Do You Know What A Muscle Is?

muscle anatomy

You probably know that you use your muscles to do just about any and every action in your body from routine actions like walking to specialized movements like yoga. But, do you really know what a muscle is? Muscles are more intricate than we often realize. While we might think of them as one solid thing, they are actually far more nuanced than that. Muscles are actually composed of a multi-layered structure. And, it's their structure is that makes them so functional. Would it surprise you if I said that they are mostly connective tissue?


We actually have three different types of muscle tissue. We have cardiac muscle which is found only in the heart. There is also smooth muscle tissue. This kind of tissue is found in our organ walls. It's involved in many of the involuntary actions that our organs do. And third, we have skeletal muscle. This is the type of muscle tissue you're probably most familiar with. Examples include many that you've heard of like the hamstrings, the biceps, the triceps, and the quadriceps. 

Skeletal muscle structure

Let’s break this down and take a deeper dive into structure. Picture a whole skeletal muscle that you’re familiar with. Let's say the biceps brachii in the arm. This “whole muscle” is really a group of what are called muscle fascicles wrapped in a layer of fascia called the epimysium. You could picture a skeletal muscle a bit like a grapefruit. The grapefruit peel is like the fascia that wraps around the fascicles. The fascicles are like the pulpy sections of the grapefruit.

We can go even deeper into layers of skeletal muscle structure, however. Each fascicle is composed of a bundle of fibers and each of those bundles is wrapped in a layer of fascia which is called the endomysium. We could compare this to an individual wedge or section of a grapefruit where a bunch of pieces of pulp are held together by a wrapping of tissue. Each of these fibers is itself a group of cells that is wrapped in fascia. At the smallest level, a muscle cell is made up of two proteins: actin and myosin.

Muscle function

What makes a muscle work or “contract” then? Contraction happens at the level of individual cells. The two types of proteins, actin and myosin, are arranged in a row. When the nervous system sends a signal that a contraction is needed, calcium is released and this triggers the two proteins to be attracted, or pulled toward one another. At a cellular level, this is what happens when a muscle contracts.


Holding this idea in our mind of skeletal muscles as multi-layered, rather than a solid thing, can help us understand how skeletal muscles and muscle tissue are not separate from the rest of the body. A single muscle is inseparable from the fascia that is interwoven within its layers. A single skeletal muscle, because of its connecting fascia, is also inseparable from the “individual” muscles that surround it. We should keep this in mind as we deepen our understanding of skeletal muscles and movement. While we may talk about “individual” muscles for the purposes of breaking down our understanding of the body into manageable chunks, movement happens with the whole body and is affected by the whole body. 


Skeletal muscles are many-layered tissues intimately connected to each other and to other structures in our body. This interconnection is what makes fluid whole-body movement possible. 

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