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