Phototransduction cascade
From Ganfyd
For biochemical details see the visual cycle which includes the phototransduction cascade and also the regeneration of the retinal pigment opsin proteins so as to detect the next photon.
Physiology
- Incident light induces a conformational change in a ligand molecule of retinal bound to an opsin membrane protein in the cone cell or rod cell. (Strictly there are a few other retinal neuronal receptors which also have photodetection properties not directly associated with vision)
- This induces a conformational change in the opsin which in this activated form is able to activate a protein and ligand amplifier cascade
- This cascade results in membrane pores closing with reduced entry of calcium and sodium cations into the photoreceptor cell and the rather polarised receptor cell (so called dark current) hyperpolarizes and usually inhibits the regular background firing rate caused bt dark current repolarisation. (Actually the photoreceptor neurotransmitter is glutamate which can depolarize some neurons and hyperpolarize others, allowing photoreceptors to interact in an antagonistic manner, especially rods, which interact with a complex network of neurons which preprocess light stimuli in the retina.)
