Term
| What two areas of the body have the most amount of somatosensory & motor cortex dedicated to them? What is the reasoning behind this? |
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Definition
Lower face & hands
Lower face - need sensory feedback and lots of motor innervation for the complex patterns of speech we produce
Hands - used as tactile tools in our everyday environment; extremely useful and we need a high dexterity and range of motion in them |
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Term
| What is true of speech areas in the brain? Where are they located? |
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Definition
Speech areas of the brain tend to be lateralized to the L hemisphere
Broca's area = L frontal lobe
Wernicke's area = L temporal lobe |
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Term
| In experiment, what areas of the brain lit up when (1) a word was heard vs. (2) a word was seen |
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Definition
(1) When hearing word, Wernicke's area in temporal lobe lit up
(2) When seeing word, occipital lobe lit up (visual cortex) |
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Term
| What is the main function of the retina? |
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Definition
| Transducing light signals into neural signals |
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Term
| Where is the optic disc located in relation to the fovea? |
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Definition
| It is lateral to the fovea in each eye (i.e. it is on the temporal side of the fovea in both eyes) |
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Term
| Emmetropia vs. Myopia vs. Hyperopia |
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Definition
Emmetropia - normal focusing of light; light converges onto fovea
Myopia - near sighted; light converges before fovea
Hyperopia - far sighted; light converges after fovea |
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Term
| What is the ability of the lens to change its shape called? |
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Definition
Accommodation
Lose this ability with age |
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Term
| The axons of which cells leave the fovea at the optic disc? |
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Definition
| The axons of the retinal ganglion cells (it is their axons that form the optic nerve) |
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Term
| The axons of RG cells form which structures going into the CNS? |
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Definition
| Form the optic nerve, chiasm and tract |
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Term
| Why can we only perceive our blind spot if we have one eye open? |
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Definition
It is because the blind spot is lateral to the fovea in both eyes (different location in each eye); therefore when both eyes are open, one eye can compensate for the blind spot on the contralateral side
When only one eye is open, there is no compensation for the location of the optic disc, and the blind spot can be perceived |
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Term
| What is the thinnest area of the retina? What is the effect of this on vision in this area? |
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Definition
The thinnest area of the retina is the FOVEA (other neural elements are pushed ou fo the way at the fovea)
Because of this, can get the highest acuity vision at the fovea because there is the least amount of distortion of incoming light |
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Term
| Do photoreceptors have tonic release of NT? |
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Definition
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Term
| What always occurs to photoreceptors after they are hit by light? |
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Definition
| Photochemical reaction causes HYPERPOLARIZATION of the photoreceptor; this causes an alteration in the release of neurotransmitter at the synapse with the bipolar neuron (second order neuron) |
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Term
| What is the main job of photoreceptors in the retina? |
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Definition
| To convert light energy into a neural signal |
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Term
| Cells involved in VERTICAL integration pathway... |
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Definition
| Photoreceptor -> Bipolar Cell -> RG cell |
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Term
| Cells involved in HORIZONTAL integration pathway... |
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Definition
| Horizontal cell (outer plexiform layer) and amacrine cell (inner plexiform layer) |
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Term
| What are phylogenetically older, rods or cones? |
|
Definition
|
|
Term
|
Definition
120-130 million in retina
High sensitivity - scotopic (night) vision
Low acuity, achromatic vision
Saturate easily |
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Term
|
Definition
6-7 million
Low sensitivity, high acuity vision - photopic (day) vision
Chromatic (essential for color vision)
Saturate only in intense light |
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Term
| Difference between convergence in retina of RODS vs. CONES and the general effect of this... |
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Definition
Rods have a high degree of convergence (many rods converge onto one bipolar cell); this causes rods to be low acuity (hard to differentiate/separate signals), but high sensitivity
Cones have very little convergence; allows for high acuity (specific signal), but low sensitivity (need more light to activate) |
