Exam 2 Vision 3 Flashcards
What is the total amount of space that can be viewed by the retina when the eye is fixated straight ahead?
Visual Field
What is the ability of the eye to distinguish between two nearby points.
–depends mainly on the spacing of the photoreceptors in the retina.
•Visual Acuity
- The __________ is the projection of the visual world onto the retina.
- The image of the target is reversed on the retina by the lens system.
visual field
Why dont we notice our blind spot?
–During binocular viewing, the monocular visual fields overlap such that each field overlays the contralateral blind spot.
–During monocular viewing, the missing part of the visual field is neurally filled-in.
What are the projections from the retina?
Optic nerve
Optic Chiasm
Optic tract
What exits the left and right eyes at the optic disks and passes through holes in the floor of the skull?
Optic nerve
What is the joining of the optic nerves of each eye just above the pituitary gland?
- The axons originating in the nasal retinas cross from one side to the other (decussation).
- This crossing of fibers allows us to see in three dimensions.
Optic Chiasm
What are the axons projecting from the optic chiasm toward specific regions of the brain?
Optic Tracts
•Remember that light from the right binocular zone falls on the left ______ hemiretina and the right _____ hemiretina.
Left temporal
right nasal
•Information from the right visual hemifield is sent to the ______ side of the brain.
left
At the lateral geniculate nucleus (LGN), inputs from the two eyes are kept _______
separate
In the right LGN, the right eye (ipsilateral) axons synapse in LGN cells in layers ________
The left eye (contralateral) axons synapse on cells in layers ________
2, 3 and 5
1, 4 and 6
–The right LGN receives information about the _________ visual field.
left
What are the two ventral layers of LGN?
What retinal ganglion cells project here?
–The two ventral layers, 1 and 2, the magnocellular layers, contain large neurons.
•M-type retinal ganglion cells project here.
What are these features of?
- have relatively large receptive fields.
- respond to stimulation of their receptive field centers with a transient burst of action potentials.
- are insensitive to differences in wavelength.
- have features just like M ganglion cells.
- are activated by only one eye (monocular).
Features of magnocellular LGN neurons:
What are the four dorsal layers of the LGN?
–The four dorsal layers, 3, 4, 5, 6,
- parvocellular LGN layers
- contain smaller cells
What type of retinal ganglion cells project in the dorsal LGN?
P-type retinal ganglion cells project here
What are these the features of?
- have relatively small, circular receptive fields.
- are activated only by one eye (monocular).
- respond to stimulation of their receptive field centers with a sustained increase in the frequency of action potentials.
- are very sensitive to differences in wavelength.
- have features just like P ganglion cells.
Features of parvocellular LGN neurons
•LGN cells project to the primary visual cortex (striate cortex) through the ________
optic radiation.
What are the three pathways from the retina to the visual cortex?
–Magnocellular pathway
–Parvocellular pathway
–Koniocellular pathway (not very well defined)
•Cells in the striate cortex that receive input from the ________________:
–have binocular receptive fields,
–sense brightness but not color,
–have direction selectivity which helps to analyze object motion
- move visual stimuli towards receptive field and then you see the response
- once they pass receptive field there is less stimulus
magnocellular pathway (M channel)
*nocturnal animals need to know which direction animal or prey is moving
•Cells in the striate cortex that receive input from the ____________:
–have binocular, rectangular receptive fields.
–are very sensitive to wavelength of light (red and green).
–are sensitive to stimulus orientation which helps to analyze object shape.
-as long as it is parallelly moved in receptor field you can see it
parvocellular pathway (P channel)
What are retinal projections where structures in the brain stem involved in orienting the eye toward a stimulus that initially appears in the peripheral field of vision.
- Output from the _______ goes to motor centers responsible for orienting behaviors.
- quick responses
- A small dark spot (fly or tasty treat?) moving at a given speed across the retina of a frog causes the frog to flick its tongue outward to capture the treat.
- A large dark shadow moving across the retina of the frog causes it to dive for cover.
- In primates the ____________ controls the automatic saccades that keep a steady image on the fovea of the retina.
superior colliculus
Describe the superior colliculus-blind spot
- Detection of stimulus and movement toward objects in the visual field even when visual perception is lost.
- Mediated by the visual pathway passing through the superior colliculus.
Name this retinal projection:
Internal biological clock
1) Synchronizes sleep/wake cycles among other biological rhythms.
2) These cycles are endogenous (internal).
3) External timing cues (zeitgebers) adapt the rhythm to the environment.
- sunlight, noise, social interactions, and alarm clocks
4) This clock can be reset.
- Jet lag, nocturnal employment.
•Regulates the timing of sleep but is not responsible for sleep itself.
Suprachiasmatic Nucleus
Name this retinal projection:
•Light reflex
–Light shining in one eye causes its pupil to constrict. It also causes the pupil to constrict in the other eye as well.
–This reflex is mediated by retinal ganglion cells that project to the pretectum.
–If the eyes do not respond in this manner, then damage to the midbrain is suspected.
Pretectum
Name this retinal projection:
- Synchronizes sleep and wakefulness with the daily dark-light cycle.
- The hypothalamus is responsive to day length for regulating circadian and seasonal rhythms.
Hypothalamus
What is the ventral visual pathway used for?
identifying objects
What is the dorsal visual pathway used for?
used for determining where an opject is located
-where it is in space
