SMYSLY FYZIOLOGIE VIDĚNÍ Zrak – nejdůležitější smysl, u člověka 80% informací přicházejících z vnějšího prostředí pro zpracování v CNS je získáno prostřednictvím zraku CNS zpracovává odlišné druhy zrakové informace současně (simultánně) a okamžitě pomocí paralelních subsystémů zrakové dráhy – na rozdíl od akustické informace, která je zpracovávána postupně (sukcesivně) Oko: optické (rohovka, komorová tekutina, čočka, sklivec) a nervové elementy (sítnice) První světlolomná plocha Ochranná funkce m.ciliaris – pod kontrolou parasympatiku Jako clona fotoaparátu Vyměňuje se každých 60 min Nitrooční tlak 15-16 mmHg Glaukom-zelený zákal poškození sítnice http://www.studentconsult.com/common/showimage.cfm?mediaISBN=0721632564&FigFile=S23283-013-f006a.jp g&size=fullsize •4 http://www.vision-and-eye-health.com/images/IrisMuscles.jpg Pupilární reflex (zúžení a rozšíření zornice) -neuronální dráha začínající v sítnici – n.opticus -oddělení do pretektální oblasti k jádrům okohybných nervů- Edinger-Westphalovo jádro -jako vlákna ANS –končí: m.sphinkter-m.dilatator pupilae The eye is a fluid-filled sphere enclosed by three layers of tissue (Figure 11.1). Most of the outer layer is composed of a tough white fibrous tissue, the sclera. At the front of the eye, however, this opaque outer layer is transformed into the cornea, a specialized transparent tissue that permits light rays to enter the eye. The middle layer of tissue includes three distinct but continuous structures: the iris, the ciliary body, and the choroid. The iris is the colored portion of the eye that can be seen through the cornea. It contains two sets of muscles with opposing actions, which allow the size of the pupil (the opening in its center) to be adjusted under neural control. The ciliary body is a ring of tissue that encircles the lens and includes a muscular component that is important for adjusting the refractive power of the lens, and a vascular component (the so-called ciliary processes) that produces the fluid that fills the front of the eye. The choroid is composed of a rich capillary bed that serves as the main source of blood supply for the photoreceptors of the retina. Only the innermost layer of the eye, the retina, contains neurons that are sensitive to light and are capable of transmitting visual signals to central targets. En route to the retina, light passes through the cornea, the lens, and two distinct fluid environments. The anterior chamber, the space between the lens and the cornea, is filled with aqueous humor, a clear, watery liquid that supplies nutrients to these structures as well as to the lens. Aqueous humor is produced by the ciliary processes in the posterior chamber (the region between the lens and the iris) and flows into the anterior chamber through the pupil. A specialized meshwork of cells that lies at the junction of the iris and the cornea is responsible for its uptake. Under normal conditions, the rates of aqueous humor production and uptake are in equilibrium, ensuring a constant intraocular pressure. Abnormally high levels of intraocular pressure, which occur in glaucoma, can reduce the blood supply to the eye and eventually damage retinal neurons. The space between the back of the lens and the surface of the retina is filled with a thick, gelatinous substance called the vitreous humor, which accounts for about 80% of the volume of the eye. In addition to maintaining the shape of the eye, the vitreous humor contains phagocytic cells that remove blood and other debris that might otherwise interfere with light transmission. The housekeeping abilities of the vitreous humor are limited, however, as a large number of middle-aged and elderly individuals with vitreal “floaters” will attest. Floaters are collections of debris too large for phagocytic consumption that therefore remain to cast annoying shadows on the retina; they typically arise when the aging vitreous membrane pulls away from the overly long eyeball of myopic individuals. 