The Middle Ear: Structure and Function

Middle Ear

• Located behind the eardrum
• Comprised of three bones: hammer, anvil, and stirrup
• Transmits vibrations from the tympanic membrane to the oval window of the inner ear
• Functions as a lever system, amplifying pressure from the eardrum to the oval window by a factor of 22
• Filters out noise generated in the body
• Protects the ear from high amplitude vibrations by switching to a less-efficient mode of vibration at high sound levels

Inner Ear

• Transforms sound wave energy into nerve impulses for the brain
• Components:
  • Cochlea: a snail-shaped structure generating fluid waves from the stapes' movement
  • Reissner Membrane: separates the scala vestibuli from the scala media
  • Basilar Membrane: separates the scala media from the scala tympani and contains sensory cells
• Basilar Membrane functions:
  • Contains outer and inner hair cells responding to different frequencies
  • Hair cells are covered by the tectorial membrane
  • Vibrations cause hair cells to shear against the tectorial membrane, triggering chemical and electrical changes
• Sound Transmission:
  • Sound energy causes basilar membrane vibrations
  • Vibration triggers hair cell shearing and electrical charges
  • Electrical charges produce neural impulses traveling along the auditory nerve to the brain
  • The brain interprets these impulses as sounds
• Frequency Detection:
  • High frequency sounds produce greatest motion near the oval window
  • Low frequency sounds produce greatest motion near the apex
  • Different areas on the basilar membrane stimulate different frequencies, resulting in varying nerve cell firings
  • The brain interprets these impulses as sounds of different pitches

This quiz covers the location, structure, and functions of the middle ear, including the role of the hammer, anvil, and stirrup bones in transmitting vibrations to the inner ear.