What is the phototransduction cascade in darkness?

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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

What is the phototransduction cascade in darkness?

Explanation:
In darkness, the photoreceptor sits in a depolarized, active state because a high level of cGMP keeps the Na+-permeable channels open. The rise in intracellular cGMP binds to cyclic nucleotide–gated channels in the outer segment, keeping them open so Na+ (and some Ca2+) flow into the cell. This influx creates a steady dark current, depolarizing the cell and driving continuous release of the neurotransmitter onto downstream neurons. In brief, darkness maintains high cGMP, opens Na+ channels, depolarizes the cell, and sustains transmitter release.

In darkness, the photoreceptor sits in a depolarized, active state because a high level of cGMP keeps the Na+-permeable channels open. The rise in intracellular cGMP binds to cyclic nucleotide–gated channels in the outer segment, keeping them open so Na+ (and some Ca2+) flow into the cell. This influx creates a steady dark current, depolarizing the cell and driving continuous release of the neurotransmitter onto downstream neurons. In brief, darkness maintains high cGMP, opens Na+ channels, depolarizes the cell, and sustains transmitter release.

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