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Term
| Why is there not a 1:1 photoreceptor to bipolar cell ratio throughout the retina (like seen in fovea) so that visual acuity can be increased? |
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Definition
| This would mean that the entire retina was low sensitivity and the light needed to activate the bipolar cells would be too intense. |
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Term
| What is true of all photoreceptor-bipolar cell synapses? |
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Definition
| ALWAYS have tonic activity (release) of NT |
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|
Term
| What happens to NT release by the photoreceptor after it is struck by light? |
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Definition
| Hyperpolarization of photoreceptor ALWAYS causes less NT to be released (remember tonic nature of synapse) |
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|
Term
| Which retinal neural component has its own receptive field? |
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Definition
| The retinal ganglion cells (on/off center, off/on surround) |
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Term
| What happens to the bi-polar cell if it is depolarized vs. hyperpolarized after the photoreceptor is hit by light? |
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Definition
If depolarized -> ON center cell
If hyperpolarized -> OFF center cell |
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Term
| What neural element in the retina is responsible for the CENTER portion of the receptive field? |
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Definition
The bipolar cell
Is either on or off center depending on whether it depolarizes (on) or hyperpolarizes (off) in response to the photoreceptor |
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|
Term
| What is responsible for the SURROUND portion of the receptive field? |
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Definition
| The horizontal integration completed by the horizontal & amacrine cells of the retina |
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Term
|
Definition
| Occurs in levels of light in which both rods AND cones contribute |
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Term
| How are changes in light intensity conveyed to the brain? |
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Definition
ALWAYS by an increase in the # of action potentials
Since we have two separate "channels" (the two flavors of RG cells), can make it so that a change is always reflected by an INCREASE in AP firing |
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Term
| What is the normal effect of Glu on the on and off center bipolar cells? |
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Definition
Normally Glu will hyperpolarize the on center and depolarize the off center cells
Recall that with photoreceptor hyperpol. get decreased NT release, so ON center will be depolarized and OFF center will be hyperpolarized (when light strikes) |
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Term
| If off surround (on center) horizontal cells have light shone on them, what is their effect on the photoreceptor? |
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Definition
They will become hyperpolarized (because light is on, and they are off surround) and cause depolarization of the hyperpolarized photoreceptor
This increases NT release and causes hyperpolarization of the ON center bipolar cell |
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Term
| What are the two classes of retinal ganglion cells? |
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Definition
| Magnocellular and parvocellular |
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Term
|
Definition
Large axons = fastest pathway
Responsible for detecting changes in our environment; transient response to sustained illumination
Achromatic - driven mainly by ROD input
Large receptive fields, therefore LOW ACUITY |
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|
Term
|
Definition
Slower pathway (depends more on accuracy than speed)
Chromatic (wavelength tuning with cones)
High acuity w/ smaller receptive fields - deals with fine detailed discrimination |
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|
Term
| Hemi-retina divisions and cross over |
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Definition
Temporal - sees contralateral visual field, remains ipsilateral
Nasal - sees ipsilateral visual field, crosses over contralaterally at chiasm |
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Term
| What does crossing over of the nasal hemi-retina RG cell axons allow for? |
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Definition
| Allows for BINOCULAR PERCEPTION of the contralateral visual field (get input from both eyes to one hemisphere) |
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Term
| What does crossing over of the nasal hemi-retina RG cell axons allow for? |
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Definition
| Allows for BINOCULAR PERCEPTION of the contralateral visual field (get input from both eyes to one hemisphere) |
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Term
| What are 4 targets of the RG cell axons in the CNS? |
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Definition
LGN in thalamus (primary site of termination)
Hypothalamus (for circadian rhythm)
Pretectum (in midbrain for pupillary light reflex)
Superior Colliculus (in midbrian; for saccadic eye movements) |
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Term
| What is the main visual relay nucleus in the brain? |
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Definition
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|
