These hairs are transducers. As the basilar membrane bellies in and out, it pushes and pulls the complex of tissues above it.
The hairs' cells of the organ of Corti ride with the basilar membrane.
The hairs have their tops embedded in the tectorial membrane and their roots fixed in the hair cells, so the motion of the basilar membrane bends and twists and pulls and pushes the hairs. Under these physical stresses the hairs generate electrical signals which stimulate the auditory nerve (also known as the acoustic nerve and the eighth cranial nerve)