Chapter Opener 15
554-575
Vision:
Describe the structural components of the eye
Explain the concepts of refraction, image
formation, accommodation
Describe the principal refraction abnormalities
Describe the processing of visual signals in the
retina
Describe the neural pathway for vision
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Eyebrows
•
•
•
•
Coarse hairs that overlie the supraorbital margins
Functions include:
– Shading the eye
– Preventing perspiration from reaching the eye
Orbicularis muscle – depresses the eyebrows
Corrugator muscles – move the eyebrows medially
Palpebrae (Eyelids)
•
•
•
•
Protect the eye anteriorly
Palpebral fissure – separates eyelids
Tarsal plates of connective tissue support the eyelids internally
Levator palpebrae superioris – elevates the upper eyelid
not responsible for terms except
__
Conjunctiva
•
Transparent membrane that:
– Lines the eyelids as the palpebral conjunctiva
– Covers the whites of the eyes as the ocular conjunctiva
– Lubricates and protects the eye. What is conjunctivitis?
___
not responsible for terms except
Figure 15.2 The lacrimal apparatus.
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Figure 15.3 Extrinsic eye muscles.
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Figure 15.4 Internal structure of the eye (sagittal section).
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Figure 15.5 Pupil constriction and dilation.
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Figure 15.6 Microscopic anatomy of the retina.
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The Retina: Ganglion Cells and the Optic Disc
•
•
Ganglion cell axons:
– Run along the inner surface of the retina
– Leave the eye as the optic nerve
The optic disc:
– Is the site where the optic nerve leaves the eye
– Lacks photoreceptors (the blind spot)
Figure 15.8 Circulation of aqueous humor.
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Figure 15.10 The electromagnetic spectrum and photoreceptor sensitivities.
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Figure 15.11 Refraction.
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Figure 15.12 Light is focused by a convex lens.
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Figure 15.13 Focusing for distant and close vision.
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Figure 15.14 Problems of refraction.
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Figure 15.15 Photoreceptors of the retina.
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Figure 15.16 The formation and breakdown of rhodopsin.
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Figure 15.17 Events of phototransduction.
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Figure 15.18 Signal transmission in the retina.
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Na+
Ca2+
1 Photoreceptor
depolarized
Photoreceptor
cell
–40 mV
–70 mV
Bipolar
cell
Ganglion
(a)
1 Photoreceptor
hyperpolarized
Light
(b)
Na+
Ca2+
1 Photoreceptor
depolarized
Photoreceptor
cell
–40 mV
–70 mV
2
Ca2+
2 Ca2+ channels
closed
Ca2+ channels
open
Bipolar
cell
Ganglion
(a)
1 Photoreceptor
hyperpolarized
Light
(b)
Na+
Ca2+
1 Photoreceptor
depolarized
Photoreceptor
cell
–40 mV
–70 mV
2
Ca2+
3
Ca2+ channels
open
2 Ca2+ channels
closed
Neurotransmitter
released
3 No neurotransmitter
released
Bipolar
cell
Ganglion
(a)
1 Photoreceptor
hyperpolarized
Light
(b)
Na+
Ca2+
1 Photoreceptor
depolarized
Photoreceptor
cell
–40 mV
–70 mV
2
Ca2+
3
Ca2+ channels
open
2 Ca2+ channels
closed
Neurotransmitter
released
3 No neurotransmitter
released
4 IPSP in bipolar
cell
Bipolar
cell
4 No IPSP, bipolar
cell depolarizes
Ganglion
(a)
1 Photoreceptor
hyperpolarized
Light
(b)
Na+
Ca2+
1 Photoreceptor
depolarized
Photoreceptor
cell
1 Photoreceptor
hyperpolarized
Light
–40 mV
–70 mV
2
Ca2+
3
Ca2+ channels
open
2 Ca2+ channels
closed
Neurotransmitter
released
3 No neurotransmitter
released
4 IPSP in bipolar
cell
Bipolar
cell
4 No IPSP, bipolar
cell depolarizes
5 No neurotransmitter
released
Ganglion
(a)
(b)
Ca2+
5 Neurotransmitter
released
Na+
Ca2+
1 Photoreceptor
depolarized
Photoreceptor
cell
1 Photoreceptor
hyperpolarized
Light
–40 mV
–70 mV
2
Ca2+
3
Ca2+ channels
open
2 Ca2+ channels
closed
Neurotransmitter
released
3 No neurotransmitter
released
4 IPSP in bipolar
cell
Bipolar
cell
4 No IPSP, bipolar
cell depolarizes
5 No neurotransmitter
released
6 No EPSP in
ganglion cell
5 Neurotransmitter
released
6 EPSP in
ganglion cell
Ganglion
(a)
Ca2+
(b)
Na+
Ca2+
1 Photoreceptor
depolarized
Photoreceptor
cell
1 Photoreceptor
hyperpolarized
Light
–40 mV
–70 mV
2
Ca2+
3
Ca2+ channels
open
2 Ca2+ channels
closed
Neurotransmitter
released
3 No neurotransmitter
released
4 IPSP in bipolar
cell
Bipolar
cell
4 No IPSP, bipolar
cell depolarizes
5 No neurotransmitter
released
Ca2+
5 Neurotransmitter
released
6 No EPSP in
ganglion cell
6 EPSP in
ganglion cell
7 No action
potentials
7 Action
potentials
Ganglion
(a)
(b)
Figure 15.19 Visual pathway to the brain and visual fields, inferior view.
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Visual Pathways
•
•
Axons of retinal ganglion cells form the optic nerve
Medial fibers of the optic nerve decussate at the optic chiasm
•
•
Most fibers of the optic tracts continue to the lateral geniculate body of the thalamus
Other optic tract fibers end in superior colliculi (initiating visual reflexes) and pretectal nuclei
(involved with pupillary reflexes)
Optic radiations travel from the thalamus to the visual cortex
A small subset of visual fibers contain melanopsin (circadian pigment) which:
– Sets daily biorhythms, biological clock
•
•
Table 15.1 Comparison of Rods and Cones
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