What Is the Muscular System? - Function & How Muscles Work in Groups

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  • 0:05 Function of the…
  • 1:58 Muscle Anatomy
  • 4:05 Origin and Insertion Points
  • 5:31 Agonists and Antagonists
  • 7:26 Synergists
  • 8:32 Lesson Summary
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Lesson Transcript
Instructor: Heather Adewale

Heather has taught reproductive biology and has researched neuro, repro and endocrinology. She has a PhD in Zoology/Biology.

Ever feel overwhelmed when you look at all those muscles in your textbooks? Well, if you do, then maybe learning a little about their anatomy and organization and how they work together will help you sort through it all. In this lesson, learn about the muscle itself and how it works with others to help the muscular system function.

Function of the Muscular System

Ahh the muscular system; it probably seems overwhelming at first, what with all those funky scientific names. There are over 600 skeletal muscles, and that number doesn't even include the smooth muscles! But, like everything else in your body, the muscular system has its own sense of organization. Once you learn a little bit about how it works, it may begin to make a little more sense to you.

Even the naming system is organized. Some muscles are named for their location, while others are named for their shape or the direction in which their fibers run. We won't get into all those names in this lesson, but we will get started with some of the basics. As you have probably guessed, the main function of the muscular system is movement, but it also helps stabilize our joints, maintain our posture and generate heat during activity.

Movement of our body can be voluntary and controlled by the skeletal muscles, or it can be involuntary and controlled by smooth muscles. Those are found mostly in your internal organs and aid in things like digestion and even eyesight. Skeletal muscles, on the other hand, are what make up what we see a human body do. They move all the different parts of the skeleton. They help us in all kinds of movements, such as walking, swimming, writing and even talking. All this movement is aided by the anatomy and organization of the muscular system. But, before we move on, we should mention you do have one other type of muscle in your body. Cardiac muscles are found in the heart and are responsible for the movement of blood through your body.

Muscle Anatomy

First, let's take a brief look at the muscles themselves. Like so many other things, muscles are made up of lots of smaller parts. We'll start at the level of the muscle fiber. A muscle fiber is simply a muscle cell, or the building blocks of muscles. See, just like the rest of your body is made up of lots and lots of individual cells, your muscles are also made up of cells.

Multiple fibers join together to make up our next level of organization, the fascicle. A fascicle is a group, or bundle, of muscle fibers. And, just like many muscle fibers join together to form a fascicle, many fascicles join together to make up a muscle.

Muscles are composed of fibers and fascicles.
Components of Muscles

Muscles are made up of groups of fascicles. When stimulated, they contract to produce motion. Without muscles, your body wouldn't be able to function. No more running, talking, walking and, well, you get the picture!

The organization of the muscle allows all the fibers, and thus the fascicles, to contract and relax as a group. Contraction is stimulated by nerve impulses and triggers the movement of the muscle, while relaxation occurs when the impulse is removed and the muscle relaxes back to its natural state. This pattern of contraction and relaxation is responsible for all the movements in your body.

The part of your body that moves in response to a muscle contraction depends on the location and origin point of the muscles themselves. To simplify things, we are going to focus on the skeletal muscles of the body. Most skeletal muscles are attached to bone, cartilage or connective tissue, which limits or directs their movement. For example, a muscle attached to the arm bone will only move the arm bone when stimulated. It cannot move the leg bone; therefore, its movement is determined by its points of attachment.

Origin and Insertion Points

Each muscle has two main points of attachment, the origin point and the insertion point. The origin of a muscle is the fixed end, the end that doesn't move. This end is usually a bone, cartilage or connective tissue. The opposite end of the muscle is the insertion point. This is the movable end of the muscle which is attached to the structure that is being moved.

The origin and insertion points of the biceps brachii
Origin Insertion Point Diagram

Let's go back to our arm muscle example. If we take a look at the upper arm bone, called the humerus, we can see a large muscle on top of it. This muscle, called the biceps brachii has a point of origin at the scapula, and its insertion point on the radius of the lower arm. When the muscle contracts, it moves the radius upwards towards the scapula, but the scapula and upper arm do not move. That is why the radius is termed the insertion point, while the scapula is the origin point.

If you're still a little confused about how to tell the difference, you can give it a try on your own. When you move your arm or your leg, take notice of which end of the muscle is doing the moving and which end is staying still. That will help you figure out which is the insertion (that's the one doing the moving) and which is the origin.

Agonists and Antagonists

When a muscle moves, it's because it is stimulated to contract by the nervous system, but what happens after that? How does it return to its starting position? To do that, it needs the help of another muscle, which pulls it back.

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