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Figure 17-4a External Features and Accessory Structures of the Eye
Eyelashes Pupil Lateral canthus Palpebra Sclera Palpebral fissure Medial canthus Lacrimal caruncle Corneal limbus Gross and superficial anatomy of the accessory structures p. 571 1
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Figure 17-5b The Sectional Anatomy of the Eye
Fibrous layer Vascular layer (uvea) Cornea Anterior cavity Iris Sclera Ciliary body Choroid Posterior cavity Neural layer (retina) Neural part Pigmented part Horizontal section of right eye p. 572 5
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Figure 17-5c The Sectional Anatomy of the Eye
Visual axis Anterior cavity Cornea Posterior chamber Anterior chamber Edge of pupil Iris Suspensory ligament of lens Nose Corneal limbus Lacrimal punctum Conjunctiva Lacrimal caruncle Lower eyelid Medial canthus Lateral canthus Ciliary processes Lens Ciliary body Ora serrata Sclera Choroid Retina Posterior cavity Ethmoidal labyrinth Lateral rectus muscle Medial rectus muscle Optic disc Fovea Optic nerve Orbital fat Central artery and vein p. 572 Horizontal dissection of right eye 7
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Figure 17-6 The Pupillary Muscles
Pupillary constrictor (sphincter) Pupil Pupillary dilator (radial) The pupillary dilator muscles extend radially away from the edge of the pupil. Contraction of these muscles enlarges the pupil. The pupillary constrictor muscles form a series of concentric circles around the pupil. When these sphincter muscles contract, the diameter of the pupil decreases. Decreased light intensity Increased sympathetic stimulation Increased light intensity Increased parasympathetic stimulation p. 574 8
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Figure 17-5c The Sectional Anatomy of the Eye
Visual axis Anterior cavity Cornea Posterior chamber Anterior chamber Edge of pupil Iris Suspensory ligament of lens Nose Corneal limbus Lacrimal punctum Conjunctiva Lacrimal caruncle Lower eyelid Medial canthus Lateral canthus Ciliary processes Lens Ciliary body Ora serrata Sclera Choroid Retina Posterior cavity Ethmoidal labyrinth Lateral rectus muscle Medial rectus muscle Optic disc Fovea Optic nerve Orbital fat Central artery and vein p. 572 Horizontal dissection of right eye 9
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Figure 17-7a The Organization of the Retina
Horizontal cell Cone Rod Pigmented part of retina Rods and cones Amacrine cell Bipolar cells Ganglion cells LIGHT The cellular organization of the retina. The photoreceptors are closest to the choroid, rather than near the posterior cavity (vitreous chamber). p. 576 11
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Figure 17-7a The Organization of the Retina
Choroid Pigmented part of retina Rods and cones Bipolar cells Ganglion cells Retina LM 350 Nuclei of ganglion cells Nuclei of rods and cones Nuclei of bipolar cells The cellular organization of the retina. The photoreceptors are closest to the choroid, rather than near the posterior cavity (vitreous chamber). p. 576 12
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Figure 17-7b The Organization of the Retina
Pigmented part of retina Neural part of retina Central retinal vein Optic disc Central retinal artery Sclera p. 576 Optic nerve Choroid The optic disc in diagrammatic sagittal section. 13
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Figure 17-7c The Organization of the Retina
Optic disc (blind spot) Fovea Macula Central retinal artery and vein emerging from center of optic disc p. 576 A photograph of the retina as seen through the pupil. 14
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Figure 17-8 A Demonstration of the Presence of a Blind Spot
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Figure 17-9 The Circulation of Aqueous Humor
Cornea Pupil Anterior cavity Anterior chamber Posterior chamber Scleral venous sinus Body of iris Conjunctiva Ciliary process Lens Ciliary body Suspensory ligaments Sclera Pigmented epithelium Posterior cavity (vitreous chamber) Choroid Retina p. 578 18
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Figure 17-12a Image Formation
Light from a point at the top of an object is focused on the lower retinal surface. p. 580 21
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Figure 17-12b Image Formation
Light from a point at the bottom of an object is focused on the upper retinal surface. p. 580 22
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Figure 17-12c Image Formation
Light rays projected from a vertical object show why the image arrives upside down. (Note that the image is also reversed.) p. 580 23
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Figure 17-12d Image Formation
Light rays projected from a horizontal object show why the image arrives with a left and right reversal. The image also arrives upside down. (As noted in the text, these representa- tions are not drawn to scale.) p. 580 24
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Figure 17-11 Accommodation
For Close Vision: Ciliary Muscle Contracted, Lens Rounded Lens rounded Focal point on fovea Ciliary muscle contracted For Distant Vision: Ciliary Muscle Relaxed, Lens Flattened Lens flattened Ciliary muscle relaxed p. 579 25
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Figure 17-11a Accommodation
For Close Vision: Ciliary Muscle Contracted, Lens Rounded Lens rounded Focal point on fovea Ciliary muscle contracted p. 579 26
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Figure 17-11b Accommodation
For Distant Vision: Ciliary Muscle Relaxed, Lens Flattened Lens flattened Ciliary muscle relaxed p. 579 27
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Figure 17-13 Refractive Problems (Part 5 of 5).
