoactive drugs. Antidepressants\u00a0like\u00a0sertraline, for example, are used to treat depression, anxiety, and\u00a0eating disorders. Anxiety disorders may also be treated with anxiolytics, such as buspirone and diazepam. Stimulants (such as amphetamines) are used to treat attention deficit disorder. Antipsychotics (such as clozapine and risperidone) \u2014 as well as mood stabilizers, such as lithium \u2014 are used to treat schizophrenia and bipolar disorder.<\/p>\n<h2>Ritual Uses<\/h2>\n<figure id=\"attachment_713\" aria-describedby=\"caption-attachment-713\" style=\"width: 278px\" class=\"wp-caption alignleft\"><img class=\" wp-image-710\" src=\"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-content\/uploads\/sites\/152\/2023\/10\/Peyote-Lophophora_williamsii_pm.jpg\" alt=\"\" width=\"278\" height=\"177\"><figcaption id=\"caption-attachment-713\" class=\"wp-caption-text\"><em>Figure 8.8.5 The peyote cactus contains a hallucinogenic drug that is still used by some Native Americans for religious rituals.<\/em><\/figcaption><\/figure>\n<p>Certain psychoactive drugs, particularly hallucinogens, have been used for ritual purposes since prehistoric times. For example, Native Americans have used the mescaline-containing peyote cactus (pictured in Figure 8.8.5) for religious ceremonies for as long as 5,700 years. In prehistoric Europe, the mushroom <em>Amanita muscaria<\/em>, which contains a hallucinogenic drug called muscimol, was used for similar purposes. Various other psychoactive drugs \u2014 including jimsonweed, psilocybin mushrooms, and cannabis \u2014 have also been used for millennia, by various peoples, for ritual purposes.<\/p>\n<p>&nbsp;<\/p>\n<div>\n<p><span style=\"font-size: 1.424em;font-weight: bold\">Recreational Uses<\/span><\/p>\n<\/div>\n<p>The recreational use of psychoactive drugs generally has the purpose of altering one\u2019s consciousness and creating a feeling of euphoria commonly called a \u201chigh.\u201d Some of the drugs used most commonly for recreational purposes are cannabis, ethanol (alcohol), opioids, and stimulants (such as nicotine). Hallucinogens are also used recreationally, primarily for the alterations they cause in thinking and perception.<\/p>\n<p>Some investigators have suggested that the urge to alter one\u2019s state of consciousness is a universal human drive, similar to the drive to satiate thirst, hunger, or sexual desire. They think that this instinct is even present in children, who may attain an altered state by repetitive motions, such as spinning or swinging. Some nonhuman animals also exhibit a drive to experience altered states. They may consume fermented berries or fruit and become intoxicated. The way cats respond to catnip (see Figure 8.8.6) is another example.<\/p>\n<figure id=\"attachment_713\" aria-describedby=\"caption-attachment-713\" style=\"width: 766px\" class=\"wp-caption aligncenter\"><img class=\" wp-image-713\" src=\"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-content\/uploads\/sites\/152\/2023\/10\/Cat-under-effects-of-catnip-by-katieb50-on-flickr.jpg\" alt=\"\" width=\"766\" height=\"574\"><figcaption id=\"caption-attachment-713\" class=\"wp-caption-text\"><em>Figure 8.8.6 This cat is taking advantage of a catnip plant and apparently enjoying its psychoactive effects.<\/em><\/figcaption><\/figure>\n<h3>Addiction, Dependence, and Rehabilitation<\/h3>\n<p>Psychoactive substances often bring about subjective changes that the user may find pleasant (euphoria) or advantageous (increased alertness). These changes are rewarding and positively reinforcing, so they have the potential for misuse, addiction, and dependence.\u00a0<strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4690_3184\">Addiction<\/a><\/strong>\u00a0refers to the compulsive use of a drug, despite negative consequences that such use may entail. Sustained use of an addictive drug may produce dependence on the drug.\u00a0<strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4690_2076\">Dependence<\/a><\/strong>\u00a0may be physical and\/or psychological. It occurs when cessation of drug use produces withdrawal symptoms. Physical dependence produces physical withdrawal symptoms, which may include tremors, pain, seizures, or insomnia. Psychological dependence produces psychological withdrawal symptoms, such as anxiety, depression, paranoia, or hallucinations.<\/p>\n<p>Rehabilitation for drug dependence and addiction typically involves psychotherapy, which may include both individual and group therapy. Organizations such as <a href=\"https:\/\/www.aa.org\/pages\/en_US\/regional-correspondent-us-and-canada\">Alcoholics Anonymous<\/a> (AA) and <a href=\"https:\/\/www.bcrna.ca\/\">Narcotics Anonymous<\/a> (NA) may also be helpful for people trying to recover from addiction. These groups are self-described as international mutual aid fellowships,\u00a0and\u00a0their primary purpose is to help addicts achieve and maintain sobriety. In some cases, rehabilitation is aided by the temporary use of psychoactive substances that reduce cravings and withdrawal symptoms without creating addiction themselves.\u00a0The drug methadone, for example, is commonly used\u00a0to treat heroin addiction.<\/p>\n<div>\n<h1>Feature: Human Biology in the News<\/h1>\n<\/div>\n<p>In North America, a lot of media attention is currently given to a rising tide of opioid addiction and overdose deaths. <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4690_3187\">Opioids<\/a><\/strong>\u00a0are drugs derived from the opium poppy or synthetic versions of such drugs. They include the illegal drug heroin, as well as prescription painkillers such\u00a0as codeine, morphine, hydrocodone, oxycodone, and fentanyl. In 2016, fentanyl received wide media attention when it was announced that an accidental fentanyl overdose was responsible for the death of music icon Prince. Fentanyl is an extremely strong and dangerous drug, said to be 50 to 100 times stronger than morphine, making risk of overdose death from fentanyl very high.<\/p>\n<p>The dramatic increase in opioid addiction and overdose deaths has been called an opioid epidemic. It is considered to be the worst drug crisis in Canadian history. Consider the following facts:<\/p>\n<ul>\n<li>In 2016, there were almost 2,500 opioid-related deaths in Canada \u2014 almost 7 per day.