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In human anatomy, the dorsal interossei (DI) are four muscles in the back of the hand that act to abduct (spread) the index, middle, and ring fingers away from the hand's midline (ray of middle finger) and assist in flexion at the metacarpophalangeal joints and extension at the interphalangeal joints of the index, middle and ring fingers.
The posterior interosseous nerve supplies all the muscles of the posterior compartment of the forearm, except anconeus muscle, brachioradialis muscle, and extensor carpi radialis longus muscle. In other words, it supplies the following muscles: Extensor carpi radialis brevis muscle — deep branch of radial nerve; Extensor digitorum muscle
4 Dorsal interossei - Abduct the digits away from the 3rd digit (away from axial line) and are bipennate. 3 Palmar interossei - Adduct the digits towards the 3rd digit (towards the axial line) and are unipennate. This is often remembered by the mnemonic PAD-DAB, as the Palmar interosseous muscles ADduct, and the Dorsal interosseous muscles ...
The anterior interosseous nerve classically innervates 2.5 muscles: which are deep muscles of the forearm flexor pollicis longus; pronator quadratus; the radial (lateral) half of flexor digitorum profundus (inserting on the second and third digits) and the inferior radioulnar, wrist and carpal joints.
The median nerve innervates the flexors of the wrist and digits, the abductors and opponens of the thumb, the first and second lumbricals. The ulnar nerve innervates the remaining intrinsic muscles of the hand. [3] [4] All muscles of the hand are innervated by the brachial plexus (C5–T1) and can be classified by innervation: [1] [4] [5]
At its origin it innervates the hypothenar muscles. As it crosses the deep part of the hand, it innervates all the interosseous muscles and the third and fourth lumbricals. It ends by innervating the adductor pollicis and the medial (deep) head of the flexor pollicis brevis.
The abductor pollicis longus muscle is innervated by the posterior interosseous nerve, which is a continuation of the deep branch of the radial nerve after it passes through the supinator muscle. Abductor pollicis longus lies close to the radial nerve. [4] The posterior interosseous nerve is derived from spinal segments C7 & C8. [5]
The palmar interossei, together with the dorsal interossei and the lumbricals, are active components of the finger's extensor mechanism. Fibers from some of the interossei contribute directly to the extensor hoods that wrap around the proximal phalanges, while other fibers may contribute to the central tendon and lateral bands of the mechanism.