Which mechanisms of hormone action is used by neurotransmitters and olfactory receptors?

Neurotransmitters and olfactory receptors use the G protein-coupled receptor (GPCR) mechanism of hormone action. GPCRs are a large family of cell surface receptors that are activated by a variety of ligands, including neurotransmitters, hormones, and odorants. When a ligand binds to a GPCR, it causes a conformational change in the receptor that activates a heterotrimeric G protein. The G protein then dissociates into its alpha and beta-gamma subunits, which go on to activate downstream effector molecules such as adenylyl cyclase, phospholipase C, and ion channels. These effector molecules then generate intracellular signals that lead to the characteristic physiological responses associated with the neurotransmitter or odorant.

The GPCR mechanism of hormone action is also used by a variety of other receptors, including those for light, taste, and smell. This mechanism is essential for the proper functioning of the nervous system and sensory organs.