Quiz 3

• The Pinna:

  • Collects sound waves
  • Helps in localization
  • Amplification (5-6 dB SPL)
• External Auditory Canal:

  • Carries the sound waves to the tympanic membrane
  • Protection
  • S-shaped
  • Two parts: Cartilaginous portion (1/3 of its length) and Osseous portion (2/3 of its length)
• Tympanic Membrane:

  • Three layers: Outer layer (skin of ear canal), Middle layer (tough, fibrous layer that contributes to vibration), Inner layer (mucous membrane that lines middle ear cavity)
  • Protection
  • Connects outer and middle ear
  • Converts sound energy to mechanical energy
• Tympanic Cavity:

  • Lateral wall is the tympanic membrane
  • Medial wall is the promontory of the cochlea
  • Anterior wall is the eustachian tube & sulcus for internal carotid artery
  • Posterior wall is the mastoid
  • Roof is the tegmen tympani of the petrous temporal bone
  • Floor is the sulcus for the internal jugular vein
• Bones of the Middle Ear (ossicular chain):

  • Malleus
  • Incus
  • Stapes
  • Pass on mechanical energy from tympanic membrane to the inner ear
  • Amplify the sound
  • Impedance matching to overcome the difference in sound pressure level between air and fluid
• Muscles of the Middle Ear:

  • Tensor tympani: Origin - eustachian tube, Insertion - malleus, Function - tenses eardrum to reduce vibration
  • Stapedius: Origin - posterior wall of middle ear, Insertion - stapes, Function - stiffens ossicular chain to reduce vibration
• Eustachian Tube:

  • Connects front wall of middle ear with nasopharynx
  • Equalizes ear pressure
  • Acts as a channel to drain middle ear fluid
  • Blockages reduce movement of tympanic membrane and can cause recurrent ear infections (otitis media)