Describe olfactory receptor neuron structure and odorant transduction.

Describe olfactory receptor neuron structure and odorant transduction.

• A. Receptors are on microvilli; GPCR odorant receptors; activation triggers Na+ influx directly.
• B. Receptors on cilia bearing GPCR odorant receptors; G-protein cascade increases cAMP, opens cyclic nucleotide-gated channels.
• C. Receptors on dendritic knobs; ligand-gated ion channels cause depolarization.
• D. Receptors on cilia with ionotropic receptors; odorant binding opens Na+ channels.

Answer: (B)

Olfactory transduction uses a metabotropic GPCR mechanism located on the ciliary membranes of olfactory receptor neurons. When an odorant binds, the GPCR activates a G-protein, which then stimulates adenylyl cyclase to raise cAMP levels. The increase in cAMP opens cyclic nucleotide-gated channels, allowing Na+ and Ca2+ to enter and depolarize the neuron. The Ca2+ influx also activates Ca2+-gated Cl- channels, amplifying the depolarization. This arrangement—receptors on cilia bearing GPCR odorant receptors, with a G-protein cascade that increases cAMP and opens cyclic nucleotide-gated channels—best explains the structure and the transduction mechanism.

Olfactory transduction uses a metabotropic GPCR mechanism located on the ciliary membranes of olfactory receptor neurons. When an odorant binds, the GPCR activates a G-protein, which then stimulates adenylyl cyclase to raise cAMP levels. The increase in cAMP opens cyclic nucleotide-gated channels, allowing Na+ and Ca2+ to enter and depolarize the neuron. The Ca2+ influx also activates Ca2+-gated Cl- channels, amplifying the depolarization. This arrangement—receptors on cilia bearing GPCR odorant receptors, with a G-protein cascade that increases cAMP and opens cyclic nucleotide-gated channels—best explains the structure and the transduction mechanism.