The brachial plexus runs down the length of the arm, starting from the shoulder and terminating inside the fingers. The name itself provides a clue, as "brachial" is an adjective referring to the arm or forelimb.
The average person has two brachial plexuses, one in each arm. Each brachial plexus consists of a group of five nerves that provide sensation and muscle movement to the limb they are contained in. The nerves originate from the spinal chord, near the base of the neck, and travel down the entire length of the arm, almost to the tips of the fingers. Each nerve has a separate function.
The brachial plexus is vulnerable to being injured by overstretching or sharp pulls that force the arm and neck in opposing directions. This sort of injury is especially common during motorcycle accidents.