What is meant by an antagonistic pair of muscles?

An antagonistic pair is two muscles positioned on opposite sides of a joint whose contractions move the bone in opposite directions, so that one relaxes while the other shortens.

Which muscle bends the elbow, and where is it attached?

The biceps bends the elbow, and it runs from the scapula of the pectoral girdle to an attachment on the radius just below the joint.

Which muscle straightens the elbow, and where is it attached?

The triceps straightens the elbow, and it runs from the scapula and humerus to the olecranon process of the ulna at the back of the joint.

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Human Musculoskeletal Anatomy: Joints

Antagonistic muscle action in the forelimb

3 things to know
Component 3

Overview

Antagonistic pair of muscles, origin of a muscle and insertion of a muscle.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Key term

Why must skeletal muscles be arranged in pairs?

Key term

What happens to the triceps while the biceps is contracting?

Key term

Explain how the arm is straightened again after it has been bent.

Questions from this subtopic

Each one with the model answer underneath.

1
Why must skeletal muscles be arranged in pairs?
Model answer
A muscle can only exert a force by shortening and pulling, and it cannot push itself back to its original length, so a second muscle is needed to pull the bone the other way and stretch the first one out again.
2
What is meant by an antagonistic pair of muscles?
Model answer
An antagonistic pair is two muscles positioned on opposite sides of a joint whose contractions move the bone in opposite directions, so that one relaxes while the other shortens.
3
Which muscle bends the elbow, and where is it attached?
Model answer
The biceps bends the elbow, and it runs from the scapula of the pectoral girdle to an attachment on the radius just below the joint.
4
Which muscle straightens the elbow, and where is it attached?
Model answer
The triceps straightens the elbow, and it runs from the scapula and humerus to the olecranon process of the ulna at the back of the joint.
5
What happens to the triceps while the biceps is contracting?
Model answer
The triceps relaxes and is passively stretched as the forearm is drawn upwards.
6
Explain how the arm is straightened again after it has been bent.
Model answer
The biceps relaxes and the triceps contracts, pulling on the olecranon process behind the joint so that the forearm swings back down, and the biceps is stretched out in the process.

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