conduction deafness: ossification of ossicle articulations attenuation reflex protects cochlea from...
TRANSCRIPT
Conduction deafness: ossification of ossicle articulations
Attenuation reflex protects cochlea from large vibrations = loud sounds
Fluid behind tympanum
“Popping ears” and equalization of pressure across tympanic membrane.
Otitis media =middle ear infection
“tube” to relieve pressure and allow drainage.
Scala vestibuli
Scala tympani
Scala media
Endolymph
Organ of Corti
Mechanosensitive K+ channels in Stereocilia
Composition of endolymph
• Open K+ channels
• Depolarize• Open Voltage-
gated Ca++ channels
• Release of NT from synaptic vesicles
Stereocilia with mechanically-gated K+ channels
Activity of Hair Cells
• Depolarization leads to more NT release• Hyperpolarization leads to less NT release
• All hair cells nearly identical• Basilar membrane thickens toward the apex
Tonotopy in CochleaBas
eApex
Coding for Pitch = frequency = tone
& Intensity• Base .... high pitch (treble)• Apex .... low pitch (bass)• Pitch coded by location of
vibrations of Organ of Corti : Which hair cells are stimulated…which set of sensory axons have action potentials
• Intensity coded by degree of displacement of stereocilia of hair cells and ultimately the frequency of action potentials in those axons that are active
Auditory Range
• Humans: 20- 20,000 Hz; optimal 1000-4000 Hz
Demo of auditory range and presbycusia
Audiogram
Decibel = unit for expressing relative loudness on a log scale
“Nerve deafness” cause by damage to hair cells.
Fourier Analysis of Complex Waves
Complex wave
Pure sine waves
Pathway to Temporal Lobe
• VIII cranial nerve
• Medial geniculate nucleus of thalamus
Organ of Corti Hair
Cells
Organ of Corti Hair
Cells
CochlearGanglion =
Spiral Ganglion
CochlearGanglion =
Spiral Ganglion
CochlearNuclei
CochlearNuclei
MG ofThalamus
MG ofThalamus
AuditoryCortex
AuditoryCortex
SuperiorOlive
SuperiorOlive
In Brainstem
Sound Localization
• Low frequency by delay in arrival of soundwave between ears
• High frequency by attenuation of intensity
• Processed in Superior Olive
• Practical Applications?
L or R speaker w/ hi and lo frequency tone
Tonotopy in Auditory Cortex
Organs of Equilibrium
Semicircular Canal
• Angular acceleration
• Three semicircular canals per ear in 3 planes
Utricle and Saccule
For static equilibrium(orentation to gravity)
Vestibular Apparatus
• Hair cells• NT release dependent upon
degree of bending of kinocilium and microvilli
• For ampula of semi-circular canals: cupula
• For utricle and saccule: otolith membrane
• Stereocilia in Endolymph (Hi K+, low Na+)
Additional Topics
• Information on cochlear implants
• Hearing Aids
• Understanding Speaker Frequency Response by Polk Audio’s Marketing Manager
• Noise cancelling technology