Review the anatomy of ears Correctly order the steps of inner ear response Explain the brain mechanism for sound localization Draw the central auditory pathway Understand the common audiometricspecial hearing tests ID: 774663
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Slide1
Auditory System
Slide2Objectives
Review the anatomy of ears
Correctly order the steps of inner ear response
Explain the brain mechanism for sound localization
Draw the central auditory pathway
Understand the common audiometric/special hearing tests
Slide3Sound waves strike the tympanic membraneThen the sound waves are transmitted through middle ear and cochlear fluid in inner earThe cochlear hair cells are activated and send the signal through CN VIII to brainstemThe signals go through several synapses before reaching thalamus, and then finally A1 cortex
Process of hearing
Slide4Ear Anatomy
Slide5The hair cells
Outer hair cells3 rows at base5 rows at apexThe number is around 12,000Connected to the projections from the descending auditory pathways
Inner hair cells
1 row
The number is around 3,500
Innervated by the cochlear nerve endings
Form most of the afferent fibers
Slide6The place principle
The pitch of a sound determines which cells are activated
base
apex
Slide7Video
How sound is converted into electric signal
https://www.youtube.com/watch?v=1JE8WduJKV4
From 1:29, or 3:31
Slide8Useful website
Journal into the world of hearing
http://www.cochlea.eu/en/ear
Slide9Auditory Pathways
Slide10Thalamus: the relay center for most of the sensory inputsReceive tonotopic input from the ipsilateral inferior colliculusSend information to the ipsilateral temporal lobe (the gyri of Heschl in the superior temporal lobe)
Slide11Hearing impairment
Conductive hearing loss
Sensorineural
hearing loss
Mixed hearing loss
Central auditory impairment
Slide12Sensorineural hearing loss
Damage to the cochlear hair cell or auditory nerveDifficulty in understanding speech, particularly in noiseCauses:Prolonged exposure to noise TumorDiseases Meniere’s diseasePresbycusis
Slide13Central auditory impairment
Lower brainstemSuperior olivary nucleus: minimal effect on hearing sensitivity, but troubles in localizing sound source and processing temporal informationLateral lemniscus: no severe hearing impairment, but subtle symptoms like impaired processing of speech in noiseUpper brainstemInferior colliculus: impaired auditory reflex and sound integrationMedial geniculate body: difficulties in sound integration and attending to soundCortical involvementNear-normal-hearing threshold, but impaired speech processing
Slide14Evaluations of Hearing impairment
Tuning fork tests
Pure tone audiometry
Tympanometry
Otoacoustic
emission
Auditory brainstem response audiometry
Slide15Pure tone audiometry
Establish the threshold of hearing across frequencyMost reliable test for evaluating hearing sensitivity
Slide16Tympanometry
Measure compliance of tympanic membrane and middle-ear pressureImpaired tympanic membrane compliance indicates middle ear pathology
Slide17Otoacoustic emmision
Measure pressure wave elicited by the movement of the outer hair cell in cochleaNewborn hearing screening program
Slide18Auditory nerve fibers
Cochlear nuclei
Superior
olivary
complex
Lateral
lemniscus
Auditory brainstem response audiometry
Measure the neuronal activity from the brainstem auditory pathwayEach peak is thought to be generated at a different anatomic point in the auditory pathway
Slide19Auditory brainstem response audiometry
Slide20Vestibular System
Slide21Objectives
The anatomy of vestibular system
Vestibular pathway
Vestibular projections and some of their functions
Examples of vestibular dysfunction
Slide22Where
Slide23Anatomy of vestibular system
Semicircular ducts
Vestibule
Utricle
Saccule
Slide24Semicircular ducts/canals
Endolymph filledRight angles to one another, detect acceleration in various planesAnteriorPosteriorLateral
Slide25Video
https://www.youtube.com/watch?v=YMIMvBa8XGs
How the three semicircular ducts detect the head motion
Start from 0:20
Slide26Vestibular nerve
Slide27Projections to Cerebellum
Most of the projections from vestibular nuclei
Form bidirectional projections
Constant and updated vestibular feedback
Monitoring body and head position
Regulate muscular adjustment
Maintenance of body equilibrium
Slide28Projections to Spinal cord
A descending projection
Enter the ventral column of the spinal cord
Terminate at different spinal levels
Maintain the muscle tone to counteract the gravity
Slide29Projections to some CNs
Through medial longitudinal
fasiculus
to
Oculomotor
CN III
Trochlear CN IV
Abducens
CN VI
Spinal accessory nerve CN XI
Coordinate eye and head movements
Slide30Some clinical correlates
Motion sickness
Subjective sensation of body rotation
Associate with dizziness, nausea, and vomiting
Repeated up and down movements
Conflict information from inner ears and eyes
Vertigo
Subjective: sensation of spinning through the space
Objective: sensation of environmental spinning around oneself
Slide31