The prominent long arm bone representing the upper arm is the humerus. It is attached to the scapula, or shoulder blade, at its “ball-shapped” end – which rests in the shallow cup called the glenoid fossa located in the scapula. Its other end meets the radius, as well as the ulna at the elbow – with which it forms a hinge that allows the arm to straighten and bend.

The deltoid muscle attaches to the humerus halfway down the bone. The large triceps muscle (Triceps Brachii) is located at the back of the upper arm and attaches to the portion of the ulna called the olecranon. It is part of a single muscle group with three different segments, or heads – the long head (originates on the border of the shoulder blade and responsible for pulling the upper arm from above the head down to the floor), the lateral head (originates on the outside of the humerus) and the medial head (originates on the back of the humerus). The primary function of each is to extend the forearm and straighten the elbow. Each head originates in a different place but comes together at a single tendon that attaches to the back of the ulna at the olecranon process.

This muscle is attached to the bone by the triceps tendon, which inserts into the back of the elbow, and permits the straightening of the elbow when it contracts. The radial nerve travels down the arm and supplies movement to the triceps muscle.

The biceps muscle (Biceps Brachii) is located on the front of the humerus and permits bending of the elbow when it contracts, as well as rotation of the forearm. The tapered ends of the biceps muscle are firmly attached by strong tendons to the periosteum of the skeleton. The upper end of the muscle is attached to the scapula by two tendons and the lower end is attached to the radius of the forearm. The radius is moved upwards as the biceps contracts. The biceps muscle is connected to the bone by the biceps tendon – the proximal biceps tendon at the shoulder joint (scapula) and the distal biceps tendon at the elbow (radius).

Medical conditions most often associated with the upper arm include radial nerve dysfunction as well as inflammation and rupture of the triceps and biceps tendons – particularly among athletes.