Muscle Contractions: Macro View

This lesson will focus on muscle contractions from a macro view by examining:

1. Muscle Groups
2. Origin and Insertion

1. Muscle Groups

We will continue using biceps and triceps as our example for how skeletal muscles interact with the skeleton to allow for movement. 

The bicep and tricep are arranged in a pair working antagonistically to one another. This means that the action of one muscle opposes the action of the other. This is allowed by something called reciprocal innervation. Reciprocal innervation acts on groups of muscles so that when one muscle contracts, no signals are sent by the nervous system to the opposing muscle; it relaxes. Reciprocal innervation also allows for the protection of joints, or areas where bones come together.

When the bicep contracts, the tricep relaxes because your nervous system is not sending any signals to your tricep. Conversely, when the tricep contracts, the bicep relaxes.

• Antagonistic contraction
• When an opposing muscle on the opposite side of a joint contracts to create an opposing movement to its muscle counterpart (example flexion vs. extension).
• 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.
• Joint
• An area where two or more bones come together.

Another type of muscle group is synergistic muscles. Instead of opposing reactions, these muscle groups are working together to increase the force or to stabilize another muscle in the body.

2. Origin and Insertion

Our muscles, bones, and tendons, which are dense connective tissues that attach bone to muscle, work together to act like a series of levers allowing for the skeleton to move. Look at the diagram below as an illustration of origin and insertion.

Origin is the end of a muscle that attaches to a stable bone, while the insertion is the end of a muscle that attaches to a bone that moves.

• Origin
• The fixed, non-moveable end of a skeletal muscle
• Insertion
• The fixed, moveable end of a skeletal muscle.
• Tendon
• A tough band of fibrous connective tissue that usually connects muscle to bone.

Looking at the bicep, the origin is going to be the scapula. This is the stable bone, so when your bicep contracts or relaxes, your scapula is not going to move. Your forearm is what moves when your bicep contracts or relaxes, so that would be the insertion.

There are two different types of muscle groups that work together to allow for movement, to stabilize joints, and even to stabilize each other. One type of muscle group works antagonistically to each other. This means when one muscle contracts, the other relaxes. The other type of group is synergistic muscles. These muscles work together at the same time to increase force. Skeletal muscles connect to bone or other muscles at the origin and insertion. The origin is the part of the muscle that connects to a stable bone, while the insertion attaches to a bone that will move.

Keep up the learning and have a great day!