The membranous chamber is filled with endolymph while the bony chamber is filled with perilymph. The wall of the membranous chamber is made up of many cells that are so tightly joined together that they prevent the two fluids from mixing. The sensory cells are called hair cells because of their appearance under the microscope. Each hair cell has a tuft of projections at one end that looks like a bad haircut. The hair cells are connected to neurons at the other end of the cell away from the stereocilia.
Neurons have long projections that conduct electrical signals to the brain.
When a hair cell is mechanically stimulated it releases a chemical that modulates the electrical activity of these neurons, thereby signaling the brain. In addition to sending information to the brain, some hair cells receive input from neurons that originate deep in the brain and send one of their long projections to the hair cells. These neurons appear to regulate the sensitivity of the hair cells, in a manner similar to changing the volume control on a radio. All Rights Reserved. Baylor College of Medicine.