色狼 is a lascivious/perverted man. 色盲 is color blindness.(色 is color, 盲 is blind) you might wonder what's their relationship between them ! Blind in this case refering to the blindness in the heart/soul/spirit of a perverted man and also actual color blindness in them due to the abuse of VIAGRA- the man uppowering drug before their evil act ! In this session, i'll try to discuss the visual transduction pathway and the action of Nitride Oxide on erectile penile tissue.
Viagra is a drug that block the action of phosphodiesterase, an enzyme that convert cGMP to GMP.
Normal man erection is a parasympathetic action which is mediated by acetylcholine. Acetylecholine release at the endothelium of erectile tissue sinusoide / arteriole stimulate the synthesis of Nitride oxide (NO) via action of Nitride oxide synthase. NO release by endothelium to activate the enzyme guanylyl cyclase at the vascular smooth muscle, which convert GTP to cGMP. cGMP mediate the relaxation of vascular smooth muscle (vasodilation) at erectile tissue, as a result blood flow is increased, due to decrease in resistance. the erection is caused by 2 mechanism, 1) increase in blood INflow 2) decrease in blood OUTflow due to the compression effect (pressure) of blood-filled sinusoid on veinous outflow (Penis is a confined space restricted by the tunica albugenia, so any increase in volume will accompany by increase in pressure, BOYLE's Law!) So Erection occurs. c-GMP which initiate this cascade is broken down/inactivated by phosphodiesterase, where the action of Viagra is to block phosphodiesterase! This is why Viagra is effective in Erectile Dysfunction because it leads to the accumulation of c-GMP which mediates vascular smooth muscle relaxation and thus more vasodilation and erection!
On the other hand, the light transduction involve another cascade but involve the similar enzyme phosphodiesterase. photopigment consist of opsin and retinal which is in 11-cis retinal form. upon exposure to light, photoisomeration convert the 11-cis retinal to all-trans retinal which activate Transducin (a G protein) Alpha subunit of transducin activate the enzyme phosphodiesterase which convert c-GMP to GMP. at dark, c-GMP increase the sodium conductance across the outer segment of photoceptor, which causes dark sodium current, and hence depolarisation occur and there is release of neurotransmitter glutamine. At light, the release of neurotransmittor is inhibited by the decrease of c-GMP and hence dark current. Of course after this transduction process, there is further visual pathway which is out of the discussion scop of this picture. Transduction means to convert adequate stimulus to electrical impulse by sensory receptor. However, a point to stress on is Viagra, a phosphodiesterease inhibitor disrupt the visual transduction process. thus the side effect of viagra is having transient blue green color vision weakness.
Note the three color i draw on the left corner, the are RGB -> red, green , blue the 3 primary color for trichromat like human. these is associated with 3 different cone which contain different pigment. a theory by Young-Helmhotlz
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