Superficial extensors of the forearm

Extensor digitorum muscle

The extensor digitorum muscle originates from the lateral epicondyle of the humerus. Distally it divides into four smaller tendons which insert at the posterior surface of the middle and distal phalanges of the second to fifth fingers.

Hereby the insertion tendons build a sheet-like tendinous expansion, the dorsal aponeurosis, covering the medial, posterior and lateral surfaces of the distal phalanges.

The dorsal aponeurosis serves as a place of insertion for various ligaments and muscles.

Extensor digiti minimi and extensor carpi ulnaris muscles

The extensor digiti minimi muscle arises from the lateral epicondyle of the humerus and inserts at the dorsal aponeurosis of the little finger. Its' muscle belly often blends with the extensor digitorum.

When it's about the extensor carpi ulnaris muscle, it has its' origin at both the lateral epicondyle of the humerus (humeral head) and the posterior side of the ulna (ulnar head). This muscle's insertion is located at the base of the fifth metacarpal bone. 

Both of the muscles extend their respective digits and the wrist joint.

Ready to test yourself? Look no further than our forearm extensor muscle quizzes and diagram labeling exercises!

Innervation

Like all extensors of the forearm, these three muscles are innervated by the radial nerve. The radial nerve divides into a superficial and deep branch at the height of the radial head. While the superficial branch continues along the brachioradialis the deep branch penetrates the supinator muscle after which it branches off the posterior interosseus nerve (C6-C8). There upon the posterior interosseus nerve supplies the superficial extensors with motor branches.

Function

As the name suggests, all superficial extensors of the forearm fulfill a dorsal extension in the wrist joint.

Furthermore, the extensor digitorum extends the metacarpophalangeal (MCP), proximal interphalangeal (PIP) and distal interphalangeal joints (DIP) of the second to fifth fingers. Due to the fact that its' insertion tendons are partly attached to each other through the dorsal aponeurosis, an extension of one finger simultaneously leads to a slight extension of the neighboring fingers.

The extensor digiti minimi extends the MCP, DIP and PIP of the little finger. The contraction of the extensor carpi ulnaris pulls the hand medially (ulnar abduction).