Muscular branches of radial nerve

Muscular branches of radial nerve innervate the muscles of the posterior compartment of the arm and forearm:

Before entering the spiral groove

The radial nerve gives off branches that innervate two heads of the triceps brachii:

• Long head of the triceps brachii

• Medial head of the triceps brachii

These branches provide motor innervation, enabling elbow extension.

Within the spiral groove

The radial nerve continues its course through the spiral groove (located on the posterior surface of the humerus) and provides motor innervation to the:

• Lateral head of the triceps brachii

• Additional branches to the medial head of the triceps brachii

These branches further contribute to the extension of the elbow joint.

In the arm’s lower region (before splitting into terminal branches)

In the distal arm, just before the nerve divides into its terminal branches (superficial and deep branches), the radial nerve supplies motor fibers to:

• Brachioradialis: A forearm muscle involved in elbow flexion, especially when the forearm is in a mid-prone position.

• Extensor carpi radialis longus: A forearm muscle that assists in wrist extension and radial deviation (abduction).

• Additionally, the radial nerve provides proprioceptive fibers to the brachialis muscle, which plays a role in elbow flexion.

Muscular branches of the posterior interosseus nerve (the deep branch of the radial nerve)

The deep branch passes between the two heads of the supinator muscle as it winds backward around the lateral side of the radius.

• Before passing between the two supinator heads, the deep branch provides motor innervation to the extensor carpi radialis brevis muscle and the supinator muscle.

• While passing through the supinator muscle, an additional branch is given off to the supinator muscle.

After emerging from the supinator muscle in the posterior compartment of the forearm, the radial nerve's deep branch emerges in the forearm's posterior compartment and becomes the posterior interosseus nerve. Here, it lies between the superficial and deep groups of extensor muscles of the forearm and gives off short and long branches.

The three short branches innervate the following muscles: the extensor digitorum, extensor digiti minimi, and extensor carpi ulnaris muscles.

The two long branches are the lateral and medial branches.

1. The long lateral branch innervates the abductor pollicis longus muscle and the extensor pollicis brevis muscle.

2. The long medial branch innervates the extensor pollicis longus muscle and the extensor indicis muscle.