In Depth: Nerves and Vessels
The shoulder plays a key role in the blood flow to the arms. The armpit and shoulder serve as the meeting place for the torso and arms, so major vessels close to the heart travel through these areas.
Oxygenated blood enters the shoulder area through the subclavian artery below the collarbone. This same vessel evolves into the axillary artery in the armpit region. Its branches serve the outer surface of the chest and the upper arm. Farther down the arm, the axillary artery is known as the brachial artery.
The brachial artery is the largest artery serving the shoulder and arm. It travels down the upper arm and through the elbow before dividing into the radial and ulnar arteries below the elbow. In the shoulder, branches of the brachial artery provide oxygenated blood to the muscles and bones.
As muscles use the oxygen from the blood, it must be returned to the lungs to once again receive oxygen. This happens via veins. The major veins of the shoulder are:
- Axillary vein: This vein drains into the larger subclavian vein on its way to the heart. It is joined by the cephalic vein and the basilic vein.
- Cephalic vein: This large vein branches off the axillary vein after traveling through the upper arm before branching near the elbow and into the forearm. It is often easily seen through the skin in the bicep region.
- Basilic vein: Opposite the cephalic vein, the basilic vein travels through the shoulder near the triceps muscle on the underside of the arm.
Nerves in the shoulder carry the brain signals that move the arms and also sense pain, touch, heat, and cold.
Three major nerves pass through the shoulder before terminating in the hand. They collect sensory information and return it to the brain, which sends out appropriate responses, such as alerting the body to extreme heat and quickly pulling the arm away from it.
Many of these nerves make up the brachial plexus, a network of nerves that starts in the spine, pass through the armpit, and runs down the arm.
- Ulnar nerve: This nerve runs through the shoulder and is just under the skin at the elbow’s “funny bone” (a knob on the humerus).
- Radial nerve: This nerve supplies the triceps and wrist extensors. Its branches cover most of the back of the hand beginning at the wrist.
- Median nerve: This nerve branches down into the hand where it serves the thumb, index, and middle finger. It is also the only nerve that passes through the carpal tunnel.
- Musculocutaneous nerve: This nerve supplies various parts of the upper arm, including the flexor muscles and the skin of the forearm.