Unit3_VisualSystem Flashcards
Wavelength = color \_\_\_\_ = 420 nm \_\_\_\_ = 530 nm \_\_\_\_ = 560 nm
Wavelength = color Blue = 420 nm Green = 530 nm Red = 560 nm
Retina: at back of inner eye - receptive organ of eye.
Output neurons = retinal ganglion cells → group together at __________ → form optic nerve
optic disc
Are there photoreceptors at the optic disc?
No!!!
No photoreceptors at optic disc = blind spot
Outline the path of cells/neurons once light hits the Photoreceptor?
Photorceptor → Bipolar Cells → horizontal cells → Ganglion Cells → optic nerve
_____ : mediate color vision, concentrated in fovea, work well only in bright light
Cones
_____ : color insensitive, work best in dim light
Rods
What cells of the retina mediate receptive field surround?
Horizontal cells
What NTs are released by Horizontal cells?
GABA; H-Cells are INHIBITORY
Photons of light are absorbed by what vitamin?
Vitamin A
What is the end goal of phototransduction with regards to the photoreceptor?
decrease cGMP → close Ca2+ channels
Does light depolarize or hyperpolarize photoreceptors?
HYPERpolarize
In the retina, what cells are the only cells that can make an AP?
Ganglion Cells.
All other communicate by graded changes in membrane potential which alters the rate of exocytosis of NT.
The following are the rules w.r.t. retina cells.
- ) Photoreceptors are ____1____ by light → less NT released
- ) Photoreceptors release ____2____,
- ) Bipolar cells ALWAYS make ____3____ synapses on ganglion cells
- hyperpolarized
- glutamate; BUT…bipolar cells can either be excited (OFF center) or inhibited (ON center) by glutamate (due to different receptor types)
- excitatory
Which type of ganglion cells are excited by light shining in their centers, inhibited by light in periphery?
On Center Ganglion Cells
ganglion cells: inhibited by light shining in their centers, excited by light in periphery
Off-Center Ganglion Cells
What is the key determinant in receptive field type of ganglion cells?
Depends on type of receptor on bipolar cells
on or off
Color-opponent ganglion Cells:
____1____ cells in fovea connected directly to one kind of cone in field center, and indirectly (via ____2____ cells) to cones with a different color preference in field surround.
- Bipolar
2. Horizontal
Color-opponent ganglion Cells:
Bipolar cells in fovea connected ____1____ to one kind of cone in field center, and ____2____ (via horizontal cells) to cones with a different color preference in field surround.
(ans: directly or indirectly)
- directly
2. indirectly
What is the pupillary eye reflex?
shine light in one eye, muscles in iris contract (pupil smaller) → consensual constriction in other eye
Pupillary eye reflex:
Light → AP in ganglion cells → ____1____ gets excitatory input from BOTH eyes → synapse in BOTH _____2_____ nuclei (R and L) → excite ____3____ ganglion cells (preganglionic parasympathetic motor neurons) → excitation of muscles in BOTH irises
- Pretectum
- Edinger-Westphal nuclei
- ciliary ganglion cells
Central Visual Pathway:
→ _______: important for pupillary eye response.
Pretectum
Central Visual Pathway:
→ ______________ : important for visceral functions of day/night cycle.
Suprachiasmatic nucleus of hypothalamus
Central Visual Pathway:
→ ___________ : coordinates head and eye movements.
Superior colliculus
The RIGHT lateral geniculate nucleus will see which side of the visual world?
LEFT!!!
LGN represents CONTRALATERAL visual field.
**Gets input from both eyes, but eye origin remains separate in LGN layers. (Think hypercolumn)
Is there bionocular interaction in the LGN?
NO!!!!
Where do the ganglion cells axons end in the visual pathway?
LGN
After LGN, axons involved in visual processing fan out to visual cortex in white matter tracts called what?
optic radiations
How man layers is the LGN comprised of and describe the interaction of the layers and their nerve tracts?
No binocular and no DIRECT interaction between eyes at the level of the LGN.
The 6 layers of the LGN:
Layers 1, 4, 6 → ____1____ eye
Layers 2, 3, 5 → ____2____ eye
(which side?)
- Contralateral Eye; (axons decussated at chiasm)
2. ipsilateral eye
Which layer(s) of the LGN recieves input from magnocellular ganglion cells?
Layers 1 & 2
Which layer(s) of the LGN recieves input from parvocellular ganglion cells?
Layers 3 thru 6
What type of vision is the Magnocellular system responsible for?
spatial vision, motion and depth.
low acuity, large receptive, responsive to motion, no color vision.
