Olfactory epithelium

The olfactory epithelium is the tissue you smell with. It is an epithelium, that is, a layer of cells that covers a surface, but a specialized one, and it sits in the upper back part of each nasal cavity, not at the entrance of the nose. That is where the cell bodies of the bipolar olfactory neurons live, the neurons that detect smell.

Each of those neurons ends in cilia, extremely fine projections, and the receptors that recognize the odor molecules, called odorants, sit on those cilia. Each neuron makes a single type of receptor. Bowman glands also secrete a fluid that helps dissolve the odorant. The odor particles dissolve in that fluid.

Then the signal leaves the nose. The axons, the cables of these neurons, cross the cribriform plate, a sheet of bone perforated like a sieve that separates the nose from the brain, and reach the olfactory bulb, where they gather into small clusters called glomeruli.