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51 Cards in this Set

  • Front
  • Back
2 major visual pathways:
1. Geniculostrate
2. Retinotectal
Function of Geniculostriate system:
Conscious visual perception
Function of Retinotectal system:
-Control of eye movments
-Visual attention
Steps in Geniculostriate pathway:
1. Retina
2. Lateral geniculate nucleus
3. Striate cortex
4. Extrastriate cortex
Steps in Retinotectal pathway:
1. Retina
2. Superior colliculus
3. Pulvinar
4. Extrastriate cortex
What carries optic impulses from the lateral geniculate nucleus to the primary visual cortex?
Optic radiations
What carries optic impulses from the retina to the optic chiasm?
Optic nerve
What carries optic impulses from the optic chiasm to the lateral geniculate nucleus?
Optic tract
What visual structure is located near the temporal lobe?
Myers' loop
What does damage to myers' loop cause?
Restricted visual field defects
What is damage to myers' loop a common side effect of?
Temporal lobectomies performed for relieving temporal lobe epilepsy.
How many pathways are there total in the visual system?
5
What are the visual pathways?
1. Geniculostriate
2. Retinotectal
3. Pupillary constriction
4. Pupillary dilation
5. Accommodation
What are the steps in the pupillary constriction pathway?
1. Retina
2. Pretectum
3. Edinger-westphal nucleus and Ciliary ganglion
4. Constrictor pupillae muscle
What are the steps in the pupillary dilation pathway?
1. Retina
2. Spinal cord
3. Superior cervical ganglion
4. Dilator pupillae muscle
What are the steps in the accommodation pathway?
1. Cortex
2. Pretectum
3. Ciliary ganglion
4. Ciliary muscle
What is the function of the pupillary control system?
To control the intensity of light entering the eye
What is Consensual light reflex and which pathway is it seen in?
The connection of the Constrictor pupillae pathway at the posterior commissure - results in both eyes constricting even if you only shine light in one.
What does the dilator pathway recieve input from?
1. SNS
2. Arousal systems - emotion
Function of accomodation:
focusing of the eye
What happens when the ciliary muscle contracts?
The eye lens thickens
How is the lens normally?
Flat; like a trampoline.
What 3 things occur reflexively when attention is directed to CLOSE things?
1. Convergence of the 2 eyes
2. Ciliary muscles contract to increase optical power
3. Pupils constrict to increase the depth of field.
How is accomodation different from the pupillary reflex?
-Can be voluntarilly controlled
-Only sensory reflex to involve the cortex
-Regulated by negative feedback
Why does the accomodation pathway involve cerebral cortex?
To determine if objects seen are blurry.
Why is the accomodation reflex regulated by negative feedback?
to automatically adjust the focal power of the lens.
What is the difference between the striate cortex and extrastriate cortex?
Striate - in calcarine fissure
Extrastriate - around it
How is the image projected onto the retina?
upside down and backwards
Where does light from the left of our body go?
To the right halves of each retina -> to the ipsilateral LGN
So light from the left sides of each retina goes to
the LEFT lgn - even though it's the left side of the left retina and right retina
So which side of the brain processes info frmo the right half of our visual field?
The left side
Where is the Pulvinar?
in the thalamus
Again what are the 3 reflexes involved in viewing close up objects?
1. Convergence
2. Constriction of pupils to increase depth of field
3. Contraction of ciliary muscles to thicken lens
How is the retinal visual system arranged?
Retinotopically organized
What is a visual receptive field?
The area of visual receptors to which a cell responds
What is the visual field of the left half of the visual cortex?
The right half of the visual field - flipped upside down.
How do we know that the visual cortex is retinotopically organized?
Because certain neurons respond only to stimuli within a restricted portion of the visual field, and cells that respond to adjacent stimuli are clustered together physically at each level of the system.
How does the retinotopic arrangement of the visual neurons behave as you ascend the hierarchy into central projections?
It is preserved.
What is the receptive field of all ganglion cells together?
The entire visual field
What is general topography?
The geometric arrangement of surface features
What creates the visual field topography?
The image of the visual field created by the cornea and lens and projected onto the retina reversed and flipped
Why do the nasal fibers cross in the optic chiasm?
So that the fibers from those retinal fields stay together - left half of visual field hits right halves of retinas and both go to the same right hemisphere.
What happens to retinotopy in the lateral geniculate nucleus?
It is preserved!
What is the resulting map of the visual field like when it reaches the primary visual cortex? (2 ways)
Distorted
In what 2 ways is the visual map distorted when it reaches the primary visual cortex?
1. Up is down and left is right!
2. The area of cortex representing the fovea is greatly expanded relative to the periphery (like homunculis)
Why is the region of cortex containing neurons for the fovea magnified?
B/c the fovea is for better acuity which means more info has to be processed which requires more cortical tissue.
How much of the visual FIELD is the fovea?
Small relative to the entire field
What is eccentricity?
The distance from the center of gaze
What happens to the # of ganglion cells for your vision as you look further into the periphery (increase eccentricity)?
They decrease
So how do lesions of visual cortex vary in terms of severity?
-Foveal representing neuron lesions are quite severe
-Periphery representing neuron lesions can go unnoticed
What is the best type of vision?
Macular vision