Skeletal and Other Muscle Types
Our Bodies Contain Both Voluntary and Involuntary Muscles
Mar 13, 2008
We can move our bodies because of the control we can exert over our skeletal muscles. But for every muscle that we can control, there are numerous others that we cannot. Cardiac muscle and smooth muscle are equally as important to our daily existence, yet we are unable to make them behave according to our will. Both voluntary and involuntary muscles are found throughout our bodies and muscles control some functions you likely never thought of.
Skeletal Muscle
Everyone knows skeletal muscle. It is the muscle type used to do work, move something, or even snap your fingers. Also known as striated muscle because of its striped appearance in the microscope, these are also known as voluntary muscles. Most, but not all, skeletal muscles are attached via tendons to bone. Conscious control from our brains leads to signals that make these muscles contract. When they contract, or shorten, they create force against tendon and bone, causing them to move. Unlike any other type of muscle in the body, skeletal muscles form as a result of many individual muscle precursor cells fusing together. The resulting larger, single cell still contains all of the nuclei from the original cells. Therefore, besides being known as voluntary, or striated, or skeletal muscle, they are also known as multinucleated muscle fibers.
Cardiac Muscle
Also known as the myocardium, this is the muscle that forms the majority of the heart and its chambers. It is obviously not a voluntary muscle. It works continuously for quite some time without our even thinking about it. Many physiological signals can control how forcefully or how quickly the myocardium contracts, but conscious thought typically does not have that great an impact on its contraction. While myocardium resembles skeletal muscle in several respects, it is structurally quite different. Remaining as individual muscle cells, not fusing like skeletal muscle, cardiac muscle cells form specialized electrical communication pathways with their neighboring cells. This is done because when the signal comes to contract, all of the myocardium in one of the heart chambers really needs to do so in unison.
Smooth Muscle
This type of involuntary muscle is the one that most people have never heard of but plays every bit as important a role as do the other types of muscle. The blood vessels all contain a layer of smooth muscle within their walls. The tonic contraction of this type of vascular smooth muscle in the arteries and arterioles plays a major role in regulating blood pressure. When food is eaten, the digestive tract is able to process it because of the work done by smooth muscles. The walls of the intestines have a layer of smooth muscle, as does the wall of the bladder. When you walk into a darkened room and your pupils dilate or conversely when you walk outside into bright sunlight and your pupils constrict, the effects are due in large part to the work of smooth muscles in the iris of the eyes. The hairs on your arms and legs can “stand on end” because of smooth muscles.
Humans are truly muscular creatures, even the couch potatoes. The body contains more than 600 skeletal muscles and many more involuntary muscles. And there is a long list of bodily functions that require muscle that we don’t even have to think about and couldn’t really control even if we wanted to. The next time something really scares you and your pulse quickens and all of the hairs on your arms and the back of your neck stand on end just say to yourself, hey, that was a pretty good flex.
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