Arm Anatomy

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Bones

The arm has three bones:

• Humerus: The only bone in the upper arm. It's a long, large bone that extends from the shoulder to the lower arm. The head of the humerus forms the ball of the shoulder joint.
• Ulna: A forearm bone. When the palm faces forward, the ulna is located medially.
• Radius: A forearm bone. When the palm faces forward, the radius is located laterally.

Other bones in the arm include:

• Scaphoid: A bone in the wrist and forearm
• Phalanges: The bones of the digits

The term "broken arm" can refer to a fracture in any of these bones.

Nerves

• Radial nerve: Runs down the thumb side of the arm and tells the triceps and extensor muscles when to contract
• Ulnar nerve: Runs down the little finger side of the arm and provides motor innervation to the forearm and hand muscles, and sensory supply to the skin of the hand
• Axillary nerve: Supplies the shoulder joint and the skin over it, and innervates the deltoid muscle and teres minor
• Median nerve: Runs down the center of the arm and provides motor innervation to the muscles of the anterior compartment of the forearm, as well as the thenar muscles and lateral two lumbricals of the hand
• Musculocutaneous nerve: Supplies muscles responsible for flexing the forearm
• Brachial plexus: A network of nerve fibers that supplies the skin and musculature of the upper limb
• Medial cutaneous nerve of arm: Provides sensation to the medial cutaneous aspect of the arm
• Supraclavicular nerve: Contributes to the superior aspect of the shoulder

Other nerves in the arm include:

Ulnar nerve, Median nerve, Musculocutaneous nerve, Brachial plexus, Medial cutaneous nerve of arm, Supraclavicular nerve.

Veins

There are several veins in the arm, including:

• Axillary vein

A major vein in the upper limb that drains the axilla, arm, and superolateral chest wall. It's formed by the union of the paired brachial veins and the basilic vein.

• Cephalic vein

A cutaneous vein that originates in the dorsolateral side of the hand and collects venous blood from the superficial structures of the lateral part of the upper extremity.

• Basilic vein

Begins in the ulnar part of the dorsal venous network and runs up the posterior surface of the ulnar side of the forearm.

• Brachial veins

Placed one on either side of the brachial artery, receiving tributaries corresponding with the branches given off from that vessel.

• Dorsal venous network

Formed by the dorsal metacarpal veins which eventually give rise to the cephalic vein and basilic vein.

• External jugular vein

Formed by the union of posterior division of retromandibular vein and posterior auricular vein.