Final answer:
The cycle of visual transduction starts with the photoisomerization of retinal in rhodopsin caused by light. This leads to a cascade of events that result in hyperpolarization of the photoreceptor membrane and altered neurotransmitter release. Option A.
Step-by-step explanation:
The process of visual transduction in photoreceptor cells begins when light triggers a change in the shape of retinal, a molecule within rhodopsin. This change, known as photoisomerization, converts retinal from a bent (cis) form to a linear (trans) isomer.
This isomerization of retinal activates rhodopsin, which in turn activates a G-protein called transducin. Transducin activates phosphodiesterase, leading to the hydrolysis of cGMP to GMP and resulting in the closing of sodium channels in the photoreceptor membrane.
Consequently, the membrane becomes hyperpolarized, and the photoreceptor cell releases less neurotransmitter into the synaptic layer, affecting the signal sent to the brain.
Over time, enzymatic changes reverse the photoisomerization, returning retinal to its 11-cis form and allowing the cycle to begin anew when new light is perceived.
Bleaching occurs when a large number of photopigments are activated, and it takes some time for the eye to recover, hence the experience of afterimages in a process that includes both photoisomerization and the consequent neural signal transduction. Option A.