5 myopie 7 •9 v v Světločivné elementy: tyčinky a čípky Obsahují zrakové pigmenty, které se působením světla chemicky rozkládají. Základ: sloučenina bílkovin opsinu a retinenu (derivát vit.A), působením světla pigment bledne, ruší se vazba mezi opsinem a retinenem. Rozpad pigmentu=nervový vzruch=akční potenciál v gangliových buňkách sítnice. Působením vit.A se vazba obnovuje. Nedostatek vit.A- šeroslepost (nyktalopie) Photopigments contain same retinal, just different forms of opsin Outer segments of cones consist of folded, stacked membrane containing other photopigments (opsins) but in lower concentration than rods therefore less sensitive to light. As with rods, the inner segment synthesizes photopigments and inserts them into membrane of vesicles which move from inner to outer segment. However, in cones the vesicles are inserted into membrane folds of outer segment Phototransduction: Dark current •11 •Partially active guanylyl cyclase keeps cytoplasmic [cGMP] high in the dark •Outer segment contains cGMP-gated cation channels •Influx of Na+ and Ca2+ •Inner segment contains non-gated K+ selective channels •K+ efflux •Resting, or dark Vm is -40 mV •concentration gradients maintained by Na+/K+ pump • Guanylyl cyclase synthesizes cGMP from GTP Outer segment membrane has cation channels which remain open in the dark whereas inner segment has K+ channels that are not regulated by light. Na+ (90%) and Ca++(10%) enter through cation channels in outer segment and K+ leaves inner segment, resulting in hyperpolarization (resting membrane potential of rods is ~ – 40 mV ) and ionic current called dark current. Na-K pump removes Na+ from inner segment and Na-Ca exchanger removes Ca++ from outer segment to maintain concentration gradients. 12 Ve tmě jsou sodíkové kanály drženy otevřené působením cGMP, Proud teče od vnitřního segmentu k zevnímu světlo kanály uzavírá – hyperpolarizace synaptických zakončení Phototransduction: mechanism •13 1.Absorption of a photon isomerizes retinal fosfodiesteráza katalyzuje cGMP-5 GMP, uzávěr cGMPkanálů-hyperpolarizace-snížené uvolňování synapt.mediátoru-odpověď bipolárních buněk a)Converts opsin to metarhodopsin II 2.Metarodophsin II activates the G-protein transducin a)Activates cGMP phosphodiesterase (PDE) 3.PDE hydrolyzes cGMP to GMP a)Decreased [cGMP] closes cGMP gated cation channels b)Photoreceptor hyperpolarizes, less glutamate released 4. 4. 4. 4. light Opsin + retinen1 Zrakový pigment v tyčinkách =rhodopsin, Jeho opsin=skotopsin Ve tmě je retinen1 v rhodopsinu Ve formě 11cis- světlo přemění Na all-trans izomer transducin exchanges GDP for GTP activated transducin (G protein) → activates cGMP phosphodiesterase → hydrolyzes cGMP to GMP (5’-guanylate monophosphate)→ ↓ [cGMP]i → closes cGMP-gated cation channels → hyperpolarization → ↓ neurotransmitter release all-trans retinal separates from opsin (bleaching) converts to retinol translocates to the pigment epithelium where it is converted back to 11-cis retinal returns to the outer segment and recombines with opsin recycling process takes several minutes •Pigment epithelium •Absorps light rays, prevention the reflection of rays back through the retina •Contains melanin to absorbs excess light •Stores Vitamin A •Photoreceptors •Transduce light energy into electrical energy •Rods and cones •Ganglion cells •Output cells of retina project via optic nerve •Bipolar cells – 12 different types occur •Horizontal cells •Amacrine cells - 29types have been described •The neural elements of retina are bound together by glial cells – Muller cells • • http://www.studentconsult.com/common/showimage.cfm?mediaISBN=0721632564&FigFile=S23283-013-f007.jpg &size=fullsize •Boron, Boulpaep, Medical Physiology, 2003 •RETINA •Its organized on layers •Visual receptors+4types of neurons. •Many different synaptic transmitters •Inner segments Despite its peripheral location, the retina or neural portion of the eye, is actually part of the central nervous system. There are five types of neurons in the retina: photoreceptors, bipolar cells, ganglion cells, horizontal cells, and amacrine cells. Absorption of light by the photopigment in the outer segment of the photoreceptors initiates a cascade of events that changes the membrane potential of the receptor, and therefore the amount of neurotransmitter released by the photoreceptor synapses onto the cells they contact. At first glance, the spatial arrangement of retinal layers seems counterintuitive, since light rays must pass through the non-light-sensitive elements of the retina (and retinal vasculature!) before reaching the outer segments of the