What are the specific mechanisms of the conversion of light stimulation to neuronal impulses?
Visual pigment molecules are the specific structures that absorb photons of light. These pigment molecules are made up of an opsin such as rhodopsin, and an actual light absorbing component, which is usually retinal. When a photon of light hits this molecule, the normal cis-configuration of the retinal is isomerized into a trans-configuration. This in turn leads to a separation between the opsin and the retinal molecule, and eventually to changes in the opsin s conformation too. When the light is absorbed by the retinal, proteins that are associated with the cell membrane are activated. This alters the cell’s membrane potential, and can eventually lead to an action potential, which is carried to the brain via a sensory neuron. At a cell s resting state, there is a certain concentration of each ion in and outside of the cell membrane. This provides for potential diffusions across the membrane. However, there are also charges on each of these ions, and there are polar gradients that do n
