Fourth Cervical Nerve

Origin

The fourth 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 C4 spinal segment and unite to form the fourth cervical nerve.

Course

The fourth cervical nerve exits the vertebral column by traveling through the intervertebral foramen situated between the third and fourth cervical vertebrae. It travels laterally a short distance and bifurcates into anterior and posterior rami.

Branches

The fourth cervical nerve divides into posterior (dorsal) and anterior (ventral) rami, both of which receive sensory and motor fibers.

The anterior ramus of the fourth cervical nerve passes anteriorly and contributes to the formation of the cervical plexus (along with the anterior rami of the first to third cervical nerves).

The posterior ramus winds posteriorly around the C4 articular pillar and divides into medial and lateral branches.

Supplied Structures

The anterior ramus of the fourth cervical nerve conveys motor fibers to the cervical plexus to innervate the longus colli and anterior and middle scalene muscles.

Sensory afferent neurons from the supraclavicular nerves also transmit general sensory information from the skin of the anterolateral neck via the anterior ramus.

The lateral branch of the posterior ramus 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, 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 posterior ramus.