L4 - Vision PDF - Human Anatomy & Physiology - Winter 2025

Special senses Vision H U M A N A N AT O M Y & P H Y S I O L O G Y – B I O L - 1 1 1 2 WIN TER 2 02 5 R E A D I N G S : C H A P T E R 1 7 , PA G E S 6 0 7 – 6 2 5  Levator palpebrae superioris muscle Orb...

Special senses Vision H U M A N A N AT O M Y & P H Y S I O L O G Y – B I O L - 1 1 1 2 WIN TER 2 02 5 R E A D I N G S : C H A P T E R 1 7 , PA G E S 6 0 7 – 6 2 5  Levator palpebrae superioris muscle Orbicularis oculi muscle Eyebrow Tarsal plate Vision Palpebral conjunctiva Overview Tarsal glands Vision is our dominant sense Cornea ◦ 70% body’s sensory receptors are in eye ◦ Nearly ½ cerebral cortex involved in some aspect Palpebral of visual processing fissure Eyelashes Bulbar conjunctiva Conjunctival sac Orbicularis oculi muscle OpenStax 14.1 Marieb 2016 Fig. 15.1 Tortora 17.3  Levator palpebrae superioris muscle Orbicularis oculi muscle Eyebrow Tarsal plate Palpebral conjunctiva Eye Tarsal glands Only 1/6 anterior eye is visible – most is Cornea enclosed & protected Eyeball Palpebral fissure ◦ Hollow sphere with 3 layered wall; internal cavity filled with humors; lens Eyelashes Accessory structures Bulbar ◦ Eyebrows, eyelids, conjunctiva, lacrimal apparatus, conjunctiva extrinsic eye muscles Conjunctival sac Orbicularis oculi muscle OpenStax 14.1 Marieb 2016 Fig. 15.1 Tortora 17.3  Levator palpebrae superioris muscle Orbicularis oculi muscle Eyebrow Eye accessory Tarsal plate Palpebral conjunctiva Eyebrow Pupil (under Iris Upper Lacrimal structures Eyelash cornea) eyelid caruncle Tarsal glands Eyebrows Cornea ◦ Help shade eyes & block perspiration Palpebral fissure Eyelids (palpebrae), eyelashes, Eyelashes & associated glands Bulbar ◦ Protects eye from physical conjunctiva danger & from drying out Conjunctival ◦ Blinking – orbicularis oculi & sac levator palpebrae muscles Orbicularis activated reflexively oculi muscle Lateral Lower Medial commissure Palpebral eyelid commissure Conjunctiva fissure (over sclera) OpenStax 14.1 Tortora Fig. 17.5; Marieb 2016 Fig. 15.1 Tortora 17.4  Levator palpebrae superioris muscle Orbicularis oculi muscle Eyebrow Eye accessory Tarsal plate Palpebral conjunctiva structures Tarsal glands Conjunctiva Cornea ◦ Transparent mucous membrane ◦ Inner surface of eyelids (palpebral) & covers Palpebral anterior surface of eye (bulbar) but not the cornea fissure ◦ Produces lubricating mucus – prevent drying out Eyelashes Bulbar conjunctiva Conjunctival sac Orbicularis oculi muscle OpenStax 14.1 Marieb 2016 Fig. 15.1 Tortora 17.4  Lacrimal Excretory lacrimal glands ducts Lacrimal puncta Eye accessory structures Lacrimal canaliculi Lacrimal apparatus Lacrimal sac Lacrimal gland – secretes dilute saline solution (lacrimal secretion or tears) Nasolacrimal duct Small ducts – drain excess fluid into nasal cavity ◦ Tears enter lacrimal canaliculi via lacrimal puncta Nasal cavity (openings) ◦ Tears drain into lacrimal sac & empty into nasolacrimal duct Lacrimal fluid (tears) Pathway of tears ◦ Contains mucus, antibodies, lysozyme lacrimal gland → lacrimal ducts → fluid flows over eye ◦ Cleanses, moistens, & protects eyes → lacrimal puncta → lacrimal canaliculus→ lacrimal sac → nasolacrimal duct → nasal cavity OpenStax 14.1 Adapted from Tortora Fig. 17.6 Tortora 17.4  Superior Trochlea rectus Superior oblique Eye accessory structures Lateral rectus Medial rectus Movement of eyeball Inferior Controlled by 6 extrinsic eye Inferior oblique rectus muscles Superior oblique Innervated by oculomotor (III), tendon abducens (VI), & trochlear (IV) Superior nerves oblique muscle Functions: Superior ◦ Maintain eyeball shape rectus ◦ Hold it in orbit muscle ◦ Precise eye movement