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The C8 nerve contributes to the motor innervation of many of the muscles in the trunk and upper limb. Its primary function is the flexion of the fingers, and this is used as the clinical test for C8 integrity, in conjunction with the finger jerk reflex.
It innervates the medial and lateral heads of the triceps brachii muscle of the arm, as well as all 12 muscles in the posterior osteofascial compartment of the forearm and the associated joints and overlying skin. It originates from the brachial plexus, carrying fibers from the posterior roots of spinal nerves C5, C6, C7, C8 and T1. [1]
The ulnar nerve originates from the C8-T1 nerve roots (and occasionally carries C7 fibers which arise from the lateral cord), [5] [6] which then form part of the medial cord of the brachial plexus, and descends medial to the brachial artery, up until the insertion point of coracobrachialis muscle (middle 5 cm over the medial border of the humerus).
A myotome is the group of muscles that a single spinal nerve innervates. [1] Similarly a dermatome is an area of skin that a single nerve innervates with sensory fibers. Myotomes are separated by myosepta (singular: myoseptum). [2] In vertebrate embryonic development, a myotome is the part of a somite that develops into muscle.
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
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 medial cutaneous nerve of the forearm (also known as the medial antebrachial cutaneous nerve) is a sensory branch of the medial cord of the brachial plexus derived from the ventral rami of spinal nerves C8-T1. It provides sensory innervation to the skin of the medial forearm and skin overlying the olecranon.
The muscle is inserted onto the radial sesamoid bone of the metacarpophalangeal joint. It acts to flex, adduct, and abduct the thumb, and is therefore also able to oppose the thumb. The superficial head is innervated by the median nerve, while the deep head is innervated by the ulnar nerve (C8-T1). [6]