Cranial Nerve VIII

Neuroanatomy block-Anatomy-Lecture 11 Editing file Objectives

At the end of the lecture, students should be able to:

01 List the nuclei related to vestibular and cochlear nerves in the brain stem. 02 Describe the type and site of each nucleus. 03 Describe the vestibular pathways and its main connections. Color guide 04 Describe the auditory pathway and its main connection. ● Only in boys slides in Green ● Only in girls slides in Purple ● important in Red ● Notes in Grey 8th CN: Vestibulocochlear ● Type: Special sensory (SSA). ● located: in & medulla. ● receiving:special afferent sensation, & equilibrium from inner ), ● Conveys: impulses from to nervous system. ● Components:

conveys impulses Vestibular part associated with body posture ,balance and conveys impulses coordination of head & associated with Cochlear part eye movements. hearing.

01 02 03

Vestibular & cochlear parts run laterally in enter the internal leave the ventral surface of posterior cranial acoustic meatus along brain stem through the fossa. with (lateral to) 7th pontomedullary sulcus (facial) nerve. ‘at cerebellopontine angle’ (lateral to facial nerve).

3 According to the boys slides 1st. Pathway

First order Second order neurons of may

● 1. Descend as lateral to ● Cells of Vestibular located in Cells of Superior, Lateral, Medial & Inferior Vestibular Nuclei in anterior horn cells of . Internal Auditory Meatus. 2. Join medial longitudinal fasciculus & descend as ● Axons make dendritic contacts with hair medulla & pons. ● medial vestibulospinal tract to anterior horn cells in vestibule & semicircular canals. Vestibular nuclei belong to special somatic afferent column in brain cells of spinal cord. 3. Pass through inferior cerebellar peduncle to stem (The nuclei of the last 10 cranial nerves are arranged in 7 columns in each of . side of the middle line in the brain stem, 4. Cross midline & ascend to ventral posterior there are medial 3 column contain motor nucleus of then to vestibular area in nuclei and the lateral 4 column contain cerebral cortex. sensory nuclei.

4

3 1 2

4 vestibular nuclei According to the girls slides belong to special 1st. Vestibular Nerve Pathway somatic afferent column in brain stem. The cell bodies (1st order neurons)

located in the within the internal auditory meatus.

The Central processes The Peripheral processes (form the vestibular nerve) (vestibular nerve fibers): make dendritic contact with hair ‘’Efferent Fibres’’: cells of the membranous labyrinth (inner ear). Mostly end up in Some fibers the lateral, medial, inferior and superior go to the cerebellum through the vestibular nuclei (2nd order neurons) of inferior cerebellar peduncle the rostral medulla, located beneath the

lateral part of the floor of 4th ventricle.

The Axons from the vestibular Nuclei may project to:

1. Ipsilateral 2. Bilaterally 3. Bilaterally 4. To Motor neurons of the flocculonodular lobe of to ventral posterior nucleus to motor nuclei of cranial spinal cord cerebellum of thalamus nerves as lateral (Ipsilateral) (vestibulo-cerebellar tract) which in turn project to the (vestibulo-ocular tract) directly & medial through inferior cerebellar cerebral cortex . through medial longitudinal vestibulospinal (Bilaterally) peduncle. ★ For conscious awareness. fasciculus. tracts through MLF. ★ For Balance. ★ For coordination of head ★ for control body posture. & eye movements.

5 Medial Longitudinal Vestibulospinal Tracts Fasciculus ● ● Extends through out the brain stem and formed of both Vestibulospinal fibers influence the activity of spinal motor descending & ascending fibers neurons concerned with the control of body posture and balance. ● Projects bilaterally ● Has two components:

two tracts

ascending component descending component (vestibulo-ocular) lateral medial

extends into the spinal establishes connections cord as the medial with the nuclei of the vestibulospinal tract to Oculomotor, Trochlear & anterior horn cell. Abducens nerves (motor arises from lateral vestibular descending part ★for control the body nuclei for extraocular (Deiter’s) nucleus, of the medial longitudinal posture and balance . muscles) descends ipsilaterally fasciculus, projects bilaterally. ★ for coordination of head & eye movements.