<\/li>\n<li>The number of prescriptions written for opioids quadrupled between 1999 and 2010.\u00a0 If you have been prescribed codeine, fentanyl, morphine, oxycodone, hydromorphone or medical heroin, then you have been prescribed an opiate.<\/li>\n<li>There are many long-term health effects of using opioids, which include:\n<ul>\n<li>Increased tolerance to the drug.<\/li>\n<li>Liver damage.<\/li>\n<li>Substance use disorder or addiction.<\/li>\n<\/ul>\n<\/li>\n<\/ul>\n<p>Doctors, public health professionals, and politicians have all called for new policies, funding, programs, and laws to address the opioid epidemic. Changes that have already been made include a shift from criminalizing to medicalizing the problem,\u00a0more\u00a0treatment programs, and more widespread distribution and use of the opioid-overdose antidote naloxone (Narcan). Opioids can slow or stop a person's\u00a0breathing, which is what usually causes overdose deaths. Naloxone helps the person wake up and keeps them breathing until emergency medical treatment can be provided.<\/p>\n<p>What, if anything, will work to stop the opioid epidemic in Canada and the United States? Keep watching the news to find out.<\/p>\n<div>\n<div class=\"textbox textbox--key-takeaways\">\n<header class=\"textbox__header\">\n<h1 class=\"textbox__title\"><span style=\"color: #ffffff\">8.8 Summary<\/span><\/h1>\n<\/header>\n<div class=\"textbox__content\">\n<ul>\n<li><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4690_3169\">Psychoactive drugs<\/a> are substances that change the function of the brain and result in alterations of mood, thinking, perception, and behavior. They include prescription medications (such as opioid painkillers), legal substances (such as nicotine and alcohol), and illegal drugs (such as LSD and heroin).<\/li>\n<li>Psychoactive drugs are divided into different classes according to their pharmacological effects. They include stimulants, depressants, anxiolytics, euphoriants, hallucinogens, and empathogens. Many psychoactive drugs have multiple effects, so they may be placed in more than one class.<\/li>\n<li>Psychoactive drugs generally produce their effects by affecting brain chemistry. Generally, they act either as agonists \u2014 which enhance the activity of particular <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4690_3056\">neurotransmitters<\/a>\u00a0\u2014 or as antagonists, which decrease the activity of particular neurotransmitters.<\/li>\n<li>Psychoactive drugs are used for various purposes, including medical,\u00a0ritual,\u00a0and recreational purposes.<\/li>\n<li>Misuse of psychoactive drugs may lead to <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4690_3184\">addiction<\/a>, which is the compulsive use of a drug despite the negative consequences such use may entail. Sustained use of an addictive drug may produce physical or psychological <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4690_2076\">dependence<\/a> on the drug. Rehabilitation typically involves psychotherapy, and sometimes the temporary use of other psychoactive drugs.<\/li>\n<\/ul>\n<\/div>\n<\/div>\n<div class=\"textbox textbox--exercises\">\n<header class=\"textbox__header\">\n<h1 class=\"textbox__title\"><span style=\"color: #ffffff\">8.8 Review Questions<\/span><\/h1>\n<\/header>\n<div class=\"textbox__content\">\n<ol>\n<li>What are psychoactive drugs?<\/li>\n<li>Identify six classes of psychoactive drugs, along with an example of a drug in each class.<\/li>\n<li>Compare and contrast psychoactive drugs that are agonists and\u00a0psychoactive drugs that are antagonists.<\/li>\n<li>Describe two medical uses of psychoactive drugs.<\/li>\n<li>Give an example of a ritual use of a psychoactive drug.<\/li>\n<li>Generally speaking, why do people use psychoactive drugs recreationally?<\/li>\n<li>Define addiction.<\/li>\n<li>Identify possible withdrawal symptoms associated with physical dependence on a psychoactive drug.<\/li>\n<li>Why might a person with a heroin addiction be prescribed the psychoactive drug methadone?<\/li>\n<li>The prescription drug Prozac inhibits the reuptake of the neurotransmitter serotonin, causing more serotonin to be present in the\u00a0synapse. Prozac can elevate mood, which is why it is sometimes used to treat depression. Answer the following questions about Prozac:\n<ol type=\"a\">\n<li>Is Prozac an agonist or an antagonist for serotonin? Explain your answer.<\/li>\n<li>Is Prozac a psychoactive drug? Explain your answer.<\/li>\n<\/ol>\n<\/li>\n<li>Name three classes of psychoactive drugs that include opioids.<\/li>\n<li><em>True or False:\u00a0<\/em>All psychoactive drugs are either illegal or available by prescription only.<\/li>\n<li><em>True or False:\u00a0<\/em>Anxiolytics might be prescribed by a physician.<\/li>\n<li>Name two drugs that activate receptors for the neurotransmitter GABA.\u00a0Why do you think these drugs generally have a depressant effect?<\/li>\n<\/ol>\n<\/div>\n<\/div>\n<\/div>\n<div class=\"textbox textbox--examples\">\n<header class=\"textbox__header\">\n<h1 class=\"textbox__title\"><span style=\"color: #ffffff\">8.8 Explore More<\/span><\/h1>\n<\/header>\n<div class=\"textbox__content\">\n<p>https:\/\/www.youtube.com\/watch?v=foLf5Bi9qXs<\/p>\n<p style=\"text-align: center\">How does caffeine keep us awake? - Hanan Qasim, TED-Ed, 2017.<\/p>\n<p>https:\/\/www.youtube.com\/watch?v=8qK0hxuXOC8<\/p>\n<p style=\"text-align: center\">How do drugs affect the brain? - Sara Garofalo, TED-Ed, 2017.<\/p>\n<p>https:\/\/www.youtube.com\/watch?v=Nlcr1jd_Tok<\/p>\n<p style=\"text-align: center\">Is marijuana bad for your brain? - Anees Bahji, TED-Ed, 2019.<\/p>\n<\/div>\n<\/div>\n<p>&nbsp;<\/p>\n<h2>Attributions<\/h2>\n<p><strong>Figure 8.8.1<\/strong><\/p>\n<p><a href=\"https:\/\/unsplash.com\/photos\/tZKwLRO904E\" rel=\"cc:attributionURL\">Cappucino Art by drew-coffman-tZKwLRO904E<\/a> [photo] by <a href=\"https:\/\/unsplash.com\/@drewcoffman\">Drew Coffman<\/a> on <a href=\"https:\/\/unsplash.com\/\">Unsplash<\/a> is used under the <a class=\"ICezk _2GAZm _2WvKc\" href=\"https:\/\/unsplash.com\/license\">Unsplash License<\/a> (https:\/\/unsplash.com\/license).