Human Skeleton Overview

The skeleton supports the body, helps it move, and protects internal organs.

Arm and leg bones have similar structure, though different shapes that allow for different functions.

A person has 12 pairs of ribs, for a total of 24 ribs.

The cranium protects the brain.

Rib cage protects the heart and lungs

Fixed joints do not move. They remain in a solid position.

The skull is an example of a fixed joint.

Moveable joints allow for movement.

A ball and socket joint allows for full range of motion.

The ball-and-socket joint in the shoulder consists of the humerus and scapula.

A hinge joint allows movement in one plane only.

The hinge joint in the elbow consists of the humerus, radius, and ulna.

Muscles generate movement through contraction and relaxation.

The bicep muscle is attached to the scapula and radius.

The triceps muscle is attached to the scapula and humerus and ulna.

'Bi' means two, and 'tri' means three, relating to the number of points of muscle attachment.

The biceps muscle shortens, pulling the radius upward, causing the arm to bend.

Bones involved in arm movement when biceps contracts, connected by tendons.

Strong tissues that connect muscle to bone, transmitting pulling force.

Two muscles that work together, one contracting while the other relaxes, pulling in opposite directions.

Contraction of the triceps muscle straightens the arm.

A muscle that is not contracting and cannot make itself longer.

Triceps contracts, biceps relaxes to straighten the arm.

Muscles only pull; they cannot push.

When one contracts, the other relaxes, allowing opposite actions.

Stretch would reduce ability to transmit pulling force effectively, damaging the arm.

Biceps can only bend the arm. Triceps is needed to straighten it by pulling in the opposite direction.