6

01 Located in the lower part of postcentral gyrus (head area).

Responsible for conscious awareness of vestibular sensation. 02

7 According to the boys slides 2nd. Auditory Pathway

First order neurons Second order neurons Third order neurons

● Cells of spiral ganglion in the ● Cells of dorsal & ventral cochlear nuclei in pons ● Cells of () .Axons form cochlear . ● Both colliculi are interconnected by nerve. commissural fibers. ● Cochlear nuclei belong to special somatic ● makes dendritic afferent column in brain stem. contact with hair cells of (in ). ● On ascending, most of axons decussate in the & form lateral leminiscus. Fourth order neurons

● Some fibers end in Superior Olivary Nucleus & ● Cells of medial geniculate nucleus Nucleus of Lateral Leminiscus. (thalamus). Axons form auditory radiation that pass through ● Superior Olivary Nucleus & Nucleus of Lateral retrolenticular part of internal Leminiscus: modulate transmission of auditory capsule. information to cochlear nerve by: ● Ends in primary 1. Sending inhibitory fibers through (superior temporal gyrus) which is ending in Organ of connected to auditory association Corti. cortex. 2. Establishing connection with motor neurons supplying tensor tympani & stapedius muscles

N.B. : Representation of cochlea is bilateral at all levels above cochlear nuclei

8 According to the girls slides 2nd. Auditory Pathway Cochlear nuclei belong to special somatic afferent column in brain stem. There are several locations between Representation of cochlea is It is a medulla and the thalamus where bilateral at all levels above multisynaptic axons may and not all the cochlear nuclei, so Hearing is pathway fibers behave in the same manner bilaterally represented.

The cell bodies (1st order neurons)

are located in the spiral ganglion within the cochlea (organ of Corti in inner ear).

The Central processes The Peripheral processes (Cochlear nerve fiber)

● Make dendritic contact ● Terminate in the dorsal and ventral with hair cells of the organ cochlear nuclei (2nd order neurons), which of Corti within the cochlear lie close to the inferior cerebellar peduncle duct of inner ear. (ICP) in open rostral medulla.

9 Auditory Pathway cont.. According to the girls slides

● From the cochlear nuclei (2nd order neurons) fibres ascend into the pons, where:

Most fibers cross the midline in Some fibers run ipsilaterally trapezoid body and terminate in and terminate in

the contralateral the nucleus of the superior olivary superior olivary trapezoid body (1) nucleus (2) nucleus (2)

● From the superior olivary nuclei, ascending fibers comprise the (3) containing both

crossed (mainly) direct (few) cochlear fibres cochlear fibres

, which runs through tegmentum of pons and terminate in the inferior colliculus (4) of the midbrain (3rd order neurons) 10 According to the girls slides Auditory Pathway cont..

● Some axons within lateral lemniscus terminate in small nucleus of the lateral lemniscus (5)

● The inferior colliculi project to medial geniculate nuclei (6) (4th order neurons) of thalamus

● The axons originating from the medial geniculate nucleus (auditory radiation) pass through sublenticular part of the internal capsule to the primary auditory cortex (Brodmann’s areas 41, 42) (7) located in the dorsal surface of the superior temporal gyrus (Heschl’s gyrus) ➔ The region surrounding the primary auditory cortex is known as the auditory association cortex or Wernick’s area (Brodmann’s areas 22) ➔ Wernick’s area is related to recognition and processing of language by the brain.

11 Found only in girl’s slides Other Functions of some nuclei

Superior olivary nucleus 1 Sends olivocochlear fibers to end in organ of Corti through the vestibulocochlear nerve. These fibers are inhibitory in function and serve to modulate transmission of sound to the cochlear nerve.

