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Neuroscience > Chapter 12: Central Visual Pathways > Flashcards

Chapter 12: Central Visual Pathways Flashcards

1
Q

The primary visual pathway goes from the ______ to the __________ in the __________ and on to the __________

A

retina,
dorsal lateral geniculate nucleus,
thalamus
visual cortex

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2
Q

Draw the primary visual pathway and label the Retina, dorsal lateral geniculate and the primary visual cortex

A

Ok

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3
Q

Visual areas in the temporal lobe are primarily involved in __________ _________,
whereas those in the parietal lobe are concerned with ________.

A

Object recognition, Motion.

  • TOR
  • PM
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4
Q

Ganglion cell axons exit the retina through a circular region in its nasal part called the ________, where they bundle together to form the _______. Axons in the optic nerve run a straight course to the _________ at the base of the __________

A

OPTIC DISK (or optic papilla), OPTIC NERVE, OPTIC CHIASM, DIECEPHALON

*OdncD

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5
Q

Once past the optic chiasm, the ganglion cell axons on each side form the ___________

A

Optic tract

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6
Q

What is the difference between the optic nerve and the optic tract?

A

The optic tract, unlike the optic nerve, contains fibers from both eyes.

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7
Q

The partial crossing of ganglion cell axons at the optic chiasm is known as

A

Decussation

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8
Q

Neurons in the lateral geniculate nucleus send their axons to the cerebral cortex via the ________ These axons pass through a portion of the internal capsule called the _________ and terminate in the primary _____________, or ___________ (also referred to as Brodmann’s area 17)

A

internal capsule, optic radiation, visual cortex (Vl}, or striate cortex (also referred to as Brodmann’s area 17)

  • IC*
  • OR*
  • VC*
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9
Q

TRUE OR FLASE?

The retinogeniculostriate pathway, or primary visual pathway, conveys information that is essential for
most of what is thought of as seeing; damage anywhere along this route results in serious visual impairment.

A

TRUE

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10
Q

What is the pretectum and where does it lie?

A

A collection of neurons that lies between the thalamus and the midbrain and is important as the coordinating center for the pupillary light reflex

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11
Q

As a general rule, information from the left half of the visual world, whether it originates from the left or right eye, is represented in the right half of
the brain, and vice versa

A

True Dat!!

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12
Q

Each eye sees a part of visual space that defines its VISUAL FIELD. For descriptive purposes, each retina and its corresponding visual field are divided into quadrants. In this scheme, the surface of the retina
is subdivided by vertical and horizontal lines that intersect at the center of the
fovea

A

superior

TEMPORAL NASAL

                             inferior
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13
Q

The point in visual space that falls on the fovea is known as the _____________

A

The Point of fixation. Vertical and horizontal lines in visual space (also called meridians) intersect here.

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14
Q

Draw and label the Retinal Field

A

superior

TEMPORAL NASAL

                             inferior
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15
Q

The area medial to the point of fixation is the __________

A

Nasal visual field.

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16
Q

The area lateral to point of fixation is the ____________

A

Temporal visual field

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17
Q

Objects in the temporal visual field is seen by our nasal retina.

A

Think about this carefully

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18
Q

Objects in the superior visual field is seen by the inferior retina.

A

Think about this carefully

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19
Q

This binocular field of view consists of two symmetrical visual hemifields (left and right). The left binocular hemifields includes the nasal visual field of the right eye and the temporal visual field of the left eye; the right hemifields includes the temporal visual field of the right eye and the nasal visual field of the left eye.

A

Draw and label

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20
Q

Point of fixation falls on our _________

A

Fovea.

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21
Q

Thalamic Relay nucleus for most RGC axons; visual perception is by the ____________

A

Lateral geniculate nucleus (LGN)

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22
Q

Optic radiations

A

output of LGN neurons to primary visual cortex

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23
Q

Nasal RGCs Decussate

A

Where the retinal ganglion cell (RGC) of the left and the retinal ganglion cell (RGC) of the right intersect each other to form an X in the optic chiasm.

Retinal ganglion cell (RGC) RGCs in the temporal retina remains on the same side.

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24
Q

The responses of cortical neurons are tuned to the orientation of edges, much like cone receptors are tuned to the wavelength of light; the peak in the tuning curve (the orientation to which a cell is most responsive) is referred to as the __________

A

Neuron’s Preferred Orientation

25
Q

Organization of primary Visual (striate) cortex. cortex Isdivided Into six principal cellular layers
that differ (1) cell packing density, (2) cellular
(3)morphology and (4) connections.

