The epithelium is represented as a lipid (fat) bilayer (round circles), the area above the lipid bilayer (oral cavity) represents the outside of the taste receptor cell, and the area below the lipid bilayer is the interior of the taste receptor cell. The channel itself is made up of three protein units (alpha, beta, and gamma) that are represented by the cylindrical structures. This channel is thought to form a tunnel through the taste receptor cell that allows Na⁺ ions outside the cell to move inside the cell. This channel is quite specific to sodium, which may explain why few compounds are purely salty. Once sodium is inside the taste receptor cell it causes a cascade of biochemical reactions that result in the release of neurotransmitters that signal salt taste to the brain.