Describe Hearing Receptors and Their Physiology

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5 Terms

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Structures for hearing

  • Cochlea: snail-shaped chamber of inner ear

  • Modiolus: bony axis of the spiral

  • Cochlear duct: membranous labyrinth in cochlea. Roof formed by vestibular membrane. Floor formed by basilar membrane

  • Scala vestibuli: chamber of bony labyrinth adjacent to vestibular membrane

  • Scala tympani: chamber of bony labyrinth adjacent to basilar membrane

  • Helicotrema: small channel connecting scala vestibuli and scala tympani

  • Spiral organ: sensory structure for hearing. Within cochlear duct. Thick sensory epithelium
    consisting of hair cells and supporting cells on basilar membrane

  • Hair cells: receptors that release neurotransmitter to sensory neurons.

    • Single row of inner hair cells

    • three rows of outer hair cells

    • Hair cells have many stereocilia (long microvilli) and one kinocilium (long cilium) at their apex

    • Stereocilia and kinocilium embedded in tectorial membrane.

    • Base of hair cells synapse with sensory neurons.

    • Cell bodies of sensory neurons are located in spiral ganglia of
      modiolus

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Pathway from sound wave to nerve signal

  1. waves vibrate tympanic membrane

  2. ossicles vibrate and transmit waves to oval window

  3. fluid pressure waves in scala vestibuli push vestibular membrane causing pressure waves in endolymph of cochlear duct

  4. specific regions of basilar membrane move

  5. hair cells distorted causing changes in NT release

  6. sensory neurons in CN VIII stimulate to fire

  7. pressure transmitted to scala tympani

  8. absorbed in round window

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Cochlear hair cell stimulation

  • basilar membrane moves up → hair cells pushed into tectorial membrane

  • hair cells release NT from base → excite sensory neuron → action potential

  • basilar membrane down → reverses process

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Perception of sound

  • sound = pressure waves from vibration

  • pitch = frequency

    • frequency = rate of vibration (Hz)

    • humans hear 20-20,00 Hz, sesnstive to 1500 and 4000

  • loudness = wave amplitude

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Deafness

conductive: inference of wave transmission in external/middle ear
sensorineural: malfunction inner ear/cochlear nerve