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Transcript of © 2015 Pearson Education, Inc. Figure 17-4a External Features and Accessory Structures of the Eye...
© 2015 Pearson Education, Inc.
Figure 17-4a External Features and Accessory Structures of the Eye
Gross and superficialanatomy of the accessory structures
Sclera
Lateral canthus
Eyelashes
Pupil
Palpebra
Palpebral fissure
Medial canthus
Lacrimal caruncle
Corneal limbus
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Figure 17-5b The Sectional Anatomy of the Eye
Cornea
Sclera
Neural part
Pigmented part
Fibrouslayer
Neural layer(retina)
Anteriorcavity
Posteriorcavity
Vascular layer(uvea)
Iris
Ciliary body
Choroid
Horizontal section of right eye
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Figure 17-5c The Sectional Anatomy of the Eye
Lacrimal punctum
Nose
Lens
Edge ofpupil
Visual axis
Anterior cavity
Posteriorchamber
Anteriorchamber
Lacrimal caruncle
Medial canthus
Ciliaryprocesses
Ciliary body
Ora serrata
Ethmoidallabyrinth
Medial rectusmuscle
Optic disc
Optic nerve
Central arteryand vein
Horizontal dissection of right eye
Orbital fat
Fovea
Lateral rectusmuscle
Posteriorcavity
Retina
Choroid
Sclera
Lateralcanthus
Lower eyelid
Conjunctiva
Corneal limbus
Suspensory ligament of lens
Iris
Cornea
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Figure 17-6 The Pupillary Muscles
Pupillary constrictor(sphincter)
Pupil
The pupillary dilatormuscles extend radially awayfrom the edge of the pupil.Contraction of these musclesenlarges the pupil.
Pupillary dilator(radial)
Decreased light intensityIncreased sympathetic stimulation
Increased light intensityIncreased parasympathetic stimulation
The pupillary constrictormuscles form a series ofconcentric circles around thepupil. When these sphinctermuscles contract, the diameterof the pupil decreases.
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Figure 17-5c The Sectional Anatomy of the Eye
Lacrimal punctum
Nose
Lens
Edge ofpupil
Visual axis
Anterior cavity
Posteriorchamber
Anteriorchamber
Lacrimal caruncle
Medial canthus
Ciliaryprocesses
Ciliary body
Ora serrata
Ethmoidallabyrinth
Medial rectusmuscle
Optic disc
Optic nerve
Central arteryand vein
Horizontal dissection of right eye
Orbital fat
Fovea
Lateral rectusmuscle
Posteriorcavity
Retina
Choroid
Sclera
Lateralcanthus
Lower eyelid
Conjunctiva
Corneal limbus
Suspensory ligament of lens
Iris
Cornea
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Figure 17-7a The Organization of the Retina
Amacrine cell
Horizontal cell Cone Rod
Pigmentedpart of retina
Rods andcones
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).
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Figure 17-7a The Organization of the Retina
Choroid
Pigmentedpart of retina
Rods andcones
Bipolar cells
Ganglion cells
The cellular organization of the retina. The photoreceptors are closest to the choroid, rather than near the posterior cavity (vitreous chamber).
Retina
Nuclei ofganglion cells
Nuclei of rodsand cones
Nuclei ofbipolar cells
LM 350
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Figure 17-7b The Organization of the Retina
Central retinal vein
Central retinal artery
Sclera
ChoroidOptic nerve
Optic disc
The optic disc in diagrammatic sagittal section.
Pigmentedpart of retina
Neural part of retina
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Figure 17-7c The Organization of the Retina
Fovea
Macula
A photograph of the retina as seen through the pupil.
Central retinal artery and veinemerging from center of optic disc
Optic disc(blind spot)
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http://www.nlm.nih.gov/medlineplus/ency/imagepages/19532.htm
http://www.uniteforsight.org/course/macular.php
© 2015 Pearson Education, Inc.
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
Lens
Scleral venous sinus
Body of iris
Conjunctiva
Ciliary body
Sclera
Choroid
Retina
Posterior cavity(vitreous chamber)
Anterior cavity
Anterior chamber
Posterior chamber
Ciliary process
Suspensoryligaments
Pigmentedepithelium
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Figure 17-12a Image Formation
Light from a point at the top of anobject is focused on the lowerretinal surface.
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Figure 17-12b Image Formation
Light from a point at the bottom ofan object is focused on the upperretinal surface.
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Figure 17-12c Image Formation
Light rays projected from a verticalobject show why the image arrivesupside down. (Note that the image isalso reversed.)
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Figure 17-12d Image Formation
Light rays projected from a horizontalobject show why the image arriveswith a left and right reversal. Theimage also arrives upside down. (Asnoted in the text, these representa-tions are not drawn to scale.)
