Your arm is divided into the upper arm and lower arm (forearm).
The upper arm consists of one bone, the humerus, whereas the forearm consists of two bones, the radius (located on the thumb side) and ulna (on the little-finger side). The elbow is a hinge joint formed at the junction between the humerus, radius, and ulna. Two movements occur at the elbow joint: flexion and extension.
During elbow flexion, the forearm moves toward the upper arm.
During extension, the forearm moves away from the upper arm.
Movement also takes place in the forearm when the radius rotates around the ulna. Supination (palm up) and pronation (palm down) take place between the radioulnar joints. The wrist joint is the junction between the lower end of the forearm bones and the small bones in the hand.
As its name suggests, the biceps muscle has two heads. The short head attaches to the coracoid process, and the long head arises from above the glenoid of the shoulder joint. The two-headed muscle passes down alongside the humerus and attaches about 1.5 inches (4 cm) below the elbow joint onto a tuberosity on the inside of the radius bone. The biceps causes flexion
at the elbow joint, raising the hand toward the face. The biceps also causes supination of the forearm, rotating the hand so the palm faces uppermost, the” get change” position.
In addition to the biceps, two other muscles flex (bend) the elbow: the brachialis and brachioradialis. The brachialis muscle lies deep beneath the biceps, arising from the lower half of the humerus and attaching to the ulna bone just below the elbow joint. S0 the brachialis lifts the ulna at the same time that the biceps lifts the radius. The brachioradialis muscle arises from the outer aspect of the lower end of the humerus and then travels down the forearm to attach to the radius just above the wrist joint.
The triceps muscle has three heads, or sections. The long head arises from beneath the glenoid fossa of the shoulder joint, the lateral (outer) head arises from the outer surface of the humerus, and the medial (inner) head from the medial and rear surfaces of the humerus.
All three heads fuse at their lower ends to form a single tendon that attaches behind the elbow joint onto the olecranon process of the ulna bone. The triceps causes extension at the elbow, moving the hand away from the face. The triceps is the only muscle that straightens the elbow joint, whereas three muscles (biceps, brachialis, and brachioradialis) bend the elbow. All three heads of the triceps muscle cross the elbow joint, but the long head also crosses beneath the shoulder joint.
Source: wikipedia.org | book – Bodybuilding Anatomy by Nick Evans