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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.
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]
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 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]
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.
In these cases, the nerve supply is preserved, and transplanted with the muscle (for example, with facial reanimation). [6] Posterior cord lesions can result in the loss of adduction of the shoulder joint, as innervation to latissimus dorsi is lost. [3]
The nerve(s) which tell the muscle to act (innervates the muscle). The term "nerve" is included for clarity. Action The movement performed by the muscle from the standard anatomical position. In other positions, other actions may be performed. Antagonist The muscle which can 'cancel' or to some degree reverse the action of the muscle.
Flexor digitorum profundus is a composite muscle innervated by the anterior interosseous nerve and ulnar nerves. The medial aspect of the muscle (which flexes the 4th and 5th digit) is supplied by the ulnar nerve (C8, T1). [5] [6] [7]