Biology 30 – Nervous System Practice Exam

What state do photoreceptors enter in response to light?

They depolarize to increase neurotransmitter release They generate action potentials to signal the brain They hyperpolarize to reduce glutamate release They become inhibited and stop responding

Correct Answer:

They hyperpolarize to reduce glutamate release

Explanation:

Photoreceptors respond to light by hyperpolarizing, not by firing action potentials. In darkness they are depolarized because cGMP keeps Na+ channels open, so they continuously release the neurotransmitter glutamate. When light hits the photoreceptors, a phototransduction cascade lowers cGMP levels, closing those channels. That causes the cell to become more negative inside (hyperpolarize) and release less glutamate. This shift in neurotransmitter release alters the signaling to bipolar and ganglion cells, helping the brain detect changes in light. The key idea is that light causes hyperpolarization and a decrease in glutamate release, which is why this option is correct.

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