Lateral rectus muscle Inferior rectus Inferior oblique muscle muscle Marieb 2016 Fig. 15.3 OpenStax 14.1 Tortora 17.4  Ciliary body Ciliary Sclera process Suspensory ligament Choroid Eyeball structure Cornea Retina Macula Overview lutea Iris Wall of eyeball is composed of 3 layers (tunics) Fovea Pupil centralis ◦ Fibrous layer Optic ◦ Vascular layer Anterior nerve cavity ◦ Retina (inner layer) (contains aqueous Layers enclose an internal cavity filled with fluids humor) – humours Lens ◦ Help maintain shape Scleral Central venous sinus artery & vein of retina Posterior cavity Optic disc (contain vitreous (blind spot) humor) OpenStax 14.1 Marieb 2016 Fig. 15.4 Tortora 17.5  Ciliary body Ciliary Sclera process Suspensory Choroid ligament Cornea Retina Macula Fibrous layer lutea Iris Outermost avascular layer Fovea Pupil centralis Two regions: Anterior Optic cavity nerve Sclera (opaque white) (contains ◦ Maintains shape of eye aqueous humor) ◦ Protects inner surface Lens ◦ Anchoring site for extrinsic eye muscles Scleral Central Cornea (clear) venous sinus artery & vein of retina ◦ Allows light to enter the eye Posterior cavity Optic disc ◦ Refracts light to focus light rays (contain vitreous (blind spot) humor) OpenStax 14.1 Marieb 2016 Fig. 15.4 Tortora 17.5  Ciliary body Ciliary Sclera process Suspensory Choroid ligament Cornea Retina Macula Vascular layer lutea Iris Highly vascularized middle layer Fovea Pupil centralis Choroid Anterior Optic ◦ Darkly pigmented region that absorbs excess light cavity nerve (contains ◦ Blood vessels – nourish eye layers aqueous humor) Ciliary body Lens ◦ Ciliary muscle – smooth muscle that regulates lens shape Scleral Central artery & vein ◦ Ciliary process – contains blood capillaries that venous sinus of retina secrete aqueous humor in anterior cavity Posterior cavity Optic disc ◦ Suspensory ligaments – extent from ciliary (contain vitreous (blind spot) humor) processes to hold lens in position & transmits tension from ciliary muscle OpenStax 14.1 Marieb 2016 Fig. 15.4 Tortora 17.5  Ciliary body Ciliary Sclera process Suspensory Choroid ligament Cornea Retina Macula Vascular layer lutea Iris Iris Fovea Pupil centralis ◦ Coloured part of eye (contains melanocytes) Optic ◦ Contains circular & radial smooth muscle Anterior nerve cavity ◦ Reflexively control pupil size & amount of light that (contains enters eye aqueous humor) Pupil constricts as sphincter Pupil Pupil dilates as dilator pupillae muscles of iris contract pupillae muscles of iris Lens (parasympathetic) contract (sympathetic) Scleral Central venous sinus artery & vein of retina Posterior cavity Optic disc (contain vitreous (blind spot) humor) Bright light Normal light Dim light OpenStax 14.1 Marieb 2016 Fig. 15.4 Tortora 17.5  Ciliary body Ciliary Sclera process Suspensory Choroid ligament Retina Cornea Macula lutea Iris Fovea Pupil centralis Anterior Optic nerve cavity Retina (contains aqueous humor) Lens Scleral Central venous sinus artery & vein of retina Posterior cavity (contain vitreous humor) Optic disc (blind spot) Innermost delicate layer Photoreceptor Pigmented layer (outer) layer ◦ Absorbs excess light to reduce Direction of nerve scattering impulses through retina Neural layer (inner) ◦ Visual part Bipolar cell ◦ Subdivided into 3 distinct layers of layer retinal neurons ◦ Photoreceptor layer ◦ Bipolar cell layer Direction of ◦ Ganglion cell layer incoming light Marieb 2016 Fig. 15.4 OpenStax 14.1 Modified from Hill 2022 Fig. 14.2 Tortora 17.5  Direction Retina of nerve impulses Photoreceptor through retina Photoreceptor layer layer Rods ◦ Dim light & peripheral vision ◦ More numerous & more sensitive to light than cones ◦ Cannot resolve