Superior olivary nucleus & the nucleus of the lateral lemniscus 2 Establish reflex connections with motor neurons of trigeminal and facial motor nuclei mediating contraction of tensor tympani and stapedius muscles as they reduce the amount of sound that gets into the inner ear in response to loud noise.

3 Inferior colliculus establish reflex connections with motor neurons in the cervical spinal segments (via tectospinal tract) for the movement of head and neck in response to auditory stimulation.

Clinical Notes

Lesion of vestibulocochlear nerve. Rostral to the cochlear nuclei Acoustic neuroma The representation of cochlea is essentially Complete Deafness produces deafness (disturbance of Of the affected ear is Benign tumour of 8th nerve cochlear nerve functions), tinnitus, bilateral at all levels. So, Lesions anywhere along the pathway essentially only caused by leads to compression of the vertigo, dizziness, nausea, nystagmus, nerve leading to attacks of usually have no obvious effect on hearing, damage to the middle ear , loss of balance and ataxia (disturbance dizziness, and profound producing weakness of hearing in both cochlea, or auditory nerve. vestibular nerve function). but mostly in the opposite ear. deafness and ataxia

12 Practice Q5: The vestibular nuclei are connected to the oculomotor nuclei through: Q1: Regarding the vestibular pathway: A. The medial longitudinal fasciculus A. The vestibular ganglion is located in the middle ear. B. The lateral leminiscus B. The vestibular nuclei are located in the midbrain. C. The lateral vestibulospinal tract C. The vestibular nuclei are connected to the cerebellum. D. The vestibular nerve D. The vestibulospinal tracts are located in the lateral white column of spinal cord. Q6:The primary auditory cortex is located in? Q2: The central processes of cochlear nerve fibers terminate in the? A .superior temporal gyrus A.Dorsal and ventral cochlear nuclei B.inferior temporal gyrus B. Dorsal cochlear nuclei C.superior frontal gyrus C. Ventral cochlear nuclei D.inferior frontal gyrus D. None of the above Q7: The vestibular cortex is located in? Q3: The third order of the auditory pathway is located in: A.central gyrus A.Medial geniculate nuclei. B. precentral gyrus B.inferior colliculus. C. postcentral gyrus C.spiral ganglion. D.post-temporal gyrus D. Dorsal and ventral cochlear nuclei. Q8 : Both Vestibular & cochlear parts leave the ventral surface of brain stem Q4: The vestibular ganglion located in? through? A. Internal auditory meatus A. inferior cereberral peduncle B. External auditory meatus B. pontocerebellar angle C. Middle auditory meatus C. anterolateral olivary sulcus D. None of the above D. basilar sulcus Answers: Q1(C) Q2(A) Q3(B) Q4(A) Q5(A) Q6(A) Q7(C) Q8(B) 13 Members board

Team leaders

● Abdulrahman Shadid ● Ateen Almutairi Girls team : Boys team: ● Ajeed Al Rashoud ● Mohammed Al-huqbani ● Taif Alotaibi ● Salman Alagla ● Noura Al Turki ● Ziyad Al-jofan ● Amirah Al-Zahrani ● Ali Aldawood ● Alhanouf Al-haluli ● Khalid Nagshabandi ● Sara Al-Abdulkarem ● Omar Alammari ● Renad Al Haqbani ● Sameh nuser ● Nouf Al Humaidhi ● Abdullah Basamh ● Jude Al Khalifah ● Alwaleed Alsaleh ● Nouf Al Hussaini ● Mohaned Makkawi ● Rahaf Al Shabri ● Abdullah Alghamdi ● Danah Al Halees ● Rema Al Mutawa ● Amirah Al Dakhilallah ● Maha Al Nahdi Contact us: ● Razan Al zohaifi ● Ghalia Alnufaei Editing file most probably you don't need this