PSL300H1 Lecture Notes - Lecture 20: Ganglion Cell, Opsin, Agnatha
Document Summary
The retina contain 2 kinds of photoreceptor cell (named due to the shapes) cones and rods. Phylogenetically - cones are older than rods, and rods evolved from cones a long time ago. The 2 cell types were already distinct in the eyes of jawless fish ~400 million years ago. Each human retina contains ~120 million rods, and ~6 million cones. Cones are less sensitive (10x) than rods they were responsible for vision in bright light and for distinguishing colours and cannot operate in dim conditions. Rods are more sensitive they can detect single photons. When the lights go dim, the rods dark adapt rebuild the stores of rhodopsin (takes ~30 minutes) It seems that in an emergency humans have better dark vision than normal (vision will adapt quicker) In the daylight they are bleached out" their photopigment (rhodopsin) is broken down, and they can"t sense light.
