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30 Cards in this Set
- Front
- Back
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Describe the pupil and its purpose.
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The pupil is an aperture of sorts, which dilates or contracts naturally depending on light conditions. It allows light to pass through to the retina.
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What control the dilation or contraction of the pupil?
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Motor neurons in the brain stem.
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What is the name of the pupil's constriction in response to light, and what can this process's absence indicate?
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The pupillary light reflex. Its absence can indicate brain stem damage.
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What are the two most common drugs used to dilate the pupils?
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Phenylephrine drops, which stimulate norepinephrine a-receptors and
homatropine drops, which block muscarinic receptors. |
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Describe the iris and its function.
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The iris gives the eye color and contains muscles to expand or contract the pupils.
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Describe the lens and its function.
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The lens is a transparent structure behind the iris. It changes shape to aid focus.
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Describe the cornea and its purpose. How does it receive nourishment without blood vessels?
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The cornea is the transparent covering of the pupil. It bends light so that it converges on the retina. The cornea is nourished by the aqueous humor behind it and the tear film in front.
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Describe the sclera and its purpose.
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The sclera is the white of the eye and contains extraocular muscles for eyeball movement.
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Describe the ciliary muscles.
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They're connected to the lens and the sclera.
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What is the vitreous humor?
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The viscous liquid in the eye that help the eye maintain its shape.
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Describe the retina and its purpose.
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The retina, at the back of the eye, contains photoreceptor cells and is part of the CNS.
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What are the different parts of the retina?
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The optic disk, where the optic nerve exits. It doesn't contain photoreceptors (blind spot).
The macula, or the middle of the retina, for central vision. The fovea, a dark spot marking the center of the retina. The pigment epithelium, which contains melanin and absorbs the light not absorbed by the retina. The optic nerve, which relays visual info to the brain. |
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What is strabismus?
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The lack of coordination of the eyes. Esotropia: cross-eyed, exotropia: divergent gazee
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What is the name for a clouding of the lens, and how may it be treated?
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Cataract. Can be treated with a lens replacement.
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What is glaucoma?
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An increase in intraocular pressure, which can lead to optic nerve damage.
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What is the name for the loss of photoreceptors from peripheral vision in?
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Retinitis pigmentosa.
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What is the name for the loss of photoreceptors from the middle and out?
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Macular Degeneration
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How does information flow from the retina?
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The photoreceptors relay information to the bipolar cells, which in turn signal the ganglion cells, which tell the brain.
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What can modify the activity along the retina -> brain pathway?
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The horizontal and amacrine cells, which go between the junctions of the photoreceptors and the bipolar cells, then the bipolar and the ganglion cells, respectively.
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What happens to photoreceptors in the dark, and what is this called?
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The dark current:
cGMP gated sodium channel is activated, which somewhat depolarizes the membrane (about -30 mV instead of -70mV) with an inward sodium movement. |
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What does the dark current trigger?
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The release of glutamate from the photoreceptors onto bipolar cells. There, glutamate can either cause depolarization (AMPA) or hyperpolarizing (G-protein coupled receptors).
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What are the two divisions of bipolar cells based on the dark current?
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OFF: depolarized, excited by light being off, receivees more excitatory glutamate
ON: hyperpolarized, excited by light, less glutamate released to inhibit it. |
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The areas of the retina in which light changes cells' membrane potentials (either depolarizing or hyperpolarizing) are called ___ ___. There's a ___ ___ ___, where photoreceptors act directly on bipolar cells. There is also a ___ ___ ___, with photoreceptors providing input to bipolars indirectly via ___ ___.
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The areas of the retina in which light changes cells' membrane potentials (either depolarizing or hyperpolarizing) receptive fields. There's a receptive field center, where photoreceptors act directly on bipolar cells. There is also a receptive field surround, with photoreceptors providing input to bipolars indirectly via horizontal cells.
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What is the function of rods? Are they more or less sensitive than cones?
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The visual pigments called rod cells are used for night vision, and are most highly concentrated in the periphery of the retina. They're more sensitive than cones (1 photon alters membrane potential!).
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What "active ingredient" do rods contain?
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They contain rhodopsin.
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What makes up rhodopsin, and how does rhodopsin function?
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A protein (opsin) and a chromophore (Retinal). Opsin has 7 membrane-spanning regions. Retinal is a derivative of vitamin A. When light hits retinal, it changes shape (the only light-dependent step of vision) This change causes a conformational change in the opsin.
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What does a change in the opsin of rhodopsin cause?
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It activates the visual g-protein (transducin), which activates a phosphodiesterase (PDE) enzyme. PDE breaks down cGMP, lessening sodium entry = hyperpolarization. Light, then, causes a lesser release of glutamate from photoreceptors.
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Which photoreceptors produce color vision, and how are these different from the other type?
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Cones. They're different from rods because their rhodopsin has a different opsin protein.
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What are the distinctions among ganglion cells?
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M. cells have large receptive fields with low resolution. These are most senstitive to movement.
P. cells have small receptive fields with fine detail discrimination. Also, ON vs. OFF, ON reacting to light. |
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Describe parallel processing and give examples.
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The processing of information in parallel: input from two eyes - depth, ON/OFF cells - light/dark, M cells/P cells - different perspectives, P cells and non-M/non-P cells carry out separate color processing.
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