An arm is a type of limb attached to the upper part of the trunk. In most modern humans there are two arms, each emerging from the body at the region of the shoulder, just below the neck. An arm terminates distally in a hand, the primary organ of grasping and fine manipulation. Together the arm and hand allow an organism to interact with objects, other people and the environment.
Structure and parts
The arm is commonly described in segments: the shoulder girdle, the upper arm, the elbow, the forearm, the wrist and the hand. Bones include the humerus in the upper arm and the radius and ulna in the forearm. Joints, muscles, tendons, ligaments and nerves coordinate to produce movement and sensation. Major muscle groups such as the biceps and triceps act on the elbow, while the rotator cuff stabilizes the shoulder joint.
Functions and uses
The arm performs a wide range of tasks from lifting and carrying to precise finger movements for writing, tool use and dressing. Hands enable complex manipulation, while larger arm muscles provide strength for pushing, pulling and throwing. Arms also play roles in nonverbal communication through gestures and in protective reflexes.
Evolution, variation and locomotion
Across mammals and especially among primates, forelimbs show adaptations to different lifestyles. Some primates use long arms for brachiation, swinging through trees, while others support themselves or knuckle-walk on the ground. Human arms are specialized for manipulative dexterity rather than locomotion, reflecting cultural and technological development.
Clinical and cultural notes
Arm injuries and conditions—fractures, nerve damage, repetitive strain—are common and often treated by orthopedics, physiotherapy or prosthetics. Prosthetic and surgical advances restore function after amputation or trauma. The arm also has strong symbolic roles in art and ritual, representing strength, embrace and work.