Cones human vision

Figure 5.5.10-2 compares the typical putative spectrums based on such a linear analysis, (3, y, p compared to the actual chromophores, Rhodonines 5, 7 9 [with Rhodonine(l 1) shown for completeness. It is not significant in human vision except for aphakic patients.] Hunt describes the (3,y p spectrums as probable sensitivity curves of the three types of cones. He did not discuss any rod spectrum in his figure. The probable sensitivity curves appear to have been normalized individually. The peak in the p spectrum appears to be at a longer wavelength than frequently suggested. However, it is still at too short a wavelength to support the known spectral response of the human eye as illustrated by the Photopic Luminosity Function. 

Fig. 1. Representative spectral sensitivities of the human retinal receptors, (-) scotopic (rod) vision, and P, y, and p cone sensitivities. The wavelengths of...

Chen, C. K., Zhang, K., Church-Kopish, J., et al. (2001) Characterization of human GRK7 as a potential cone opsin kinase. Mol. Vision. 7, 305-313. 

Two types of photoreceptor cell are found in the human retina—rods and cones. Rods are sensitive to low levels of light, while the cones are responsible for color vision at higher light intensities. 

Rod and cone cells are the light sensitive receptor cells in the retina of the human eye. About three million rod cells are responsible for our vision in dim light, whereas the hundred million cone cells are responsible for our vision in the bright light and for the perception of bright colours. In the rod cells, ll-cw-retinal is converted to rhodopsin. 

Stockman, A., Sharpe, L. Fach, C. (1999) The spectral sensitivity of the human short-wavelength cones derived from thresholds and color matches. Vision Res., vol. 39, pp. 2901-2927... 

Merbs, S. Nathans, J. (1992) Absorption spectra of human cone pigments. Nature, vol 356, pp 433-435 1390prian, D. Asenjo, A. Lee, N. Pelletier, S. (1991) Design, chemical synthesis, and expression of genes for the three human color vision pigments. Biochemistry, vol 30, pp 11367-372... 

Cryptochromes in the human eye have a considerable sequence and structure homology with the photolyases, binding both methylene tetrahydrofolate and FAD. They have the same DNA binding pocket as photolyase, although they do not catalyze the reduction of DNA pyrimidine dimers. They are found in the nucleus of cells of the inner layer of the retina, behind the rods and cones involved in vision (Section 2.3.1), and absorb blue light, with maximum absorbance at 420 nm. 

Vertebrates have two types of light-responsive photoreceptor cells the rods and the cones. The photoreceptor cells convert light into nerve impulses. Cones are responsible for colour vision and function only in bright light, whereas rods also function in dim light. The retina in the human eye contains about 3 million cones and 100 million rods. 

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