Auditory Physiology: Hair Cell Nanomechanics and the Cochlear Amplifier

Vocabulary flashcards covering the nanomechanics, molecular components, and active cochlear amplification mechanisms of inner and outer hair cells based on the lecture.

Prestin

A motor molecule embedded in the lateral walls of outer hair cells that changes its shape up to $70\text{ kHz}$ ($70{,}000\text{ Hz}$) to shorten or elongate the cell without requiring ATP or calcium.

Cochlear Amplifier

A term coined by Hallowell Davis describing the acoustic gain of low-level stimuli achieved through the active motility of outer hair cells.

Equalization

A perceptual benefit of outer hair cell motility that enables the auditory system to appreciate both a soft tone and a loud tone presented simultaneously.

Tone on Tone Suppression

A form of inhibition in which the traveling waves of two simultaneously presented pure tones that are too close together interfere, causing one tone to mask the other.

Olivocochlear Bundle

A neural feedback pathway from the superior olivary complex to hair cells that can modulate hair cell motility to help focus on signals in the presence of background noise.

Outer Hair Cell Motility

The rapid shape-shifting response of outer hair cells driven by membrane potential changes, where depolarization causes the cell to get shorter and hyperpolarization causes it to get taller.

Nanomechanics

The sequence of mechanical and molecular events within a hair cell that enables it to convert the physical motion of sound into an electrical signal readable by innervating neurons.

Signal Transduction

The universal process by which sensory receptor cells convert incoming physical energy into an electrical signal that can be transmitted to neurons.

Kinocilium

The single tallest specialized cilium on a hair cell toward which the remaining stereocilia must deflect in order to stimulate the receptor.

Tip Links

Tiny molecular threads anchored at one end to the top of a shorter stereocilium and at the other end to the lateral wall of the adjacent taller stereocilium.

Cadherin 23

A structural protein that forms part of the tip link; genetic mutations in this molecule are one of the most common causes of inherited deafness.

Protocadherin 15

A structural protein that pairs with cadherin 23 to compose the functional tip link thread between stereocilia.

Mechanoelectric Transducer (MET) Channel

A mechanical ion channel linked to the tip link that pops open when stereocilia deflect toward the kinocilium, allowing positively charged ions to flood into the hair cell.

TMC1 and TMC2

Transmembrane channel-like proteins 1 and 2, which constitute the core components of the mechanoelectric transducer gate in hair cells.

Hair Cell Resting Membrane Potential

The baseline electrical polarization maintained by a resting hair cell, established at approximately $-50\text{ mV}$.