Which of the following statements are true of olfactory sensory neurons? (Select all that apply.)
以下关于嗅觉感觉神经元的描述哪些是正确的？（可多选）

Question

BlackTom AI · Accepted Answer

Odorant binding activates G-protein–coupled olfactory receptors, leading to production of cyclic AMP (cAMP) and opening of cyclic nucleotide–gated (CNG) cation channels; this molecular cascade explains the true statement.

1) Relevant knowledge points and concepts
- Olfactory sensory neurons (OSNs) express GPCR odorant receptors coupled to the G protein Golf. Activation stimulates adenylyl cyclase III, raising cAMP.
- cAMP opens CNG channels, permitting Na+ and Ca2+ influx; the Ca2+ also opens Ca2+-activated Cl− channels, amplifying depolarization.
- OSN axons pass through the cribriform plate and converge onto specific glomeruli in the olfactory bulb where they synapse principally with mitral and tufted cells; granule cells interact with mitral cells in deeper layers via dendrodendritic synapses.
- Individual odorant receptors are broadly tuned; odors are encoded by combinatorial activation patterns across many receptors.

2) Step-by-step reasoning/process (transduction cascade)
- Odorant binds receptor (GPCR) on OSN cilia.
- GPCR activates Golf → activates adenylyl cyclase III.
- Adenylyl cyclase converts ATP to cAMP (cAMP increases).
- cAMP binds/open cyclic nucleotide–gated (CNG) channels.
- CNG channels allow Na+ and Ca2+ influx → receptor potential (depolarization).
- Increased intracellular Ca2+ opens Ca2+-activated Cl− channels → Cl− efflux → further depolarization → action potential generation.

3) Intermediate steps shown above (molecular sequence, ionic flows).

4) Why the correct answer is correct
- The described depolarization mechanism explicitly involves activation of CNG cation channels by cAMP produced after odorant receptor activation. This is the canonical and well-established transduction pathway in vertebrate OSNs.

5) Why other options are incorrect
- "OSN synapse with granule cells in the glomeruli": incorrect — OSNs synapse in glomeruli primarily onto mitral and tufted (and periglomerular) cells; granule cells form reciprocal dendrodendritic synapses with mitral cells in deeper layers, not direct OSN targets in glomeruli.
- "Each odorant receptor is responsive to only one odorant": incorrect — receptors are broadly tuned; odor identity arises from combinatorial receptor activation.
- "Axons ... synapse in the closest glomerulus": incorrect — OSN axons expressing the same receptor converge to specific, stereotyped glomeruli (not merely the anatomically closest), producing organized convergence maps.

6) Conclusion
- The correct true statement is that odorant-initiated depolarization of the OSN is due to activation of a cyclic nucleotide–gated cation channel, which matches the provided answer.

Which of the following statements are true of olfactory sensory neurons? (Select all that apply.) 以下关于嗅觉感觉神经元的描述哪些是正确的？（可多选）多项选择题

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