Quick Facts
Origin: Formed by the union of anterior and posterior roots emerging from the C8 spinal cord segment.
Course: Travels laterally for a short distance to the bifurcation of anterior and posterior rami.
Branches: Anterior and posterior rami.
Supply: Motor innervation to the muscles of the upper limb and back. Sensory innervation to the skin above trapezius and the medial side of the upper limb.
Origin
The eighth cervical nerve is a mixed nerve formed by the union of its posterior nerve root (sensory nerve fibers) with its anterior nerve root (motor nerve fibers). The roots emerge from the posterolateral and anterolateral sulci of the C8 spinal segment and unite to form the eighth cervical nerve.
Course
The eighth cervical nerve exits the vertebral column through the intervertebral foramen situated between the first thoracic vertebra below and the seventh cervical vertebra above. It travels laterally a short distance and bifurcates into anterior and posterior rami.
Branches
The eighth cervical nerve divides into posterior (dorsal) and anterior (ventral) rami, both of which receive sensory and motor fibers.
The anterior ramus of the seventh cervical nerve passes anteriorly and contributes to the formation of the brachial plexus (along with the anterior rami of the fifth to eighth cervical and first thoracic nerves).
The posterior ramus winds posteriorly around the T1 articular pillar and divides into medial and lateral branches.
Supplied Structures
The anterior ramus of the eighth cervical nerve conveys motor fibers to the inferior trunk of the brachial plexus. Fibers that enter the medial cord of the brachial plexus provide motor innervation to the pectoralis major and minor muscles, flexor digitorum profundus, palmaris brevis, palmar and dorsal interossei, third and fourth lumbricals, adductor pollicis, and hypothenar muscles. Fibers that enter the posterior cord provide motor innervation to the latissimus dorsi, triceps, anconeus, extensor carpi radialis brevis, extensor digitorum, extensor digiti minimi, extensor carpi ulnaris, abductor pollicis longus, extensor pollicis brevis, extensor pollicis longus, and extensor indicis.
Some sensory fibers from the skin around the medial aspect of the upper limb travel via the anterior ramus of the eighth cervical nerve.
The lateral branch of the dorsal ramus of the eighth cervical nerve provides somatic motor innervation to the longissimus colli, splenius colli, and iliocostalis colli muscles. Those which pass through the medial branch provide motor innervation to multifidus, semispinalis colli, semispinalis capitis, splenius colli, and trapezius, before becoming cutaneous.
The sensory afferent neurons, which provide innervation to the skin above the trapezius, transmit general sensory information regarding pain, touch, pressure, vibration, etc. via the medial branch of the dorsal ramus.