<\/p>\n<p><strong>Figure 8.8.2<\/strong><\/p>\n<ul>\n<li><a href=\"https:\/\/commons.wikimedia.org\/wiki\/File:3804,_Saint-Laurent,_Montreal_-_Cannabis_Culture_shop.jpg\">3804, Saint-Laurent, Montreal - Cannabis Culture shop<\/a> by\u00a0<a class=\"external text\" href=\"https:\/\/www.flickr.com\/people\/29442760@N00\" rel=\"nofollow\">Exile on Ontario St<\/a> (Montreal, Canada) on Wikimedia Commons is used under a <a href=\"https:\/\/creativecommons.org\/licenses\/by-sa\/2.0\/deed.en\">CC BY SA 2.0 <\/a>(https:\/\/creativecommons.org\/licenses\/by-sa\/2.0\/deed.en) license.<\/li>\n<li><a href=\"https:\/\/www.flickr.com\/photos\/theunabonger\/478021002\">Drive Through Cigarette Store<\/a> by <a class=\"owner-name truncate no-outline\" title=\"Go to Cosmo Spacely's photostream\" href=\"https:\/\/www.flickr.com\/photos\/theunabonger\/\" data-track=\"attributionNameClick\">Cosmo Spacely<\/a> on <a href=\"http:\/\/flickr.com\">Flickr<\/a> is used under <a href=\"https:\/\/creativecommons.org\/licenses\/by-nc-sa\/2.0\/\">CC BY-NC-SA 2.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-nc-sa\/2.0\/) license.<\/li>\n<li><a href=\"https:\/\/www.flickr.com\/photos\/ventriloblog\/126224469\/\">Franklin-Nicollet Liquors<\/a> by <a class=\"owner-name truncate\" title=\"Go to Max Sparber's photostream\" href=\"https:\/\/www.flickr.com\/photos\/ventriloblog\/\" data-track=\"attributionNameClick\">Max Sparber<\/a> on <a href=\"http:\/\/flickr.com\">Flickr<\/a> is used under a <a href=\"https:\/\/creativecommons.org\/licenses\/by\/2.0\/deed.en\">CC BY 2.0<\/a> (https:\/\/creativecommons.org\/licenses\/by\/2.0\/deed.en) license.<\/li>\n<\/ul>\n<p><strong>Figure 8.8.3<\/strong><\/p>\n<p><a href=\"https:\/\/commons.wikimedia.org\/wiki\/File:Ecstasy_monogram.jpg#file\" rel=\"cc:attributionURL\">Ecstasy_monogram<\/a> by <i><a class=\"extiw\" title=\"w:Drug Enforcement Administration\" href=\"https:\/\/en.wikipedia.org\/wiki\/Drug_Enforcement_Administration\">Drug Enforcement Administration<\/a> <\/i>on Wikimedia Commons is in the <a class=\"mw-redirect\" title=\"Public domain\" href=\"https:\/\/commons.wikimedia.org\/wiki\/Public_domain\">public domain<\/a> (https:\/\/en.wikipedia.org\/wiki\/Public_domain).<\/p>\n<p><strong>Figure 8.8.4<\/strong><\/p>\n<p><a href=\"https:\/\/commons.wikimedia.org\/wiki\/File:US_Navy_030513-N-1577S-001_Lt._Cmdr._Joe_Casey,_Ship%27s_Anesthetist,_trains_on_anesthetic_procedures_with_Hospital_Corpsman_3rd_Class_Eric_Wichman_aboard_USS_Nimitz_(CVN_68).jpg\" rel=\"cc:attributionURL\">US Navy 030513-N-1577S-001 Lt. Cmdr. Joe Casey, Ship's Anesthetist, trains on anesthetic procedures with Hospital Corpsman 3rd Class Eric Wichman aboard USS Nimitz (CVN 68)<\/a> by U.S. Navy photo by Photographer\u2019s Mate Airman Timothy F. Sosais on Wikimedia Commons is in the <a class=\"mw-redirect\" title=\"Public domain\" href=\"https:\/\/commons.wikimedia.org\/wiki\/Public_domain\">public domain<\/a> (https:\/\/en.wikipedia.org\/wiki\/Public_domain).<\/p>\n<p><strong>Figure 8.8.5<\/strong><\/p>\n<p><a href=\"https:\/\/commons.wikimedia.org\/wiki\/File:Lophophora_williamsii_pm.jpg\" rel=\"cc:attributionURL\">Peyote Lophophora_williamsii_pm<\/a> by <a title=\"User:PeterMansfeld\" href=\"https:\/\/commons.wikimedia.org\/wiki\/User:PeterMansfeld\">Peter A. Mansfeld<\/a> on Wikimedia Commons is used under a <a href=\"https:\/\/creativecommons.org\/licenses\/by\/3.0\/deed.en\">CC BY 3.0<\/a> (https:\/\/creativecommons.org\/licenses\/by\/3.0\/deed.en) license.<\/p>\n<p><strong style=\"text-align: initial;font-size: 1em\"><br \/>\nFigure 8.8.6<\/strong><\/p>\n<section class=\"standard post-764 chapter type-chapter status-publish hentry focusable\" data-type=\"chapter\">\n<div class=\"media-atttributions\">\n<p><a href=\"https:\/\/www.flickr.com\/photos\/10233916@N03\/2526930264\/in\/photolist-3QtaE-4Zhtt7-844WT6-5HED3R-4Ribkb-6aaVt7-ekhNvK-9QFDgP-7Khsf-21p6zx-HPAcuZ-4wKSaH-RTW4nt-8KBR3K-9K4Hg2-9K7wTL-pCriyp-C4XKJ-7Q5Q-9K4HY2-6CaNK5-dZ5sqL-8yJNjk-7feRXF-JJpCF-S1Be3J-dYYKWx-dYYKTp-auB7co-7UmiU5-adcRHZ-7fiJF9-3jnSVf-9BpzN3-7fiFjb-7fiJJ1-7fiJVA-7fiJs7-dYYL96-7feRGP-dZ5sho-6KLkkz-7feRKP-7feSbx-7feSeV-7feNyR-7feRQT-7fiJMb-f87VTi-c2TF8J\" rel=\"cc:attributionURL\">Cat under effects of catnip\/Self Indulgence<\/a> by\u00a0<a href=\"https:\/\/www.flickr.com\/photos\/10233916@N03\/\" rel=\"dc:creator\">Katieb50<\/a> on <a href=\"https:\/\/www.flickr.com\/\" rel=\"cc:attributionURL\">Flickr<\/a> is used under a\u00a0<a href=\"https:\/\/creativecommons.org\/licenses\/by\/2.0\/deed.en\">CC BY 2.0<\/a> (https:\/\/creativecommons.org\/licenses\/by\/2.0\/deed.en) license.<\/p>\n<p>&nbsp;<\/p>\n<\/div>\n<div class=\"glossary\"><span style=\"font-size: 1.424em;font-weight: bold;color: #333333\">References<\/span><\/div>\n<div><\/div>\n<\/section>\n<p class=\"hanging-indent\">Alcoholics Anonymous World Services, Inc. (n.d.). Regional correspondent U.S. and Canada [website]. https:\/\/www.aa.org\/pages\/en_US\/regional-correspondent-us-and-canada<\/p>\n<p class=\"hanging-indent\"><span style=\"color: #373d3f;font-size: 1em;text-align: initial;text-indent: -1em\">Belzak, L., &amp; Halverson, J. (2018). The opioid crisis in Canada: a national perspective. La crise des opio\u00efdes au Canada : une perspective nationale. <\/span><i style=\"color: #373d3f;font-size: 1em;text-align: initial;text-indent: -1em\">Health promotion and chronic disease prevention in Canada : research, policy and practice<\/i><span style=\"color: #373d3f;font-size: 1em;text-align: initial;text-indent: -1em\">,\u00a0<\/span><i style=\"color: #373d3f;font-size: 1em;text-align: initial;text-indent: -1em\">38<\/i><span style=\"color: #373d3f;font-size: 1em;text-align: initial;text-indent: -1em\">(6), 224\u2013233. https:\/\/doi.org\/10.24095\/hpcdp.38.6.02<\/span><\/p>\n<p class=\"hanging-indent\">British Columbia Regional Service Committee of Narcotics Anonymous. (n.d.). Welcome to the B.C. region of N.A. [website]. https:\/\/www.bcrna.ca\/<\/p>\n<p class=\"glossary hanging-indent\"><span style=\"text-align: initial;color: #333333;font-size: 1em\">Centers for Disease Control and Prevention (CDC). (2011 November 4). <\/span>Vital signs: overdoses of prescription opioid pain relievers\u2014United States, 1999\u20132008.