Rod photoreceptors

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Rod photoreceptors (cells) are highly specialised, extended cells, that permit vision at low light levels because of the disc filled outer segment. Within the discs is a vast amount of rhodopsin. This visual pigment absorbs dim light best at a wavelength of 495nm. Once the light is received by rhodopsin, the signal is transduced into chemical signals via G-proteins  and a decrease in cGMP  that causes a knock on closure of sodium channels whilst the potassium ions continue to flow out of the cell. The cell membrane now becomes hyperpolarized to -70mv. Therefore, the number of glutamate neurotransmitters released from the rod cell decreases. Rod cells go on to produce a response in the nerve signal pathways to the Optic Nerve via a bipolar and ganglion cell. Rod cells get bleached in high intensities of light.[1]

References

  1. Alberts et al, Molecular Biology of the Cell (2008), Fifth Edition, Garland Science, Pages 917-918.
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