Which type of hair cells is responsible for enhancing basilar membrane motion?

Outer hair cells play a crucial role in enhancing the motion of the basilar membrane within the cochlea. They are involved in a mechanism known as electromotility, where these cells change shape in response to electrical stimuli. This change in shape allows them to contract and elongate, effectively amplifying the movement of the basilar membrane in response to sound waves. This amplification is vital for improving the sensitivity of the auditory system, particularly for soft sounds, and is a key component of our ability to hear a wide range of frequencies.

Inner hair cells, while essential for transducing sound vibrations into electrochemical signals to be sent to the brain, do not actively enhance the motion of the basilar membrane. Stereocilia are the tiny hair-like projections on the surface of both outer and inner hair cells that are involved in the process of converting mechanical stimuli into electrical signals but do not contribute to the motion of the membrane itself. Supporting cells have a different function, mainly providing structural support and maintaining the homeostasis of the cochlea, rather than contributing to the dynamic motions required for sound amplification.

Given this context, outer hair cells are specifically responsible for enhancing the motion of the basilar membrane, making them integral to hearing.