<span style=\"text-align: initial;color: #333333;font-size: 1em\"><em> Morbidity and Mortality Weekly Report (MMWR),<\/em><em>60<\/em>(43):1487-1492. https:\/\/www.cdc.gov\/mmwr\/preview\/mmwrhtml\/mm6043a4.htm<\/span><\/p>\n<p class=\"hanging-indent\"><span style=\"text-align: initial;color: #333333;font-size: 1em\">TED-Ed. (2017, June 29). How do drugs affect the brain? - Sara Garofalo. YouTube. https:\/\/www.youtube.com\/watch?v=8qK0hxuXOC8&amp;feature=youtu.be<\/span><\/p>\n<p class=\"hanging-indent\">TED-Ed. (2017, July 17). How does caffeine keep us awake? - Hanan Qasim. YouTube. https:\/\/www.youtube.com\/watch?v=foLf5Bi9qXs&amp;feature=youtu.be<\/p>\n<p class=\"hanging-indent\">TED-Ed. (2019, December 2). Is marijuana bad for your brain? - Anees Bahji. YouTube. https:\/\/www.youtube.com\/watch?v=Nlcr1jd_Tok&amp;feature=youtu.be<\/p>\n<p>&nbsp;<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_4690_2804\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_4690_2804\"><div tabindex=\"-1\"><p>Created by CK-12 Foundation\/Adapted by Christine Miller<\/p>\n<figure id=\"attachment_718\" aria-describedby=\"caption-attachment-718\" style=\"width: 1023px\" class=\"wp-caption aligncenter\"><img class=\"wp-image-718\" src=\"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-content\/uploads\/sites\/152\/2019\/06\/Alzheimers_Disease.jpg\" alt=\"\" width=\"1023\" height=\"791\"><figcaption id=\"caption-attachment-718\" class=\"wp-caption-text\"><em>Figure 8.9.1 Molecular and cellular changes occur in a brain with Alzheimer\u2019s disease (AD).<\/em><\/figcaption><\/figure>\n<h1>Case Study Conclusion: Fading Memory<\/h1>\n<p>The illustration above (Figure 8.9.1) shows some of the molecular and cellular changes that occur in Alzheimer\u2019s disease (AD). Rosa was diagnosed with AD at the beginning of this chapter after experiencing memory problems and other changes in her cognitive functioning, mood, and personality. These abnormal changes in the brain include the development of amyloid plaques between brain cells and neurofibrillary tangles inside of neurons. These hallmark characteristics of AD are associated with the loss of synapses between neurons, and ultimately the death of neurons.<\/p>\n<p>After reading this chapter, you should have a good appreciation for the importance of keeping neurons alive and communicating with each other at synapses. The nervous system coordinates all of the body\u2019s voluntary and involuntary activities. It interprets information from the outside world through sensory systems, and makes appropriate responses through the motor system, through communication between the PNS and CNS. The brain directs the rest of the nervous system and controls everything from basic vital functions (such as heart rate and breathing) to high-level functions (such as problem solving and abstract thought). The nervous system\u00a0can\u00a0perform these important functions by generating action potentials in neurons in response to stimulation and sending messages between cells at synapses, typically using chemical neurotransmitter molecules. When neurons are not functioning properly, lose their synapses, or die, they cannot carry out the signaling essential for the proper functioning of the nervous system.<\/p>\n<p>AD is a progressive neurodegenerative disease, meaning that the damage to the brain becomes more extensive as time goes on. The picture in Figure 8.9.2 illustrates how the damage progresses from before AD is diagnosed (preclinical AD), to mild and moderate AD, to severe AD.<\/p>\n<figure id=\"attachment_718\" aria-describedby=\"caption-attachment-718\" style=\"width: 644px\" class=\"wp-caption aligncenter\"><img class=\" wp-image-3192\" src=\"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-content\/uploads\/sites\/152\/2023\/10\/Alzheimers-Disease-stagess-scaled-1.jpg\" alt=\"\" width=\"644\" height=\"1388\"><figcaption id=\"caption-attachment-718\" class=\"wp-caption-text\"><em>Figure 8.9.2 Illustration showing the areas of the brain that become damaged as Alzheimer\u2019s disease (AD) progresses. This is a side view along the middle of the brain, with the front of the brain shown to the left. Damaged areas are shown in blue.<\/em><\/figcaption><\/figure>\n<div>\n<p>&nbsp;<\/p>\n<\/div>\n<p>You can see that the damage starts in a relatively small location toward the bottom of the brain. One of the earliest brain areas to be affected by AD is the hippocampus. As you have learned, the hippocampus is important for learning and memory, which explains why many of Rosa\u2019s symptoms of mild AD involve deficits in memory, such as trouble remembering where she placed objects, recent conversations, and appointments.<\/p>\n<p>As AD progresses, more of the brain is affected, including areas involved in emotional regulation, social behavior, planning, language, spatial navigation, and higher-level thought. Rosa is beginning to show signs of problems in these areas, including irritability, lashing out at family members, getting lost in her neighborhood, problems finding the right words, putting objects in unusual locations, and difficulty in managing her finances. You can see that as AD progresses, damage spreads further across the cerebrum, which you now know controls conscious functions\u00a0like\u00a0reasoning, language, and interpretation of sensory stimuli. You can also see how the frontal lobe \u2014 which controls executive functions such as planning, self-control, and abstract thought \u2014 becomes increasingly damaged.<\/p>\n<p>Increasing damage to the brain causes corresponding deficits in functioning. In moderate AD, patients have increased memory, language, and cognitive deficits, compared to mild AD. They may not recognize their own family members, and may wander and get lost, engage in inappropriate behaviors, become easily agitated, and have trouble carrying out daily activities such as dressing. In severe AD, much of the brain is affected. Patients usually cannot recognize family members or communicate, and they are often fully dependent on others for their care. They begin to lose the ability to control their basic functions, such as bladder control, bowel control, and proper swallowing. Eventually, AD causes death, usually as a result of this loss of basic functions.