photoreceptors, where photons are absorbed. The reason for this curious feature of retinal organization lies in the special relationship that exists between the outer segments of the photoreceptors and the pigment epithelium. The outer segments contain membranous disks that house the light-sensitive photopigment and other proteins involved in the transduction process. These disks are formed near the inner segment of the photoreceptor and move toward the tip of the outer segment, where they are shed. The pigment epithelium plays an essential role in removing the expended receptor disks; this is no small task, since all the disks in the outer segments are replaced every 12 days. In addition, the pigment epithelium contains the biochemical machinery that is required to regenerate photopigment molecules after they have been exposed to light. It is presumably the demands of the photoreceptor disk life cycle and photopigment recycling that explain why rods and cones are found in the outermost rather than the innermost layer of the retina. Disruptions in the normal relationships between pigment epithelium and retinal photoreceptors such as those that occur in retinitis pigmentosa have severe consequences for vision •15 •Periphery of retina ¨High degree of convergence à large receptive field ¨High sensitivity to light, low spatial resolution •Fovea ¨Low convergence à small receptive fields ¨Lower sensitivity to light, high resolution (visual acuity) http://www.studentconsult.com/common/showimage.cfm?mediaISBN=0721632564&FigFile=S23283-013-f008.jpg &size=fullsize At the periphery of the retina there is convergence of synaptic input from many photoreceptors onto bipolar and ganglion cells, reducing spatial resolution because receptive fields are larger, but increasing sensitivity because more photoreceptors collect light Outside fovea density of cones drops and density of rods rises; there are no photoreceptors at optic disc where ganglion cell axons leave retina (blind spot). Fovea is region 300-700 m in diameter located in center of retina and contains the highest density of cones Over most of retina, light must travel through several layers to reach photoreceptors; at fovea layers of neurons are shifted aside, reducing distortion due to light scatter Most photoreceptors in fovea synapse on only one bipolar cell which in turn synapses on only one ganglion cell, resulting in smallest receptive fields and greatest resolution Neural circuits of retinal receptive fields •16 centre surround surround Ganglion cell receptive field •P •P •P •B •B •G •G •H •H •_ •_ On-center bipolar and ganglion cells Off-center bipolar and ganglion cells On center bipolar cells hyperpolarized by glutamate Off center bipolar cells depolarized by glutamate Center photoreceptors always synapse onto bipolar cells of each type, on center and off center Surround photoreceptors synapse on horizontal cells which mediate signals via lateral inhibitory connections Neural Circuits of Retinal Receptive Fields •17 •Light stimulus on center: ¨↓ glu release from central photoreceptor ¨↓ inhibition of on-center bipolar cell à depolarization ¨↑ NT release à on-center ganglion cell excited ¨less glu available to excite off-centre bipolar cell à hyperpolarization ¨↓NT releaseà off-center ganglion cell inhibited light On center bipolar cells hyperpolarized by glutamate Neural Circuits of Retinal Receptive Fields •18 light light •Light stimulus on surround: ¨↓ glu release from surround photoreceptor ¨↓ excitation of horizontal cells à ↓ inhibitory NT released ¨↓ inhibition of central photoreceptor à ↑ glu released ¨↑ glu hyperpolarizes on-center bipolar cell and depolarizes off-center bipolar cell ¨On-center ganglion cell inhibited, off-center ganglion cell excited Receptive fields •19 ¨On-center/off-surround ¤Light shines on center of ganglion cell receptive field à ganglion cell increases AP firing ¤Light on surround region à decreased AP firing ¨Off-center/on-surround ¤Light on center à decreased AP firing ¤Light on surround à increased AP firing ¤ C:\Users\Felix\Documents\KIN 306\JPEGs\images\008008B.jpg C:\Users\Felix\Documents\KIN 306\JPEGs\images\008008G.jpg B&L Figure 8-8 Always have a tonic release of AP, but their frequency is mediated by center/surround receptive fields 20 Tyčinky a