Arm

From ArticleWorld

The arm is one of a pair of upper extremities that a bipedal animal uses for many functions. An arm can function in reaching, in holding items, in pushing items, in lifting an item and in small movements, such as those involving the fingers or in holding a small object.

Anatomy

An arm contains multiple bones, ligaments, blood vessels, muscles, tendons and other connective tissue. The upper arm is attached via a ball-in-socket joint that connects the clavicle and scapula in the upper trunk to the proximal rounded end of the humerus. The humerus is a long bone that ends at the elbow joint, where it connects to the radius and ulna in the forearm. The forearm bones end distally in connections to multiple bones in the wrist, called the carpal bones.

The arm muscles work collectively and form several compartments that are bundled into connective tissue bundles. The shoulder is raised and lowered by the deltoid muscle and the trapezius muscle in the neck, back and shoulder. The upper arm is dominated by the extensor muscles that extend the elbow. The triceps muscle provides much of the extensor function. The flexor muscles of the elbow are dominated by the biceps muscle.

There are muscles, including the brachioradialis muscle, which originate in the upper arm but end in the forearm that allow for pronation and supination of the elbow. These terms are those that describe the turning of the palm upward (supination) or downward (pronation).

The nerve supply of the arm is from the nerve roots labeled C5, C6 and T1. Many of the nerves to the arm come together in what is called the brachial plexus in the axilla (the underarm). The radial nerve travels along the humerus along side a deep artery inside the arm. The median nerve and the ulnar nerve also travel through the upper arm.

The main arterial supply to the arm is the brachial artery. This artery travels between the biceps and triceps muscles, sending off branches to supply the structures of the arm. The brachial artery ends in the antecubital fossa (the inside of the elbow), where it sends off branches to the forearm and continues down the forearm.

Function

The primary functions of the arm (i.e. the upper arm) are raising and lowering the arm at the shoulder, as well as rotating the shoulder internally or externally. The muscles of the arm also provide for the flexion and extension of the elbow.