<\/p>\n<p>For now, Rosa only has mild AD and is still able to function relatively well with care from her family. The medication her doctor gave her has helped improve some of her symptoms. It is a cholinesterase inhibitor, which blocks an enzyme that normally degrades the neurotransmitter acetylcholine. With more of the neurotransmitter available, more of it can bind to neurotransmitter receptors on postsynaptic cells. Therefore, this drug acts as an agonist for acetylcholine, which enhances communication between neurons in Rosa\u2019s brain. This increase in neuronal communication can help restore some of the functions lost in early Alzheimer\u2019s disease and may slow the progression of symptoms.<\/p>\n<p>But medication such as this is only a short-term measure, and does not halt the progression of the underlying disease. Ideally, the damaged or dead neurons would be replaced by new, functioning neurons. Why does this not happen automatically in the body? As you have learned, neurogenesis is very limited in adult humans, so once neurons in the brain die, they are not normally replaced to any significant extent.\u00a0Scientists, however, are studying the ways in which neurogenesis might be increased in cases of disease or injury to the brain.\u00a0They are also investigating the possibility of using stem cell transplants to replace damaged or dead neurons with new neurons. But this research is in very early stages and is not currently a treatment for AD.<\/p>\n<p>One promising area of research is in the development of methods to allow earlier detection and treatment of AD, given that the changes in the brain may actually start ten to 20 years before diagnosis of AD.\u00a0A\u00a0radiolabeled chemical called Pittsburgh Compound B (PiB) binds to amyloid plaques in the brain, and in the future, it may be used in conjunction with brain imaging techniques to detect early signs of AD. Scientists are also looking for biomarkers in bodily fluids (such as blood and cerebrospinal fluid) that might indicate the presence of AD before symptoms appear. Finally, researchers are also investigating possible early and subtle symptoms (such as changes in how people move or a loss of smell) to see whether they can be used to identify people who will go on to develop AD. This research is in the early stages, but the hope is that patients can be identified earlier, allowing for earlier and more effective treatment, as well as more planning time for families.<\/p>\n<p>Scientists are also still trying to fully understand the causes of AD, which affects more than five million Americans. Some genetic mutations have been identified\u00a0as contributors, but environmental factors also appear to be important. With more research into the causes and mechanisms of AD, hopefully a cure can be found, and people like Rosa can live a longer and better life.<\/p>\n<div>\n<div class=\"textbox textbox--learning-objectives\">\n<header class=\"textbox__header\">\n<h1 class=\"textbox__title\"><span style=\"color: #ffffff\">Chapter 8 Summary<\/span><\/h1>\n<\/header>\n<div class=\"textbox__content\">\n<p>In this chapter, you learned about the human nervous system. Specifically, you learned that:<\/p>\n<ul>\n<li>The <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4690_2908\">nervous system<\/a> is the organ system that coordinates all of the body\u2019s <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4690_3004\">voluntary<\/a> and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4690_3005\">involuntary<\/a> actions by transmitting signals to and from different parts of the body. It has two major divisions: the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4690_2579\">central nervous system<\/a> (CNS) and the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4690_3009\">peripheral nervous system<\/a> (PNS).\n<ul>\n<li>The CNS\u00a0includes\u00a0the brain and spinal cord.<\/li>\n<li>The PNS consists mainly of nerves that connect the CNS with the rest of the body. It has two major divisions: the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4690_3014\">somatic nervous system<\/a> and the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4690_2533\">autonomic nervous system<\/a>. These divisions control different types of functions, and often interact with the CNS to carry out these functions. The somatic system controls activities that are under voluntary control. The autonomic system controls activities that are involuntary.\n<ul>\n<li>The autonomic nervous system is further divided into the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4690_3015\">sympathetic division<\/a> (which controls the fight-or-flight response), the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4690_3016\">parasympathetic division<\/a> (which controls most routine involuntary responses), and the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4690_2650\">enteric division<\/a> (which provides local control for digestive processes).<\/li>\n<\/ul>\n<\/li>\n<\/ul>\n<\/li>\n<\/ul>\n<ul>\n<li style=\"list-style-type: none\"><\/li>\n<li>Signals sent by the nervous system are electrical signals called <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4690_2266\">nerve impulses<\/a>. They are transmitted by special, electrically excitable cells called <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4690_2984\">neurons<\/a>, which are one of two major types of cells in the nervous system.<\/li>\n<li><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4690_2985\">Neuroglia<\/a> are the other major type of nervous system cells. There are many types of glial cells, and they have many specific functions. In general, neuroglia function to support, protect, and nourish neurons.<\/li>\n<li>The main parts of a neuron include the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4690_2576\">cell body<\/a>, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4690_2622\">dendrites<\/a>, and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4690_2535\">axon<\/a>. The cell body contains the nucleus. Dendrites receive nerve impulses from other cells, and the axon transmits nerve impulses to other cells at axon terminals. A synapse is a complex membrane junction at the end of an axon terminal that transmits signals to another cell.<\/li>\n<li>Axons are often wrapped in an electrically-insulating <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4690_3028\">myelin sheath<\/a>, which is produced by oligodendrocytes or schwann cells, both of which are types of neuroglia. Electrical impulses called <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4690_3049\">action potentials<\/a>\u00a0occur at gaps in the myelin sheath, called <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4690_3041\">nodes of Ranvier<\/a>, which speeds the conduction of nerve impulses down the axon.