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The steklovidnoe body represents transparent gel, with-standing from an extracellular liquid with collagen and гиалуроновой acid in коллоидном a solution and not containing neither nerves, nor blood vessels.
The eye cannot is equally accurate to see subjects, отстоящие from it on different distance and to adapt an eye for clear vision разноудаленных subjects, accommodation process is necessary. If the person looks afar, цинновы sheaves are tense, and цилиарные muscles are weakened, thus the crystalline lens уплощен is a rest of accommodation.
At examining of subjects close located from eyes цилиарные muscles are reduced, цинновы sheaves are weakened, the crystalline lens becomes more convex is a pressure of accommodation. Tsiliarnye muscles иннервируются parasympathetic fibres глазодвигательного a nerve.
Introduction in eye M-holinolitika – atropine blocks excitation transfer to цилиарной to a muscle and breaks accommodation at examining of close located subjects. And xenical generic the contrary, introduction M-holinomimetikov – пилокарпина and эзерина promotes reduction цилиарной muscles and to accommodation process. Optical system of an eye The optical device of an eye consists of a transparent cornea, the forward and back chambers filled with a watery moisture, an iris of the eye surrounding a pupil, хрусталикас a transparent bag and стекловидного bodies.
As a whole is the system of the lenses forming on a retina the is xenical over the counter and reduced image of considered subjects. Refracting force of optical system is expressed in dioptries. The dioptry is a refracting force of a lens with focal length 100 accommodations refracting force see At rest is equal 58 – to 60 dioptries and is called as a refraction.
Anomalies of a refraction At a normal refraction parallel beams from far located subjects gather weight loss xenical a retina in the central pole, such eye is called эмметропическим. Кнарушениям refractions short-sightedness when parallel beams are focused not on a retina, and ahead of it fig. 31 concerns миопия, or.
It arises at excessively big length of an eyeball or refracting force of an eye. Close subjects short-sighted sees well, and removed – it is indistinct. Correction mi-opium – use of disseminating biconcave lenses. A picture i_032. jpg Гиперметропия, or the far-sightedness is such infringement xenical alli a refraction when parallel beams from far located subjects because of small length of an eyeball or weak refracting ability of an eye are focused behind a retina.
For correction гиперметропии convexo-convex, collecting lenses are used. Course of beams in эмметропическоммиопическом ; гиперметропическом eyes; the Guide – correction of short-sightedness and a far-sightedness by means of lenses There is a senile far-sightedness, or пресбиопия, connected with loss by a crystalline lens of elasticity which badly changes the curvature at a tension цинновых sheaves. Therefore the point of clear vision is not on distance of 10 sm from an eye, and is removed from it and close located subjects are visible vaguely.
For correction пресбиопии use convexo-convex lenses. Световоспринимающий, or рецепторный the eye device It is presented by a retina. Fotoretseptornye cages – sticks and колбочки consist of two segments – external light sensitive to action and containing a visual pigment, and internal in which are a kernel and митохондрии, responsible for power process in a cage.
Feature of topography of sticks and колбочек consists that they are turned by the external photosensitive segments to a layer of pigmentary cages, i. aside, opposite to light. Sticks are more sensitive to light, than колбочки. So, only one quantum of light can raise a stick, and колбочку – there is more than hundred quanta. At a bright daylight the maximum sensitivity possess колбочки which are concentrated in the xenical prescription of a yellow stain or the central pole.
xenical cheap weak illumination in twilight the retina periphery where there are basically sticks is most sensitive to light. At action of quantum of light in retina receptors there is a chain of the photochemical reactions connected with disintegration of visual pigments родопсина and йодопсина and them ресинтез in the dark.
Родопсин – a pigment of sticks – the high-molecular connection consisting from ретиналя – vitamin A and fiber aldehyde опсина. At absorption of quantum of light by a molecule родопсина 11tsis-retinal is straightened and turns to a trance-retinal. It occurs during 1 “2сек. The albuminous part of a molecule becomes colourless and passes in a condition метародопсина II which co-operates with примембранным fiber гуанозинтрифосфатсвязанным fiber is xenical over the counter.
Last starts exchange reaction гуанозиндифосфата ГДФ on гуанозинтрифосфат ГТФ that leads to strengthening of a light signal. ГТФ together with трансдуцином the squirrel – enzyme фосфодиэстеразы ФДЭ which destroys a molecule cyclic гуанозинмонофосфата цГМФ activates a molecule примембранного, causing still большее strengthening of a light signal. The maintenance цГМФ falls and channels for Na and Sa2 are closed that leads to hyperpolarization of a membrane of a photoreceptor and occurrence рецепторного potential.
Hyperpolarization occurrence on a photoreceptor membrane distinguishes it from other receptors, for example acoustical, vestibular where excitation is connected with деполяризацией membranes. Hyperpolarizing рецепторный the potential arises on a membrane of an
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segment, further extends along a cage to it пресинаптического the terminations and leads to reduction of speed of allocation mediatora-glutamata.
That рецепторная the cage could answer the following light signal, is necessary ресинтез родопсина, which occurs in the dark темновая adaptation from a vitamin A tsis-isomeasure, therefore at a lack of a vitamin A organism, develops insufficiency of twilight sight “night blindness”.
Retina photoreceptors are connected with a bipolar cage with the help синапса. At action of light reduction глутамата in пресинаптическом the photoreceptor termination leads to hyper-polarisation постсинаптической membranes of a bipolar nervous cage which also синаптически is connected with ганглиозными cages. In these синапсах it is allocated ацетилхолин, causing деполяризацию постсинаптической membranes ганглиозной cages.
In аксональном a hillock of this cage there is an action potential. Аксоны ганглиозных cages form cost of xenical nerve fibres on which in
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brain electric impulses direct. Distinguish three basic types ганглиозных the cages answering inclusion of light on-answer; on deenergizing of light Off-answer and to that and another onoff-answer increase фоновыхразрядов. In the central pole everyone колбочка is connected with one bipolar cage, which, in turn – with one ганглиозной.
It provides the high spatial permission, but sharply reduces light sensitivity. To periphery from the central pole the set of sticks contacts to one bipolar cage and a little колбочек, and with ганглиозной – set bipolar, forming рецептивное a field ганглиозной cages.
It raises light sensitivity, but worsens the spatial permission. In a layer of bipolar cages two types brake нейронов – horizontal and амакриновые the cages limiting distribution of excitation in a retina settle down.
The total electric potential of all elements of a retina is called электроретинограммой ЭРГ. It can be for-registrirovana as from the whole eye, and is direct from a retina. On ЭРГ it is possible to judge intensity of colour, the size and duration of action of a light signal. It is widely used in clinic for diagnostics and control of treatment of diseases of a retina. Spending ways of the visual analyzer The first нейрон the visual analyzer is the bipolar cage, the second нейрон – ганглиозная.