Term
| Are the signals from the two eyes mixed in the LGN? |
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Definition
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|
Term
| Contralateral vs. ipsilateral eye input into LGN |
|
Definition
Layers 1, 4, 6 - CONTRALATERAL
Layers 2, 3, 5 - IPSILATERAL |
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|
Term
| Magno vs. Parvo input into LGN layers... |
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Definition
Magnocellular = Layers 1 & 2
Parvocellular = Layers 3-6 |
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|
Term
| Does signal integration occur in layer IV of the striate cortex? |
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Definition
| NO. Still only a relay area. Integration begins when information is transferred to layers 2/3, or 5/6 |
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Term
| What is the majority of the visual cortex devoted to and why? |
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Definition
| Majority is devoted to the fovea (macula); this is because of the high acuity vision that the fovea is capable of producing |
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|
Term
| Is the cortex a homogenous representation of the visual field? |
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Definition
| NO. Majority is devoted solely to the fovea. |
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Term
| Why must the axons going to the upper and lower banks of the striate cortex take different paths? |
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Definition
1) Due to the depth of the calcarine sulcus
2) Due to the presence of the lateral ventricles |
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|
Term
| Path of LGN upper bank axons |
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Definition
These represent the LOWER visual field
They travel dorsally and upwards deep to parietal cortex in the white matter to reach upper bank |
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|
Term
| Path of LGN lower bank neurons |
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Definition
These neurons represent the UPPER visual field
First travel rostrally, then come back around (Meyer's loop) to get down to lower bank |
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|
Term
|
Definition
|
|
Term
|
Definition
No binocular vision
Lose the lateral side of each visual field (lose nasal hemi-retina) |
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|
Term
|
Definition
|
|
Term
| With a unilateral lesion to the visual cortex, why is the fovea preserved in most scenarios? |
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Definition
1) So much of the visual cortex is devoted to the fovea it is difficult to completely wipe it out
2) The fovea is represented bilaterally (in both hemispheres) |
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Term
| Where does output from layers II/III and layers V/VI of the cortex travel, respectively? |
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Definition
II/III output - ASCENDING to higher up processing
V/VI output - DESCENDING to brain stem & SC |
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Term
| How do the receptive fields in layer IV differ from those seen in layer V in the visual cortex? |
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Definition
In layer IV, receptive fields have the center-surround (concentric) organization like what is seen in the RG cells
In layer V, receptive fields are more complicated, being oriented as line segments in specific orientations |
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|
Term
| What are two different occurrences which can cause a long cone to increase its firing frequency? |
|
Definition
1) Shine red light on it (560 nm)
2) Increase the luminance at ANY frequency |
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Term
| What is the main problem with the trichromatic theory? |
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Definition
| Cones cannot distinguish between increases in luminance and light of a certain wavelength because both cause an increase in firing frequency of the photoreceptor |
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|
Term
| At what cellular level does colour opponency occur? |
|
Definition
| At the level of the RG cells in the retina |
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|
Term
| What are the 3 defined channels as part of the Colour Opponent Theory? |
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Definition
Magnocellular - only detects luminance changes (ALL cones)
Parvocellular - NO luminance, only red-green colour (L + M cones)
Konicellular - little luminance; blue-yellow colour (S-(M+L)) |
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Term
| Two pieces of evidence for the trichromatic & colour opponent theories of colour vision? |
|
Definition
Hue Cancellation
After-Images |
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|
Term
|
Definition
| Have Purple light shining with its two constituent colours (Red and Green) |
|
|
Term
|
Definition
| EXAMPLE - Have Purple light shining with its two constituent colours (Red and Blue); when green is introduced, it cancels out the red and the purple is perceived as blue |
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|
Term
|
Definition
Happens when you stare at one colour because of ADAPTATION
Example - for RED, look at parvocellular pathway
When L cones > M cones (activity), then red is perceived; if M>L then green is perceived; if both equal then white is perceived
When we look at red light, there is more activity in L cones than M cones so we perceive red
But after a while looking, the cones adapt such that when a white background is shown, the L cones have a lower baseline activity than the M cones so we see green |
