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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