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23 Cards in this Set

  • Front
  • Back
Auditory System
very sensitive to sound pressure, and can distinguish small changes in frequency.

Transduction is non-linear.
Cochlear Potentials
cochlea contains endolymph and perilymph that create an 80 mv potential difference.

The hair cells and auditory nerve generate biochemical potentials based on sodium and potassium flow.
Types of Electrical Potentials

Alternating Current and Direct Current.
Alternating Current
potentials change as a function of tissue vibration within the cochlea.
Direct Current
baseline potential changes that do not vary once they occur.
Potentials That Can Be Recorded From the Cochlea
Resting Potentials
Summating Potentials
Cochlear Microphonics
Auditory Action Potentials
Cochlear Microphonic
AC potential difference appearing only during acoustic stimulus.

Reflects the intensity and frequency components of sound input.

Thought to originate at cilia bearing end of outer hair cells.
Auditory Action Potential
AC potential generated by the auditory nerve, rather than the cochlear structures.

Not a true cochlear potential.

Neurons near the base are stimulated before the apex.
Auditory Action Potential Stimulation
The differences in stimulation (base vs. apex) means that the neurons have timing differences.

Potentials can cancel each other out, or sum partially.

With a tone, the basal end is stimulated initially, with less synchronous firing from the apical portions.
Auditory Action Potential Charge
large potential is created by sum of synchronous discharges.

AP is usually negative, then positive, then later negative potential from central sources.

Reflects the neural output of the cochlea.
Hair Cells
Stimulate a neural response.

Remember that the basilar membrane and tectorial membrane move differently.
different for inner and outer hair cells.

shearing is a particular type of bending where the tops of the stereocilia move more than the bottom.
Shearing of Stereocilia
mechanical energy is transduced into electrochemical energy.

the stereocilia need to be strong in order to resist breakage; otherwise they can get lost in the tectorial membrane.
Outer Hair Cell Shearing
stereocilia are attached to the tectorial membrane.
Inner Hair Cell Shearing
fluids trapped between stereocilia and tectorial membrane.

this fluid is theorized to help with the shearing action.
Neural Transduction
inner hair cells are neural transducers that start the neural process of hearing.

transduction in the inner hair cells takes place near the top of the hair cells (region of stereocilia).
Tip Links
act like a trap door by stretching and contracting; open like a gate and allow positive ion charge to enter hair cell.
Outer Hair Cells
acoustical pre-amplifiers.

feed energy back into the cochlea, and provide a cochlear amplifier for transducing small vibrations into neural impulses which can be "heard" by the brain.

Exhibit a type of active response; change in size due to acoustic stimulation. Prestin allows for a very fast motile response.
Outer Hair Cell Motility
changes in length and width, and the changes vary with the level of voltage.

changes affect the connection between the basilar membrane, and the tectorial membrane.

Changes in the biochemical vibratory pattern of the cochlea at the time of stimulation is due to the changes in the OHC length.

Changes allow for the high sensitivity of cochlear responses, ability to hear different sound frequencies, and non-linear cochlear function.
length of the outer hair cell DECREASES with increasing voltage.
length of the outer hair cells INCREASES with decreasing voltage.
Resting Potentials
Direct current potentials that exist without acoustic stimulation.

there are three DC potentials that can be seen in the resting and responding cochlea.

The most significant is the EP; endocochlear or endolymphatic potential.
Summating Potentials
DC potentials occuring only when there is an acoustic stimulus.

Baseline shift when a stimulus is present.