In the dark, cGMP keeps Na+/Ca2+ channels open in photoreceptors, causing a dark current that depolarizes them and inhibits bipolar cells, preventing signal transmission.
Dans l'obscurité, le cGMP maintient ouverts les canaux Na+/Ca2+ des photorécepteurs, provoquant un courant noir qui les dépolarise et inhibe les cellules bipolaires, empêchant la transmission du signal.
| Front | What is the physiology of photoreceptors in the dark |
|---|---|
| Back | 1. In the dark, Na+/Ca2+ channels in the photoreceptor plasma membrane are kept opened by the presence of cGMP molecules 2. This causes an influx of Na+ into photoreceptor called the dark current which depolarizes the photoreceptor 3. Depolarized photoreceptor releases NT onto bipolar cells (due to Ca influx) that inhibits them from firing 4. Inhibited bipolar cells are prevented from releasing NT in order to stimulate the ganglion cells 5. Result - no impulse is conducted through the optic nerve |
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