Arm

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In anatomy, an arm is one of the upper limbs (also called forelimbs) of an animal. The term arm can also be used for analogous structures, such as one of the paired upper limbs of a four-legged animal, or the arms of cephalopods.

In anatomical usage, the term arm refers specifically to the segment between the shoulder and the elbow,[1][2] while the segment between the elbow and wrist is the forearm. However, in common, literary, and historical usage, arm refers to the entire upper limb from shoulder to wrist.

In primates the arms are richly adapted for both climbing and for more skilled, manipulative tasks. The ball and socket shoulder joint allows for movement of the arms in a wide circular plane, while the presence of two forearm bones which can rotate around each other allows for additional range of motion at this level.

Contents

Anatomy of the human arm

The human arm contains 30 bones, joints, muscles, nerves, and blood vessels. Many of these muscles are used for everyday tasks.

Bony structure and joints

The humerus is the (upper) arm bone. It joins with the scapula above at the shoulder joint (or glenohumeral joint) and with the ulna and radius below at the elbow joint.

Elbow joint

The elbow joint is the hinge joint between the distal end of the humerus and the proximal ends of the radius and ulna. The humerus cannot be broken easily. Its strength allows it to handle loading up to 300 lbs.

Osteofascial compartments

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