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Auditory System. Lecture 13. The Stimulus. What kind of energy is sound? mechanical movement of air molecules Waves intensity = amplitude pitch = frequency (wavelength) Audible range in humans 20 Hz – 20 kHz ~. Anatomy of the Ear. Tympanic membrane Middle ear - ossicles

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auditory system

Auditory System

Lecture 13

the stimulus
The Stimulus
  • What kind of energy is sound?
    • mechanical
    • movement of air molecules
  • Waves
    • intensity = amplitude
    • pitch = frequency (wavelength)
  • Audible range in humans
    • 20 Hz – 20 kHz ~
anatomy of the ear
Anatomy of the Ear
  • Tympanic membrane
  • Middle ear - ossicles
    • Malleus (hammer)
    • Anvil (incus)
    • Stapes (stirrup)
  • Inner ear -
    • Oval window
    • Cochlea - fluid filled
    • Round window ~
structure cochlea
Structure: Cochlea
  • 2 continuous chambers
    • Scala Vestibuli
    • Scala Tympani
    • filled with perilymph
  • Scala Media
    • between others
    • filled with endolymph
    • high K+ concentration ~

Scala Vestibuli

Scala Media

Scala Tympani

slide7

Uncoiled Cochlea

Oval

Window

Scala Vestibuli

Scala Media

Scala Tympani

Round

Window

organ of corti
Organ of Corti
  • Auditory receptor organ
    • in scala media
  • Tectorial membrane
    • roof of scala media
  • Basilar membrane
    • floor of scala media
  • Hair cells ~
hair cells auditory receptors
Hair Cells - Auditory Receptors
  • Mechanoreceptors
    • Anchored to basilar membrane
  • Cilia
    • tiny appendages (“eyelashes”)
    • top of hair cells ~
organ of corti10
Organ of Corti

Tectorial Membrane

Basilar Membrane

hair cells transduction
Hair Cells - Transduction
  • Receptor Potential
    • Depolarization
    • K+ influx
    •  NT release from receptor
  • Cilia
    • tip-links
    • K+ channels
    • cilia bend  open/close channels ~
slide13

Force

Force

Resting rate

Excitation

Inhibition

Hair Cells - Transduction

APs in Cochlear Nerve Axon

the auditory pathway
The Auditory Pathway
  • Complex pathway
    • focus on most direct
    • hierarchical processing
    • parallel processing
  • Bilateral output
    • contralateral stronger
    • ipsilateral weaker
  • Cochlear Nerve  Cochlear Nucleus ~
slide16

A1

A1

Auditory

Pathway

Thalamus: MGN

Inferior Colliculus

Hair Cell

More NT

Superior Olive

Cochlear Nuclei

Auditory Nerve - VIII

pitch perception
Pitch Perception
  • Frequency Theory
  • Rate neurons
    • vibration of basilar membrane
    • frequency vibration  frequency APs
    • *text max. frequency = *1000 Hz (1 kHz)
  • Low frequency sounds only
    • < 100 - 200 Hz ~
pitch perception18

High Medium Low

Base Apex

Pitch Perception
  • Place Theory
  • Place neurons
    • Part of basilar membrane stimulated
    • high frequency near oval window
    • low frequency near end ~
loudness perception
Loudness Perception
  • Intensity
    • amplitude of wave
  • place neurons
    • rate of firing
  • rate neurons
    • number of neurons firing ~
sound localization

< 3000 Hz

> 3000 Hz

Sound Localization
  • Superior Olives
  • Low frequency
    • Phase differences
  • High frequency
    • Intensity differences ~