Neurologic Anatomy of the Ear

Aka: Neurologic Anatomy of the Ear, Ear Neuroanatomy, Hearing, Sound Perception, Auditory Function

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II. Physiology: Hearing

  1. See Vestibular Function
  2. Outer Ear
    1. Sound waves enter the external auditory canal and reach the Tympanic Membrane (Ear Drum)
    2. Tympanic Membrane vibrates in response to sound waves
  3. Middle Ear
    1. Ossicles vibrate as a sequence of gears, amplifying the vibration signal from the Tympanic Membrane
      1. Malleus (hammer)
      2. Incus (anvil)
      3. Stapes (stirrup)
    2. Stapes attaches to the oval window, passing the vibratory signal into the Cochlea of the inner ear
    3. Middle ear communications
      1. Eustachian tube
        1. Functions as a Pressure Equalization Tube to allow for Tympanic Membrane vibration
        2. Exits to the posterior nasopharynx
      2. Mastoid antrum
        1. Communicates with the mastoid air cells
  4. Inner Ear: Cochlea
    1. Inner ear contains two sensory organs
      1. Cochlea (snail shell shape)
        1. Converts sound waves to electrical sensory signals transmitted centrally by the Cochlear Nerve
      2. Semicircular canals
        1. Three semicircular canals sense head position and transmit centrally via the Vestibular Nerve
        2. See Vestibular Anatomy
    2. Sound waves are transmitted to a fluid filled chamber (scala vestibuli) via the oval window
      1. Perilymph fluid within the scala vestibuli carries sound waves to the Cochlear duct
      2. Perilymph fluid surrounds the Cochlear duct
        1. Returns to the base of the Cochlea via the scala tympani
        2. Scala tympani ends at the round window (inferior to the oval window) at the middle ear
    3. Signal vibrates the tectorial membrane and Organ of Corti hair cells
      1. Different sound frequencies vibrate different hair cells along the course of the Organ of Corti
    4. Organ of Corti hair cells generate impulses in response to vibration
      1. Signal is transmitted centrally via the Cochlear Nerve
  5. Inner: Ear: Perilymphatic fluid
    1. Surrounds vestibular apparatus (semicircular canals and otolithic organs)
    2. Communicates with the perilymph of the Cochlea (from oval window to round window)
    3. Communicates with perilymphatic duct (and the subarachnoid space)

III. Components

  1. Vestibulocochlear Nerve
  2. Chorda Tympani
  3. Organ of Corti
  4. Internal Auditory Canal

IV. References

  1. Goldberg (2014) Clinical Physiology, Medmaster, Miami, p. 118-9

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