Thanks to lateral inhibition, we can see sharp edges even though several receptor cells in the retina might be stimulated. We can hear pure tones in music even though several neighbouring hair-cells in the inner ear all vibrate to a greater or lesser extent.
protein (rhodopsin) changes its shape and activates an enzyme that removes the "molecular wedge". The sodium channels then close, the cell is de-activated, and no inhibitory neurotransmitters are released; so a signal is sent to the brain. This mechanism seems Byzantine but it is highly efficient, because the rhodopsin shape change also leads to a slow manufacture of "wedge" molecules, enabling the cell to adapt to continued light irradiation.
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