Lecture 22: Physiology of the Visual System Flashcards

1
Q

What is rod-mediated vision called?

What is it called when rod-vision is lost?

A

Scotopic vision

Night Blindness

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2
Q

What is cone-mediated vision called?

A

Photopic Vision

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3
Q

What is mesopic vision called?

A

Rods and cones are both activated

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4
Q

Which retinal cells are horizontally oriented?

A

Horizontal cells

Amacrine cells

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5
Q

Which retinal cells are vertically oriented?

A

Receptor cells (Rods and cones)

Bipolar cells

Ganglion cells

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6
Q

What do rods and cones converge to?

A

Rods/Cones –> Bipolar Cells –> Amacrine Cells

Multiple rods converge to one bipolar cell but only one cone contacts one bipolar cells

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7
Q

In the retina, where are rods most abundant?

Where are cones most abundant?

A

Rods - Just off center

Cones - Directly center (fovea)

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8
Q

What NT is released by rods/cones?

A

Glutamate

Glutamate is constantly released despite dark/light

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9
Q

What visual conditions cause higher glutamate release?

A

Dark Current

Darkness: cells are constantly depolarized, releasing GLU

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10
Q

What visual conditions cause lower glutamate release?

A

Bright light

Light causes hyperpolarization –> less release of GLU

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11
Q

What is the specialized glutamate receptor found on on-center bipolar cells?

When are they activated?

A

mGluR6: Gi GPCR

  • Activated with low concentrations of GLU (light)
  • High concentrations of GLU will inactivate (dark)
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12
Q

What is the specialized glutamate receptor found on off-center bipolar cells?

When are they activated?

A

AMPA (non-NMDA)

  • Activated with high concentrations of GLU (dark)
  • Low concentrations of GLU will inactivate (light)
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13
Q

What NT causes depolarization of a ganglion cell?

A

Glutamate

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14
Q

Where are ganglion cells found?

What do ganglion cell axons form?

A

Inner Plexiform Layer

Fibers of Optic Nerve

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15
Q

In activation of a rod photoreceptor, what cell acts as an interneuron between bipolar cells?

What NT is released?

A

Amacrine cell

GABA or glycine (inhibitory)

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16
Q

What is the purpose of on and off center cells?

A

Increase ability to detect edges and sharpen our vision

  • On Center: Where something is
    • Excited by bright spot in center of receptor field
  • Off Center: Where something ends
    • Excited by dark spot in center of receptor field
17
Q

What does the lateral genicular body do?

A
  • Control the motions of the eyes to converge on a point of interest
  • Control the focus of the eyes based on distance
  • Determine relative position of objects to map them in space
  • Detect movement relative to an object.
18
Q

What does the superior colliculus do?

A
  • Creates a map of visual space to activate appropriate motor responses
  • Coordinates head and eye movement to visual targets
19
Q

What tract is associated with the superior colliculus?

A

Tectospinal

20
Q

What does the pretectum do?

A
  • Reflex control of pupil and lens
  • Sends projections to Edinger-Westphal then on to ciliary ganglion
21
Q

What does the hypothalamus do?

A
  • Retinohypothalamic tract (from optic tract) terminate in nuclei in the hypothalamus
  • Visual input to the hypothalamus drives the light–dark entrainment of neuroendocrine function and other circadian rhythms
22
Q

What does the medial temporal area (MTA)/V5 do?

A
  • Contains neurons that responds selectively to the direction of a moving edge.
  • Tracks the motion across a scene in terms of directionality and background/foreground contex
  • Ignores color
23
Q

What does the accessory optic nuclei do?

A
  • Advanced visual processing
  • Important role in eye movements of compensation and pursuit particularly in alternation with saccadic-type eye movements, responding to prolonged watching of large field motion.
24
Q

What is the major function of V1?

A

Identify edges and contours of objects

  • Used to identify what and where objects are
  • Retinotopic organization is maintained
  • Local image: size, orientation, direction of movement
25
Q

What is the main function of V2?

A

Depth perception

  • Analyzes disparity between two eyes
26
Q

What is the main function of V3a?

A

Identification of motion occuring

27
Q

What is the main function of V4?

A

Complete processing of color input

28
Q

What type of input do ocular dominance columns respond to?

A

Each column will prefer input from either right of left eye but not both

29
Q

What type of input do the orientation columns respond to?

A

Each orientation column responds various angles

30
Q

What type of input are the blobs of the primary visual cortex responsive to?

A

Specific wavelengths on the color absorption spectra associated with a specific cone (Red, green, blue)

31
Q

What is the difference between achromatopsia and color blindness?

A
  • Achromatopsia: cones work fine but there is damage to cortical areas
  • Color Blindness: improper functioning of cones
32
Q

Where do melanopsin ganglion cells project to?

What color are they sensitive to?

A

Project to suprachiasmaatic nucleus

Sensitive to blue

33
Q

What are non-image-forming light-responsive systems important for regulating?

A

Circadian rhythms

34
Q

What is the function of the ventral pathway?

Where does it begin and travel to?

A
  • Interprets images and complex patterns (recognizing or copying shapes, forms, faces)
  • Begins in primary visual cortex and travels to inferior temporal cortex
35
Q

What is the function of the dorsal pathway?

What part of the visual cortex does it pass through?

A

Completes motor acts based on visual input

Passes through V3 (from primary visual cortex to parietal/frontal cortex)