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Figure 17-11 Accommodation
For Close Vision: Ciliary Muscle Contracted, Lens Rounded
Lens rounded
Ciliary musclecontracted
Focal pointon fovea
Lens flattened
Ciliary musclerelaxed
For Distant Vision: Ciliary Muscle Relaxed, Lens Flattened
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Figure 17-11a Accommodation
For Close Vision: Ciliary Muscle Contracted, Lens Rounded
Lens rounded
Ciliary musclecontracted
Focal pointon fovea
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Figure 17-11b Accommodation
Lens flattened
Ciliary musclerelaxed
For Distant Vision: Ciliary Muscle Relaxed, Lens Flattened
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Figure 17-13 Refractive Problems (Part 5 of 5).
Surgical Correction
Variable success at correcting myopia andhyperopia has been achieved by surgery thatreshapes the cornea. In photorefractivekeratectomy (PRK) a computer-guidedlaser shapes the cornea to exact specifications.The entire procedure can be done in less thana minute. A variation on PRK is called LASIK(Laser-Assisted in-Situ Keratomileusis). In thisprocedure the interior layers of the cornea arereshaped and then recovered by the flap of originalouter corneal epithelium. Roughly 70 percent of LASIKpatients achieve normal vision, and LASIK has become the mostcommon form of refractive surgery. Even after surgery, many patients still need reading glasses,and both immediate and long-term visual problems can occur.
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Figure 17-14a Structure of Rods, Cones, and Rhodopsin Molecule.
In a cone, the discs are infoldings of
the plasma membrane, and the outer
segment tapers to a blunt point.
In a rod, each disc is an independent
entity, and the outer segment forms
an elongated cylinder.
Discs
Connecting
stalks
Mitochondria
Golgi
apparatus
Nuclei
Pigment Epithelium
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.
Melanin granules
Outer Segment
The outer segment of a
photoreceptor contains
flattened membranous
plates, or discs, that
contain the visual pigments.
Cone Rods
Inner Segment
The inner segment contains
the photoreceptor’s major
organelles and is responsible
for all cell functions other
than photoreception. It also
releases neurotransmitters.
Each photoreceptor
synapses with a bipolar cell.
Bipolar cell
LIGHT
Structure of rods and conesa
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Figure 17-14b Structure of Rods, Cones, and Rhodopsin Molecule
In a rod, each disc is an independententity, and the outer segment formsan elongated cylinder.
Rhodopsinmolecule
OpsinRetinal
Structure ofrhodospin molecule.
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Figure 17-16 Photoreception (Part 8 of 8).
IN LIGHT
ACTIVE STATE
−70 mV
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 +
Dark current isreduced and rate ofneurotransmitterrelease declines
4
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Figure 17-17 Bleaching and Regeneration of Visual Pigments.
Na+
Na+
2Opsin activation changesthe Na+ permeability of theouter segment, and thischanges the rate ofneurotransmitter releaseby the inner segment atits synapse with a bipolar cell.
3
1On absorbing light, retinal changesto a more linear shape. This changeactivates the opsin molecule.
11-trans retinal
Photon
ADP ATP
6
11-cis retinal andopsin are reassembled
to form rhodopsin.
Opsin
Opsinenzyme
11-cisretinal
11-transretinal
Once the retinal has beenconverted, it can recombinewith opsin. The rhodopsinmolecule is now readyto repeat the cycle. Theregeneration processtakes time. After exposureto very bright light,photoreceptors areinactivated while pigmentregeneration is under way.
4
5
Neuro-transmitterrelease
Bipolarcell
Ganglioncell
Changes inbipolar cellactivity aredetected byone or moreganglion cells.The location ofthe stimulatedganglion cellindicates thespecific portionof the retinastimulated bythe arrivingphotons.
After absorbing aphoton, the rhodopsinmolecule begins tobreak down into retinaland opsin. This isknown as bleaching.
The retinal is converted toits original shape. Thisconversion requires energyin the form of ATP.
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Figure 17-15 Cone Types and Sensitivity to Color.
RodsRedcones
Bluecones
Violet Blue Green Yellow Orange Red400 450 500 550 600 650 700
WAVELENGTH (nm)
Greencones
100
75
50
25
0
Lig
ht
abso
rpti
on
(per
cen
t o
f m
axim
um
)
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Figure 17-20 The Visual Pathways
Combined
Left side Right side
onlyRight eye
onlyBinocular visionLeft eye
Retina
Optic disc
SuprachiasmaticnucleusDiencephalon
andbrain stem
The VisualPathway
Photoreceptorsin retina
Optic nerve(N II)
Optic chiasm
Optic tract
Lateralgeniculate
nucleus
Superiorcolliculus
Right cerebralhemisphere
Left cerebralhemisphere
Projection fibers(optic radiation)
Visual cortexof cerebral
hemispheres
Visual Field
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