Which mechanism causes hair cell depolarization as stereocilia bend in response to sound waves?
a. receptor cells release atp to stimulate neighboring cells.
b. otoliths shift to stimulate hair cells.
c. tip links open ion channels, which causes membrane depolarization.
d. rhodopsin absorbs energy to stimulate photoreceptor cells.

c. Tip links open ion channels, which causes membrane depolarization.

Explanation:

Mechanically gated cation channels are present in the membrane of stereocilia. The tip link proteins connect these cation channels to the tip of the tallest stereocilium neighbor.  The vibration of the basilar membrane leads to the opening of these cation channels to allow the entry of cations (primarily K+) into the cytosol of hair cells. The entry of cations generates depolarizing receptor potential.

The vibration of the basilar membrane makes the stereocilia to bend towards the tallest stereocilium. This results in stretching of tip links and the opening of cation channels in the adjacent shorter stereocilia to allow entry of the large amounts of K+ and Ca2+ into the hair cells. The result is graded depolarization.