Physiology of the Auditory System Quiz

Cochlear Fluids

• Perilymph is an extracellular fluid with low potassium and high sodium levels.
• Endolymph is an intracellular fluid with high potassium and low sodium levels.

Basilar Membrane Structure

• The base of the Basilar Membrane is narrow and stiff.
• The apex of the Basilar Membrane is wide and soft.

Hair Cells

• Hair cells are both mechanoreceptors and epithelial cells.
• The reticular lamina is a tight junction epithelium that separates the hairs from the hair cell bodies.

Deafness

• Mutations in the tip links of hair cells can cause deafness.

Traveling Wave and Pressure Wave

• The pressure wave inside the cochlea is generated by the vibration of the stapes.
• The pressure wave causes the Basilar Membrane to vibrate.
• The traveling wave is the vibratory motion of the Basilar Membrane.
• The amplitude of the traveling wave differs at different locations along the Basilar Membrane.
• The base of the Basilar Membrane always responds before the apex.

Phase Difference

• There is a greater phase difference ahead of the traveling wave peak than behind it.

Place Code for Frequency

• Changes in sound frequency impact the traveling wave peak along the Basilar Membrane, creating a place code for frequency (tonotopy structure).

Envelope of the Traveling Wave

• The envelope of the traveling wave shows the location of maximum amplitude for pure tone stimuli.

Place Theory and Its Limitations

• The place theory suggests that the traveling wave for low frequency sounds stretches a long distance and vibrates mostly at the base of the Basilar Membrane.
• The place theory fails to explain why high frequency sounds stimulate mostly at the base of the Basilar Membrane.
• Three reasons that explain why the base of the Basilar Membrane likes high frequency sounds:
  • Basilar Membrane width and mass increase.
  • Stereocilia become longer, causing mass to increase.
  • Unknown reason.

Patterns of Excitation

• The patterns of excitation of complex sounds tell us about frequency, amplitude, and temporal variation.

Mechanical Tuning

• Mechanical tuning occurs at the Basilar Membrane of the organ of Corti.
• Mechanical tuning can be described as bandpass filters with steep roll-off for high frequency and shallow roll-off for low frequency.

Frequency Tuning

• Frequency tuning, or Characteristic Frequency (CF), is the frequency at which the sound level reaches a minimum to obtain a criterion displacement for a specific position on the Basilar Membrane.
• Mechanical tuning and frequency tuning are two different ways of describing the same quality.

Displacement of the Basilar Membrane

• The displacement of the Basilar Membrane is not linear with stimulus level.
• The Basilar Membrane motion is less than the sound level at CF, exhibiting compressive linearity.

Deflection and Excitation of Outer and Inner Hair Cells

• Outer hair cells are bent by mechanical shearing (by the tectorial membrane).
• Inner hair cells are bent by fluid shearing motion.

Temporal Distortions

• The traveling wave brings temporal distortions because low frequency sounds are transduced after high frequency sounds on the Basilar Membrane.
• The Basilar Membrane has numerous broadly tuned bandpass filters.
• The outer hair cells can amplify sound by jumping on the Basilar Membrane.
• The Basilar Membrane filters become sharper due to the outer hair cells.