The radial nerve is a component of the human nervous system, involved in movement and sensation of the arm and hand. It is a primary nerve in the upper limb, extending from the shoulder region down to the fingers. This nerve facilitates actions like straightening the elbow, wrist, and fingers, and provides sensory information for a considerable area of the hand.
The Brachial Plexus Connection
The radial nerve begins as a branch of the brachial plexus, a complex network of nerves. This plexus originates from nerve roots that emerge from the spinal cord in the lower neck and upper chest region (C5 through T1). Within the brachial plexus, the radial nerve is the largest terminal branch of the posterior cord. This intricate origin allows the nerve to gather a wide range of nerve fibers for its diverse roles in motor control and sensory perception throughout the arm. The brachial plexus efficiently bundles these nerve fibers, providing a pathway for signals between the brain and the upper limb.
Journey Through the Arm
Emerging from the armpit (axilla), the radial nerve descends along the posterior aspect of the humerus, the upper arm bone. It passes through a shallow depression known as the radial groove. This close association with the humerus means the nerve wraps around the bone, making it susceptible to injury from humeral fractures. As it continues its descent, the radial nerve travels towards the elbow, positioning itself anterior to the lateral epicondyle of the humerus.
Near the elbow, the radial nerve divides into two branches: a superficial branch and a deep branch. The superficial branch carries sensory information, while the deep branch is responsible for motor functions. The deep branch, also called the posterior interosseous nerve in its distal course, continues to supply muscles in the posterior forearm.
Key Roles and Functions
The radial nerve is involved in both movement and sensation in the arm and hand. Its motor functions include extending the elbow, by innervating the triceps brachii muscle. It also controls the muscles responsible for extending the wrist and fingers, enabling actions like opening the hand or lifting objects. These movements are necessary for daily activities such as writing, typing, and gripping.
For sensation, the radial nerve provides feeling to areas of the upper limb, including the skin on the back of the arm and forearm. It supplies sensation to the back of the hand, encompassing the thumb, index finger, middle finger, and part of the ring finger. Damage to the radial nerve can impair these functions, leading to conditions like “wrist drop,” where the individual is unable to extend their wrist and fingers. This highlights the nerve’s role in maintaining dexterity and sensory awareness in the upper extremity.