Sight (vision) - Passage 2

The phototransduction cascade is responsible for converting light rays into neural impulses. This cascade occurs within the rods and cones of the retina, and a diagram of the cascade is shown below:

Retinal is essential to this cascade, and is synthesized from vitamin A, which is found in certain foods like carrots. The cascade begins with light converting 11-cis retinal to all-trans retinal:

This activates transducin, leading to the activation of cGMP phosphodiesterase, the hydrolyzation of cGMP, and the closing of cGMP dependent Ca++/Na+ channels.

If the cGMP-dependent Na+ channels involved in the phototransduction cascade were open in the absence of cGMP, what would occur if light was shined into the retina?

(Choice A)
Rods would fire in the presence of light, while cones would fire in the absence of light.
(Choice B)
Both rods and cones would not fire in the presence of light.
(Choice C)
Rods would fire in the absence of light, while cones would fire in the presence of light.
(Choice D)
Both rods and cones would fire in the presence of light.

MCAT

Kurs: MCAT > Rozdział 4

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