Otitis media middle ear infection Fluid behind tympanum

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