Final answer:
In vertebrate photoreceptors, light causes hyperpolarization by activating a cascade that closes Na+ channels due to the conversion of cGMP to GMP, decreasing neurotransmitter release.
Step-by-step explanation:
In the vertebrate photoreceptor, light triggers a complex biochemical process. When light strikes rhodopsin, which consists of opsin and retinal, retinal undergoes a shape change from a cis form to a trans form, activating the G-protein transducin. This activation leads to a cascade of events where phosphodiesterase is activated, which then converts cyclic guanosine monophosphate (cGMP) to guanosine monophosphate (GMP), leading to the closing of sodium (Na+) channels.
As a result, the photoreceptor membrane becomes hyperpolarized rather than depolarized, which is the typical response in other sensory neurons. The hyperpolarization leads to a decrease in the release of the neurotransmitter glutamate to the bipolar cell, impacting the visual signal transmitted to the brain.