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section 3, chapter 12: vision
- 1. ivyanatomy.co m section 3, chapter 12 vision
- 2. Sense of Sight • Visual accessory organs • Eyelids • Lacrimal apparatus • Extrinsic eye muscles 2
- 3. Eyelid Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. • Palpebra • Composed of four (4) layers: • Skin • Muscle • Connective tissue • Conjunctiva • Orbicularis oculi – closes eyelid • Levator palpebrae superioris – opens eyelid • Tarsal glands – secrete oil onto eyelashes • Conjunctiva – mucous membrane; lines eyelid and covers portion of eyeball Tendon of levator palpebrae superioris Superior rectus Orbicularis oculi Eyelid Tarsal glands Eyelash Cornea Inferior rectus Conjunctiva 3
- 4. Lacrimal Apparatus • Lacrimal gland • Lateral to eye • Secretes tears Lacrimal gland • Canaliculi • Collect tears Superior and inferior canaliculi • Lacrimal sac Lacrimal sac • Collects from canaliculi Nasolacrimal • Nasolacrimal duct duct • Collects from lacrimal sac • Empties tears into nasal cavity Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 4
- 5. Extrinsic Eye Muscles • Superior rectus • Rotates eye up and medially Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Medial Superior rectus rectus Superior oblique • Inferior rectus • Rotates eye down and medially • Medial rectus • Rotates eye medially Lateral rectus (cut) Inferior rectus Inferior oblique 5
- 6. Extrinsic Eye Muscles • Lateral rectus • Rotates eye laterally Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Medial Superior rectus rectus Superior oblique • Superior oblique • Rotates eye down and laterally • Inferior oblique • Rotates eye up and laterally Lateral rectus (cut) Inferior rectus Inferior oblique 6
- 7. Structure of the Eye The eye has three distinct layers “tunics” 1.Fibrous tunic 2.Vascular tunic 3.Nervous tunic
- 8. Outer Tunic • Cornea • Anterior 1/6th of eye • “window of the eye” • Transparent • Light transmission • Sclera • Posterior portion • Opaque • Protection
- 9. Middle Tunic • Choroid coat • Provides blood supply • Pigments absorb extra light • Iris “rainbow” • Anterior portion • Pigmented • Controls light intensity • Ciliary body • Anterior portion • Pigmented • Suspensory ligaments holds lens • Ciliary muscles moves lens for focusing
- 10. Anterior Portion of Eye • Filled with aqueous humor
- 11. Lens • The lens is an elastic, biconvex, and transparent structure largely composed of epithelial cells, called lens fibers. •The lens lies behind the iris and is held in place by suspensory ligaments of ciliary body
- 12. Accommodation • Changing of lens shape to view objects Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Ciliary muscle fibers contracted Suspensory ligaments relaxed Lens thick (a) Ciliary muscle fibers relaxed Suspensory ligaments taut Lens thin 12 (b)
- 13. Aqueous Humor • Fluid in anterior cavity of eye • Secreted by epithelium on inner surface of the ciliary body • Provides nutrients • Maintains shape of anterior portion of eye • Leaves cavity through Canal of Schlemm Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Cornea Aqueous humor Anterior chamber Iris Scleral venous sinus (canal of Schlemm) Lens Sclera Ciliary body Ciliary process Ciliary muscles Vitreous humor Posterior chamber 13
- 14. Ciliary Body • Forms internal ring around the front of the eye • Ciliary processes – radiating folds • Ciliary muscles – contract and relax to move lens Figure 12.28 Lens and ciliary Figure 12.28 Lens and ciliary body viewed from behind. body viewed from behind.
