Describe the structure and function of the olfactory epithelium. How does the sense of smell come about? (pages \(309-10\) ).

The olfactory epithelium, located in the nasal cavity, is responsible for detecting odorant molecules and is composed of olfactory receptor neurons, supporting cells, and basal cells. Olfactory receptor neurons, each expressing a unique odorant receptor (OR), bind to specific odorant molecules and initiate a signal transduction pathway. This process involves the activation of a G-protein, G_olf, which increases cyclic AMP (cAMP) production, leading to the opening of cyclic nucleotide-gated (CNG) ion channels, calcium and sodium influx, and the generation of action potentials. These action potentials travel to the olfactory bulb and higher brain regions, such as the piriform cortex and amygdala, for the perception and identification of different odors.