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62 Cards in this Set
- Front
- Back
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Retinal Targets
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LGN
SC Pretectum Hypothalamus |
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LGN
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Lateral geniculate nucleus
The primary relay center for visual information received from the retina of the eye |
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SC
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Superior colliculus
Tectum - midbrain |
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Pretectum
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Edinger-westphal nucleus
Controls pupillary constriction |
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Hypothalamus
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Suprachiasmatic nucleus
Synchronization of diurnal rhythms with the day-night cycle |
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Wavelengths: short, long, visible
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Short = gamma rays
Long = radio waves Visible = 400 - 700 nm |
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Visual Acuity
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The capacity of the visual system to resolve fine spatial detail
Three factors: 1) The eye 2) The stimulus 3) The central visual pathways |
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Snellen Acuity
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Chart viewed at 20 feet
20/20 - viewer can detect 1 deg critical features 20/40 - you can see like normal people at 40 feet, lower acuity 20/15 - you can see like normal people at 15 feet, higher acuity |
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Legal Blindness
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When a persons best-corrected vision is 20/200 or worse
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Pupil
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Hole in the center
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Iris
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The color of your eye, regulates the size of the pupil
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Cornea
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A clear sheet in front of the pupil and iris
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Sclera
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The white part of the eye
The majority of the eyeball |
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Conjuctivita
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Inside of the eyelid
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How many extraocular eye muscles are there?
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6
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Optic Nerve
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Nerves gather, blind spot, no photoreceptors
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Eye Cross Section
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Lens, ciliary muscles, aqueous humor, vitreous humor, retina, fovea
*Diagram page 92 |
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Aqueous Humor
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Between the cornea and the lens
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Vitreous Humor
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Between the lens and the retina
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Fovea
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No arteries or veins
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Photoreceptors
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The two classic photoreceptor cells are rods and cones
Light sensitive cells |
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Bipolar Cells
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Connect rods&cones to ganglion cells
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Ganglion Cells
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Output cells of the retina
Form action potentials and send axons out of the retina The axon cells form the optic nerve |
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Amacrine and horizontal cells
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The two other basic cell types of the retina
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Nuclear Retinal Layer
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Where the cell bodies are
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Plexiform Layers
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Where the synapses and axons are
Six Layers: 1. Ganglion 2. Inner plexiform 3. Inner nuclear 4. Outer plexiform 5. Outer nuclear 6. Photoreceptor outer segments |
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The Retina
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A sheet of several layers of cell that lies against the back wall of the eye
Set up backwards to the way that you would expect it to be - light goes through processors then goes to the photoreceptors Epithelium pigment lines the back of the retina, against the photoreceptors |
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Epithelium
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Final light absorption
Not all animals absorb - cats reflect |
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Photoreceptors
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Have two major parts
1) Outer segment - the photosensitive part 2) Inner segment - contains cell body Two Types: Rods & Cons |
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Rods
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Light sensitive, used during dim lighting conditions (scotopic vision)
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Cones
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Color sensitive
Used during daylight conditions (photopic vision) Cones are much smaller than rods Diagram page 96 |
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The Nasal Retina
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Larger than the temporal retina
Contains the blind spot - no photoreceptors |
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Fovea
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Contains only cones
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How many rods and cones are in each retina?
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5 million cones
120 million rods |
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Rod and Cone Distribution
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Rods are concentrated in peripheral vision and outnumber cones 20:1
Cones are concentrated in the central visions fovea (the fovea contains no rods) No photoreceptors are found on the optic disk |
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The Blind Spot
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Receptors are on the back wall of the eye and block ganglion cell axons from leaving the eye
The blind spot has no receptors - it is where 1 million ganglion cell axons leave the eye to form the optic nerve The brain fills in the blind spot and blends left & right worlds into one |
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The Fovea
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A pit with the ganglion and bipolar cells pushed to the side so the light has an easier time striking the photoreceptors
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Phototransduction and The Eye
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Turning light into electricity
The photoreceptor outer segment is where light acts to create electricity Outer segment contains stacks of discs which contain visual pigment molecules *Diagram page 100 |
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Visual Pigment Molecules
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Two components:
1. Large protein called opsin 2. Small light sensitive molecule called retinal |
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Retinal
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Absorbs one photon of light
Retinal changes its shape, a process called isomerization |
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Rod Phototransduction
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The conversion of light energy into changes in membrane potentials
Membrane potential of rod outer segments is normally -30mV... this is caused by a steady influx of sodium ions Cyclic gyanosine monophosphate (cGMP) is produced in the cell and its action keeps the channels open Light reduces cGMP, causing the sodium channels to close This makes the membrane more negative/hyperpolarized |
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Photoreceptors and the light response/prolonged rod illumination
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Hyperpolarize in response to light!
Prolonged rod illumination causes cGMP levels to fall to a point whrre no more hyperpolarization is possible (saturated) |
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Rhodopsin
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The photopigment in rod outer segments
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Rod Saturation
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When rods are illuminated for too long and cGMP levels fall so no more hyperpolarization is possible
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Cone Phototransduction
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Three principle cone types: blue, green, red
Each type is sensitive to different ranges in the color spectrum Cones fire in different patterns to get all of the colors we see |
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Color Blindness
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2% of men lack red or green pigment... red-green color blind and are dichromats
6% have red or green pigments that do not absorb the same wavelengths as everyone else 8% of all males have colorblindness... it is an x linked chromosome! |
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How many degrees is the visual field? How many degrees can each eye see?
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Visual field = 180 degrees
Eye = 150 degrees |
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The Optic Chiasm
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Ganglion cell axons originating from nasal retina cross to the contralateral side
Axons from temporal retina do not cross, they stay ipsilateral |
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Which neurons cross over at the optic chiaam?
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Optic neurons from the nasal part of the eye
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Why do the nasal retina fibers cross?
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The left hemisphere sees the right side of your wold and vice versa
Therefore the left side of each retina must go to the left hemisphere and vice versa The temporal retina stays ipsilateral and nasal retina crosses to the contralateral side |
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What happens if you cut an optic nerve?
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:)
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What happens if you cut an optic chiasm?
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:)
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What happens if you cut an optic tract?
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:)
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Where is the primary visual cortex?
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Occipital lobe... very far posterior in the brain
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V1 Facts
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All neocortex, including V1, contain six layers
#1 is on the surface, #6 is the deepest It is 2-3mm thick V1 is the first place on the brain where cells receive signals from both eyes Info from both eyes merges in the primary visual cortex |
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Information Processing in V1
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Neurons are specialized to respond best to specific aspects of stimuli, such as orientation, movement and size
Specializations can be demonstrated physiologically, by recording from neurons |
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What information is being carried in the right optic nerve?
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Info from the right eye
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What information is being carried in the right optic tract?
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Info from the left visual field
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V1 Physiology
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Spots of light stimulate ganglion cells
Spots of light do little to stimulate neurons in V1 Sliding a slit of light across the visual field caused neurons to discharge V1 neurons respond best to bar-like stimuli with specific orientations |
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V1 Neurons
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Cortical neurons fire in response to specific features of the stimulus, such as orientation or direction of motion
These neurons are called feature detectors As we move farther from the retina, neurons will be found to only respond to more complex stimuli |
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Dorsal Stream
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Where or how pathway
Parietal cortex Spatial analysis Motion Visual control of movement |
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Ventral Stream
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What pathways
Temporal cortex Object and pattern identification |
