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Radial Nerve

03, Feb, 2024

The radial nerve is one of the major nerves in the human arm, originating from the brachial plexus (a network of nerves that arise from the neck and upper back). The radial nerve travels down the arm, branching out to various muscles and providing sensation to certain areas.

Overview

Nerve roots – C5-T1.

Sensory – Innervates most of the skin of the posterior forearm, the lateral aspect of the dorsum of the hand, and the dorsal surface of the lateral three and a half digits.

Motor – Innervates the triceps brachii and the extensor muscles in the forearm.

Anatomical Course

The radial nerve runs down the back of the upper arm, following the course of the humerus bone. It then continues down the forearm and into the hand.

The nerve arises in the axilla region, where it is situated posteriorly to the axillary artery. It exits the axilla inferiorly (via the triangular interval), and supplies branches to the long and lateral heads of the triceps brachii.

The radial nerve then descends down the arm, travelling in a shallow depression within the surface of the humerus, known as the radial groove.

As it descends, the radial nerve wraps around the humerus laterally, and supplies a branch to the medial head of the triceps brachii. During much of its course within the arm, it is accompanied by the deep branch of the brachial artery.

To enter the forearm, the radial nerve travels anterior to the lateral epicondyle of the humerus, through the cubital fossa. The nerve then terminates by dividing into two branches:

Deep branch (motor) – innervates the muscles in the posterior compartment of the forearm.

Superficial branch (sensory) – contributes to the cutaneous innervation of the dorsal hand and fingers.

Motor Functions

Muscle Innervation: The radial nerve innervates the muscles located in the posterior arm and posterior forearm, including the triceps brachii (which is responsible for extending the forearm at the elbow joint) and various muscles involved in wrist and finger extension.

In the arm, it innervates the three heads of the triceps brachii, which acts to extend the arm at the elbow. The radial nerve also gives rise to branches that supply the brachioradialis and extensor carpi radialis longus (muscles of the posterior forearm).

A terminal branch of the radial nerve, the deep branch, innervates the remaining muscles of the posterior forearm. As a generalisation, these muscles act to extend at the wrist and finger joints, and supinate the forearm.

Sensory Functions

The radial nerve provides sensory information to the skin on the back of the hand, including the thumb and first three fingers. It does not innervate the pinky finger or the palm.

Lower lateral cutaneous nerve of arm – Innervates the lateral aspect of the arm, inferior to the insertion of the deltoid muscle.

Posterior cutaneous nerve of arm – Innervates the posterior surface of the arm.

Posterior cutaneous nerve of forearm – Innervates a strip of skin down the middle of the posterior forearm.

The fourth branch – the superficial branch – is a terminal division of the radial nerve. It innervates the dorsal surface of the lateral three and half digits and the associated area on the dorsum of the hand.

Injury or compression of the radial nerve can result in symptoms such as weakness in wrist and finger extension, as well as numbness or tingling in the back of the hand. Common causes of radial nerve issues include trauma, fractures, compression during sleep, or conditions like radial tunnel syndrome.