Näköpigmenteissä

Näköpigmenteissä, scientific term for visual pigments, are molecules responsible for detecting light in the eyes of animals. These light-sensitive compounds are located within photoreceptor cells, namely rods and cones, in the retina. When a photon of light strikes a visual pigment molecule, it undergoes a conformational change, initiating a cascade of biochemical events that ultimately leads to a nerve signal being sent to the brain. This signal is then interpreted as vision.

The most well-known visual pigment is rhodopsin, found in rod cells, which are crucial for vision in low light conditions (scotopic vision). Rhodopsin is composed of a protein called opsin and a chromophore, 11-cis-retinal, a derivative of vitamin A. In cone cells, responsible for color vision and sharp detail in bright light (photopic vision), different types of opsins combine with retinal to form cone pigments. Humans have three types of cone pigments, each sensitive to different wavelengths of light, corresponding to red, green, and blue colors.

The process of light detection by visual pigments is a complex photochemical reaction. Upon absorbing a photon, 11-cis-retinal isomerizes to all-trans-retinal, causing a change in the opsin protein's structure. This activation triggers a G-protein signaling pathway that modulates ion channels in the photoreceptor cell membrane, altering its electrical potential and generating a neural impulse. After activation, the pigment needs to be regenerated in a process called photobleaching and resensitization for the cell to respond to subsequent light stimuli. Variations in visual pigments and their distribution contribute to the diversity of visual capabilities observed across the animal kingdom.