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SNEAK PREVIEW: Photoreceptors

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We’re getting closer by the day to our summer release at Complete Anatomy HQ, with everything in the final stages of testing. In the meantime, get an exclusive look at the latest addition to our Cell Biology family – The Photoreceptors.

Did you know that there are two types of light-sensitive photoreceptors in theĀ retina?šŸ’”TheseĀ cells are known asĀ the rods and cones.Ā At night, when light levels are low, the rods are the main photoreceptorsĀ šŸŒ›.Ā  ThisĀ type of visionĀ is referred to asĀ scotopic visionĀ and has high sensitivity,Ā but a lack of color vision. On the other hand, the cones are the primary photoreceptors used in the daytime when natural light levels are highšŸŒž. This is calledĀ photopic visionĀ and providesĀ color vision, whileĀ theĀ overall clarity of vision is high. Mesopic vision occurs when both rods and cones are used and is common after sunset or before sunrise.Ā 

Despite their different functions, rods and cones have several structural similarities. They both have an outer segment composed of membranous disks which contain photopigment. Photopigments undergo structural change in response to light. They also feature an inner segment that houses the cell nucleus and gives rise to synaptic terminals that connect to the bipolar or horizontal cells discussed in last weekā€™s snippet šŸ‘€. 

But how do photoreceptors convert light to an electrical signal?Ā To understand this process, it helps to think of phototransduction asĀ a 3-person relay raceĀ šŸƒ. When a photon of light contacts a visual pigment molecule it is like the starting gunĀ šŸ’„.Ā A series of proteins are activated that lead to hyperpolarization of the photoreceptor, the first sprinter. When the photoreceptors become hyperpolarized, the amount of neurotransmitter released by the photoreceptors is decreased. The bipolar cells respond with a change in their membrane potential. Think of them as the middle runner,Ā transmitting the signal from photoreceptors to ganglion cellsĀ šŸ”›. The ganglion cells are the only cells in the retina with axons that leave the eyeĀ andĀ theyĀ run the final leg of the raceĀ šŸ.Ā These electrical signals travel through the optic nerve toĀ theĀ occipital, parietal and temporal lobesĀ of the brain,Ā and eventually get processed in the brain. But thatā€™s a for another snippet!

We’re working round the clock to deliver our biggest update of the year, and we’re very nearly there. Be sure to opt-in for New Technology Previews in your email preference, and be the first to find out when our summer release lands on the app stores.