color or sharp images Bipolar cell layer Cones Direction ◦ Bright light & high resolution colour of vision incoming ◦ Less sensitive & best adapted to light bright light ◦ 3 types – blue, green, red OpenStax 14.1 Modified from Hill 2022 Fig. 14.2 Tortora 17.5  Retina NASAL TEMPORAL Macula lutea SIDE SIDE Lateral to blind spot Macula lutea Optic disc At its center – Fovea centralis ◦ Highest density of cones for detailed colour vision ◦ Move our eyes to focus image on Retinal blood fovea vessels Fovea centralis Left eye OpenStax 14.1 Tortora Fig. 17.9 Tortora 17.5  Direction Retina of nerve impulses Bipolar & through retina Photoreceptor layer ganglion layers Bipolar cells – Relay information from photoreceptors to ganglion cells Ganglion cells – axons converge at Bipolar cell optic disc; form optic nerve (II) layer Amacrine & horizontal cells also Direction aid in visual processing of incoming light OpenStax 14.1 Modified from Hill 2022 Fig. 14.2 Tortora 17.5 NASAL TEMPORAL SIDE SIDE Macula lutea Optic disc Retina Retinal blood Optic disc vessels Fovea centralis Where optic nerve exits eye Left eye No photoreceptors (cannot resolve an image without receptors) ◦ i.e., blind spot OpenStax 14.1 Tortora Fig. 17.9; 17.10 Tortora 17.5  Ciliary body Ciliary Sclera process Suspensory Choroid ligament Cornea Retina Macula Lens lutea Iris Avascular, biconvex structure Fovea Pupil centralis Held in place by suspensory ligaments Anterior Optic cavity nerve Changes shape to focus image (contains aqueous Cells contain transparent crystalline protein humor) ◦ Cataract – clouding of lens due to changes in proteins Lens Scleral Central venous sinus artery & vein of retina Posterior cavity Optic disc (contain vitreous (blind spot) humor) OpenStax 14.1 Marieb 2016 Fig. 15.4, Fig. 15.9 Tortora 17.5  Iris Posterior cavity Lens (contains Cornea vitreous humor) Anterior cavity In front of lens Aqueous humor Anterior Anterior chamber Suspensory ◦ Continuously produced (ciliary cavity ligament (contains Posterior chamber processes) & drained away (scleral aqueous venous sinus) humor) Scleral venous Ciliary ◦ Provides oxygen & nutrients to lens sinus processes & cornea; removes wastes Ciliary ◦ Maintains intraocular pressure to body Ciliary support eyeball internally muscle Glaucoma Sclera ◦ Drainage of aqueous humor is blocked → ↑ pressure → compress retina & optic nerve → blindness OpenStax 14.1 Marieb 2016 Fig. 15.8 Tortora 17.5  Posterior cavity Behind lens Vitreous humor (gel-like) ◦ Formed during embryonic life, NOT replaced ◦ Transmits light ◦ Holds retina in place ◦ Maintains intraocular pressure OpenStax 14.1 Moyes & Shulte 2015 Fig. 7.37 Tortora 17.5  Gamma X rays UV Infrared Micro- Radio- rays rays waves waves Physiology of vision Light & optics 400 nm 700 nm Visible light Electromagnetic radiation exists in waves Orange Yellow Indigo Green Violet Blue Red ◦ Long radio waves to short x-rays Visible light (400–700 nm wavelengths) (a) Electromagnetic spectrum ◦ Eyes – special organs used to detect light Wavelength ◦ Different wavelengths are perceived as different colours Perceived colours are reflections of those wavelengths ◦ Objects absorb some wavelengths & reflect others ◦ E.g., grass is green because it absorbs all colours Electromagnetic wave except green (which is absorbed by our green cones) (b) An electromagnetic wave OpenStax 14.1 Tortora Fig. 17.4 Tortora 17.3  Light ray before refraction Air Refraction & lenses Refraction of light rays ◦ Light bends as it passes through objects of Light ray after different densities Water refraction Lens – transparent object curved on one or both sides ◦ Light refracts as it hits the curve at an angle Focal point – where light rays focus Point Focal ◦ ↑ converging (convex) lens → ↑ bending → sources points ↓ focal distance OpenStax Physics 26.2 Tortora Fig. 17.12; Marieb 2016 Fig. 15.12 Tortora 17.6  Lens Focus light on retina Cornea – greatest role in focusing image (75%) Cornea ◦ Large difference in optical density between air & corneal tissue ◦ Fixed curvature Lens – fine tunes the focus (25%) ◦ Avascular, biconvex ◦ Transparent flexible structure – can change shape to allow precise focusing of light on retina Light is bent 3 times when it enters the eye 1. Entering cornea 2. Entering lens 3. Leaving lens OpenStax Physics 26.2 Tortora Fig. 17.12; 17.13 Tortora 17.6  Distant vision Nearly parallel light rays approach eye for distant objects ◦ Cornea & at-rest lens focus light from distant objects precisely on retina Ciliary muscles are relaxed (↓ width) ◦ ↑ tension on suspensory ligaments Suspensory Ciliary muscle (relaxed) ◦ Lens flattens (less light refraction/bending needed) ligaments (taut) Nearly parallel light rays Far point of vision – distance beyond which no change in lens shape (accommodation) is Distant required (normal eye, ~6 m or 20’) Lens (thinner & flat) object OpenStax Physics 26.2 Tortora Fig. 17.12; Sherwood et al. 2013 Fig. 6-31 Tortora 17.6  Close vision Diverging light rays approach eye for close objects – eye makes three adjustments: 1. Accommodation of lens – thickens & ↑ light refraction (bending) ◦ Ciliary muscle contract (↑ width) ◦ ↓ tension on suspensory ligaments Suspensory ligaments Ciliary muscle (contracted) ◦ Lens becomes more rounded (loose) ◦ Near point of vision – point of maximal thickening of Divergent light rays lens (normal eye, ~10 cm or 4”) Close object 2. Constriction of pupils – better directs light to lens Lens (thicker & rounder) 3. Convergence of eyeballs – allows object to remain focused on fovea OpenStax Physics 26.2 Tortora Fig. 17.12; Sherwood et al. 2013 Fig. 6-31 Tortora 17.6  Vision problems Myopia (near-sighted) ◦ Close objects seen clearly; distant objects blurred ◦ Objects focus in front of retina ◦ Eyeball too long or lens too curved/thick (too much refraction) ◦ Correct by ↓ refraction (diverging/concave lens) Hyperopia (far-sighted) ◦ Distant objects seen clearly; close objects blurred ◦ Objects focus behind retina ◦ Eyeball too short or lens too flat/thin (not enough refraction) ◦ Correct by ↑ refraction (converging/convex lens) Astigmatism ◦ Irregular curvature of lens or cornea; blurred images OpenStax Physics 26.2 Tortora Fig. 17.13 Tortora 17.6  Pigment epithelial cell Photoreceptors Outer segment Outer segment Melanin granules Discs Rods & cones – modified neurons Folds Outer segments – inserted into pigmented Mitochondrion layer of retina Golgi complex ◦ Location of photopigments (visual pigments) found in discs – change shape as they absorb light Inner segment Inner segment Nucleus Synaptic terminal Synaptic vesicles Rod Cone Light direction OpenStax 14.1 Tortora Fig. 17.14 Tortora 17.6 Rods vs. cones Rods ◦ Single pigment – perception of one colour ◦ Highly sensitive → dim light; can detect a single photon ◦ Many rods converge into one ganglion → fuzzy & indistinct image Cones ◦ Three pigments – vivid colour detection ◦ Less sensitive → bright light required for activation ◦ Less convergence (sometimes having own ganglion cells) → high resolution image projected to brain OpenStax 14.1 Moyes & Shulte 2015 Fig. 7.40 Tortora 17.6  Disc Visual pigments Rod Photopigments contain: ◦ Retinal – light absorbing pigment (vitamin A derivative) ◦ Opsin – G protein-coupled receptor ◦ Differences in amino acid sequences of different opsins = Photopigment sensitivity to different wavelengths (rhodopsin): Retinal Rods – contain a single opsin, rhodopsin Opsin Cones – opsins named after range of wavelengths Disc they absorb (blue, green, & red) membrane OpenStax 14.1 Tortora Fig. 17.15 Tortora 17.6  Cone wavelengths Cone wavelengths overlap One wavelength can activate more than one cone Can perceive a variety of colour hues ◦ E.g., yellow light stimulates red & green cones equally OpenStax 14.1 Sherwood et al. 2013 Fig. 6-37 Tortora 17.6  Normal vision Red & green opsins Genes for red & green opsins are located very close to one another on the X chromosome ◦ Highly homologous – only differ by Red-green colour blindness 11 a.a. ◦ High overlap between perceived wavelengths Red-green colour blindness ◦ Lack red OR green cones OpenStax 14.1 Sherwood et al. 2013 Fig. 6-37; https://www.colourblindawareness.org/colour-blindness/types-of-colour-blindness/ Tortora 17.6  11-cis-retinal 1 Pigment synthesis: 11-cis-retinal, derived from vitamin A, is combined with opsin to form rhodopsin. 2H+ Vitamin A Oxidation Capturing light 11-cis-retinal Reduction Rhodopsin 1. Pigment synthesis – rhodopsin forms in dark 2 Pigment bleaching: ◦ Vitamin A oxidized (isomerized) to 11-cis-retinal & 2H+ Light absorption by rhodopsin triggers a combined with opsin rapid series of steps in 3 Pigment Dark Light which retinal changes regeneration: Enzymes slowly convert shape (11-cis to all- trans) and eventually releases from opsin. 2. Pigment bleaching all-trans-retinal to its 11-cis form in cells of the ◦ When rhodopsin absorbs light, 11-cis-retinal → pigmented layer; requires ATP. all-trans-retinal ◦ All-trans-retinal (colour portion) separates from opsin 3. Pigment regeneration Opsin ◦ Enzymes convert all-trans-retinal → 11-cis-retinal and ◦ 11-cis-retinal rejoins opsin All-trans-retinal Similar process in cones, but higher intensity of light required to activate cones OpenStax 14.1 All-trans-retinal Marieb 2016 Fig. 15.16 Tortora 17.6  In the dark In the light Light cGMP-gated channels cGMP-gated channels open, + close; cation influx stops. Phototransduction Na allowing cation influx. Ca2+ Photoreceptor Light Photoreceptor depolarizes. hyperpolarizes. Photoreceptor cell (rod) Photoreceptors release inhibitory neurotransmitter when depolarized −40 mV −70 mV Dark conditions – depolarized Ca2+ Inhibitory neurotransmitter No inhibitory ◦ Inhibit downstream visual neurotransmitter transmission released released Bipolar cell hyperpolarizes Bipolar cell Light conditions – hyperpolarized depolarizes ◦ Stop inhibiting downstream visual Bipolar cell transmission Depolarization stimulates Hyperpolarization neurotransmitter release inhibits neurotransmitter Ca2+ release Action potentials in Ganglion ganglion cell & propagate No action potentials in cell along optic nerve ganglion cell & along Marieb 2016 Fig. 15.18 OpenStax 14.1 optic nerve Tortora 17.6  In the dark In the light Light cGMP-gated channels cGMP-gated channels open, Na+ close; cation influx stops. allowing cation influx. Ca2+ Photoreceptor Light Photoreceptors Photoreceptor depolarizes. hyperpolarizes. Photopigment phospho- Guanylyl Photoreceptor cell (rod) Opsin diesterase cyclase cis-Retinal (inactive) Inhibitory neurotransmitter released Bipolar cell hyperpolarizes Ca2+ No inhibitory neurotransmitter released Bipolar cell depolarizes cGMP- in dark Bipolar Transducin gated Hyperpolarization inhibits neurotransmitter cell Ca2+ Depolarization stimulates neurotransmitter release (inactive) channel Photoreceptors are slightly release High cGMP depolarized Action potentials in concentration Na+ No action potentials in Ganglion cell ganglion cell & propagate along optic nerve ◦ cGMP is high in “unstimulated” cells