Anatomy of the Vessels and Nerves of the Head and Neck (Angioneurology) - Chornokulskyi S.T. 2009

Nerves of the Head and Neck
Vestibulocochlear nerve

[VIII] (n. vestibulocochlearis) (Fig. 27, 28, 40, 41, 42)

Sensory in nature and actually represented by two nerves:

— the vestibular nerve (n. vestibularis), and

— the cochlear nerve (n. cochlearis).

Nuclei of the vestibular nerve:

— superior vestibular Nucleus (Bechterew's nucleus), nuc. vestibularis superior;

— lateral vestibular nucleus (Deiters' nucleus), nuc. vestibularis lateralis;

— inferior vestibular nucleus (Roller's nucleus), nuc. vestibularis inferior;

— medial vestibular nucleus (Schwalbe's nucleus), nuc. vestibularis medialis.

Nuclei of the cochlear nerve:

— anterior cochlear nucleus (nuc. cochlearis anterior):

— posterior cochlear nucleus (nuc. cochlearis posterior).

All of the aforementioned nuclei project onto the vestibular area (area vestibularis) of the Rhomboid fossa. The two roots of the vestibulocochlear nerve are located in the cerebellopontine angle and represent the axons of bipolar Neurons from the vestibular and cochlear ganglia entering the Brainstem.

Vestibular ganglion (ganglion vestibulare)

Located at the Cytology/practical/108.html">Fundus of the internal acoustic meatus as a cluster of bipolar neurons, whose dendrites are connected to the receptors of the statokinetic analyzer.

Cochlear ganglion (ganglion cochleare)

Situated within the spiral canal of the cochlea and also forms a cluster of bipolar neurons, whose dendrites extend toward the auditory receptor—the spiral organ (organum spirale).

The axons of the bipolar neurons pierce the fundus of the internal acoustic meatus, forming the vestibular and cochlear areas there, and proceed to The Cell bodies of the second-order neurons (the nuclei of the 8th cranial nerve).

Pathways of the Vestibulocochlear Organ (Fig. 40, 41, 42)

Pathways of the Auditory Analyzer

The cell body of the first-order neuron (bipolar neurocyte) is located in the spiral ganglion (ganglion spirale), which lies within the spiral canal of the modiolus (canalis spiralis modioli). The dendrites of the bipolar neurocytes reach the receptor—the spiral organ—from which they transmit the Nerve Impulse. The axons of the bipolar neurocytes conduct the nerve impulse to the cell bodies of the second-order neurons, forming the cochlear nerve (nervus cochlearis).

Within the meatus acusticus internus, the vestibular nerve (n. vestibularis) joins it. The vestibulocochlear nerve (n. vestibulocochlearis) thus formed penetrates the Brain substance.

The axons of the first-order neurons of the auditory analyzer reach the neurocytes of the anterior and posterior cochlear nuclei (the cell bodies of the second-order neurons), where they synapse.

The axons of the neurocytes from the posterior cochlear nucleus form the striae medullares of the Fourth ventricle On the surface of the rhomboid fossa. Most of these fibers cross to the opposite side to join the lateral lemniscus, while a smaller portion reaches the lateral lemniscus on its own side. A small fraction of the crossing axons synapse on the neurocytes of the trapezoid body nuclei (third-order neurons). The axons of these neurocytes also contribute to the lateral lemniscus.

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Fig. 40. Auditory pathway (neuron-by-neuron):

1 - cochlea;

2 - cochlear duct (ductus cochlearis);

3 - spiral ganglion (Corti), 1st neuron (ganglion spirale Cortii);

4 - fundus of the internal acoustic meatus (fundus meatus acustici interni);

5 - internal acoustic meatus (meatus acusticus internus);

6 - internal acoustic pore (porus acusticus internus);

7 - cochlear part of the eighth cranial nerve (pars cochlearis n. octavi).

8 - Pons;

9 - 2nd neuron:

9a - dorsal cochlear nucleus (nuc. cochlearis dorsalis);

9b - ventral cochlear nucleus (nuc. cochlearis ventralis);

10 - medullary striae of the fourth ventricle (striae medulläres ventriculi quarti);

11 - dorsal Nucleus of the trapezoid body (nuc. dorsalis corporis trapezoidei);

12 - trapezoid body (corpus trapezoideum);

13 - lateral lemniscus (lemniscus lateralis);

14 - medial geniculate body (corpus geniculatum mediale), (3rd and 4th neurons);

15 - internal capsule (capsula interna);

16 - superior temporal gyrus (gyrus temporalis superior);

