nature of the binding between neurotransmitter and receptor site
Ligand (biochemistry) Ligand binding to a receptor protein alters the chemical conformation by affecting the three-dimensional shape orientation. The conformation of a receptor protein composes the functional state. Ligands include substrates, inhibitors, activators, and neurotransmitters. The rate of binding is called affinity, and this measurement typifies a tendency or strength of the effect. Binding affinity is actualized not only by host-guest interactions, but also by solvent effects that can play a dominant, steric role which drives non-covalent binding in solution.[3] The solvent provides a chemical environment for the ligand and receptor to adapt, and thus accept or reject each other as partners.
Olfactory receptor In vertebrates, the olfactory receptors are located in both the cilia and synapses of the olfactory sensory neurons[4] and in the epithelium of the human airway.[5]  In insects, olfactory receptors are located on the antennae and other chemosensory organs.[6] Sperm cells also express odor receptors, which are thought to be involved in chemotaxis to find the egg cell.[7]