Transcript Audition and Equilibrium

Otitis media =
middle ear infection
Fluid behind tympanum
“Popping ears” and equalization of pressure across tympanic membrane.
Conduction deafness: ossification of ossicle articulations
Attenuation reflex protects cochlea from large vibrations = loud sounds
“tube” to relieve
pressure and allow drainage.
Scala
vestibuli
Scala media
Scala tympani
Endolymph
Organ of Corti
Mechanosensitive K+
channels in Stereocilia
Composition
of endolymph
Stereocilia with
mechanicallygated K+
channels
• Open K+
channels
• Depolarize
• Open Voltagegated Ca++
channels
• Release of NT
from synaptic
vesicles
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 Cochlea
Base
Apex
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
In Brainstem
Organ of
Corti Hair
Cells
Cochlear
Ganglion =
Spiral
Ganglion
• VIII cranial nerve
• Medial geniculate
nucleus of thalamus
Cochlear
Nuclei
Superior
Olive
MG of
Thalamus
Auditory
Cortex
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