Structures of the Ear Eustachian tube “Popping” ears Outer, middle, & inner ear

“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 tympani

Endolymph Organ of Corti

Open K+ channels Depolarize Open Voltage- gated Ca++ channels Release of NT from synaptic vesicles Stereocilia with mechanically- gated K+ channels

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: ,000 Hz; optimal Hz Whales: ,000 Hz Bats: ,000 Hz Frogs: Hz Fish: Hz Crickets: Hz

Audiogram Decibel = unit for expressing relative loudness on a log scale “Nerve deafness” cause by damage to hair cells.

Pathway to Temporal Lobe VIII cranial nerve Medial geniculate nucleus of thalamus Organ of Corti Hair Cells Organ of Corti Hair Cells Cochlear Ganglion = Spiral Ganglion Cochlear Ganglion = Spiral Ganglion Cochlear Nuclei Cochlear Nuclei MG of Thalamus MG of Thalamus Auditory Cortex Auditory Cortex Superior Olive Superior Olive 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

Fire!

Tonotopy in Auditory Cortex

Structures of the Ear Utricle & saccule inside Organs of Equilibrium

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 implantscochlear implants Hearing Aids Understanding Speaker Frequency Response by Polk Audio’s Marketing ManagerUnderstanding Speaker Frequency Response Noise cancelling technology