What type of vision is the Parvocellular system responsible for?
object vision, color, details and form.
High acuity, small receptive field, not responsive to motion, color vision (input from cones)
Is one of the functions of the Magnocellular system color vision?
NO!
Are cones ~ with Parvocellular or Magnocellular ganglionic cells?
Parvocelular
T/F?
Both the Magnoceullar and Parvocellular systems established in retina, remain segregated at LGN, and travel in separate, but parallel pathways through visual cortex.
TRUE!
Lesions in what tracts will result in the following visual deficits?:
- ) _______ deficit → no information from right eye
- ) _______ deficit → no information from nasal portion of each retina
- ) _______ deficit → no info from left visual field
- ) _______ deficit → deficit in upper contralateral quadrant
- ) R optic nerve deficit
- ) Optic chiasm deficit
- ) R. optic tract deficit
- ) R. optic radiation deficit
Visual cortex: area 17, above and below ________ fissure of occipital lobe
calcarine
The visual cortex is what Boardmann area?
B.A. 17
Describe Line Orientation:
Line orientation: lines in visual field lie in different rays of pinwheels.
All cells in a vertical column are sensitive to same orientation.
Orientation column pinwheels spin out over cortical surface, interconnected with neighboring hypercolumns
______________: requirement that dissimilar dimensions (e.g. color and form) must be analyzed by separate, but parallel, neural systems
Parallel processing
______________: use successive synaptic integrations of highly specific synaptic inputs to construct higher and higher levels of representation of the retinal image until eventually we have cells that respond only to the complete form of an objec
Hierarchical processing: use successive synaptic integrations of highly specific synaptic inputs to construct higher and higher levels of representation of the retinal image until eventually we have cells that respond only to the complete form of an objec
What cells in the ventral pathway cares about color only, don’t care about shape, get input from color-opponent neurons
Blob cells
What are the 2 primary parallel pathways?
Dorsal pathway
Ventral pathway
Which primary parallel pathway travels from V1 dorsally to parietal lobe?
Dorsal Pathway
Which primary parallel pathway travels ventrally from V1 to temporal lobe?
Ventral pathway
Which primary parallel pathway is responsible for spatial vision?
Dorsal Pathway;
Spatial vision - Motion, depth perception, “WHERE” pathway
Which primary parallel pathway is responsible for object recognition?
Ventral pathway;
Object recognition - color, form, pattern vision, “WHAT” pathway
___________ cells: responsive to lines with certain orientations
Cortical simple cells;
Cells with an ON/OFF area that is a narrow line at some preferred orientation that is flanked on each side by OFF/ON areas.
Max stimulation by narrow line of light covering all ON areas.
Tightly tuned within a few degrees of its best orientation.
Cells in the same penetration show same orientation selectivity.
Generated by several overlapping LGN and ganglion cells that converge on one cortical cell in area V1.
____________ cells: receptive fields like simple cells but they abstract for position.
Cortical complex cells;
Line or edge can be anywhere within receptive field and these cells like to see lines or edges moving across the field.
Generated by excitatory synapses onto complex cells by convergence of several simple cells whose positions are slightly offset.
What type of cells receive input from LGN from both eyes?
Binocular Cells.
- Receptive fields of two eyes are identical in orientation, region of retina, width, and on/off organization
- Found at borders of ocular dominance columns.
- Mediate depth perception - select cells fire when object is certain distance away.
Strabismus: ?
Strabismus: one extraocular muscle (medial rectus) cut, lateral deviation of one eye
Ocular dominance:?
Ocular dominance: a measure of relative synaptic input to a cell from each eye
Types of eye movements involves:
tracking (to keep an object on the fovea)
Smooth Pursuit
Types of eye movements involves:
rapid, ballistic (to bring an object onto the fovea)
Saccades
Types of eye movements involves:
combination of pursuit and saccades
4) Vergence: moving the fovea to an object close (convergence) or farther away (divergence)
Vestibular Ocular Reflex (VOR) and Optokinetic Nystagmus (OKN)
Types of eye movements involves:
moving the fovea to an object close (convergence) or farther away (divergence)
Vergence
___________ nuclei: contain motor neurons for medial rectus, inferior and superior rectus, and inferior oblique muscles
Oculomotor (III) nuclei
___________ nuclei: contain motor neurons innervating superior oblique
Trochlear (IV) nuclei
____________ nucleus: contain motor neurons for lateral rectus muscle
Abducens (VI)
Lateral and medial recti → moves he eye how?
horizontal rotation
Superior and inferior rectus → moves he eye how?
vertical displacement
Superior and inferior oblique → moves he eye how?
rotation about visual axis, and some vertical movement
What is a Conjugate vs. Vergence Eye movement?
