Special Senses - Vision

Question	Answer
Accessory Structures	eyebrows eyelids conjunctiva lacrimal apparatus extrinsic eye muscles
Key Structures	Fibrous layer Vascular layer Neural layer Optical chamber Lens and cataracts
Eyebrows	UV barrier prevent perspiration from entering eyes orbicularis muscle - depresses corrugator muscle - moves medially
Eyelids	Palpabrae fissure - separates upper/lower lids medial/lateral canthus lacrimal caruncle - lubrication, sebaceous/sweat glands tarsal plate - CT structure/support palpabrae superioris - moves upper lid
Conjunctiva	palpebral conjunctiva - lines lids bulbar conjunctiva - lines sclera doesnt cover cornea lubrication/protection
Lacrimal apparatus	superolateral glands secrete fluid (tears), enters laterally, spreads across eye, exits medially, drains into lacrimal sac, through lacrimal fossa and into nasal cavity - contains mucous, enzymes and antibodies
Eyelashes	protection protrudes outwards blinking reflex contains lubricating glands (tarsal glands, sebaceous glands, ciliary/sweat glands)
Extrinsic eye muscles	LR = moves lat MR = moves med SR = elevates, moves med IR = depresses, moves med SO = depresses, moves lat IR = elevates, moves med LR6SO4 all surrounded by annular ring (tendonous)
Fibrous Layer	Contains clear cornea + cloudy sclera Sclera - post./protects, anchors muscles, cont. with dura mater Cornea - ant./lets light in/aqueous humor behind/ext. stratified + int. simple squamous pain receptors = reflex. blinking
Vascular layer	choroid - dark brown, supply blood, post. part of uvea ciliary body - thick ring tissue surr. lens/smooth muscle bundles/anchors susp. lig./zonules holds lens in place iris - cont. with CB/central opening, pupil - 2 muscles (dilator pupillae - symp/distant vis/dim light & sphinter pupillae - parasymp./close vis/bright light)
Sensory Layer - Retina	1. Pigmented epth. layer (outer layer, absorbs light/prevents scattering, engulf dead photorec. cells/ store Vit A 2. Neural layer (transparent inner layer, 3 types; A) photoreceptors = transduce light B) bipolar cells = body in middle C) ganglion cells (generate AP) visual processing via amacrine & horizontal cells
Optic Disk	site where optic nerve leaves eye blind spot NOT COVERED BY SCLERA!!! lacks photoreceptors
Photoreceptors - Rods and Cones	Rods = resp. dim light (sensitive)/peripheral vision Cones = resp. bright light (less sensitive/high acuity colour vision/posterior lateral to blind spot) Macula lutea = mostly cones Fovea centralis = only cones
Optical Chambers (Post. Seg)	vitreous humor forms in embryo lasts lifetime transmits light supports post. surface of lens holds neural retina against pig. layer counteracts pulling force from muscles
Optical Chamber (Ant. Seg)	Ant. Chamber = btn cornea & iris Post. Chamber = btwn iris & lens Contains aqueous humor prod. by CB in Post. Chamber, flows up nourishes lens, passes thru pupil, flows back to ant. chamber, drains into canal at edge of cornea supports/nourishes/removes waste!
Lens	Transparent, flexible, elastic, avascular, biconvex 2 Regions: 1. Lens Epth. = ant. lens surface + cuboidal cells 2. Lens Fibres = bulk of lens, no nuclei, filled with transparent protein crystallin Optical comp. admits/focus light = humors, cornea, lens!
Refraction & Lens	Light passes from one transparent medium to another, changing speed and bending (refracting) Light passes thru convex lens (in eye) is bent so rays converge to one point - retina
Pathway for Light	Moves through 1. Cornea 2. Aqueous humor 3. Lens 4. Vitreous humor 5. Thickness of neural layer Light bends when A) entering cornea B) entering lens C) leaving lens
Distant Vision Focussing	Lens is thin Ciliary muscles relaxed Little refraction adjustment - light rays are parallel from distance Sympathetic system
Close Vision Focussing	Thick lens ACCOMMODATION = Ciliary muscles change lens shape (rounder) to increase refraction power, loosen zonule fibres Pupillary reflex constricts pupils to prevent bright rays entering eye med. rot. of eyeball
Problems with Refraction	Emmetropic Vis = normal eye, light focused properly with close vis, lens accomodated Myopic Eye = nearsighted, no distance vis, focal point IN FRONT of retina, corrected with concave lens Hyperopic Eye = shortsighted, no close vis, focal point BEHIND retina, corrected with convex lens Presbyopia = same as hyperopic eye but caused by ageing
Photoreception	Eye detects light energy Rods/Cones contain vis. pig./Photo-pigment = Rhodopsin in rods, one for each cone as they respond to diff colours
Photopigments in Photoreceptor Cells	Disks parallel to retina, stacked on top of one another Each photopigment contains Opsin (integral protein) Opsin = surrounds and binds chromophore molec, filters light, differs in each type of photopigment, enables diff photopigments to absorb light at diff wavelength Chromophore = light sensitive part of photopigment, same in all four photopigments, retinal - Vit A variant
Rods & Cones Comparison	Cones - 3 million/bright light to activate/low sensitivity/pigments for colour vis/each cone synapses with 1 ganglion cell/vision detailed + high res Rods - 100million/sensitive to dim light/night vision/absorb wavelengths of visible light/grey tones only/many rods feed into 1 ganglion cell/fuzzy + indistinct images
Excitation of Rods	Rhodopsin breaks down when stim by light Converts cis retinal to all-trans retinal, changing shape, released from opsin + bleaches pigment Dark phase reverses from all-trans retinal/Vit A to cis retinal via ATP enzyme, joins back to opsin to form rhodopsin REGEN - rods = slow 5 mins, cones = fast 90 sec
Excitation of Cones	3 Types of Cones 1. Blue = 420nm wvlth 2. Green = 530nm wvlth 3. Red = 560nm wvlth Intermediate colours are combination of cones Excitation similar to rods
Phototransduction	1. Light converts retinal to trans form 2. Activates G-protein transducin 3. Transducin activates phosphodiesterase (PDE) 4. Converts cGMP to GMP 5. ↓ cGMP = closure of cation channels Results in hyperpolarisation of the photoreceptor
Phototransduction Dark	1. Photoreceptors depolarised from flux of cations thru cGMP channels 2. Open gated Ca2+ channels 3. Cont. release of neurotransmitter 4. Hyperpolarises bipolar cells 5. Inhibits neurotransmitter release 6. No excitation of ganglion cells 7. No AP
Phototransduction Light	1. Light activates molec of retinal, causing it to change shape, ↓cGMP 2. Cation channels close, K+ channels stay open 3. Membrane hyperpolarises + neurotransmitter is released 4. Bipolar cell is disinhibited 5. Depolarises and releases neurotransmitter 6. Depolarises ganglion cell 7. Creates AP

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Special Senses - Vision

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	Created by Caitlin French over 6 years ago