Vision vertebrates

Vitamin A (retinol) and its naturally occurring and synthetic derivatives, collectively referred to as retinoids (chemical structure), exert a wide variety of profound effects in apoptosis, embryogenesis, reproduction, vision, and regulation of inflammation, growth, and differentiation of normal and neoplastic cells in vertebrates. 

Rhodopsin is a seven ot-helix trans-membrane protein and visual pigment of the vertebrate rod photoreceptor cells that mediate dim light vision. In this photoreceptor, retinal is the chromophore bound by opsin protein, covalently linked to Lys296 by a Schiff base linkage. Kpega et al.64 have studied NMR spectra of Schiff bases being derivatives of all-frans retinal and amino-p-cyclodextrins as a model of rhodopsin, where p-cyclodextrin plays a role of a binding pocket. On the basis of analysis of the chemical shift differences for the model compound in the presence and in the absence of adamantane carboxylate, it has been shown that the derivative of 3-amino-p-cyclodextrin forms dimer in water and retinoid is inserted into p-cyclodextrin cavity [31]. 

An important basis for the choice of Phycomyces as a model system is its wide range of sensitivity to light which covers about nine decades and which is therefore similar to vertebrate vision. This makes the organism especially suitable for the study of range adjustment, i.e., the phenomenon of adaptation. The potential of Phycomyces as a model system for investigation of differentiation and photo-differentiation has not yet been fully exploited. 

Cyclic nucleotides which are involved in vertebrate vision (Miki et al., 1973) also seem to play a role in the light-growth response of Phycomyces. Cohen (1974b) showed that 1 min after a step-up of light the level of cAMP of Stage IVb sporangio-... 

There has been little study of the olfactory abilities of the great apes. Olfactory stimuli play an important role in guiding behaviour in many species (Stod-dart 1980). In the great apes, however, the role of olfaction has been questioned due to the perceived primacy of vision and audition in influencing behaviour (King and Forbes 1974 Dominy, Ross and Smith 2004). This has led to the label of micros-matic being applied to the apes. For most vertebrates, e.g. the dog, there is much evidence of the importance of olfaction in behaviour, and these species are termed macrosmatic (Smith and Bhatnagar 2004). 

The study of the mechanism of vision in vertebrates 23>24) has progressed to the point where the first consequence of photon absorption has been described as an activation of the isomerization of the 11 -cis retinal chromophore of rhodopsin to all-trans. That triggers a complex sequence of reactions leading to the mysterious inside of the brain. Brrr, I had better get back — it looks dark in there. But the brain can generate sensations of light. Maybe, one day, we will be able to see enough to understand, but we ll go back just the same to a safer subject. 

See also individuality, biochemical as an enemy, 204-206 blood differences, 3-4 deviates, 6-7 normal ranges and, 2-4 quantitative research and, 204, 205 research into, 7 vertebral anatomy, 45 vision, 202-203 vitamin A, 162-166, 169, 199 animal studies, 163-164 growth rate relationship to intake of, 166f human needs award contest, 162-163... 

Shand J, Foster RG 1999 The extraretinal photoreceptors of non-mammaKan vertebrates. In Archer SN, Djamgoz MBA, Loew ER, Partridge JC, Vallerga S (eds) Adaptive mechanisms in the ecology of vision. Kluwer Academic Publishers, Dordrecht, Netherlands, p 197—222 Smyth RD, Saranak J, Foster KW 1988 Algal visual systems and their photoreceptor pigments. Prog Phycol Res 6 255-286... 

Cyclic GMP has a second mode of action in the vertebrate eye it causes ion-specific channels to open in the retinal rod and cone cells. We return to this role of cGMP in the discussion of vision in Section 12.7. 

Vision, olfaction, and gustation in vertebrates employ serpentine receptors, which act... 

A 64-year-old man with giant cell arteritis was given prednisolone 60 mg/day. Within 5 days he developed double vision and agitation and became drowsy and confused. A cranial MRI scan showed recent cerebral lesions and a Doppler scan showed high-resistant blood flow in both vertebral arteries. He had an episode of complete loss of vision and was given dexamethasone... 

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. 

In the body, vitamin A is converted to 11 -c/s-retinal, the light-sensitive compound responsible for vision in all vertebrates (Section 21.11B). It is also needed for healthy mucous membranes. 

Thu molecular mechanism of action of vitamin A in the visual process has been under investigation for many years. Wald in 1(168 and Morton in 1972" characterized this mechanism of action. The chemistry of vision was reviewed comprehensively in Accotmi.t of Clwmical Research (1975) by numerous investigators. These reviews include theoretical studies of the visual chromophorc. characleri/alion of ihfldopsin in synthetic systems, dynamic processes in vertebrate rod visual pigments and their membranes, and the dynamics of the visual protein opsin. ""... 

The Baylor doctors reported in 1967 a case of right vertebral artery blockage. The vertebral arteries are small, extremely important, and totally inaccessible blood vessels that travel from the heart, up the back of the spinal column, to the back of the brain. If one or both of these arteries become blocked you are in deep trouble. You lose speech, vision, and balance. Some victims of this type of blockage have "drop attacks." They drop to the floor just as if someone had cut their legs from under them. This happens without the slightest loss of consciousness. An inexperienced doctor will think the patient is faking because of the lack of mental change with the episode. It is a peculiar and mysterious medical phenomenon. 

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