Conjugate Movements: eyes move same amount in same direction.
Vergence Movements: eyes moving in opposite directions.
What are 2 examples of Conjugate Movements?
- ) VOR: eyeball rotation precisely opposing head rotation
- ) Optokinetic nystagmus: rhythmic pattern of saccades and tracking movements - visually evoked nystagmus due to a moving visual stimulus
- Can be fast (saccades), or slow (tracking movements)
- Elicited by visual and vestibular inputs
What is an example of Vergence Movements of the eyes?
Near Reflex: both eyes town nasally to focus on near object.
- Both medial recti contract → pull eyes nasally
- Pupils constrict to increase depth of field
- Ciliary muscle contract → lens becomes fatter (for focus on near object)
All motor neurons and preganglionics in _________ nuclei, driven by visual input to association areas of visual cortex
oculomotor
(what type of eye movement): rapid eye movement that brings eyes to a predetermined target or position
Saccade
What is the Pattern generator for horizontal saccades called?
Paramedian Pontine Reticular Formation (PPRF) (near abducens nucleus)
Horizontal saccades driven CONTRALATERALLY - saccade to left driven by activity in right frontal eye field
What are the two important control center for saccades?
cortex and superior colliculus
Frontal eye field, anterior to head representation in motor cortex, can activate saccades via what two pathways?
- ) Direct to reticular formation
2. ) Via superior colliculus to reticular formation
Damage what? → saccades less accurate, occur less often, but still happen
superior colliculus
Damage to what? → TEMPORARY loss of ability to generate saccades
frontal eye field
Damage ______ & ______ → permanent loss of ability to make saccades.
superior colliculus and frontal eye field
Stroke in what? → “Blind sight response” = light flashed in dark room, eyes foveate to light, but the say they didn’t see anything → superior colliculus still drives saccade
visual cortex
What is the “blind slight response”?
light flashed in dark room, eyes foveate to light, but the say they didn’t see anything → superior colliculus still drives saccade
Parietal Eye Field (PEF)= ____1____ direction of saccade.
Frontal Eye Field (FEF)= ____2____ generated saccade
- reflexive
2. voluntarily
Where are the High Centers of visual processing and what do they do?
in frontal cortex provide planning inhibition, and coordination.
Name the High Centers? (4)
- ) Dorsolateral Prefrontal Cortex = DLPC
- ) Supplementary Eye Fields = SEF
- ) Substantia Nigra (Pars Reticulata) = SNPR
- ) Caudate Nucleus = CN
What does the Dorsolateral Prefrontal Cortex (DLPC) do?
Inhibits reflex saccades, provides advanced planning of saccades
What does the Supplementary Eye Fields (SEF) do?
Coordinates saccades with body movement
What does the Substantia Nigra (Pars Reticulata) = SNPR, do?
Inhibits superior colliculus
What does the Caudate Nucleus do in terms of visual processing?
Inhibits substantia nigra pars reticulata;
CN inhibition of SNPR → activation of SC
What is Internuclear Ophthalmoplegia, and what is its cause?
- Caused by MLF damage resulting in disconnection in the coordination of medial and lateral recti during horizontal gaze movements.
- Common in patients with MS
What is nystagmus?
aka: vestibular nystagmus
- Sawtooth movement of eyes, slow ramp opposite to head rotation, fast saccade to center of eye position
Presbyopia: ?
results when eye progressively loses ability to focus on near objects.
- Caused by natural aging as lens becomes less flexible
- Around age 40-50 years
- Treatment with simple magnifying lenses or bifocals can help improve near vision
____________: optical power of eye is too large and causes light to focus in front of the retina
Nearsightedness
____________ : optical power of eye is too small and causes light to focus behind the retina
Farsightedness
____________ : shape of cornea causes light to focus in front or behind retin
Astigmatism
What are the components of the basic eye exam?
- Visual Acuity: one eye at a time at 20 foot distance
- Visual Fields: Ocular Motility: follow finger left, right, up and down.
- Pupils: round, reactive to light, equal.
- External exam (eyelids, conjunctiva, cornea)
- Fundoscopic exam (red reflex, disc, retina)
What area of the eye is responsible for sharp/detailed vision?
Fovea
When both eyes adduct as when looking from far to near is called?
Convergence
When both eyes Abduct as when looking from near to far is called?
Divergence
What type of eye movement is a slow, sustained eye movement to keep a moving object in focus that is controlled by the occipital eye fields.