17 - lateral sulcus (sulcus lateralis);

18 - inferior colliculus of the Midbrain tectum (colliculus inferior tecti mesencephali);

19 - tectospinal tract (tractus tectospinalis);

20 - medial longitudinal fasciculus (fasciculus longitudinalis medialis);

21 - nucleus of the medial longitudinal fasciculus (Darkševič) (nuc. fasciculi longitudinalis medialis);

22 - Spinal Cord (medulla spinalis);

23 - anterior ROOT and spinal nerve;

24 - Skeletal Muscle

The axons of the neurons in the anterior cochlear nucleus form the trapezoid body of the pons, extending to the opposite side and partially synapsing on the neurons of the trapezoid body nuclei (the cell body of the third neuron). The axons of these neurons also form the lateral lemniscus, within the nuclei of which a small number of axons from the second neuron synapse.

Thus, the axons of the second- and third-order neurons within the lateral lemniscus reach the neurons of the medial geniculate body nucleus (the fourth neuron) and the neurons of the inferior colliculus nucleus of the mesencephalon tectum (the subcortical reflex center).

The axons of the fourth neuron pass through the posterior limb of the internal capsule, where they form the acoustic radiation and reach the transverse temporal gyri (the cortical center of the auditory analyzer).

The axons of the neurons located in the nuclei of the inferior colliculus of the midbrain tectum form the crossed tectospinal tract, which mediates reflex and protective motor responses to inappropriate auditory stimuli.

Pathways of the statokinetic analyzer

The cell body of the first neuron (bipolar neurons) is located in the vestibular ganglion (ganglion vestibulare). The dendrites of these neurons extend from the receptors (static — maculae utriculi et sacculi; kinetic — cristae ampulares), while their axons form the vestibular nerve and reach the vestibular nuclei (the cell body of the second neuron). A small portion of these axons bypasses the vestibular nuclei and reaches the flocculonodular lobe of the Cerebellum via the inferior cerebellar peduncles.

The axons of the second-order neurons (the superior, inferior, medial, and lateral vestibular nuclei) project:

✵ to the contralateral thalamic nuclei as part of the medial lemniscus (lateral nucleus of the thalamus — the third neuron);

✵ to the cerebellum (fastigial nuclei) as part of the tractus vestibulocerebellaris (exerting an indirect influence on the extrapyramidal system);

✵ to the spinal cord as the vestibulospinal tract (tractus vestibulospinalis);

✵ to the medial longitudinal fasciculus, thereby reaching the nuclei of cranial nerve pairs III, IV, VI, and XI, as well as the motor neurons of the anterior horns of the cervical spinal cord;

✵ to the reticular formation as the vestibuloreticular tract (tractus vestibuloreticularis), and via its connections, to the nuclei of cranial nerve pairs IX and X.

These specific neural connections account for the autonomic symptoms experienced during vestibular overstimulation.

The axons of the lateral thalamic nucleus neurons (the third neuron) reach the cortex of the middle and inferior temporal gyri (the cortical center of the statokinetic analyzer). However, its exact localization remains not fully understood.

Fig. 41. Pathway of the statokinetic analyzer (by neuron):

1 - membranous labyrinth (labyrinthus membranaceus);

2 - vestibular ganglion (ganglion vestibulare) — 1st neuron;

3 - dendrites of the bipolar neurons of the vestibular ganglion;

4 - axons of the bipolar neurons of the vestibular ganglion;

5 - rhomboid fossa (fossa rhomboidea);

6 - vestibular nuclei

(nn. vestibulares) - 2nd neuron:

6a - superior

(nuc. vestibularis superior);

6b - lateral

(nuc. vestibularis lateralis);

6c - inferior

(nuc. vestibularis inferior);

6d - medial

(nuc. vestibularis medialis);

7 - vestibulocerebellar tract (tractus vestibulocerebellaris);

8 - direct vestibulocerebellar tract;

9 - fastigial nucleus (nuc.fastigii);

10 - vestibulothalamic tract (tractus vestibulothalamicus);

11 - tectum of the midbrain (tectum mesencephali);

12 - thalamus (thalamus) — 3rd neuron;

13 - thalamocortical tract (tractus thalamocorticalis);

14 - cortex (cortex);

15 - connection with the medial longitudinal fasciculus;

16 - connection with the reticular formation;

17 - reticulospinal tract (tractus reticulospinalis);

18 - connection with autonomic nuclei (CN IX, X);

19 - vestibulospinal tract (tractus vestibulospinalis);

20 - spinal cord (medula spinalis)