03 Dec. 2012Special-vision.ppt1 Special Senses Vision

03 Dec. 2012Special-vision.ppt2 Vision Eye converts electromagnetic radiation (light) to action potentials Impulses carried over optic nerves & optic tracts to primary visual cortex

03 Dec. 2012Special-vision.ppt3 Eye: Accessory structures Eyebrow Eyelids Eyelashes

03 Dec. 2012Special-vision.ppt4 Eye: Accessory structures Orbicularis oculi muscle closes eye Conjunctiva –Mucous membrane under lid and over surface of sclera

03 Dec. 2012Special-vision.ppt5 Eye: Accessory structures Lacrimal apparatus Lacrimal gland, Excretory ducts, Lacrimal puncta, Lacrimal canaliculi, Nasolacrimal duct

03 Dec. 2012Special-vision.ppt6 Eye: Extrinsic Muscles Six muscle aim each eye –Superior rectus –Inferior rectus –Medial rectus –Lateral rectus (abducens) –Superior oblique (trochlear) –Inferior oblique

03 Dec. 2012Special-vision.ppt7 Eye Three layers (tunics) –Fibrous tunic Sclera Cornea –Vascular tunic Choroid Ciliary body Iris –Sensory tunic = Retina

03 Dec. 2012Special-vision.ppt8 Eye Anterior chamber Aqueous humor secreted by ciliary body Drained through Canal of Schlemm (scleral venous sinus) Posterior cavity with Vitreous humor

03 Dec. 2012Special-vision.ppt9 Eye: Refraction Cornea –More refraction –Fixed (not focusable) Lens –Connected to ciliary body by suspensory ligaments –Changes shape to focus Flatten for distance Thicken for near vision

03 Dec. 2012Special-vision.ppt10 Focusing, Accomodation Lens changes shape to focus Flatten for distance Sympathetic Thicken for near vision Parasympathetic

03 Dec. 2012Special-vision.ppt11 Regulating Light Intensity Bright light stimulates parasympathetic reflex to constrict pupils Dim light stimulates sympathetic reflex to dilate pupils –Atropine (Norepinephrine mimic) used to dilate pupils

03 Dec. 2012Special-vision.ppt12 Eye Neural tunic = Retina –Extension of brain –Optic disc Attachment, origin of optic nerve Central artery & vein –Macula lutea & fovea centralis

03 Dec. 2012Special-vision.ppt13 Eye: Retina Retina built “backwards” Light passes through 3-4 layers of cells before reaching photoreceptors Retinal cells Ganglion cells Cell bodies of optic nerve fibers Bipolar cells Rods, ~ 125 M Cones, ~6 M

03 Dec. 2012Special-vision.ppt14 Structure of Retina Pigment epithelium –Absorbs excess photons Rods & Cones Outer segment Inner segment Bipolar cells

03 Dec. 2012Special-vision.ppt15 Eye: Retina Rods & Cones absorb light energy, secrete neurotransmitter to bipolar cells Photopigments –Retinal + opsin –4 kinds of opsins (protein)

03 Dec. 2012Special-vision.ppt16 Eye: Retina Rods –Retinal + opsin  rhodopsin –Absorbs light across whole visual spectrum Can’t distinguish color –Sensitive to dim light –Few rods in macula lutea More concentrated in peripheral parts of retina

03 Dec. 2012Special-vision.ppt17 Eye: Retina Cones –3 kinds of cones with three opsins –Each absorbs most in part of visual spectrum –Used to see color –Concentrated in macula lutea & fovea centralis

03 Dec. 2012Special-vision.ppt18 Impulse transmission from Retina Retinal cells have high metabolic activity Dark –Depolarized –Release of neurotransmitter –IPSP in bipolar cells Light –Hyperpolarized –No neurotransmitter release to bipolar cells, inhibition removed –Bipolar cells stimulate ganglion (optic n.) cells