By Elizabeth A. Murray, Mount St. Joseph University
The skeletal muscle is given this name because of its general ability to move the bones of the skeleton through its attachments. It is a voluntary muscle tissue, subject to our conscious control. However, it can develop what become more or less subconscious patterns of muscle action—sometimes called muscle memory—like knowing how to swing a tennis racket, throw a ball, drive a car, or perform a particular dance routine, without really thinking about it.
Bodily Movements
As a tissue, skeletal muscle has several major functions. Body part movement is an obvious function, but not all skeletal muscle movements are as plain to see, such as our more subtle movements, like breathing and the voluntary phase at the start of swallowing.
Skeletal muscle movements are also used in our communication, whether through speech and handwriting or through nonverbal communication with our facial expressions and body language.
Though cardiac and smooth muscle also cause movements, those are more internal, and are typically not obvious from the body surface, with a few exceptions like goosebumps or the dilation and constriction of the pupil. Additionally, we can feel and hear the heart beat and sometimes our stomach churning.
Stabilizing Joints
By contrast, some of our stillness also comes from muscle contraction, like the postural muscles that keep our spine erect or our legs straight when we are standing. Skeletal muscles that surround joints can also hold fast to help stabilize those joints.
This is because skeletal muscle can contract and generate force without actually causing movement. Imagine yourself being really upset about something and tightening up all your muscles in your upper limbs, for instance, without actually moving any body parts.
Regulating Urinary and Digestive Systems
In addition, skeletal muscle sphincters govern the outlets of the urinary and digestive systems. In each case, there’s a smooth muscle sphincter that is more internal and a voluntary skeletal muscle sphincter that is more external.
When the bladder or bowel is full, the involuntary sphincter will relax, but when we were potty trained, we developed learned voluntary control of the external sphincters, which will help us stall elimination until we get to the right time and place. And, people want to retain that voluntary control since without it they become incontinent and lose control over bladder or bowel functions.
This article comes directly from content in the video series How We Move: The Gross Anatomy of Motion. Watch it now, on Wondrium.
Producing Body Heat
A lesser-known role of skeletal muscle tissue is in heat production. As much as about 85% of our normal body heat—our roughly 98.6°—is due to the action of skeletal muscles. The reactions that occur within the muscles generate heat as a by-product.
This is why we get hot when we exercise vigorously, and why we sweat to dissipate some of that body heat. Another example would be waiting at a cold bus stop as a kid, jumping up and down and rubbing your arms to generate some extra heat from the friction. Even though we didn’t know why it worked, but it did help us stay warm.
Controlling Blood Sugar
Lastly in terms of physiology, skeletal muscle activity helps regulate glycemic control. In other words, exercise is good for the proper maintenance of blood sugar. Muscle action doesn’t just use up glucose—which is the transport form of sugar in the blood—cells need insulin to take up and utilize the glucose from the blood.
Scientific research shows that regular exercise can improve the body’s use of and sensitivity to insulin. Of course, if someone is diabetic, all this should be checked with a physician, since anyone taking insulin could have their blood sugar lowered too much during exercise, when the muscles begin to utilize the blood sugar for their metabolism.
Skeletal Muscles as an Organ
Moreover, each muscle is considered an individual organ, since organs are composed of multiple tissue types. Skeletal muscle tissue qualifies as an organ because it also has some connective tissues within it to help it work and give it more stability.
Those connective tissues become one with the tendons at either end of a muscle—or you could say that the tendons that connect muscle to bone don’t disappear—they spread out throughout the muscle and compartmentalize it into bundles of related muscle cells that act as a unit.
Functions Determined by Muscle Structure
The packing of muscle cells into groups called fascicles gives skeletal muscle a “grain,” —a striated appearance of directionality that we will see is very helpful in understanding a muscle’s action. Muscles do come in different shapes and sizes, and those shapes not only have names, but also relate to the action of that muscle.
Muscles and the cells within them shorten to execute movement, so the ability to see the directionality, or grain, within a muscle is key to understanding how it acts on the bones it’s connected to. Because all muscles aren’t shaped the same way, they don’t function the same way—since, in anatomy, structure determines function.
Common Questions about Functions of the Skeletal Muscles
Skeletal muscle tissue qualifies as an organ because it also has some connective tissues within it to help it work and give it more stability. Those connective tissues become one with the tendons at either end of a muscle, they spread out throughout the muscle and compartmentalize it into bundles of related muscle cells that act as a unit.
A lesser-known role of skeletal muscle tissue is in heat production. As much as about 85% of our normal body heat—our roughly 98.6°—is due to the action of skeletal muscles. The reactions that occur within the muscles generate heat as a by-product. This is why we get hot when we exercise vigorously, and why we sweat to dissipate some of that body heat.
Skeletal muscle activity helps regulate glycemic control. In other words, exercise is good for the proper maintenance of blood sugar. Muscle action doesn’t just use up glucose—which is the transport form of sugar in the blood—cells need insulin to take up and utilize the glucose from the blood.