<\/li>\n<li><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4690_3025\">Neurogenesis<\/a>, or the formation of new neurons by cell division, may occur in a mature human brain \u2014 but only to a limited extent.<\/li>\n<li>The nervous tissue in the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4690_2554\">brain <\/a>and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4690_3010\">spinal cord<\/a> consists of gray matter \u2014 which contains mainly unmyelinated cell bodies and dendrites of neurons \u2014 and white matter, which contains mainly myelinated axons of neurons. Nerves of the peripheral nervous system consist of long bundles of myelinated axons that extend throughout the body.<\/li>\n<li>There are hundreds of types of neurons in the human nervous system, but many can be classified on the basis of the direction in which they carry nerve impulses. <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4690_3030\">Sensory neurons<\/a> carry nerve impulses away from the body and toward the central nervous system, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4690_3031\">motor neurons<\/a> carry them away from the central nervous system and toward the body, and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4690_3032\">interneurons<\/a> often carry them between sensory and motor neurons.<\/li>\n<li>A nerve impulse is an electrical phenomenon that occurs because of a difference in electrical charge across the plasma membrane of a neuron.<\/li>\n<li>The <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4690_2287\">sodium-potassium pump<\/a> maintains an electrical gradient across the plasma membrane of a neuron when it is not actively transmitting a nerve impulse. This gradient is called the resting potential of the neuron.<\/li>\n<li>An action potential is a sudden reversal of the electrical gradient across the plasma membrane of a resting neuron. It begins when the neuron receives a chemical signal from another cell or some other type of stimulus. The action potential travels rapidly down the neuron\u2019s axon as an electric current.<\/li>\n<li>A nerve impulse is transmitted to another cell at either an electrical or a chemical <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4690_3040\">synapse<\/a>. At a chemical synapse, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4690_3056\">neurotransmitter<\/a> chemicals are released from the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4690_3052\">presynaptic cell<\/a> into the synaptic cleft between cells. The chemicals travel across the cleft to the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4690_3053\">postsynaptic cell<\/a> and bind to receptors embedded in its membrane.<\/li>\n<li>There are many different types of neurotransmitters. Their effects on the postsynaptic cell generally depend on the type of receptor they bind to. The effects may be excitatory, inhibitory, or modulatory in more complex ways. Both physical and mental disorders may occur if there are problems with neurotransmitters or their receptors.<\/li>\n<li>The CNS includes the brain and spinal cord. It is physically protected by <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4690_2552\">bones<\/a>, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4690_2929\">meninges<\/a>, and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4690_2589\">cerebrospinal fluid<\/a>. It is chemically protected by the blood-brain barrier.<\/li>\n<li>The brain is the control center of the nervous system and of the entire organism. The brain uses a relatively large proportion of the body\u2019s energy, primarily in the form of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4690_1945\">glucose<\/a>.<\/li>\n<\/ul>\n<ul>\n<li style=\"list-style-type: none\">\n<ul>\n<li>The brain is divided into three major parts, each with different functions: the forebrain, the midbrain and the hindbrain.\n<ul>\n<li>The forebrain includes the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4690_2592\">cerebrum<\/a>, the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4690_3095\">thalamus<\/a>, the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4690_2937\">hypothalamus<\/a>, the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4690_3096\">hippocampus<\/a> and the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4690_2512\">amygdala<\/a>. The cerebrum is further divided into left and right hemispheres. Each hemisphere has four lobes: frontal, parietal, temporal, and occipital. Each lobe is associated with specific senses or other functions.\u00a0 The cerebrum has a thin outer layer called the cerebral cortex. Its many folds give it a large surface area. This is where most information processing takes place.<\/li>\n<\/ul>\n<\/li>\n<li>The thalamus, hypothalamus, hippocampus and amygdala are all part of the limbic system which helps regulate memories, coordination and attention<\/li>\n<\/ul>\n<\/li>\n<li>The <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4690_3010\">spinal cord<\/a> is a tubular bundle of nervous tissues that extends from the head down the middle of the back to the pelvis. It functions mainly to connect the brain with the PNS. It also controls certain rapid responses called reflexes without input from the brain.\n<ul>\n<li>A spinal cord injury may lead to paralysis (loss of sensation and movement) of the body below the level of the injury, because nerve impulses can no longer travel up and down the spinal cord beyond that point.<\/li>\n<\/ul>\n<\/li>\n<li>The PNS consists of all the nervous tissue that lies outside of the CNS. Its main function is to connect the CNS to the rest of the organism.<\/li>\n<li>The tissues that make up the PNS are <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4690_3011\">nerves<\/a> and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4690_2699\">ganglia<\/a>. Nerves are bundles of axons and ganglia are groups of cell bodies.\u00a0Nerves are classified as sensory, motor, or\u00a0a mix of the two.\n<ul>\n<li>The PNS is not as well protected physically or chemically as the CNS, so it is more prone to injury and disease. PNS problems include injury from diabetes, shingles, and heavy metal poisoning. Two disorders of the PNS are Guillain-Barre syndrome and Charcot-Marie-Tooth disease.