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Term
| In what areas of the visual pathway to V1 do we see concentric (center surround) visual fields? |
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Definition
| In the retina (RG cells), in LGN of thalamus, and in layer IV of V1 (primary visual cortex) |
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|
Term
| How are the line segment receptive fields seen in the layers of V1 formed? |
|
Definition
Based on the integration of concentric receptive fields to form some preferential line segment
"Simple cell" in layer II/III or V/VI sums input from concentric cells to form some oriented line segment that is its visual field (seen in the chunk of visual cortex) |
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Term
| Dorsal Extrastriate Pathway |
|
Definition
Receives magnocellular input from the retina (achromatic, transient, high speed, low acuity, detects change)
Known as ACTION pathway
Travels through to the PARIETAL CORTEX
Deals with SPATIAL RELATIONSHIPS of objects |
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|
Term
| Ventral Extrastriate Pathway |
|
Definition
Receives PARVOCELLULAR input from retina (colour, high acuity, slower, fine discrimination & detail)
Known as PERCEPTION pathway
Travels through to the inferotemporal cortex
Concerned with OBJECT RECOGNITION |
|
|
Term
| What two areas does V1 output go to through the extrastriate pathways? |
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Definition
| V4 (via ventral) and MT (via dorsal) |
|
|
Term
| Is columnar organization preserved in extrastriate cortex (V4/MT)? |
|
Definition
|
|
Term
| What receptive fields are seen in the MT and IT extrastriate cortices? |
|
Definition
MT - specific vectors of motion
IT - specific objects/faces |
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|
Term
| In slot task, what was seen in the different patients with dorsal/ventral stream lesions? |
|
Definition
Dorsal Lesion -> could identify angles of slot, but could not put card into slot (lack of action)
Ventral Lesion -> could put card into slot, but could NOT identify angles (lack of perception) |
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|
Term
| Consciousness of dorsal vs. ventral stream? |
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Definition
Dorsal - unconscious
Ventral - conscious (perception) |
|
|
Term
| Important visual structures in bottom-up vs. top-down control of attention? |
|
Definition
Bottom-up - thalamus, superior collic., V1
Top-down - fronto-parietal network (DORSAL stream) |
|
|
Term
| What are the two fundamental movements why we move our eyes? |
|
Definition
To stabilize eyes and compensate for self motion
To align the fovea with something of interest |
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|
Term
| What kind of head movements does the VO reflex compensate for? |
|
Definition
| High frequency head movement |
|
|
Term
| When will the VO reflex be rendered ineffective? |
|
Definition
With smooth, circular, constant velocity momentum changes
Also with slow frequency head movement |
|
|
Term
| Input for VO reflex vs. optokinetic reflex |
|
Definition
VO reflex - vestibular input from semicircular canals
Optokinetic reflex - full field visual motion |
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|
Term
| When is the optokinetic reflex used? |
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Definition
| Used when the input is full field visual motion, which only occurs if the VO reflex has adapted and been rendered ineffective (from slow frequency head movement/constant velocity in circular motion) |
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|
Term
| What kind of eye movements are more recently evolved? |
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Definition
| Those which align the fovea with a specific target (saccades, fixation, smooth pursuit, vergence) - because evolutionarily the fovea has developed more recently |
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|
Term
| What do saccadic eye movements allow us to do? |
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Definition
| Focus our fovea (attention) on the parts of a scene with the most significant visual information (allow us to inspect a scene) |
|
|
Term
| Difference between input for optokinetic reflex vs. smooth pursuit |
|
Definition
Optokinetic - full field visual motion
Smooth Pursuit - small target in visual field |
|
|
Term
| What are vergent eye movements? |
|
Definition
| Movement of the eyes in different directions |
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|
Term
| What functions to drive vergent eye movements? |
|
Definition
| Retinal disparity (difference in location of the image on the two retina); retinal disparity is derived from extrastriate areas in DORSAL stream |
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|
Term
| What kind of eye movements are intorsion/extorsion? |
|
Definition
They are completely INVOLUNTARY
They are driven by vestibular input (part of VO reflex) - done involuntarily to compensate for head movement |
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Term
| Why do the eyes always have a tendency to move back to center? |
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Definition
Because there is a net vector average of the passive forces exerted by the extraocular muscles in the center
Therefore the eye has a tendency to go back to center (need active force by muscles to keep it away from center) |
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Term
| Why dos tonic activity of a motoneuron increase as the position of an eye moves farther and farther away from center? |
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Definition
| Because it needs to exert an active force on the eye to keep it away from center (net vector avg of extraoc. muscles in center); therefore, farther from center, stronger the force needed |
