Biomedical Engineering 403

Hearing Loss: Hearing Aid or Cochlear Implants; Section Review

Today's topic:

Now I haven't seen the exam yet, so I don't know what's on it. But I'd wager big money that most of what will be on it will come right out of what was covered today's review portion.

Here's what he talked about first (Before the review). Be familiar with this stuff:

• Audiogram
• Hearing aids
  • since every person's audiogram is unique, hearing aids must be tailored to each person to supplement that person's unique pattern of hearing loss.
• Cochlear Implants (Way cool)
  • Electrodes for these devices are inserted through the round window.
  • These electrodes have tonotopic arrangements in their design
  • An external coil is worn behind the pinna. An external microphone sends the signal to a microprocessor, which feeds it to the coil. The coil then beams the signal into the head.
  • An internally implanted coil receives the signal (the pair of coils are essentially a transformer) and sends the signal to the electrodes, which stimulate the cochlea.
• The ABI is a brainstem implant that performs a similar task, but bypasses the auditory nerve altogether. Patients with neurofibromatosis type II frequently present with bilateral tumors in the auditory nerves. These tumors have to be removed, and when they are, the patients are left with a complete hearing loss. Enter the ABI. Electrodes are slipped into place to stimulate the nucleus of the auditory nerve. These devices work much like a cochlear implant except that they stimulate the auditory system at a higher level.

REVIEW SECTION

Please know these topics for the midterm. You'll be happy you did.

• Sound is the perception of pressure waves transmitted through a matter medium such as air.
• Sound Pressure Level (SPL) is measured in dB
• SPL can be calculated according to either of the following equations:

  
  10 log (I/I0)
  
  20 log (P/P0)
  
  

• The key relation here is that Intensity is proportional to Pressure squared (Intensity is typically defined as the square of amplitude).

  
  I = k P^2
  
  

• Dr. Z stated that, in order to correctly solve a problem such as Homework Problem #2, you must know whether amplitude is being given in terms of pressure or in terms of intensity. For the exam, he will tell you which.
• Be familiar with the concept of the RMS (Root Mean Square) function.
• Know the anatomy and function of the ear:
  • Outer Ear = anything you can touch from the outside (DON'T touch your eardrum)
    • Concha (also called "pinna" or "auricle")
    • External Ear Canal
    • Tympanic Membrane (also called "eardrum")
  • Middle Ear = air-filled part that connects with your respiratory system through the eustachian tube
    • Ossicles
      • Malleus
      • Incus
      • Stapes
      • Both the malleus & incus are involved in impedance matching and amplification
    • Oval window
      • The tympanic membrane is much bigger than the oval window. Using the relation P1/V1 = P2/V2, the transmission of sound waves from the eardrum to the oval window results in a big amplification.
    • Round Window. It's got a membrane. Make sure you understand the answers to question 5 from the homework.
    • Stapedius muscle: smallest muscle in the body. Attaches to the stapes. Involved in the attenuation of very loud sounds.
  • Inner Ear = Fluid-filled parts in their own little compartment.
    • Scala Vestibuli
    • Scala Media
    • Scala Tympani
    • Endolymph
    • Perilymph
    • POSSIBLE EXAM QUESTION! Where is endolymph found? Where is perilymph found?
    • Know the functions of the Basilar Membrane
    • How is the Basilar Membrane involved in detecting sound?
    • Organ of Corti
    • Hair Cells
      • Inner
      • Outer
      • POSSIBLE EXAM QUESTION! Which hair cells are involved in sound detection?
    • Stereocilia
    • Tectorial Membrane
      • What is the relation between Stereocila and the Tectorial Membrane?
    • Place Principle (very important)
    • Base
    • Apex
    • The auditory nerve innervates hair cells. The innervation consists of both afferent nerves and efferent nerves.
• Know your psychophysics:
  • R = f(s)
    • R = sensation
    • s = stimulus
  • Method of Limits
  • Method of Adjustment
  • Method of Constant Stimuli
  • Phon
  • Sone
  • Masking Effect
    • Probe Tone
    • Masking Noise
    • Critical Band

And that's All, Folks!

No!
Please don't make me go to any of those pages!
I want to go somewhere completely different!