Briefly summarize the major steps in phototransduction in rods.

Q: Explain the process of phototransduction in rod cells. A: Phototransduction in rod cells starts with the absorption of light by the photopigment rhodopsin in the outer segment of the rod cell. The light causes a change in the retinal molecule's configuration, which activates the opsin protein and the G-protein transducin. This triggers a cascade of enzymatic reactions involving the activation of phosphodiesterase (PDE) enzyme and the breakdown of cGMP to GMP. The decrease in intracellular cGMP levels leads to the closure of CNG ion channels, causing a reduction in Na+ and Ca2+ ion influx, and hyperpolarization of the rod cell. This hyperpolarization reduces neurotransmitter release at the synaptic region, ultimately leading to the transmission of visual signals to the brain via bipolar cells and the optic nerve.