The structure that is in physical contact with the auditory receptor stereocilia is the

The structure that is in physical contact with the auditory receptor stereocilia is the tectorial membrane.

Explanation:

The tectorial membrane is a structure or a thin layer of tissue that is floating in the endolymph on the stereocilia of the ciliated cells. Ciliated cells, which are sensory cells attached to the surface of the basilar membrane.

When the ciliated cells move up and down, microscopic projections similar to sows (known as stereocilia), which are located above the ciliated cells, cause the cilia to lean towards the side wall of the cochlea. This inclination makes that some channels that look like pores open, which are at the tips of the stereocilia. When this happens, certain chemicals enter the cells, thus generating an electrical signal. The inner ciliated cell is activated, probably by a direct contact of its stereocilia with the Hensen band of the tectorial membrane, the synapse between the ciliated cell and the auditory nerve fibers, send a message to the brain, which converts it into sounds that we can recognize and understand.