Auditory Vestib Pathways

8/17/2019 Auditory Vestib Pathways

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AUDITORY AND

VESTIBULAR PATHWAYS

Alexandria R. Bayaoa, M.D.

Department of Anatomy

UERMMMC, Inc.


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Objectives:

Function of the cochlear system

Receptors for hearing

Tracing the pathway of soundfrom the environment to the

sense organ for hearing


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Objectives:

Describing the origin, course,

and termination of the cochlear

nerve Tracing the central auditory

pathway from the organ of

Corti until the nerve impulsereaches the auditory cortex


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Objectives:

Role of the olivocochlear bundle

of Rasmussen in sound

perception Pathways of auditory reflexes

Differentiating between

conductive and sensory

deafness


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Objectives:

Explaining tinnitus, Rinne’s &

Weber’s test

Function of the vestibular system

Parts of Static labyrinth vs

kinetic labyrinth

Location of the receptors for

vestibular control


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Objectives:

Origin, course, and termination

of the vestibular nerve

Describing the role of: MLF,medial vestibulospinal tract,

lateral vestibulospinal tract in

the maintenance of equilibrium


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Objectives:

Connections of the vestibular

apparatus with the cerebellum

Define: vertigo and nystagmus

Tests for vestibular function

Clinical manifestations ofdisturbances in vestibular

apparatus


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EAR


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Functions of the Cochlear System


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Cochlea:


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Auditory Pathway:


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COCHLEAR NERVE NUCLEI

Snell, Richard; Clin.

Neuroanatomy, 7th ed, 2010


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Auditory Pathway:


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Descending Pathway


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Auditory pathway lesion

Unilateral lesions of the receptors, cochlear

nerve/nuclei result to TOTAL DEAFNESS OF

THE AFFECTED EARCentral unilateral lesions (cortex, medial

geniculate body, lateral lemniscus) result in

IMPAIRED HEARING IN BOTH EARS BUTMORE MARKED ON THE OPPOSITE SIDE


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Auditory Reflexes:

Audiomotor reflexes-

contractions of the tensor

tympani and stapedius ms.General acoustic muscle reflex-

generalized jerking of the body

in response to a loud, suddensound


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Auditory Reflexes:

Auditory-palpebral reflex- blinkof the eyelids to a loud noise

Auditory-oculogyric reflex-deviation of the eyes in thedirection of a sound

Cochleopupillary reflex-dilation of the pupils to loudnoise


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Doll’s eye/vestibulo-ocular reflex

test of brainstem function

Head is moved from one side to the

other The eyes will normally lag behind

then assume a midline position

Failure to lag/assume a midline=lesion on the ipsilateral side


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CHL vs SNHL

During the Weber test , the stem of a

vibrating tuning fork is placed on the

head in the midline.

If the tone is perceived in the affected

ear, this indicates a unilateral

conductive hearing loss.

In the case of unilateral sensorineuralhearing loss, the tone is heard in the

unaffected ear instead.


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Rinne Test

The stem of the tuning fork is placed on the mastoid

and the subject is asked to indicate when she or he

stops hearing the sound.

The fork is then held 2.5 cm from the pinna, and the

patient is asked if she or he still hears the sound.

If the sound is still audible, air conduction is greater

than bone conduction (AC > BC in normal ear); ifnot, BC > AC.


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Proper recording of the Rinne test should be

"AC > BC" or "BC > AC" for each ear;

For the Weber test, "Weber → R" or

"Weber → L" or "Weber not referred.“


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Static vs Kinetic Labyrinth


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Dynamic/Kinetic


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Dynamic vs Static

Semicircular canals: detect

motion of the head in space

(angular acceleration)Utricle: detect position of the

head (and body) in space

(linear acceleration)


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Vestibular Pathway


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Vestibular Pathway


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Vestibulospinal tract


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Vestibuloocular pathway


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Calorics

Lying down, head tilted 30 deg

Seated, head tilted backward 60

deg

Irrigation with cold/warm water

Convection current in the endolymph

Nystagmus COWS


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Vestibular lesions

Result in impaired postural adjustments :if unilateral•the eyes, head and body will turn to the affected side

•There will be vertigo and a tendency to fall to the side of the

lesion

•Spontaneous nystagmus is presentNystagmus is characterized by slow movement of the eyes

in one direction ff by rapid return to opposite side

Vestibular nerve and/or receptors : horizontal and rotatory

with fast component opposite the diseased ear

Vestibular nuclie and their central connections : usually

vertical


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1. Snell, R. Clinical Neuroanatomy, 7th ed. 2010

2. Gilman, S. Newman SW. Manter and Gantz’s

Essentials of Clinical Neuroanatomy and

Neurophysiology, 10th ed. 2003

3. Carague-Lansang,EN, et al. 4th ed. Lansangnotes: Modules in Neuroanatomy. 2006

References:


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Auditory Vestib Pathways