36 Muscular Integration of Systems
Think of all of the activities you do that require function of your muscular system. These include walking, chewing, swallowing, breathing, talking, etc. Dysfunctions of this system (such as weakness or hypertonia) can prevent the body from carrying out any of these activities normally. This in turn can affect many other systems. For example, if we can’t bring in appropriate nutrients and oxygen, every other system in the body would be affected, as they are all dependent on fuel sources.
Muscles require a large amount of energy and thus require a constant supply of oxygen and nutrients. Blood vessels enter muscle at its surface, after which they are distributed through the entire muscle. Blood vessels are found in the connective tissue that surrounds muscles, allowing oxygen and nutrients to be supplied to muscle and metabolic waste to be removed. The epimysium houses the arteries and veins that allow blood to enter and exit muscle. The blood vessels then branch into the epimysium to serve each fascicle and then further branch in the endomysium to form a capillary network that contacts each muscle fiber. The flexible, extensively branched capillary networks are able to withstand muscle contractions without being damaged.
Skeletal muscles are under neural control, which means that nerves must be present for the muscle to function. The epimysium contains nerve fibers that branch through the perimysium and epimysium to connect neurons to individual muscle fibers.
Cardiac and Smooth Muscles
Although this unit has primarily focused on skeletal muscle, don’t forget about cardiac and smooth muscle, both of which play vital roles in the cardiovascular system (and smooth muscle in other systems as well). Your heart needs to continuously contract in order to keep blood flowing to your organs, and in turn, supply them with needed oxygen and nutrients. But smooth muscle also plays a vital role. It is found in the walls of all blood vessels except for capillaries, and its function is to dilate or constrict, depending on the needs of the body and the downstream tissues. For example, if the skeletal muscles in your legs increase their metabolic rate because you start running, smooth muscle cells in the arteries feeding these muscles will relax. This dilates these arteries, allowing for a greater blood flow to the muscles of the legs. In fact, arteries to other regions (such as the gastrointestinal tract) may partially constrict in an effort to shunt more blood toward the legs. It is these smooth muscles that play a vital role in sending higher amounts of blood to where it is needed most. Skeletal muscles also play a role within the cardiovascular system. The heart acts as the pump to move blood out to the body cells, but the skeletal muscles assist with the movement of blood back to the heart. Because of valves in the veins that prevent back flow, the contraction of skeletal muscles around the major veins helps move the blood from one compartment to the next, slowly returning blood back to the heart.
Muscles in the Digestive System
Muscles are extremely important in the digestive system as well. The muscles of our mouth, tongue and jaw are responsible for biting and chewing our food. Within our digestive tract, sphincters located throughout the digestive system are responsible for compartmentalizing the digestive processes within discrete organs. We are most familiar with the anal sphincter that we are able to control to excrete waste from the digestive system. Also, throughout the digestive system, smooth muscle helps generate small forces to mix food in the stomach and help maintain movements throughout the digestive process.