Smooth pursuit
What type of eye movement is a rapid, conjugate eye movement towards a particular target that is controlled by the frontal eye fields and superior colliculus?
Saccade
A saccade eye movement is controlled by what two things?
Frontal eye fields and superior colliculus
What type of eye movement allows for sequential fixation on a series of stationary targets passing in front of a viewer’s eye?
Optokinetic eye movements;
it can be thought of as a mix of smooth pursuit and saccadic eye movements.
Initiation of saccadic eye movement begins in ______1______, whereas control and coordination of saccadic movement is in the ____2____.
- cortical centers (frontal eye fields)
2. brainstem
Involuntary saccadic eye movements occur when the frontal eye fields project indirectly to the __________ _________ _________ __________ formation through the ipsilateral superior colliculus. Compared to voluntary saccadic eye movements, involuntary saccadic eye movements bypass the primary visual cortex.
contralateral paramedian pontine reticular fromation
Involuntary saccadic eye movements occur when the frontal eye fields project indirectly to the contralateral paramedian pontine reticular formation through the ____1____ superior colliculus. Compared to voluntary saccadic eye movements, involuntary saccadic eye movements bypass the _____2_____.
- ipsilateral
2. primary visual cortex
What is a major difference between a voluntary and involuntary saccadic eye movement?
Compared to voluntary saccadic eye movements, involuntary saccadic eye movements bypass the primary visual cortex.
Voluntary saccadic eye movement is initiated when the frontal eye fields sends a signal to where?
the contralateral paramedian pontine reticular formation (PPRF).
Where does the contralateral paramedian pontine reticular formation (PPRF) project information to?
the IPSILATERAL CN VI nucleus
The CN-VI (abducens nucleus) will project to where?
CONTRALATERAL medial longitudinal fasiculus (MLF)
where does the MLF synapse?
MLF synapses on the nucleus of CN III (near the superior colliculus)
if the LEFT frontal eye fields were activated, they would send a signal to the ___1___ PPRF. The right PPRF would project to the ___2___ CN VI and the ___3___ MLF and CN III.
If LEFT frontal fields was activated:
- Right PPRF
- Right CN VI
- Left MLF and then the Left CN III
Lesions to what, causes internuclear ophthallmoplegia (INO)
lesions to MLF
internuclear ophthalmoplegia (INO) is a results of a lesion to what? and what diseases is INO associated with?
lesions to MLF; ~ Multiple Sclerosis
In internuclear ophthalmoplegia, the eye will be unable to adduct when looking in the ___________ direction.
contralateral
So when looking left, the right eye will not adduct and the left eye will experience nystagmus.
Which eye movement is controlled by the occipital eye fields?
Smooth pursuit
What cells are found on the borders of ocular dominance columns?``
Binocular Cells
Where are Binocular Cells found?
found in the primary visual cortex where the initial stage of binocular convergence begins.
Binocular neurons receive inputs from both the right and left eyes and integrate the signals together to create a perception of depth.
From where do binocular cells recieve input from?
Binocular cells get input from the LGN of BOTH eyes.
The receptive field of both eyes are identical in orientation, region of retina, width, and on/off organization.
What is the receptive field shape of a ganglion cells?
donut
Are ganglion cells orientation selective?
NO
Where are “Simple” cells of the visual system locatated and whare is the shape of their receptive field?
loc: cortec
receptive field: Bar shaped
Y/N: For a complex cell in the cortex:
- ) Orientation selective: ?
- ) Binocular driven: ?
- ) Position sensitive: ?
- ) Orientation selective - YES
- ) Binocularly driven - YES
- ) Position sensitive - NO
w.r.t to visual system, what is the sensitive period?
2-3 year period of time after birth when connections can be altered by visual experience (corresponds with time babies eyes are moving farther apart)
If visual deficits not repaired soon after birth → irreversible damage to vision
What is ocular dominance?
a measure of relative synaptic input to a cell of each eye.
- can range from only sensitive to ipsilateral eye, to
- only response to contralateral eye, or,
- only responsive to both eyes.
___________: deviation of one eye
Strabismus:
Normal visual stimuli, but each eye saw a different part of visual world
→ Very few binocular cells!
Almost all cells driven exclusively by one eye or the other (half and half)
No sync, no link - synchronous activity from both eyes is necessary to insure proper synaptic connections form during development in visual cortex
Showed: Cells that fire together wire together; Done via NMDA receptor plasticity mechanism (AMPA upregulation etc.)
Color information is separated out from spatial information in retina, and handled in central regions of hypercolumns called what?
BLOBS