Surgical Correction Variable success at correcting myopia and hyperopia has been achieved by surgery that reshapes the cornea. In photorefractive keratectomy (PRK) a computer-guided laser shapes the cornea to exact specifications. The entire procedure can be done in less than a minute. A variation on PRK is called LASIK (Laser-Assisted in-Situ Keratomileusis). In this procedure the interior layers of the cornea are reshaped and then recovered by the flap of original outer corneal epithelium. Roughly 70 percent of LASIK patients achieve normal vision, and LASIK has become the most common form of refractive surgery Even after surgery, many patients still need reading glasses, and both immediate and long-term visual problems can occur. p. 582
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Figure 17-14a Structure of Rods, Cones, and Rhodopsin Molecule.
Pigment Epithelium In a cone, the discs are infoldings of the plasma membrane, and the outer segment tapers to a blunt point. The pigment epithelium absorbs photons that are not absorbed by visual pigments. It also phagocytizes old discs shed from the tip of the outer segment. In a rod, each disc is an independent entity, and the outer segment forms an elongated cylinder. Melanin granules Outer Segment The outer segment of a photoreceptor contains flattened membranous plates, or discs, that contain the visual pigments. Discs Connecting stalks Inner Segment Mitochondria The inner segment contains the photoreceptor’s major organelles and is responsible for all cell functions other than photoreception. It also releases neurotransmitters. Golgi apparatus Nuclei Cone Rods Each photoreceptor synapses with a bipolar cell. Bipolar cell p. 583 LIGHT a Structure of rods and cones
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Figure 17-14b Structure of Rods, Cones, and Rhodopsin Molecule
In a rod, each disc is an independent entity, and the outer segment forms an elongated cylinder. Rhodopsin molecule Retinal Opsin Structure of rhodospin molecule. 36
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Figure 17-16 Photoreception (Part 8 of 8).
IN LIGHT ACTIVE STATE −70 mV 4 Dark current is reduced and rate of neurotransmitter release declines The reduction in the rate of Na+ entry reduces the dark current. At the same time, active transport continues to export Na+ from the cytoplasm. When the sodium channels close, the membrane potential drops toward –70 mV. As the plasma membrane hyperpolarizes, the rate of neurotransmitter release decreases. This decrease signals the adjacent bipolar cell that the photoreceptor has absorbed a photon. After absorbing a photon, retinal does not spontaneously revert to he 11-cis form. Instead, the entire rhodopsin molecule must be broken down into retinal and opsin, in a process called bleaching. It is then reassembled. Na + p. 585
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Figure 17-17 Bleaching and Regeneration of Visual Pigments.
On absorbing light, retinal changes to a more linear shape. This change activates the opsin molecule. 2 Opsin activation changes the Na+ permeability of the outer segment, and this changes the rate of neurotransmitter release by the inner segment at its synapse with a bipolar cell. Na+ Na+ 11-trans retinal Photon 11-cis retinal and opsin are reassembled to form rhodopsin. 6 Once the retinal has been converted, it can recombine with opsin. The rhodopsin molecule is now ready to repeat the cycle. The regeneration process takes time. After exposure to very bright light, photoreceptors are inactivated while pigment regeneration is under way. 3 ADP ATP Changes in bipolar cell activity are detected by one or more ganglion cells. The location of the stimulated ganglion cell indicates the specific portion of the retina stimulated by the arriving photons. Neuro- transmitter release enzyme 11-trans retinal Opsin 11-cis retinal Opsin Bipolar cell 4 After absorbing a photon, the rhodopsin molecule begins to break down into retinal and opsin. This is known as bleaching. 5 Ganglion cell The retinal is converted to its original shape. This conversion requires energy in the form of ATP. p. 586
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Figure 17-15 Cone Types and Sensitivity to Color.
100 Rods Red cones Blue cones Green cones 75 Light absorption (percent of maximum) 50 25 WAVELENGTH (nm) Violet Blue Green Yellow Orange Red p. 583
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Figure 17-20 The Visual Pathways
Combined Visual Field Left side Right side Left eye Right eye only Binocular vision only p. 589 The Visual Pathway Photoreceptors in retina Retina Optic disc Optic nerve (N II) Optic chiasm Optic tract Suprachiasmatic nucleus Diencephalon and brain stem Lateral geniculate nucleus Projection fibers (optic radiation) Visual cortex of cerebral hemispheres Superior colliculus Left cerebral hemisphere Right cerebral hemisphere 49
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