Additional nerve

The accessory nerve is the motor. It consists of two parts - cerebral and spinal. This is due to the fact that the nuclei of the accessory nerve (nervus accessorius) are located in two places. One core (cerebral) is a two-core ( Latin nucleus ambiguus ), common with glossopharyngeal and vagus nerves. The fibers extending from this nucleus form the cerebral part of the accessory nerve, which leaves the sulcus of the medulla oblongata , behind the olive.

The second nucleus - the nucleus of the accessory nerve ( lat. Nucleus n.accessorii ) lies in the posterolateral part of the anterior horn of the gray matter of the spinal cord over the upper 5-6 cervical segments.

Roots emerging from the medulla oblongata in an amount of 4-5 form the superior or cerebral root.

The roots extending from the lateral cord of the spinal cord between the anterior and posterior spinal roots, combining, form the spinal root of n.accessorius, which rises up and penetrates through the large occipital foramen ( lat. Foramen magnum ) into the cranial cavity. Here, both groups of fibers join and form the trunk of n.accessorii. This trunk through the jugular opening ( lat. Foramen jugulare ) (together with IX and X pairs) comes out of the cranial cavity and is divided into 2 branches:

1. The internal branch ( Latin ramus internus ) approaches the vagus nerve and is part of it
2. The outer branch ( lat. Ramus externus ) follows down and at the level of the angle of the lower jaw deviates posteriorly under the sternocleidomastoid muscle ( lat. M.sternocleidomastoideus ); here n.accessorius gives her a number of muscle branches, connecting in its thickness with the branches of the cervical plexus (third cervical nerve). Further, the nerve leaves from under the outer edge of this muscle, above the middle of its extension, into the region of the lateral cervical triangle, enters under the front edge of the trapezius muscle ( lat. M.trapezius ) and innervates the latter.

The accessory nerve carries motor nerve fibers to mm.sternocleidomastoideus et trapezius, respectively, the function of the accessory nerve is identical to the function of these muscles. Thus, the function of n.accessorius is to turn the head in the opposite direction (m.sternocleidomastoideus), raise the shoulder, shoulder blade and acromial part of the clavicle up (shrug), pull the shoulder girdle posteriorly and bring the shoulder blade to the spine, as well as raise the shoulder above the horizontal ( what m.trapezius is responsible for).

It should be noted that n.accessorius spinal portion neurons receive impulses from the cerebral cortex from both sides, but mainly from the opposite side. In addition, neurons receive extrapyramidal and reflex nerve impulses along the tectospinal ( lat. Tractus tectospinalis ), vestibulospinal ( lat. Tractus vestibulospinalis ) paths and the medial longitudinal bundle ( lat. Fasciculus longitudinalis medialis ), which are likely to be responsible for involuntary turning your head in response to sound or harsh light.

Damage to the accessory nerve can be either due to central (intramedullary, intracerebral) or peripheral pathological processes. Violation of its function may be due to a primary infectious or toxic in nature lesion of the nerve itself or its nucleus (poliomyelitis, tick-borne encephalitis, etc.), but it can also be of secondary origin and occur in lesions of the cervical vertebrae and in pathological processes in the posterior cranial fossa or neck.

• With unilateral damage to the projection zones of the cortex of n.accessorius, violations of its function are usually not observed, due to the fact that the nucleus of the accessory nerve receives nerve impulses from both hemispheres.
• The nucleus n.accessorius receives fibers from the extrapyramidal system. Muscle cramps innervated by the XI nerve are more often one-sided and are the result of cortical or subcortical irritation. Tonic cramp gives a picture of spastic torticollis ( lat.torticollis spasticus ); clonic - twitching the head in the opposite direction, sometimes with simultaneous raising of the shoulder.
• Bilateral clonic spasm leads to nodding head movements (Salaam spasm, spasmus nutans).
• The defeat of the XI nerve leads to the development of peripheral paralysis or paresis of mm.sternocleidomastoideus et trapezius. Their atrophy sets in , usually leading to asymmetry. The shoulder on the sore side is lowered, the scapula moves away from the spine with the lower angle and is shifted outward and upward (the “pterygo-shaped scapula”). Difficulty raising the shoulder girdle ("shrug") and the ability to raise a hand above a horizontal level. Turning the head in the opposite direction is significantly difficult due to paresis of m.sternocleidomastoideus. With bilateral lesions, a drooping head is noted.
• Defeat n.accessorius is usually accompanied by deep, difficult to localize pain in the arm on the affected side, which is caused by overstretching of the joint bag and ligamentous apparatus of the shoulder joint due to paralysis or paresis of the trapezius muscle.
• In the case of unilateral destruction of the anterior horns of the spinal cord at the level of 1-4 cervical segments ( polio , trauma, asymmetric syringomyelia ), flaccid paralysis of n.accessorius develops on the side of the lesion. Flaccid paralysis of n.accessorius is also observed with peripheral damage to its external branch. Flaccid paralysis of n.accessorius caused by damage to the anterior horns of the spinal cord and its external branch has one slight difference. So peripheral damage is accompanied by flaccid paralysis of m.sternocleidomastoideus, while in m.trapezius paresis develops only in its rostral (upper) part, since this muscle is also innervated by C3-C4 spinal motor roots.

After examination and palpation of the muscles innervated by the accessory nerve, the patient is offered to turn his head first to one side and then to the other side, raise his shoulders and arm above a horizontal level, bring the shoulder blades closer. To identify paresis of the muscles, the examiner exerts resistance in performing these movements. For this purpose, the patient’s head is held by the chin, and the patient’s hands are laid on the shoulders. While raising the shoulders, the examiner holds them by force.

Due to excessive sagging of the arm on the affected side of the patient, standing at attention with hands lowered at the seams, it can be noted that the arm on the side where the insufficiency of the XI nerve function is noted is omitted lower than on the healthy side. If the patient is invited to stretch his arms forward in front of him, so that the palms touch each other while the fingers are extended, then the ends of the fingers on the affected side will protrude more than on the healthy side.

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1. ↑ ^{1 2} Foundational Model of Anatomy
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