Editing Auditory system (section)

==== Hair cell ====
{{main|Hair cell}}
Hair cells are columnar cells, each with a "hair bundle" of 100–200 specialized [[stereocilia]] at the top, for which they are named. There are two types of hair cells specific to the auditory system; ''inner'' and ''outer'' ''hair'' ''cells''. Inner hair cells are the mechanoreceptors for hearing: they transduce the vibration of sound into electrical activity in [[nerve fiber]]s, which is transmitted to the brain. Outer hair cells are a motor structure. Sound energy causes changes in the shape of these cells, which serves to amplify sound vibrations in a frequency specific manner. Lightly resting atop the longest [[cilia]] of the inner hair cells is the [[tectorial membrane (cochlea)|tectorial membrane]], which moves back and forth with each cycle of sound, tilting the cilia, which is what elicits the hair cells' electrical responses.

Inner hair cells, like the [[photoreceptor cell]]s of the eye, show a  [[postsynaptic potential|graded response]], instead of the [[action potential|spikes]] typical of other neurons.  These graded potentials are not bound by the "all or none" properties of an action potential.

At this point, one may ask how such a wiggle of a hair bundle triggers a difference in membrane potential. The current model is that cilia are attached to one another by "[[Stereocilia (inner ear)#Design and constellation|tip links]]", structures which link the tips of one cilium to another. Stretching and compressing, the tip links may open an ion channel and produce the receptor potential in the hair cell. Recently it has been shown that [[CDH23|cadherin-23 CDH23]] and [[PCDH15|protocadherin-15 PCDH15]] are the adhesion molecules associated with these tip links.<ref name="Lelli Kazmierczak 2010">{{Cite journal |vauthors=Lelli A, Kazmierczak P, Kawashima Y, Müller U, Holt JR |date=August 2010 |title=Development and regeneration of sensory transduction in auditory hair cells requires functional interaction between cadherin-23 and protocadherin-15 |journal=The Journal of Neuroscience |volume=30 |issue=34 |pages=11259–69 |doi=10.1523/JNEUROSCI.1949-10.2010 |pmc=2949085 |pmid=20739546}}</ref> It is thought that a [[calcium]] driven motor causes a  shortening of these links to regenerate tensions. This regeneration of tension allows for apprehension of prolonged auditory stimulation.<ref name="Peng 2011">{{Cite journal |vauthors=Peng AW, Salles FT, Pan B, Ricci AJ |date=November 2011 |title=Integrating the biophysical and molecular mechanisms of auditory hair cell mechanotransduction |journal=Nature Communications |volume=2 |pages=523 |bibcode=2011NatCo...2..523P |doi=10.1038/ncomms1533 |pmc=3418221 |pmid=22045002}}</ref>