Module 10: Figure phototransduction
Summary of the ON and OFF reactions of the phototransduction cascade in rods and cones.
Rods and cones have a similar transduction process, which begins with the arrival of a photon (top left) and culminates in membrane hyperpolarization and a decrease in transmitter release following closure of the cyclic nucleotide-gated channel (CNGC) (bottom right). In the dark, there is a high level of cyclic GMP (cyclic GMP), which keeps the CNGC open, thereby depolarizing the membrane to maintain a tonic release of transmitter. The signalling events that occur during a light response can be divided into a series of interacting cycles that contain both ON reactions (red arrows) and OFF reactions (blue arrows), as described in the text.