Under which condition would the release of neurotransmitter by photoreceptors in the retina be greatest?

• A. In bright light
• B. In complete darkness
• C. When exposed to red light only
• D. During rapid eye movement (REM) sleep

Answer: (B)

Verified step by step guidance

1. Understand the basic functioning of photoreceptors (rods and cones) in the retina: photoreceptors release neurotransmitters in response to light conditions, but their activity varies depending on the amount of light present.
2. Recall that in darkness, photoreceptors are depolarized and continuously release neurotransmitters, whereas in bright light, they hyperpolarize and reduce neurotransmitter release.
3. Recognize that the release of neurotransmitters is greatest when photoreceptors are in their depolarized state, which occurs in complete darkness because the ion channels remain open, allowing neurotransmitter release.
4. Consider that exposure to specific wavelengths of light (such as red light) or states like REM sleep do not directly increase neurotransmitter release from photoreceptors compared to complete darkness.
5. Conclude that the condition for the greatest neurotransmitter release by photoreceptors is complete darkness, due to their depolarized state and continuous neurotransmitter release in the absence of light.