Cervical Plexus

CERVICAL PLEXUS (plexus cervicalis) is formed by loop-like connections between the anterior branches of the first four cervical nerves C_i-iv (Fig. 1). These connections are called ansae cervicales; three of them are present within the plexus itself—ansa cervicalis prima, s. atlantis, secunda, tertia; the fourth loop is inconstant, connecting the cervical plexus with the brachial plexus. The cervical plexus lies upon the corresponding cervical vertebrae and the muscles attaching to the posterior tubercles of the transverse processes; it is covered by the sternocleidomastoid muscle.

In addition to the brachial plexus, the cervical plexus connects with: 1) C_i-iii with the hypoglossal nerve, forming the ansa hypoglossi, s. ansa cervicalis profunda; 2) C_i with the accessory nerve; 3) with the superior cervical ganglion and the bordering sympathetic trunk. The cervical plexus gives off cutaneous and muscular branches. From the individual cervical nerves before the formation of the plexus emerge muscular branches to the rectus capitis anterior and lateralis, longus colli, longus capitis, intertransversarii, scalenus anterior and medius, and levator scapulae

Figure 1. Formation of the cervical plexus and nerves emerging from it: I-II-III-IV-V-VI cervical spinal nerves: 1-nerve for the rectus capitis muscle; 2 and 3-nerves for the longus capitis muscle; 4-nerve for the intertransversarii muscles; 5-nerve for the longus capitis and colli muscles; 6-nerve for the intertransversarii muscles; 7-nerve for the levator scapulae muscle; 8-nerve for the longus colli muscle; 9-nerve for the intertransversarii muscles; 10-nerve for the scalenus medius muscle; 11-nerve for the levator scapulae muscle (see Muscles); 12-nerve for

the scalenus anterior muscle; 13-nerve for the scalenus medius muscle; 14-nerve for the sternocleidomastoid muscle; 15, 18-nerves for the levator scapulae muscle; 16-phrenic nerve; 17-nerves from C_iii-iv (supraclavicular branches); 19-ansa hypoglossi; 20-nerve for the trapezius muscle; 21-great auricular nerve; 22-lesser occipital nerve; 23-descending branch of the hypoglossal nerve; 24-lesser occipital nerve; 25-nerve for the rectus capitis muscle; 26-hypoglossal nerve.

from C_iii-iv—the phrenic nerve (see Phrenic Nerve). Among the cutaneous branches of the cervical plexus are known: the lesser occipital nerve, great auricular nerve, transverse cervical nerve, and supraclavicular nerves. The lesser occipital nerve originates from the second loop and appears externally at the posterior border of the sternocleidomastoid muscle (Fig. 2), then ascends upward and terminates in the occipital region. The great auricular nerve arises from C_iii, like the preceding nerve, emerges outwardly at the posterior border of the sternocleidomastoid muscle, where it divides into 2 branches—anterior and posterior—and innervates the skin of the auricle and the parotid-masseteric region. The transverse cervical nerve originates from C_iii; emerging at the posterior border of the sternocleidomastoid muscle, it curves around it and runs along the outer surface toward the hyoid bone, dividing into branches: the superior branch innervates the skin of the suprahyoid region, where it anastomoses with the facial nerve, and the inferior branch supplies the skin of the infrahyoid region. The supraclavicular nerve arises from C_iv, upon emerging externally consists of several branches which divide into anterior, middle, and posterior supraclavicular nerves and run forward, backward, and laterally, supplying the skin of the neck, shoulder, and upper regions of the chest (see Nerves). Thus, the cervical plexus supplies: with sensory fibers—the skin behind the ear, the skin of the auricle, occiput, neck, and shoulders; with motor fibers: a) short deep suboccipital muscles, of which two—the rectus capitis posterior major and minor—pull the head backward, two muscles—the obliquus capitis superior and inferior—turn the head to the side, and the rectus capitis lateralis tilts the head to the side; b) posterior muscles of the neck, of which three—the longus colli, longus capitis, and rectus capitis anterior—tilt the head forward, while the scalenus anterior, medius, and posterior (these three muscles simultaneously receive

Figure 2. Cutaneous branches of the cervical plexus: 1-occipital muscle; 2-posterior auricular muscle; 3-posterior auricular nerve; 4-parotid gland; 5-branches of the facial nerve; 6-cervical branch of the facial nerve; 7-transverse cervical nerve; 8-external jugular vein; 9-platysma; 10-omohyoid muscle; 11-anterior supraclavicular nerves; 12-middle supraclavicular nerves; 13-posterior supraclavicular nerves; 14-muscular branches for the trapezius muscle; 15-supraclavicular nerves; 16-trapezius muscle; 17-scalene medius muscle; 18-external branch of the accessory nerve; 19-sternocleidomastoid muscle; 20-levator scapulae muscle; 21-splenius capitis muscle; 22-great auricular nerve; 23-third occipital nerve; 24-lesser occipital nerve; 25-great auricular nerve; 26-greater occipital nerve.

innervation from the brachial plexus) flex the cervical part of the spine; in addition, the cervical plexus competes with the accessory nerve in the innervation of the sternocleidomastoid, trapezius, and levator scapulae muscles. The most important nerve of the cervical plexus is the phrenic nerve, which goes to the diaphragm. Pathology of the cervical plexus. Lesions of the cervical plexus can be either unilateral or bilateral; the latter form is observed more frequently and is manifested by paralysis of the neck muscles or their spasms, depending on the process, and by neuralgias. In paralysis, the neck muscles do not function—the patient's head hangs forward so limply and strongly that the chin touches the sternum (Fig. 3); the patient cannot lift the head upward. Paralysis of the phrenic nerve leads to paralysis of the diaphragm. Spasms most frequently spread to the obliquus capitis, splenius, and diaphragm. With unilateral clinical spasms of the inferior oblique muscle of the head, the head is constantly turned toward the affected side; with bilateral spasm, the head rotates to both sides—rotatory spasms of the head, or tic rotatoire. In tonic spasms, the head freezes for some time in the turned position. With unilateral spasm of the splenius muscle, the head is tilted backward and to the affected side. In the diaphragm, clonic spasms are observed more frequently, manifested by hiccup. Neuralgia is localized mainly in the region

of the greater and lesser occipital nerves and the great auricular nerve—occipital neuralgia, or cervico-occipital neuralgia. In neuralgias, pains are localized along the course of these nerves; objectively, there is painful hyperesthesia, tenderness upon pressure on the plexus above the clavicle—the supraclavicular point, synonymous with Erb's point. The cervical plexus can be affected in general infections, intoxications, but most often it suffers in processes in the surrounding tissues on the neck or in diseases of the upper cervical spine.

Treatment depends on the etiological moment, as well as symptomatic: for paralysis—physiotherapy; for neuralgia—diathermy, counter-irritants.

E. Kononova.