Phototransduction is the process that occurs in the retina where light is converted into electrical signals that can be understood by the rest of the nervous system. In this video, I explain the mechanism underlying phototransduction in rod photoreceptor cells. This process is a little complicated; I'd suggest at least having a good understanding of membrane potential before you try to grasp phototransduction. You can learn more about membrane potential in this video: https://youtu.be/tIzF2tWy6KI TRANSCRIPT: Welcome to 2 minute neuroscience, where I explain neuroscience topics in 2 minutes or less. In this installment I will discuss phototransduction. Phototransduction is the process that occurs in the retina where light is converted into electrical signals that can be understood by the nervous system. It primarily takes place in photoreceptor cells, of which there are two main types: rods and cones. I will discuss phototransduction in rods, although the process is similar in cones. In the dark, positively charged sodium ions flow into rod cells through ion channels that are activated by a substance called cyclic guanosine monophosphate, or cGMP. This influx of positively charged ions causes cells to remain in a depolarized state, leading to the continuous release of the neurotransmitter glutamate. Inside the rod cell there is a substance called rhodopsin, which is made up of a protein called opsin and a molecule called retinal, which is capable of absorbing light. When retinal absorbs light, its configuration changes, an event that prompts opsin to activate a protein called transducin. Transducin activates a type of enzyme known as a phosphodiesterase, which begins breaking down cGMP. As cGMP levels fall, the ion channels that are opened by cGMP begin to close. Thus, less sodium enters the cell and the cell becomes hyperpolarized due to potassium ions that regularly leave the cell. Consequently, glutamate release decreases. Strangely enough, this decrease in neurotransmitter release acts as a signal that a light stimulus is present. The rod cell returns to its normal state quickly when activated rhodopsin is inactivated, and a protein called arrestin subsequently binds to it. Arrestin blocks the ability of rhodopsin to activate transducin, which makes the cascade unable to continue. A complex process then restores retinal to its original configuration, making it ready to absorb light once again. References: Meister M, Tessier-Lavigne M. Low-Level Visual Processing: The Retina. In: Kandel ER, Schwartz JH, Jessell TM, Siegelbaum SA, Hudspeth AJ, eds. Principles of Neural Science. 5th ed. New York: McGraw Hill; 2013. Purves D, Augustine GJ, Fitzpatrick P, Hall WC, Lamantia AS, Mooney RD, Platt ML, White LE, eds. Neuroscience. 6th ed. New York: Sinauer Associates; 2018.

• published: 11 Jul 2019
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