ganglion cell & along Cytosol optic nerve Rod ◦ Ion (Na+) channels are open in Large Na+ response to high cGMP levels → cell is inflow more positive Depolarization Release inhibitory neurotransmitters to bipolar cells Voltage-gated Ca2+ Inhibited bipolar cells cannot Ca2+ channel stimulate the ganglion cells, leading to inhibition of visual response Tortora Fig. 17.16 OpenStax 14.1 Neurotransmitter Marieb 2016 Fig. 15.18 Tortora 17.6 rk In the light Photopigment phospho- Light cGMP-gated channels Opsin Guanylyl Photoreceptors Na+ close; cation influx stops. Ca2+ Light Photoreceptor hyperpolarizes. trans- diesterase cyclase Retinal (active) Photoreceptor cell (rod) No inhibitory neurotransmitter released 1 2 Transducin 3 4 in light Bipolar cell depolarizes (active) cGMP-gated Bleaching of pigment hyperpolarizes Bipolar Decreased 5 channel cell Depolarization stimulates neurotransmitter release cGMP photoreceptors Ca2+ LIght concentration ◦ Light-activated rhodopsin activates a Na+ Ganglion Action potentials in ganglion cell & propagate signaling pathway to break down cell along optic nerve Cytosol cGMP Decreased Na+ inflow ◦ ↓ cGMP → ion (Na+) channels close → 6 cell is more negative (hyperpolarized) Hyperpolarizing receptor potential Less inhibitory neurotransmitter is Voltage-gated released to bipolar cells Ca2+ channel 7 Bipolar cells stimulate the ganglion cells, leading to a visual response OpenStax 14.1 Tortora Fig. 17.16 Neurotransmitter Tortora 17.6  Photoreceptors in light Extent of light determines the magnitude of the response (hyperpolarizing receptor potential) Dim light – partially turn off inhibitory neurotransmitter (NT) release Somewhat More Bright light – turn off inhibitory NT hyperpolarized hyperpolarized more completely Less inhibitory Even less NT release inhibitory NT release OpenStax 14.1 Hill et al. 2022 Fig. 14.25 Tortora 17.6  Light & dark adaptation Light adaptation (darkness → bright light) Initially, both rods & cones strongly stimulated Large amounts of photopigment broken down – produces a glare Pupils constrict to ↓ light reaching retina After ~5–10 mins – ↑ visual acuity & ↓ retinal sensitivity as rods turn off & only cones remain “on” OpenStax 14.1 Moyes & Shulte 2015 Fig. 7.31 Tortora 17.6  Light & dark adaptation Dark adaptation (bright light → darkness) Cones cannot function in low-intensity light Previously bleached rods require time to reactivate Pupils dilate to ↑ light reaching retina ↑ rhodopsin of rods in dark, max ↑ visual acuity at 20–30 min OpenStax 14.1 Moyes & Shulte 2015 Fig. 7.31 Tortora 17.6  Fixation point Visual perception Optic nerve – retinal ganglion cells merge at Right eye Left eye back of eyeball Optic nerve Supra- Optic chiasma – fibers from medial aspect of chiasmatic Optic chiasma each eye cross to opposite side nucleus Pretectal Optic tract Optic tracts – carry information from the same nucleus half of the visual field Optic tracts project to lateral geniculate nucleus of thalamus Lateral geniculate Uncrossed Optic radiations – project to primary visual nucleus of (ipsilateral) fiber thalamus Crossed cortex in occipital lobes for visual processing (contralateral) fiber Optic Superior Primary visual radiation colliculus cortex OpenStax 14.2 Marieb 2016 Fig. 15.19 (occipital lobe) Tortora 17.6  Fixation point Visual field Binocular zone Right eye Left eye ◦ Each eye’s visual field is ~ 170 degrees Optic nerve ◦ Considerable overlap between right & left visual fields, Supra- chiasmatic but each eye sees a slightly different view Optic chiasma nucleus ◦ Area processed on both sides of brain → allows for Pretectal Optic tract comparison of image properties from each eye nucleus ◦ One of