<\/li>\n<\/ul>\n<\/li>\n<li>The human body has two major types of senses: special senses and general senses. Special senses have specialized sense organs and include vision (eyes), hearing (ears), balance (ears), taste (tongue), and smell (nasal passages). General senses are all associated with touch and lack special sense organs. Touch receptors are found throughout the body but particularly in the skin.<\/li>\n<li>All senses depend on sensory receptor cells to detect sensory stimuli and transform them into nerve impulses. Types of sensory receptors include <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4690_3124\">mechanoreceptors<\/a>\u00a0(mechanical forces), <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4690_3125\">thermoreceptors<\/a>\u00a0(temperature), <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4690_3126\">nociceptors<\/a>\u00a0(pain), <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4690_3127\">photoreceptors<\/a>\u00a0(light), and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4690_3128\">chemoreceptors<\/a>\u00a0(chemicals).\n<ul>\n<li><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4690_3129\">Touch<\/a> includes the ability to sense pressure, vibration, temperature, pain, and other tactile stimuli. The skin includes several different types of touch receptor cells.<\/li>\n<li><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4690_3164\">Vision<\/a> is the ability to sense light and see. The eye is the special sensory organ that collects and focuses light, forms images, and changes them to nerve impulses. Optic nerves send information from the eyes to the brain, which processes the visual information and \u201ctells\u201d us what we are seeing.\n<ul>\n<li>Common vision problems include <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4690_3144\">myopia<\/a> (nearsightedness), <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4690_3145\">hyperopia<\/a> (farsightedness), and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4690_3165\">presbyopia<\/a> (age-related decline in close vision).<\/li>\n<\/ul>\n<\/li>\n<li><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4690_3151\">Hearing<\/a> is the ability to sense sound waves, and the ear is the organ that senses sound. It changes sound waves to vibrations that trigger nerve impulses, which travel to the brain through the auditory nerve. The brain processes the information and \u201ctells\u201d us what we are hearing.<\/li>\n<li>The ear is also the organ responsible for the sense of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4690_3155\">balance<\/a>, which is the ability to sense and maintain an appropriate body position. The ears send impulses on head position to the brain, which sends messages to skeletal muscle via the peripheral nervous system. The muscles respond by contracting to maintain balance.<\/li>\n<li><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4690_3157\">Taste<\/a> and smell are both abilities to sense chemicals. Taste receptors in taste buds on the tongue sense chemicals in food, and olfactory receptors in the nasal passages sense chemicals in the air. The sense of smell contributes significantly to the sense of taste.<\/li>\n<\/ul>\n<\/li>\n<li><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4690_3169\">Psychoactive drugs<\/a> are substances that change the function of the brain and result in alterations of mood, thinking, perception, and behavior. They include prescription medications (such as opioid painkillers), legal substances (such as nicotine and alcohol), and illegal drugs (such as LSD and heroin).<\/li>\n<li>Psychoactive drugs are divided into different classes according to their pharmacological effects. They include <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4690_3171\">stimulants<\/a>, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4690_3172\">depressants<\/a>, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4690_3173\">anxiolytics<\/a>, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4690_3174\">euphoriants<\/a>, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4690_3175\">hallucinogens<\/a>, and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4690_3176\">empathogens<\/a>. Many psychoactive drugs have multiple effects, so they may be placed in more than one class.<\/li>\n<li>Psychoactive drugs generally produce their effects by affecting brain chemistry. Generally, they act either as <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4690_3178\">agonists<\/a>, which enhance the activity of particular neurotransmitters, or as <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4690_3179\">antagonists<\/a>, which decrease the activity of particular neurotransmitters.<\/li>\n<li>Psychoactive drugs are used for\u00a0medical, ritual, and recreational\u00a0purposes.<\/li>\n<li>Misuse of psychoactive drugs may lead to <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4690_3184\">addiction<\/a>, which is the compulsive use of a drug, despite its negative consequences. Sustained use of an addictive drug may produce physical or psychological <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_4690_2076\">dependence<\/a> on the drug. Rehabilitation typically involves psychotherapy, and sometimes the temporary use of other psychoactive drugs.<\/li>\n<\/ul>\n<ul>\n<li style=\"list-style-type: none\"><\/li>\n<\/ul>\n<p>In addition to the nervous system, there is another system of the body that is important for coordinating and regulating many different functions \u2013 the endocrine system. You will learn about the endocrine system in the next chapter.<\/p>\n<\/div>\n<\/div>\n<div class=\"textbox textbox--exercises\">\n<header class=\"textbox__header\">\n<h1 class=\"textbox__title\"><span style=\"color: #ffffff\">Chapter 8 Review<\/span><\/h1>\n<\/header>\n<div class=\"textbox__content\">\n<ol>\n<li>Imagine that you decide to make a movement. To carry out this decision, a neuron in the cerebral cortex of your brain (neuron A) fires a nerve impulse that is sent to a neuron in your spinal cord (neuron B). Neuron B then sends the signal to a muscle cell, causing it to contract, resulting in movement. Answer the following questions about this pathway.