To illustrate the size of a hair cell, I have electronically pasted the image of the hair cell to scale on this slide. You will have to zoom in on the hair cell to be able to see it. Hair cells are small. But hair cells are themselves complex micromechanical systems whose function relies on an array of even smaller mechanical parts. Displacements of hair bundles generate electrical responses in hair cells via mechanically sensitive ion channels in the cell membrane.
Ion channels are proteins that are integral parts of the membranes of all cells.
Most of the cell's membrane is lipid and acts as a chemical and electrical barrier between the inside and outside of the cell. Ion channels have pores that act as conduits for ionic currents to pass through the membrane. The state of conduction of an ion channel can be modulated by external stimuli. For example, some ion channels have chemical binding sites, and their state of ionic conduction depends on whether the binding site is occupied. Such ion channels act as chemical sensors.