A 
1
2
3
4A, 4B, 4C
5
6
26
Q

Lateral geniculate axons terminate primarily in cortical layer ________, which is composed of a class of neuron (spiny stellate) whose axons convey the activity supplied by the lateral geniculate nucleus to other cortical layers

A

4C

27
Q

Orientation Tuning Columns of the Cortex

A

..

28
Q

Although the lateral geniculate nucleus receives inputs from both eyes, the inputs are segregated
in separate layers. In many species, including most primates, inputs from the two eyes remain segregated in the ocular dominance columns of layer 4. Layer 4 neurons send their axons to
other cortical layers; it is at this stage that the information from the two eyes converges onto individual neurons

A

Signals from the
two eyes converge as the axons from layer 4 neurons in adjacent monocular
stripes synapse on individual neurons in other cortical layers

29
Q

Bringing together the inputs from the two eyes at the level of the striate cortex provides a basis for_________

A

Stereopsis, the sensation of depth that arises from viewing nearby objects with two eyes instead of one

30
Q

Because the two eyes look at the world from slightly different angles, objects that lie in front of or behind the plane of fixation project to non-corresponding points on the two retinas.

A

Explain to Adorkor

31
Q

The layers in the lateral geniculate are also distinguished on the basis of cell size. Two ventral layers are composed of large neurons and are referred to as the ______________, while more dorsal layers are composed of small neurons and are referred to as the _______________

A

Magnocellular layers, Parvocellular layers.

MP

The magno- and parvocellular layers receive inputs from distinct populations of ganglion cells that exhibit corresponding differences in cell size.

32
Q

The response properties of the M and P ganglion cells provide important clues about the contributions of the magno- and parvocellular pathways to visual perception. M ganglion cells have larger receptive fields than P cells, and
their axons have faster conduction velocities.

A

Draw & label

33
Q

P ganglion cells can transmit information about color, whereas M cells cannot. P cells convey color information because their receptive field centers and surrounds are driven by different classes of cones (i.e., cones responding with greatest sensitivity to short-, medium-, or long-wavelength
light)

A

Damage to the magnocellular layers has little effect on visual acuity or color vision but sharply reduces the ability to perceive rapidly. In contrast, damage to the parvocellular layers has no effect on
motion perception but severely impairs visual acuity and color perception

34
Q

Koniocellular or K-cell pathway

A

Found within the lateral geniculate nucleus. Although the contribution of the K-cell pathway to perception is not understood, it appears that some aspects of color vision, especially information
derived from short-wavelength-sensitive cones, may be transmitted via the K-cell rather than the P-cell pathway.

35
Q

__________ contains neurons
that respond selectively to the direction of a moving edge without regard to its
color.

A

Middle temporal area (M1)

Draw & label

36
Q

_________ contains a high percentage of neurons that respond selectively to the color of a visual stimulus without regard to its direction of movement.

A

V4

37
Q

Cerebral akinetopsia

A

Unable to appreciate the motion of objects.

Trouble following a dialogue because she could not follow the movements of the speaker’s mouth.

Crossing the street was potentially terrifying
because she couldn’t judge the movement of approaching cars.

38
Q

cerebral achromatopsia

A

These patients lose the ability to see the
world in color, although other aspects of vision remain in good working order.

The normal colors of a visual scene are described as being replaced by “dirty” shades of gray, much like looking at a poor-quality black-and-white movie.

Achromatopsic individuals know the normal colors of objects-that a school bus is yellow, an apple red- but can no longer see them. When asked to draw
objects from memory, they have no difficulty with shapes but are unable to appropriately color the objects they have represented

39
Q

V4, V3

A

for color vision. Inferior region of occipital lobe.

40
Q

V5, V3A

A

For visual motion. Superior region of occipital lobe; where pathway.

41
Q

Dorsal Stream guide movement unconsciously

A

Ventral Stream allows conscious recognition of objects

42
Q

The ganglion cell axons in the optic tract reach a number of structures in the diencephalon and midbrain.

A

The major target in the diencephalon is the dorsal lateral geniculate nucleus of the thalamus

43
Q

axons pass through a portion of the internal capsule called the

A

optic radiation and terminate in the primary visual cortex (Vl}, or striate cortex (also referred to as Brodmann’s area 17), which lies largely along and
within the calcarine fissure in the occipital lobe. The retinogeniculostriate pathway, or primary visual pathway, conveys information that is essential for
most of what is thought of as seeing; damage anywhere along this route results in serious visual impairment.

