Phototransduction Pathway

The cascade of a visual signal from the photon to the perceived color. The pathway is often described as the chain of cells that the signal travels through on its way to the brain:

• Photoreceptor Cell – Rods and Cones
• Horizontal Cell – Sometimes
• Bipolar Cell
• Amacrine Cell – Sometimes
• Retinal Ganglion Cell – comprising the optic nerve

However, it can also be described more finely as the molecular chain of events within the Photoreceptor:

• Chromophore – catches the photon
• Opsin – tunes the Chromophore Peak Wavelength and interfaces with Transducin
• Transducin – a type of G-protein
• Phosphodiesterase – converts cGMP to GMP
• Sodium Channels – on the Photoreceptor close, leading to hyperpolarization (a potential across the cell membrane).
• Synapse – the photoreceptor releases Glutamate to trigger the Bipolar Cell.

Parallel to the Phototransduction is the Visual Cycle, where Retinal goes through several steps to be regenerated after it is activated by a photon.