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Muscle Contractions: Macro View

Muscle Contractions: Macro View

Author: Amanda Soderlind

This lesson will give an overview of how a specific muscle contracts to allow movement in the body.

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Source: Images and Video Created by Amanda Soderlind

Video Transcription

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Welcome to this lesson today on muscle contractions, macro view. So we're going to be discussing the large scale view on how muscle contractions allow for the movement of our skeleton. So we're talking about how skeletal muscles interact with our skeleton in order to allow for movement.

So our example that we're going to use today is going to be with our bicep and tricep. So the bicep and tricep are arranged in a pair, and they are antagonistic to one another. So what this means is that the action of one muscle opposes the action of the other.

So for example, when the bicep contracts, the tricep relaxes. And when the triceps contracts, the bicep relaxes. So they're antagonistic to one another, and this is allowed for by something called reciprocal innervation.

So reciprocal innervation acts on groups of muscles, so that when one muscle contracts, no signals are sent to the opposing muscle so it relaxes. So that's how when your bicep contracts, your tricep relaxes. Because when that bicep contracts, your nervous system is not sending any signals to your tricep, which allows for it to relax.

So our muscles, our bones, our tendons, they're working together to act like a series of levers in order to allow for our skeleton to be able to move. So we're going to take a look at our diagrams, here, to describe our following terms, origin and insertion. So origin is the end of a muscle that attaches to a stable bone. Well insertion is the end of a muscle that attaches to a bone that moves.

OK, so like I said, our skeleton, and our muscles, and our tendons are working together like a series of levers. When a muscle contracts, it's allowing part of your skeleton to be able to move. So our origin in this example, if we're using our bicep as an example, is going to be our scapula.

So we have our bicep muscle, here. We have the tendon, which is a dense connective tissue that attaches bone to muscle, that's attached to our scapula. So when your bicep contracts or relaxes, your scapula is not going to move.

So that's our origin, or stable bone, that's not moving when that muscle contracts or relaxes. However, our forearm is what does move when our biceps contracts or relaxes. So that would be our insertion, here.

OK, so when our biceps contracts or relaxes, or when our tricep does that, it's allowing for our forearm to move up and down. OK, so when the bicep contracts, the tricep relaxes, and our arm is going to move up. OK, now let's take a look at what happened when our triceps contracts.

So in this case if our tricep contracts, our bicep, then, relaxes, and our arm moves down. So you can try this with your arm. If you relax or contract your bicep, you'll notice how it allows your forearm to move up or down.

OK, so as we said, these are antagonistic muscles. They work antagonistically where the action of one opposes the action of the other. Another type of group of muscles are synergistic muscles.

Whereas instead of opposing reactions, you have these muscle groups that are working together to increase the force or to stabilize another muscle in the body. OK, so you can have synergistic groups of muscles or antagonistic groups of muscles. So this lesson has been a large scale overview on how muscle contractions allow for skeletal movement.

Terms to Know
Antagonistic contraction

When an opposing muscle on the opposite side of a joint contracts to create an opposing movement to its muscle counterpart. For example, your biceps pull your forearm toward you upper arm, while your triceps help you straighten out your arm; biceps are antagonistic to triceps.


The fixed, moveable end of a skeletal muscle.


An area where two or more bones come together.


The fixed, non-moveable end of a skeletal muscle

Reciprocal innervation

The nervous system controlling muscle groups that oppose and work against one another; allows for a variety of movements and protection of joints.

Synergistic contraction

When a group of muscles work together to create the same movement; an example would be your bicep brachii and brachialis muscle contraction simultaneously to create flexion (bending) of your elbow.


A tough band of fibrous connective tissue that usually connects muscle to bone.