Outer and middle ear structure and function

  1. Pinna
    • front or back localization and level
    • -changes in acoustic signal triggers this localization
  2. External auditory canal
    • formed by cartilage, inner portion of the ear drum.
    • -deep centre portion called the concha which leads to the opening of the external auditory meatus
  3. middle ear structures
    • tympanic membrane, Ossicles (malleus, incus, stapes)
    • -this portion of the ear converts air vibration to mechanical vibration
    • -connected to the nasopharynx by the Eustachian tube
  4. Tympanic membrane
    • cone shaped, relatively transparent, extremely thin
    • 3 layers:outer is bony inner is mucous middle layer is the most important
    • any small movement is enough to produce a threshold
    • -It is connected to the malleus
  5. Sound transmission through the system
    inner ear communicates with environment by means of a funnel (pinna) a thin membrane (tympanic) and 3 small bones
  6. Outer ear
    Torso and head provide obstacles to sound. they change it before it hits the outer ear. High Hz have high attentuation
  7. head related transfer function
    • higher freq sounds have more attenuation
    • -transfer functions give pressure to the sound. You get more out then you put in from the source
    • -the pinna and ear canal provide a pressure gain
  8. ear canal
    amplifies speech freq
  9. sound travels through middle ear in three ways
    • 1) bone conduction (direct to inner ear)
    • 2) the air in the middle ear
    • 3)through the ossicle chain-most effective
  10. impedance mismatch
    air can not easily move the fluid in the inner ear.  which is why it needs to be converted to mechanical force first by the ossicles
  11. Two main functions of the middle ear plus one minor
    • 1) transfer function- move air pressure to fluid. pressure gain in the middle ear by the ossicles. (impedance mismatch)
    • 2)middle ear system must stay open for transfer function to work so the drum can vibrate maximally. ¬†These means there needs to be equal pressure on both sides (eustachian tube)
    • 3) sound reduction through muscles
  12. Stapes muscle
    • stiffens the middle ear bones
    • -used as a reflex to loud sounds (stapedious reflex)
    • -when it is contracted, the stapes moves to the side and tenses the membrane of the oval window which reduces sound
  13. Tensor tympani
    responds reflexively bilaterally
Card Set
Outer and middle ear structure and function
Outer and middle ear structure and function