TRAVELING WAVE
HHMI Cochlea animation

• pressure wave passes through the cochlea INSTANTANEOUSLY
  (speed of sound in seawater is ~1500 m/s; length of the human cochlea is ~35 mm!)

• establishment of the traveling wave pattern is INDEPENDENT of how the motion is initiated in the perilymph  i.e., don't need to deliver sound via the oval window

  • this is the basis of the RINNE test

Nolte Figure 14-4

• in response to a sinusoidal stimulus, the basilar membrane vibrates with a wave that gradually grows in amplitude as it moves along the cochlear duct, away from the stapes in the base, toward the apex – it reaches a peak at a specific point that is determined (in part) by the resonant properties of the cochlear partition – same direction of travel is observed if the sound is introduced into the apex

• COCHLEAR PLACE CODE: the peak of the travelling wave occurs at a different place along the cochlear partition for each frequency (the basilar membrane movement is said to be “tuned”)

• low frequencies peak near the apex; high frequencies near the base