What is mechanotransduction in hair cells?

• A. The diffusion of neurotransmitters across synaptic cleft without depolarization.
• B. The generation of action potentials within hair cells themselves.
• C. The conversion of electrical signals into mechanical motion.
• D. The conversion of mechanical shear into an electrical signal via ion channels.

Answer: (D)

Mechanotransduction in hair cells is the process by which mechanical forces, such as sound-induced deflection of the hair bundle, are converted into an electrical signal through mechanically gated ion channels. When the bundle tilts toward the tallest stereocilia, tension opens these channels, allowing cations (primarily K+ and Ca2+) to flow in and depolarize the hair cell. This depolarization then opens voltage-gated Ca2+ channels at the base, triggering neurotransmitter release onto the afferent nerve fibers and generating a neural signal. This is not simply diffusion of neurotransmitters across a synapse without depolarization, nor is it generation of action potentials within hair cells themselves, and it is not the process of converting electrical signals into mechanical motion (that’s outer hair cell electromotility). It specifically describes the conversion of mechanical shear into an electrical signal via ion channels.