the processes that underlies depth perception Lateral geniculate Uncrossed nucleus of (ipsilateral) fiber thalamus Crossed (contralateral) fiber Optic Superior Primary visual radiation colliculus cortex OpenStax 14.2 Marieb 2016 Fig. 15.19 (occipital lobe) Tortora 17.6  Visual pathway summary Visual field Visual field of right eye of left eye Binocular visual field Light Optic (II) nerves Optic chiasm Photoreceptor cells Midbrain Lateral geniculate nucleus of thalamus Bipolar neurons Optic Optic radiation tracts Ganglion neurons Exit eye as optic nerve Primary visual cortex in occipital lobe of cerebum Optic chiasma Axons from medial half of each retina cross Optic tract Direction of Direction of nerve Thalamus (lateral geniculate nucleus) incoming impulses through light retina Primary visual cortex in occipital lobe of cerebrum Moyes & Shulte 2015 Fig. 7.39; Tortora Fig. 17.17 Check your knowledge Describe the structure & function of accessory eye structures, eye layers, the lens, & humours of the eye. What is the purpose of the lacrimal apparatus? What pathway do tears follow? Compare & contrast the different layers of the eyeball, associating their structures with their functions. What property of the cornea explains why a cornea transplant is nearly always successful? What is the role of the pigmented regions in the vascular layer & retina? ________________________ is lateral to the blind spot & the _______________________ is at its center, where the highest density of cones is present. Describe the causes & consequences of cataracts & glaucoma. Check your knowledge Trace the pathway of light through the eye to the retina. Explain how light is focused for distant & close vision. Describe the causes & consequences of astigmatism, myopia, & hyperopia. Describe the events that convert light into a neural signal. What portion of the photoreceptor absorbs light & changes shape? Where in the photoreceptor are these found? Compare and contrast the roles of rods & cones in vision. Why would vitamin A deficiency result in vision issues? What is pigment bleaching? What is involved in this process? Check your knowledge Explain how it is possible for photoreceptors to be depolarized in the dark but result in inhibition of a visual response. How is it possible for photoreceptors to detect different intensities of light? How is this translated to a visual response? Compare & contrast light & dark adaptation. Trace the visual pathway to the visual cortex. Check your knowledge True OR false – the conjunctiva is a transparent membrane that covers the inner surface of the eyelids only. True OR false – extrinsic eye muscles allow the pupil to dilate or contract. True OR false – ciliary processes contains blood capillaries that secrete aqueous humor into the posterior cavity True OR false – the bipolar cells within the retina relay information from photoreceptors to the ganglion cells. True OR false – Vitreous humor is found in the anterior cavity & is continually produced & drained. True OR false – the lens can change shape to allow for precise focusing of light on the retina. Check your knowledge True OR false – a converging/convex lens can correct hyperopia by increasing refraction of the light. True OR false – Photoreceptors are of epithelial origin. True OR false – Rods are more sensitive but converge less than cones, allowing for higher resolution image projection to the brain. True OR false – the depolarization of photoreceptors in light conditions results in stimulation of the bipolar &, subsequently, the ganglion cells. True OR false – The binocular zone is processed by both sides of the brain & is one of the processes that underlies depth perception.