Retinoids in Mammalian Vision

摘要: The vertebrate visual process is remarkable in its properties. Visual pigments characterized from various species vary their maximum wavelength sensitivity 380 nm to 620 nm, yet each has the same chromophore, 11-cis-retinal (or 3-dehydro- or 3-hydroxy-derivative), which absorbs at 383 (393 3-dehydroretinal). dynamic range of system enormous, allowing detection contrast over an approx. 1010-fold background intensities. This accomplished, part, by employing highly sensitive rod photoreceptors low levels illumination and less cone higher illumination. In addition, are capable reducing response increasing (adaptation), contributing system. extreme photostimulation requires a dark noise, condition met enveloping chromophore within interior protein (opsin) form structure with isomerization activation barrier 45kcallmole (Birge 1990), ensuring that thermal rhodopsin rare event (but see Barlow et al. 1993). resulting t ½ complex for excitation 420 years (Baylor 1984). Some results participation summation pools, output hundreds rods converges on one downstream neuron (a ganglion cell).