čípky reagují na světlo hyperpolarizací Horizontální buňky - hyperpolarizací Bipolární buňky hyperpolarizací nebo depolarizací Amakrinní – depolarizační potenciály a hroty typu generátorového potenciálu sloužící pro vznik AP v gangliových buňkách Colour Vision •21 q3 types of cones, each contain photopigment with different absorption spectra q420 nm – blue q530 nm – green q560 nm - red qColour interpreted by ratio of cone stimulation qOrange (580nm) light stimulates: qBlue cone – 0% qGreen cone – 42% qRed cone – 99% q0:42:99 ratio of cone stimulation interpreted by brain as orange • Guyton Figure 50-8 Rod Vnímání barev je dáno poměrem frekvence vzruchů ve 3 Systémech čípků Cones actually respond to violet, yellow-green, and yellow-red but called blue green red by convention Rod peak wavelength at 500nm Red green colour blindness: red or green cones missing, therefore cannot distinguish red from green because the colour spectra overlap. •23 File:Ishihara 9.png The spots are arranged so that a normal vision person sees a 74, whereas a red-green colour blind person sees a 21 Binokulární vidění •Okohybné svaly –společná jednotka •Funkce obou očí – kyklopské oko •Fixujeme-li předmět a jiný je blíže – heteronymní diplopie (vidíme jej zkříženě a dvojitě) •Fixujeme-li předmět a jiný je dále – homonymní diplopie Hloubkové vidění - stereoskopické •Vzniká transformací trojrozměrného prostoru na dvojrozměrný v receptorech sítnice •Teorie vysvětluje toto vidění projekcí předmětů na tzv.korespondující a nekorespondující body sítnice •Korespondující – to jsou ta místa kam je promítán obraz bodu fixovaného foveou – tyto body definují horopter (množina všech bodů v prostoru, jejichž obraz dopadá na korespondující místa •Geometrická aproximace – horopterová kružnice •Fúze (splynutí obrázků obou očí v jeden prostorový) SLUCH Bubínek – přechod mezi vnějším a středním uchem (funkčně patří ke střednímu uchu) Foramen rotundum m. tensor tympani Třmínek – překrývá foramen ovale Kladívko kovadlinka Spánková kost Bubínková dutina Střední ucho – zabezpečuje převod akustických signálů vzduchem Scala vestibuli Membrana vestibularis membrána tectoria Vláskové buňky foramen rotundum Eustachova trubice 20 000Hz 1 500 Eust.tr.-vyrovnání vzdušného tlaku ve středouší s vnějším barometrickým, normálně je uzavřená Vnitřní ucho – místo receptorů Struktura vláskové buňky Laterálním pohybem vlásků se dráždí receptor – receptorový potenciál Pro rovnovážný smysl sluchový i rovnovážný Kostěné a blanité struktury vnitřního ucha vestibulum Scala tympani scala media endolymfa perilymfa Scala media Membrana tectoria vnitřní vnější vláskové buňky Intenzita zvuku se kóduje jako amplituda receptorového potenciálu, v dostředivých vláknech Jako frekvence AP; vyjádření v decibelech Výška tónu s frekvencí (počtem vln/čas) ČICH Chemoreceptory čichové sliznice -Drážděny látkami, které se rozpustí v nosovém hlenu, -plocha 5 cm2 -Fylogeneticky nejstarší smysl - - -Henningova klasifikace pachů: -Květinový, ovocný, živicový, -Kořenitý, hnilobný, spáleninový - -Citlivý smysl (metylmerkaptan=česnek-400pg/1 l vzduchu) - receptory se rychle adaptují -Hypoosmie –anosmie -hyperosmie Řasinky čichových receptorů-primární senzorické neurony Bulbus olfaktorius Sekundární čichové neurony Tractus olfaktorius Poznámka: nervová zakončení vláken n.trigeminus – čpavek, mentol, chlor-spouští se reflexní odpovědi na dráždivé látky – zastavení dýchání, kýchání, slzení CHUŤ Chuťové pohárky a chuťové chemoreceptory drážděny chuťovými látkami rozpuštěnými ve slinách Chuťové receptory v pohárkách na sliznici jazyka, epiglottis, patře a faryngu Vejcovitý tvar, 50-60mikrom, 40 vlastních chuťových Receptorů=vláskové buňky přečnívající do ústní dutiny Aferentní vlákna přiléhají na spodinu chuťové buňky (50 vláken na 1 pohárek) Základní chutě: sladká (hrot jazyka)-slaná (zadní okraje) -kyselá (přední okraje)-hořká (kořen jazyka) Návrh na 5.typ: umami Chuťové dráhy Z předních 2/3 jazyka –chorda tympani – nervus trigeminus Ze zadní části – nervus glossopharyngeus Ncl.tractus solitarius v prodl.míše Receptory jsou také adaptabilní, Nízká rozlišovací schopnost mezi dvěma látkami Neustále se obnovují Hypogeuzia (pokles chuťové aktivity) Ageuzia - hypergeuzia Tractus solitarius n.facialis Chorda tympani n.trigeminus n.glossophar.