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1H06 Anatomy & Physiology: CNS – Vision.docx

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McMaster University
Health Sciences
Alexander Ball

Vision  More than half sensory receptors in eyes  Cerebral cortex highly dedicated in processing visual information Electromagnetic Radiation  Energy waves radiating from sun  Includes gamma rays, x-rays, UV rays, visible light, infrared radiation, microwaves, radio waves called electromagnetic spectrum  Eyes responsible for visible light detection (wavelengths 400-700nm)  Object can absorb certain wavelengths of visible light and reflect others o Green apple is green because it reflects mostly green light and absorbs most other wavelengths of visible light Accessory Structures of Eye Eyelids  Shade eyes during sleep  Protect eyes from excessive light and foreign objects  Spread lubricating secretions over eyeballs  Upper eyelid more movable than lower and contains in superior region the levator palpebrae superioris muscle  Twitch in eyelid associated with stress and fatigue Eyelashes and Eyebrows  Protect eyeballs from foreign objects, perspiration, and direct rays of sun  Sebaceous ciliary glands release lubricating fluid into follicles  Infection of these glands causes swelling called sty. Lacrimal Apparatus  Group of structures that produces and drains lacrimal fluid or tears  Lacrimal glands supplied by parasympathetic fibers of facial nerves  Lacrimal fluid is watery solution containing salts, mucus, lysozyme (bctericidial enzyme) Extrinsic Eye Muscles  Orbits – depressions of skull where eyes sit  Orbits protect eyes, stabilize and anchor to muscles  Periorbital fat surrounds extrinsic eye muscles  Superior rectus, inferior rectus, lateral rectus, medial rectus, superior oblique, and inferior oblique move each eye. Anatomy of Eyeball  Wall of eyeball consists of three layers: fibrous tunic, vascular tunic, and retina Fibrous Tunic  Superficial layer  Consists of anterior cornea and posterior sclera  Cornea – transparent coat that covers colored iris  Sclera – layer of dense connective tissue of collagen fibers and firoblasts o Covers whole eyball except cornea, gives shape and rigidity  Scleral venous sinus – opening at junction of sclera and cornea  Aqueous humor – drains into sinus Vascular Tunic  Middle layer of eyeball  Composed of choroid, ciliary body, and iris  Choroid – lines most of internal surface of sclera o Blood vessels provide nutrients to posterior retina o Contains melanocytes  Ciliary body – extends from ora serata to point posterior to junction of sclera and cornea o Ciliary processes contain blood capillaries secreting aqueous humor o Ciliary muscle – circular band of smooth muscle  Iris – colored portion of eyeball o Between cornea and lens and attached to ciliary processes o Consists of melanocytes and circular and radial smooth muscle fibers o Eyes brown to black = much melanin o Blue = little melanin o Green = moderate melanin Retina  Beginning of visual pathway  Lines posterior eyeball  Blood vessels can be viewed directly and examined for pathological changes o Optic disc – optic nerve exits eyeball o Central retinal artery o Central retinal vein  Pigmented layer and neural layer o Pigmented – melanin epithelial cells between choroid and neural retina. Melanin helps to absorb stray light rays o Neural – processes visual data before sending nerve impulses into axons that form optic nerve  Distinct layers of retinal neurons – photoreceptor layer, bipolar cell layer, and ganglion cell layer  Horizontal and amacrine cells present in bipolar cell layers and both synaptic  Photoreceptors – cells that begin process by which light rays are converted to nerve
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