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Lecture 4

NROC64H3 Lecture Notes - Lecture 4: Hair Cell, Vestibular Duct, Cochlear Nerve

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Matthias Niemeier

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NROC64H3S Sensory and
Motor Systems
Lecture 4 02.03.12
SAQ: Describe the 3 pathways of
the visual system that are
differently specialized for
motion, colour and shape
- Sense of Hearing, Audition
Detect sound, perceive and
interpret nuances
- Sense of balance, vestibular
Head and body location, head
and body movements
The Nature of Sound
- Sound
Audible variations in air
pressure, water, pressure etc.
Sound Frequency: # of
cycles/second expressed in Hz
Cycle: Distance b/w successive
compressed patches
Hi frequency: More cycles in same space
Range: 20-20,000 HZ
Pitch: Perceptual aspect of frequencies
Loudness: Perceptual aspect of intensity
Frequency depends on how many cycles,
what the amplitude is
The Structure of the Auditory System
- Early Auditory Pathway Stages
Sound waves
Tympanic Membrane
Oval Window
Cochlea Fluid
Movement of basilar and tectorial
membrane: sheering forces
Sensory neuron response
- The Middle Ear
Function of Ossicles: Sound Force
Lever analogy balancing of the sound
greater pressure, ossicles work like levers
Pressure = Force/area 20x greater pressure at oval window than tympanic membrane, moves fluids
Attenuation Reflex: Response where onset of loud sound causes tensor tympani and stapedius muscle contraction.
Functions: Adapt ear to loud sounds; avoid saturations, damage, filter out low frequency, understand speech better
(high freq), reduce sound of our own voice
- The Inner Ear
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Perilymph: Fluid in sacala vestibuli and scala tympani
Endolymph: Fluid in scala media, high K+, stria vascullaris (weird cause other neurons have K+ efflux)
Endcochlear potential: Endolymph electric potential 80 mV more positive than perilymph
Basilar membrane in uncoiled cochlea (Apex-x5 wider, 100x less stiff) like a flipper, will move depending on which
frequency is moving through the membrane, achieve tonotopy from mechanical reasons
Physiology of the Cochlea
- Physiology of the Cochlea: Pressure at oval window, pushes perilymph into scala vestibuli, round widow
membrane bulges out
- Endolymph movement bends basilar membrane near base, wave moves towards apex
- Basilar membrane; place code
- Organ of Corti and Associated Structures
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