44
Q

The Retinotopic Representation of the Visual Field

A

Most of these structures receive information from both eyes, requiring that these inputs be integrated to form a coherent map of individual points in
space. As a general rule, information from the left half of the visual world, whether it originates from the left or right eye, is represented in the right half of the brain, and vice versa.

45
Q

Nasal RGCs Decussate

A

RGCs in the nasal retina cross the optic chiasm (decussate).

RGCs in the temporal retina remains on the same side.

The boundary between decussating and non-decussating axons runs through the fovea.

Objects in the left visual field (pink) falls on the nasal retina of the left eye and temporal retina of the right eye.

Axons from both of these regions (pink) travel together in the right optic tract to the right LGN.

46
Q

Visual Field Deficits

A

Relatively large visual field deficits are called

anopsias; smaller ones are called scotomas

47
Q

Visual Field Deficits

A

Damage to the retina or one of the optic nerves before it reaches the optic chiasm
results in a loss of vision that is limited to the eye of origin

In contrast, damage in the region of the chiasm or more centrally- results in specific types of deficits that involve the visual fields of both eyes

48
Q

Meyer’s loop

A

Meyer’s loop carries information from the superior portion of the contralateral visual field.

Damage to parts of the temporal lobe with involvement of Meyer’s loop can thus result in a superior homonymous quadrantanopsia

49
Q

Neurons in the primary Visual cortex respond selectively to oriented edges.

A 
A) An anesthetized animal
is fitted With contact lenses to focus the
eyes on a screen where images can be
projected; an extracellular electrode
records the neuronal responses.

(B) Neurons
in the primary visual cortex typically
respond vigorously to a bar of light oriented
at a particular angle and less strongly-or not at all-to other orientations.

(C) Orientation tuning curve for a
neuron in primary visual cortex. In this
example the highest rate of action potential
discharge occurs for vertical edges the
neurons "preferred" orientation.
50
Q

To appreciate how the properties of an image might be represented by populationsvof neurons that are tuned to different orientations, an image can be
decomposed into its frequency components (an analytical approach discovered by the French mathematician Joseph Fourier) and then filtered to create a set of images whose spectral composition simulate the information that would be conveyed by neurons tuned to different orientations

A 
Each class of orientation-selective neuron transmits only a fraction of the information in the scene-the part that matches its filter properties- but the information from these different filters contains all the spatial information necessary to generate a
faithful representation of the original image.
51
Q

Orientation preference is only one of the qualities that defines the filter properties of neurons in primary visual cortex. A substantial fraction of cortical neurons are also tuned to the direction of stimulus motion

A

for example responding much more vigorously when a stimulus moves to the right than
when it moves to the left. Neurons can also be characterized by their preference for spatial frequency (the coarseness or fineness of the variations in contrast that fall within their receptive fields) as well as temporal frequency (rate of
change in contrast).

52
Q

Lateral geniculate axons terminate primarily in cortical layer 4C, which is composed of a class of neuron (spiny stellate)

A

whose axons convey the activity supplied by the lateral geniculate nucleus to other cortical layers

53
Q

What cannot be discerned from a cursory examination of anatomical sections
is that the cortex also exhibits a striking degree of organization in the radial
dimension.

A

Microelectrode penetrations perpendicular to the cortical surface encounter columns of neurons that have similar receptive field properties, responding, for example, to stimulation arising from the same region of visual space and exhibiting preferences for similar stimulus properties, such as edge ori

54
Q

contralateral

A

relating to or denoting the side of the body opposite to that on which a particular structure or condition occurs.

55
Q

ipsilateral

A

belonging to or occurring on the same side of the body.

56
Q

Inputs from both eyes are present at the level of the lateral geniculate nucleus, but contralateral and ipsilateral retinal axons terminate in separate layers,

A

so that individual geniculate neurons are strictly monocular, driven either by the left or right eye but not by both

57
Q

V1 —-> V2 —-> V3 [Dynamic Form] —-> V4 [Color] —-> Temporal Area

A

[Object Recognition]

58
Q

V1 —-> V2 —-> V3A [Form] —-> V5 [Motion] —-> Parietal Area

A

[Motion]

Neuroscience (6 decks)

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