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PHY238Y Lecture 12

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the endolymph fluid in the cochlear duct. The fluids differ in terms of their ... Cochlear implants: electronic devices designed to provide sound information in ... – PowerPoint PPT presentation

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Title: PHY238Y Lecture 12


1
PHY238YLecture 12
  • The human inner ear
  • Physics of hearing (IV)
  • References
  • Hallett et al. Physics for the life sciences,
    4th ed., Ch.2 (2.6)
  • Some of the pictures were taken from Hyper
    Physics
  • Hyper Physics http//hyperphysics.phy-astr.gsu.ed
    u/hbase/sound/ear.htmlc1
  • Thanks to dr. Rod Nave for the permission to use
    the above resource

2
PHY238YLecture 12
  • The inner ear contains specialized sense organs
    for transducing sound into neural impulses
  • - the semicircular canals which serve as the
    body's balance organ
  • - the cochlea which serves as the body's
    microphone, converting sound pressure impulses
    from the outer ear into electrical impulses which
    are passed on to the brain via the auditory
    nerve.

3
PHY238YLecture 12
  • The semicircular canals are the body's balance
    organs, detecting acceleration in the three
    perpendicular planes. These accelerometers make
    use of hair cells which detect movements of the
    fluid in the canals caused by angular
    acceleration about an axis perpendicular to the
    plane of the canal.
  • The canals are connected to the auditory nerve.

4
PHY238YLecture 12
  • Cochlea has three fluid filled sections.
  • The perilymph fluid in the canals (almost
    identical to spinal fluid)
  • the endolymph fluid in the cochlear duct.
  • The fluids differ in terms of their
  • electrolytes and if the membranes
  • are ruptured so that there is mixing of
  • the fluids, the hearing is impaired.
  • The organ of Corti is the
  • sensor of pressure variations.

5
PHY238YLecture 12
  • Cochlea is a coiled tube (10 mm diameter 35 mm
    long) bisected by cochlear partition and
    supporting the basilar membrane
  • Peak frequencies along the basilar membrane high
    frequencies close to the base low frequencies at
    the apex end.

6
PHY238YLecture 12
Traveling waves of different frequencies along
the basilar membrane (Fig. 6.5 from K. Bogdanov
Physics in Biology)
7
PHY238YLecture 12
  • The basilar membrane of the inner ear plays a
    critical role in the perception of pitch
  • The theory that won the Nobel prize for
    Physiology or Medicine (1961) Traveling Waves
    propagate along the basilar membrane (Georg von
    Bekesy)
  • Basilar membrane does not respond to vibrations
    in a simple waybut to sinusoidal vibrations and
    traveling waves
  • - High frequencies peak near base
  • - Low frequencies peak near apex

8
PHY238YLecture 12
  • Organ of Corti is situated on the basilar
    membrane in one of the three compartments of the
    cochlea.
  • It contains four rows of hair cells which
    protrude from its surface.
  • Above them is the tectorial (tectoral) membrane
    which can move in response to pressure variations
    in the fluid - filled tympanic and vestibular
    canals.
  • Movement of tectorial membrane relative to
    basilar membrane causes hair cells to tilt. A
    lilt of 0.3 nm can be converted into a nervous
    signal

9
PHY238YLecture 12
  • Taking electrical impulses from the cochlea and
    the semicircular canals, the auditory nerve makes
    connections with both auditory areas of the
    brain.

10
PHY238YLecture 12
  • Cochlear implants electronic devices designed to
    provide sound information in people with intact
    auditory nerve, but injured cochlea.
  • 22 electrodes are surgically inserted inside the
    inner ear
  • They receive harmonics from a microphone speech
    processor system
  • They send signals to the corresponding nerve
    terminals from the inner ear
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