Systems Physiology II 6010

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Systems Physiology II 6010
Lecture 10 Sensory system Hearing
Bradley Greger, PhD
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Sound

• Fourier any sound wave can be decomposed into a
  superposition of elementary waves of varying
  frequencies and amplitudes

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Sound

• Fourier any sound wave can be decomposed into a
  superposition of elementary waves of varying
  frequencies and amplitudes
• Should be simple to decode into neural signal

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Anatomy of the Ear

• Outer Ear
• Pina
• Important for quality of sound
• Plasticity to fake pina
• Auditory Meatus
• Ear canal
• Intra-aural line neurosurgical landmark

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Anatomy of the Ear

• Middle Ear
• Tympanic Membrane
• Ear drum
• Three Osicles
• Malleus (Hammer)
• Incus (Anvil)
• Stapes (Stirrup)
• Eustachian tube
• Infections
• Pressure changes

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Anatomy of the Ear

• Inner ear
• Cochlea
• snail
• The retina of hearing

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Anatomy of the Ear

• Inner Ear
• Cochlea
• Oval window
• Scala vestibuli
• Scala tympani
• perilymph
• Round window
• Pressure relief
• Scala media
• Basal Membrane
• Organ of Corti

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Cochlea

• Inner Ear
• Cochlea
• Scala media (cochlear duct)
• Basal Membrane
• Organ of Corti
• Endolymph
• High concentration of potassium
• Spiral ganglion
• Auditory nerve
• Modiolus
• Bony structure

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Cochlea Sound transduction

• Mechanical frequency decomposition
• High frequencies at base, near windows
• Low frequencies at apex, furthest from windows
• 100Hz 15,000-20,000Hz
• Kid only ringtone

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Cochlea Sound transduction

• Pressure waves
• Travel through perilymph
• Oval window to round window
• Much of the basilar membrane distorted by
  traveling waves
• Complex patterns in cochlea, even for simple
  sinusoids
• Not simple Fourier decomposition

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Cochlea Sound transduction

• Organ of Corti
• Basilar membrane
• Hold hair cells
• Tectorial membrane
• roof over top of hair cells
• Afferent fibers of spiral ganglion cells
• Efferent fibers
• Feedback to dampen response to loud sounds

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Cochlea Sound transduction

• Traveling wave in scala vestibuli and typani
  distort scala media
• Relative shearing motion of basilar membrane and
  tectorial membrane

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Cochlea Sound transduction

• Stereocilia
• hairs
• In endolymph
• Embeded in tectorial membrane
• Motion changes cation permeability
• One direction hyperpolarizes
• The other direction depolarizes
• Release neurotransmitters onto bi-polar spiral
  ganglion cells

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Cochlea Sound transduction

• Inner Hair Cells
• 3500
• smaller
• Innervated by 10 ganglion cells
• One hair cell per ganglion cell
• Outer Hair Cells
• 12000
• Larger
• Innervated by several ganglion cells
• Many hair cells per ganglion cell

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Cochlea Sound transduction
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CF
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stimulus

• Mechanical resonance
• Determined by mechanical properties of the
  cochlea and stereocilia
• Location of cell along the cochlea
• Electrical resonance
• Spontaneous oscillations, frequency differs
  according to position
• Matches mechanical resonance frequency

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Central Auditory Pathway

• Cochlear nucleus
• Lateral Lemniscus
• Nucleus of lateral lemniscus
• Inferior coliculus
• Medial geniculate nucleus
• Thalamus
• Primary auditory cortex

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Superior Olive Sound Localization

• Temporal differences
• High frequency
• Cells have medial and lateral dendrites
• Each receives input from ispilateral and
  contralateral cochlear nucleus
• Timing differences of the arrival of action
  potentials
• Amplitude (Loudness) differences
• Low frequency
• Sound shadow

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Response Fields

• Response of spiral ganglion cells to tones
• Initial burst
• Sustained activity
• Undershoot
• Change in gain of response due to amplitude of
  tone

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Response Fields Characteristic Frequency

• Auditory response fields
• Amplitude frequency
• Characteristic preferred frequency
• Frequency at which cell response with lowest
  amplitude

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Primary Auditory Cortex

• Tonotopy
• Distribution of CFs
• Similar frequencies are next to each other
• Rostral caudal, high to low frequency
• True in cats, may not be true for non-human
  primates, and humans
• Columnar organization
• Summation columns
• Binaural response greater than monaural response
• Suppression columns
• One ear dominant, greater than binaural response

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Cochlear Implant
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Cochlear Implant
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Applications Cochlear Implant
Michael Chorost
What does a cochlear implant sound like?