When light strikes the eye there is an increase in which of the following?: (A) The activity of the transducin, (B) The amount transmitter released from the photoreceptors, (C) The concentration of all-trans retinal within the photoreceptors, (D) The concentration of calcium within the photoreceptors
Answer is A. Transducin is the G protein activated. by rhodopsin when light strikes the eye. Transducin activates a phosphodiesterase that hydrolyzes cGMP When cGMP concentrations within the rods or cones decrease, sodium channels close, sodium conductance decreases, and the cell membrane potential increases (hyperpolarizes). Hyperpolarization of the cell causes a decrease in the release of neurotransmitter. Eventually the all- trans retinal dissociates from opsin and reduces the concentration of rhodopsin in the cell.