- 15. Iris • Composed of connective tissue and smooth muscle • Pupil is hole in iris • Dim light stimulates radial muscles and pupil dilates • Bright light stimulates circular muscles and pupil constricts
- 16. Inner Tunic • Retina • Contains visual receptors • Continuous with optic nerve • Fovea centralis – center of macula lutea; produces sharpest vision •Macula lutea – yellowish spot in retina • Optic disc – blind spot; contains no visual receptors • Vitreous humor – thick gel that holds retina flat against choroid coat
- 17. Posterior Cavity • Contains vitreous humor – thick gel that holds retina flat against choroid coat Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Lateral rectus Retina Ciliary body Suspensory ligaments Choroid coat Sclera Vitreous humor Iris Lens Fovea centralis Pupil Cornea Aqueous humor Anterior cavity Anterior chamber Posterior chamber Optic nerve Optic disc Posterior cavity Medial rectus 17
- 18. Layers of the Eye 18
- 19. Light Refraction • Refraction • Bending of light • Occurs when light waves pass at an oblique angle into mediums of different densities Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Perpendicular line Air Light wave Glass Refracted light wave 19
- 20. Types of Lenses • Convex lenses cause light waves to converge • Concave lenses cause light waves to diverge Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Light wave Air Convex surface Concave surface Glass Converging light waves (a) Diverging light waves (b) 20
- 21. Focusing On Retina • As light enters eye, it is refracted by: • Convex surface of cornea • Convex surface of lens • Image focused on retina is upside down and reversed from left to right Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Light waves Image Retina Object Cornea 21
- 22. Major Groups of Retinal Neurons • Receptor cells, bipolar cells, and ganglion cells - provide pathway for impulses triggered by photoreceptors to reach the optic nerve • Horizontal cells and amacrine cells – modify impulses Figure 12. Notice that photoreceptors (rods and cones) are the posterior most cells in this circuit. Light waves stimulate the photoreceptors, which send impulses forward to horizontal cells and ganglion cells before leaving the eye through the optic disc.
- 23. Visual Receptors • Rods • Long, thin projections • Contain light sensitive pigment called rhodopsin • Hundred times more sensitive to light than cones • Provide vision in dim light • Produce outlines of objects • Cones • Short, blunt projections • Provide vision in bright light • Produce sharp images • Produce color vision • Pigments include: • Erythrolabe – responds to red • Chlorolabe – responds to green • Cyanolabe – responds to blue Color perceived depends on which sets of cones are stimulated
- 24. Figure 12.38 Rods and cones. (a) Several Figure 12.38 Rods and cones. (a) Several rods converge onto a single sensory nerve rods converge onto a single sensory nerve fiber to the brain (b) separate sensory nerve fiber to the brain (b) separate sensory nerve fibers transmits impulses from the cones to fibers transmits impulses from the cones to the brain. (c) Scanning electron micrograph of the brain. (c) Scanning electron micrograph of rods and cones.. rods and cones
- 25. 12.6 Clinical Application Refraction Disorders • Concave lens corrects nearsightedness • Convex lens corrects farsightedness Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Lens Point of focus Uncorrected point of focus Cornea Light waves Light waves (a) Eye too long (myopia) Point of focus Concave lens (a) Corrected point of focus Light waves Retina Uncorrected point of focus (b) Normal eye Point of focus Light waves Convex lens (c) Eye too short (hyperopia) (b) Corrected point of focus 25
- 26. Visual Pigments • Rhodopsin • Light-sensitive pigment in rods • Decomposes in presence of light • Triggers a complex series of reactions that initiate nerve impulses • Impulses travel along optic nerve • Pigments on cones • Each set contains different lightsensitive pigment • Each set is sensitive to different wavelengths • Color perceived depends on which sets of cones are stimulated • Erythrolabe – responds to red • Chlorolabe – responds to green • Cyanolabe – responds to blue 26
- 27. Stereoscopic Vision • Provides perception of distance and depth • Results from formation of two slightly different retinal images Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Light waves Left eye Right eye 27
- 28. Visual Nerve Pathways Axons from ganglion cells in retina leave the eyes to form the optic nerves. Some of the fibers decussate at the optic chiasm. • Fibers from the nasal (medial) half of retina cross over • Fibers from temporal half (lateral) of retina do not cross over Most fibers of the optic tract continue to the lateral geniculate nucleus of the thalamus, which relays impulses towards the visual cortex.
- 29. Figure 12.41 The visual pathway Figure 12.41 The visual pathway includes the optic nerve, optic includes the optic nerve, optic chiasma, optic tract, and optic chiasma, optic tract, and optic radiations. radiations. End of Chapter 12