How does light affect the activity of photoreceptor cells in a normal functioning system?

How does light affect the activity of photoreceptor cells in a normal functioning system?

• A. It diminishes the sensitivity due to negative feedback
• B. It increases cGMP levels
• C. It activates cGMP phosphodiesterase
• D. It allows for greater sensitivity due to adaptation

Answer: (C)

Photoreceptor cells, such as those in the retina, respond to light by undergoing a series of biochemical changes that influence their activity. The correct answer indicates that light activation leads to the activation of cGMP phosphodiesterase. When light strikes the photoreceptors, specifically the visual pigment rhodopsin is activated. This activation triggers a cascade of events that ultimately leads to the hydrolysis of cyclic guanosine monophosphate (cGMP) by phosphodiesterase. As cGMP levels decrease, it causes the closure of cGMP-gated sodium channels in the cell membrane. This closure results in hyperpolarization of the photoreceptor cell, thereby reducing the release of neurotransmitters (such as glutamate) and altering the signal sent to retinal ganglion cells. This process is critical for converting light signals into electrical signals, effectively allowing the photoreceptors to respond to changes in light conditions. The activation of cGMP phosphodiesterase is a central component of the phototransduction pathway and is essential for normal vision. In contrast, the other choices refer to different mechanisms or outcomes that do not accurately describe the effects of light on photoreceptor cells in this context. For example,

Photoreceptor cells, such as those in the retina, respond to light by undergoing a series of biochemical changes that influence their activity. The correct answer indicates that light activation leads to the activation of cGMP phosphodiesterase.

When light strikes the photoreceptors, specifically the visual pigment rhodopsin is activated. This activation triggers a cascade of events that ultimately leads to the hydrolysis of cyclic guanosine monophosphate (cGMP) by phosphodiesterase. As cGMP levels decrease, it causes the closure of cGMP-gated sodium channels in the cell membrane. This closure results in hyperpolarization of the photoreceptor cell, thereby reducing the release of neurotransmitters (such as glutamate) and altering the signal sent to retinal ganglion cells.

This process is critical for converting light signals into electrical signals, effectively allowing the photoreceptors to respond to changes in light conditions. The activation of cGMP phosphodiesterase is a central component of the phototransduction pathway and is essential for normal vision.

In contrast, the other choices refer to different mechanisms or outcomes that do not accurately describe the effects of light on photoreceptor cells in this context. For example,