In the dark state, which description applies to photoreceptors?

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Study for the Neurophysiology Test with flashcards and multiple choice questions, each with hints and explanations. Enhance your understanding of cell types, signals, and sensory pathways. Ace your exam!

Multiple Choice

In the dark state, which description applies to photoreceptors?

Explanation:
In darkness, photoreceptors stay depolarized because the level of cGMP remains high, which keeps the cGMP-gated Na+ channels open. This ongoing Na+ (and Ca2+) influx creates the dark current, so the cell is tonically depolarized and continuously releases glutamate onto bipolar cells. The photopigment is in its inactive state in the dark, and there’s no activation of the phototransduction cascade to lower cGMP. So the best description is: continuous synthesis of cGMP, open Na+ channels, and ongoing glutamate release.

In darkness, photoreceptors stay depolarized because the level of cGMP remains high, which keeps the cGMP-gated Na+ channels open. This ongoing Na+ (and Ca2+) influx creates the dark current, so the cell is tonically depolarized and continuously releases glutamate onto bipolar cells. The photopigment is in its inactive state in the dark, and there’s no activation of the phototransduction cascade to lower cGMP. So the best description is: continuous synthesis of cGMP, open Na+ channels, and ongoing glutamate release.

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