Muscles of the Arm
The muscles of the arm move the forearm.
Biceps brachii is a muscle of the proximal anterior arm (Fig.1.16) that is familiar because it bulges when the forearm is flexed. It also supinates the hand when a doorknob is turned or the cap of a jar is unscrewed. The name of the muscle refers to its two heads that attach to the scapula, where it originates. The biceps brachii inserts on the radius.
Brachialis originates on the humerus and inserts on the ulna. It is a muscle of the distal anterior humerus and lies deep to the biceps brachii. It is synergistic to the biceps brachii in flexing the forearm.
Triceps brachii is the only muscle of the posterior arm (Fig.1.17). It has three heads that attach to the scapula and humerus, and it inserts on the ulna. The triceps extends the forearm. It is sometimes called the fiboxers muscle because it extends the elbow when a punch is thrown. The triceps is also used in tennis to do a backhand volley.
Muscles of the Forearm
The muscles of the forearm move the hand and fingers. Note that extensors of the wrists and fingers are on the lateral forearm and flexors are on the medial forearm.
Flexor carpi and extensor carpi muscles originate on the bones of the forearm and insert on the bones of the hand. The flexor carpi flex the wrists and hands, and the extensor carpi extend the wrists and hands.
Flexor digitorum and extensor digitorum muscles also originate on the bones of the forearm and insert on the bones of the hand. The flexor digitorum flexes the wrist and fingers, and the extensor digitorum extends the wrist and fingers (i.e., the digits).
