Transcript Audition and Equilibrium

Outer, middle, & inner ear
Structures of the Ear
Eustachian tube
“Popping” ears
“Tubes in the Ears”
Fluid behind
tympanum
Cranial
Nerve
VIII
Ossicles: incus,malleus, stapes. For transmission & amplification
Conduction deafness: ossification of ossicle articulations
Attenuation reflex protects cochlea from large vibrations
Scala
vestibuli
Scala media
Scala tympani
Endolymph
Organ of Corti
Stereocilia with
mechanicallygated K+
channels
• Open K+
channels
• Depolarize
• Open Voltagegated Ca++
channels
• Release of NT
from synaptic
vesicles
Mechanosensitive K+
channels in Stereocilia
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
Pitch (frequency) & 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
Tonotopy
Fourier Analysis of Complex Waves
Complex wave
Pure sine waves
Auditory Ranges
• Humans: 20- 20,000 Hz; optimal 10004000 Hz
• Whales: 20 - 100,000 Hz
• Bats: 1500 - 100,000 Hz
• Frogs: 600 - 3000 Hz
• Fish: 20 - 3000 Hz
• Crickets: 500 - 5000 Hz
Audiogram
Decibel = unit for expressing relative loudness on a log scale
“Nerve deafness” cause by damage to hair cells.
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
Fire!
Tonotopy in Auditory Cortex
Organs of Equilibrium
Structures of the Ear
Utricle & saccule inside
Semicircular Canal
• Angular acceleration
• 3 planes
Vestibular Apparatus
• Hair cells
• NT release dependent upon
degree of bending of
kinocilium and microvilli
• For utricle and saccule:
otolith membrane
• For ampula of semi-circular
canals: cupula
• 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