\n<ol type=\"a\">\n<li>Which part of the brain is neuron A located in \u2014 the cerebellum, cerebrum, or brain stem? Explain how you know.<\/li>\n<li>The cell body of neuron A is located in a lobe of the brain that is involved in abstract thought, problem solving, and planning. Which lobe is this?<\/li>\n<li>Part of neuron A travels all the way down to the spinal cord to meet neuron B. Which part of neuron A travels to the spinal cord?<\/li>\n<li>Neuron A forms a chemical synapse with neuron B in the spinal cord. How is the signal from neuron A transmitted to neuron B?<\/li>\n<li>Is neuron A in the central nervous system (CNS) or peripheral nervous system (PNS)?<\/li>\n<li>The axon of neuron B travels in a nerve to a skeletal muscle cell. Is the nerve part of the CNS or PNS? Is this an afferent nerve or an efferent nerve?<\/li>\n<li>What part of the PNS is involved in this pathway \u2014 the autonomic nervous system or the somatic nervous system? Explain your answer.<\/li>\n<\/ol>\n<\/li>\n<li>What are the differences between a neurotransmitter receptor and a sensory receptor?<\/li>\n<li>\n<div id=\"h5p-130\">\n<div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-130\" class=\"h5p-iframe\" data-content-id=\"130\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"8.3 Review Questions Neurons and Neuroglia\"><\/iframe><\/div>\n<\/div>\n<\/li>\n<li>If a person has a stroke and then has trouble using language correctly, which hemisphere of their brain was most likely damaged? Explain your answer.<\/li>\n<li>Electrical gradients are responsible for the resting potential and action potential in neurons. Answer the following questions about the electrical characteristics of neurons.\n<ol type=\"a\">\n<li>Define an electrical gradient, in the context of a cell.<\/li>\n<li>What is responsible for maintaining the electrical gradient that results in the resting potential?<\/li>\n<li>Compare and contrast the resting potential and the action potential.<\/li>\n<li>Where along a myelinated axon does the action potential occur? Why does it happen here?<\/li>\n<li>What does it mean that the action potential is \u201call-or-none?\u201d<\/li>\n<\/ol>\n<\/li>\n<li>Compare and contrast Schwann cells and oligodendrocytes.<\/li>\n<li>For the senses of smell and hearing, name their respective sensory receptor cells, what type of receptor cells they are, and what stimuli they detect.<\/li>\n<li>Nicotine is a psychoactive drug that binds to and activates a receptor for the neurotransmitter acetylcholine. Is nicotine an agonist or an antagonist for acetylcholine? Explain your answer.<\/li>\n<\/ol>\n<\/div>\n<\/div>\n<\/div>\n<h2>Attributions<\/h2>\n<p><strong>Figure 8.9.1<\/strong><\/p>\n<p><a href=\"https:\/\/commons.wikimedia.org\/wiki\/File:Alzheimers_Disease.jpg\" rel=\"cc:attributionURL\">Alzheimers_Disease<\/a> by <a title=\"User:BruceBlaus\" href=\"https:\/\/commons.wikimedia.org\/wiki\/User:BruceBlaus\">BruceBlaus<\/a> on Wikimedia Commons is used under a <a href=\"https:\/\/creativecommons.org\/licenses\/by-sa\/4.0\/\" rel=\"license\">CC BY-SA 4.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-sa\/4.0\/deed.en) license.<\/p>\n<p><strong>Figure 8.9.2<\/strong><\/p>\n<p><a href=\"https:\/\/www.flickr.com\/photos\/nihgov\/24524716351\/\" rel=\"cc:attributionURL\">Alzheimer\u2019s Disease stagess<\/a> by <a class=\"owner-name truncate no-outline\" title=\"Go to NIH Image Gallery's photostream\" href=\"https:\/\/www.flickr.com\/photos\/nihgov\/\" data-track=\"attributionNameClick\">NIH Image Gallery<\/a> on <a href=\"http:\/\/flickr.com\">Flickr<\/a> is in the <a class=\"photo-license-url\" href=\"https:\/\/creativecommons.org\/publicdomain\/mark\/1.0\/\" target=\"_newtab\" rel=\"license cc:license noopener noreferrer\">public domain<\/a> (https:\/\/en.wikipedia.org\/wiki\/Public_domain).<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_4690_5711\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_4690_5711\"><div tabindex=\"-1\"><p>The smallest particle of an element that still has the properties of that element.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_4690_5779\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_4690_5779\"><div tabindex=\"-1\"><p>A molecule is an electrically neutral group of two or more atoms held together by chemical bonds.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><\/div>","protected":false},"author":32,"menu_order":2,"template":"","meta":{"pb_show_title":"on","pb_short_title":"","pb_subtitle":"","pb_authors":[],"pb_section_license":"cc-by-nc"},"chapter-type":[48],"contributor":[],"license":[55],"class_list":["post-4690","chapter","type-chapter","status-publish","hentry","chapter-type-numberless","license-cc-by-nc"],"part":4681,"_links":{"self":[{"href":"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-json\/pressbooks\/v2\/chapters\/4690","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-json\/pressbooks\/v2\/chapters"}],"about":[{"href":"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-json\/wp\/v2\/types\/chapter"}],"author":[{"embeddable":true,"href":"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-json\/wp\/v2\/users\/32"}],"version-history":[{"count":4,"href":"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-json\/pressbooks\/v2\/chapters\/4690\/revisions"}],"predecessor-version":[{"id":6426,"href":"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-json\/pressbooks\/v2\/chapters\/4690\/revisions\/6426"}],"part":[{"href":"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-json\/pressbooks\/v2\/parts\/4681"}],"metadata":[{"href":"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-json\/pressbooks\/v2\/chapters\/4690\/metadata\/"}],"wp:attachment":[{"href":"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-json\/wp\/v2\/media?parent=4690"}],"wp:term":[{"taxonomy":"chapter-type","embeddable":true,"href":"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-json\/pressbooks\/v2\/chapter-type?post=4690"},{"taxonomy":"contributor","embeddable":true,"href":"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-json\/wp\/v2\/contributor?post=4690"},{"taxonomy":"license","embeddable":true,"href":"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-json\/wp\/v2\/license?post=4690"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}