Auditory System Lesson 14

The Stimulus n What kind of energy is sound? l mechanical l movement of air molecules n Waves l intensity = amplitude l pitch = frequency (wavelength) n Audible range in humans l 20 Hz – 20 kHz ~

Anatomy of the Ear n Tympanic membrane n Middle ear - ossicles l Malleus (hammer) l Anvil (incus) l Stapes (stirrup) n Inner ear - l Oval window l Cochlea - fluid filled l Round window ~

Cochlea

Structure: Cochlea n 2 continuous chambers l Scala Vestibuli l Scala Tympani l filled with perilymph n Scala Media l between others l filled with endolymph l high K + concentration ~ Scala Media Scala Tympani Scala Vestibuli

Uncoiled Cochlea Scala Media Scala Vestibuli Scala Tympani Round Window Oval Window

Organ of Corti n Auditory receptor organ l in scala media n Tectorial membrane l roof of scala media n Basilar membrane l floor of scala media n Hair cells ~

Hair Cells - Auditory Receptors n Mechanoreceptors l Anchored to basilar membrane n Cilia l tiny appendages (“eyelashes”) l top of hair cells ~

Basilar Membrane Tectorial Membrane Organ of Corti

n Receptor Potential l Depolarization l K+ influx l  NT release from receptor n Cilia l tip-links l K + channels l cilia bend  open/close channels ~ Hair Cells - Transduction

Hair Cell Cilia K+ Tip Link Hair Cells - Transduction

Force Inhibition Resting rateExcitation APs in Cochlear Nerve Axon Hair Cells - Transduction

The Auditory Pathway n Complex pathway l focus on most direct l hierarchical processing l parallel processing n Bilateral output l contralateral stronger l ipsilateral weaker n Cochlear Nerve  Cochlear Nucleus ~

The Auditory Pathway LeftRight

Hair Cell More NT Auditory Nerve - VIII Cochlear Nuclei Medulla Inferior Colliculus Thalamus: MGN Superior Olive Pons Auditory Pathway A1

Pitch Perception n Frequency Theory n Rate neurons l vibration of basilar membrane l frequency vibration  frequency APs l text max. frequency = 1000 Hz (1 kHz) n Low frequency sounds only l < Hz ~

Pitch Perception n Place Theory n Place neurons l Part of basilar membrane stimulated l high frequency near oval window l low frequency near end ~ Base Apex High Medium Low

Loudness Perception n Intensity l amplitude of wave n place neurons l rate of firing n rate neurons l number of neurons firing ~

Sound Localization n Superior Olives n Low frequency l Phase differences n High frequency l Intensity differences ~ < 3000 Hz > 3000 Hz