arm

The arm is the region of the upper limb between the shoulder and the elbow. It contains the humerus, major muscles, nerves, and blood vessels that power and control movements of the shoulder and elbow. In anatomical terms, the arm is distinct from the forearm, which extends from the elbow to the wrist, and from the hand.

Bony anatomy and joints: The arm is centered on the humerus, the long bone of the upper limb. The shoulder joint (glenohumeral) connects the humerus to the scapula, allowing a wide range of motion. The elbow joint, formed by the humerus with the radius and ulna, enables flexion and extension. The arm’s muscular compartments include an anterior group that flexes the elbow and helps with shoulder flexion (biceps brachii, brachialis, coracobrachialis) and a posterior group that extends the elbow (triceps brachii). The deltoid muscle crosses the shoulder and contributes to arm movement. The brachial plexus provides motor and sensory innervation, with the musculocutaneous nerve serving the anterior flexors, the radial nerve the extensor muscles, and the median and ulnar nerves supplying various forearm and hand muscles. The brachial artery travels along the arm and divides into the radial and ulnar arteries near the elbow.

Function and clinical aspects: The arm enables lifting, pushing, pulling, and positioning of the hand. Movements include shoulder abduction, flexion, extension, and rotation, as well as elbow flexion and extension. Common clinical issues involve humeral fractures, shoulder dislocations, and nerve injuries within the brachial plexus, along with tendinopathies such as epicondylitis. Understanding arm anatomy aids in diagnosing and treating upper-limb conditions.