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|
Term
| What are the two components to motoneuron discharge? |
|
Definition
Pulse -> eye velocity component
Tonic -> step; eye position component |
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Term
| In what two situations may nystagmus develop? |
|
Definition
1) Lesion to one of the vestibulocochlear afferents coming from the semicircular canals (CN VIII lesion)
2) Damage to the neural integrator (mismatch in velocity & position signals to the eyes) |
|
|
Term
| Structures of the Basal Ganglia |
|
Definition
CN + Putamen = STRIATUM
Putamen + GP = Lentiform Nucleus
GPe & GPi; SNpr & SNpc
STN
Input = striatum
Output = GPi, SNpr |
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|
Term
| What is true about all BG output synapses? |
|
Definition
| All BG output synapses use GABA as their NT AND all have TONIC activity |
|
|
Term
| Hyperdirect Pathway (Path & Net Effect) |
|
Definition
Cortex to STN to GPi/SNpr to Thalamus
Get increased inhibition on the thalamus (decrease excitability in thalamus & cortex by increasing BG output) |
|
|
Term
| Direct Pathway (Path & Net Effect) |
|
Definition
Cortex to Striatum to GPi/SNpr to Thalamus
Get decrease in BG output, exciting the Thalamus and Cortex (disinhibition of the thalamus) |
|
|
Term
| Indirect Pathway (Path & Net Effect) |
|
Definition
Cortex to Striatum to GPe to STN to GPi/SNpr to Thalamus
Get inhibition of cortex/thalamus by increasing BG output (more GABA released from SNpr/GPi) |
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|
Term
| Location and Description of Gaze Centers (Saccadic Control) |
|
Definition
PPRF - located in the PONS (next to abducens); location of HORIZONTAL gaze center
R iMLF - located in the MIDBRAIN (next to oculomotor); location of the VERTICAL gaze center |
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|
Term
|
Definition
| Movement of both eyes in the same direction at the same time (made possible by interneurons connecting contralateral abducens & oculomotor nuclei) |
|
|
Term
|
Definition
Bring motor command from PPRF to abducens nucleus for horizontal saccade
Synapse on motoneuron & interneuron in ipsilateral abducens; also synapse on inhibitory burst in PPRF
Generate the burst/eye velocity command |
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|
Term
|
Definition
Have somae in PPRF (like exc. burst)
Excitatory burst synapse w/ somae
Axons cross mid-line to contralateral abducens to inhibit contralateral LR muscle contraction |
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|
Term
| What kind of tonic activity is seen in excitatory burst neurons? |
|
Definition
| NONE. Cannot have tonic activity or else visual system would not function (need eyes to be stationary for visual system to function) |
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|
Term
| What is the main function of the omnipause neurons in saccadic control pathways? |
|
Definition
| Inhibit the excitatory AND inhibitory burst neurons at rest |
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|
Term
| What kind of tonic activity is seen by the omnipause neurons? |
|
Definition
| HIGH tonic activity (needed for potent inhibition of burst neurons in PPRF) |
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|
Term
| Tonic Neuron (Saccade Pathway) |
|
Definition
Present in different nucleus; part of NEURAL INTEGRATOR
Generates the position signal needed by motoneuron for eye movement (generates "step")
Synapse on same motoneurons as the burst neurons in the abducens |
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|
Term
| What can be said about the activity of omnipause neurons and the position of the eye? Compare this to the tonic activity of a motoneuron? |
|
Definition
Activity of omnipause neurons is INDEPENDENT of eye position -> tonic firing rate is constant no matter where the eye is positioned in the orbit
Tonic activity of the motoneuron is DEPENDENT on the eye position (higher tonic activity with more extreme positions) |
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|
Term
| What are the downstream effects of the bursts sent by the superior colliculus? |
|
Definition
| Inhibit the omnipause neurons AND activate the burst neurons (both excitatory and indirectly, inhibitory) |
|
|
Term
| What structure decides when you will make a saccade? |
|
Definition
|
|
Term
| Which gaze center does the superior colliculus send projections to? |
|
Definition
| BOTH the PPRF (horizontal) and the R iMLF (vertical) |
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|
Term
| What inputs can we use in the superior colliculus to drive eye movements? |
|
Definition
Top-down - from frontal eye field in frontal cortex
Bottom-up - visual input from the RG cells of the retina |
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|
Term
| Dopamine receptors in the striatum... |
|
Definition
D1 - in direct pathway; increase excitability to get more GABA release onto BG output; disinhibition of thalamus
D2 - in indirect pathway; get less GABA release onto GPe; net disinhibition of thalamus |
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|
Term
|
Definition
Input into putamen; output from GPi
Into VL, VA (thalamus)
Final targets = motor & premotor cortices |
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|
Term
|
Definition
Input into CN (body); output from SNpr
Into MD, VA (thalamus)
Final targets = frontal eye fields |
|
|
Term
|
Definition
Input into CN (head); output from GPi/SNpr
Into MD, VA (thalamus)
Final targets = prefrontal cortex |
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|
Term
|
Definition
Input into CN & Putamen; output from GPi/SNpr
Into MD. VA (thalamus)
Final targets = cingulate gyrus; orbital frontal cortex |
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