Phototransduction

Phototransduction is the process by which light is converted into electrical signals in the rod cells, cone cells and photosensitive ganglion cells of the retina of the eye. This process allows the visual system to respond to light stimuli and is essential for vision.

Process of Phototransduction

Phototransduction begins when a photon of light interacts with a molecule of rhodopsin, a light-sensitive protein found in the rod and cone cells of the retina. This interaction causes a conformational change in the rhodopsin molecule, activating it and triggering a cascade of biochemical reactions.

The activated rhodopsin molecule activates a protein called transducin, which in turn activates an enzyme called phosphodiesterase. This enzyme breaks down a molecule called cyclic guanosine monophosphate (cGMP), reducing its concentration in the cell.

The decrease in cGMP levels causes ion channels in the cell membrane to close, preventing the influx of positively charged sodium ions. This leads to a change in the electrical potential across the cell membrane, creating an electrical signal that can be transmitted to the brain.

Role in Vision

Phototransduction is a crucial step in the process of vision. The electrical signals generated by phototransduction are transmitted to the brain via the optic nerve, where they are interpreted as visual images.

Different types of photoreceptor cells are responsible for different aspects of vision. Rod cells, which are more sensitive to light, are primarily responsible for night vision and peripheral vision. Cone cells, on the other hand, are less sensitive to light but are capable of color vision and provide the high spatial acuity of daytime vision.

See Also

• Visual system
• Visual perception
• Photoreceptor cell
• Signal transduction