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NeuroEndo Exam 3 > Physiology of the Visual System (Pierce) > Flashcards

Physiology of the Visual System (Pierce) Flashcards

1
Q

What are the synaptic connections of rods and cones

A

Rods/Cones –> Bipolar Cells –> Ganglion Cells

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2
Q

What NTs is released in the synapse between:

  1. Photoreceptor + Bipolar cell
  2. Bipolar cell + Ganglion cell
A
  1. Glutamate
  2. Glutamate
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3
Q

Which photoreceptor sacrifices acuity to gain sensitivity and can operate in dim light

A

Rod system

Many rods synapse on many bipolar cells. Bipolar cells synpase on one ganglion cell

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4
Q

What photoreceptor has the most acuity

A

Cones

1 cone + 1 bipolar cell + 1 ganglion cell

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5
Q

In the retina, where are rods most abundant?

Where are cones most abundant?

A

Rods - 20 degrees away from fovea

Cones - Center of fovea

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6
Q

What visual conditions cause higher glutamate release from rods/cones?

A

Darkness

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7
Q

What visual conditions cause lower glutamate release from rods/cones?

A

Light

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8
Q

How does Glutamate serve as a inhibitory NTs when it is typically an excitatory NTs?

A

The receptor that glutamate binds to determines it’s functionality.

When bound to NMDA, AMPA or Kainate it is excitatory

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9
Q

What receptor is expressed by Bipolar cells

A

mGluR6

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10
Q

What is the function of mGluR6

A

Closes cGMP-gated Na+ channels.

This allows a typically excitatory NTs like Glutamate to act inhibitory

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11
Q

What receptor is expressed on the ganglion cells

A

Normal NMDA or non-NMDA receptors

Gluatamate acts as a typical excitatory NTs.

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12
Q

Explain what happens in photoreceptors in conditions of darkness

A

Photoreceptor depolarized –> graded potential –> Glutamate released –> Glutamte acts as inhibitor –> Bipolar cell not depolarized –> No impulse sent to brain

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13
Q

Explain what happens to photoreceptors in conditions of light

A

Photoreceptor hyperpolarized –> Graded potential not generated –> No inhibitory Glutamate released –> Bipolar cell spontaneously depolarizes –> visual ipulse is sent to brain

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14
Q

What are the direct targets of the retina

A

Lateral geniculate nucleus/body (LGB)

Superior Colliculus

Pretectum

Hypothalamus

Accessory Optic Nuclei (AON)

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15
Q

What is the major target of the retina and regulates the flow of information to the primary visual cortex

A

Lateral geniculate nucleus/body (LGN/LGB)

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16
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.
17
Q

What is the function of the Superior Colliculus?

A

Directing eye movement

  1. Connects with tectospinal tract to send projections to cervical anterior horn cells
  2. Creates a map of visual space to activate appropriate motor responses required to move the eyes into their intended position within the orbits
  3. Specifies movement intention rather than fixation of movement upon a target
18
Q

What tract is associated with the superior colliculus?

A

Tectospinal Tract

19
Q

What does the pretectum do?

A

Pupillary light reflex: sends projections to Edinger-Westphal then on to ciliary ganglion

20
Q

Function of the hypothalamus as a direct target of the retina

A
  • Receives a small number of optic fibers at the supraoptic, suprachiasmatic and paraventricular nuclei.
  • Receives visual inputs which drives the light–dark entrainment of neuroendocrine function and other circadian rhythms
21
Q

Where does the retinohypothalamic tract originate and terminate

A

Origin: A small number of fibers that branch off the optic tract

Terminate: Supraoptic, suprachiasmatic & paraventricular nuclei of the hypothalamus

22
Q

What does the Accessory Optic Nuclei (AON) do?

A

Advanced visual processing, optokinetic nystagmus in response to prolonged large field motion

23
Q

What is the major function of V1?

A

Identify edges and contours of objects & decodes visual input to redirect information in subsequent steps of anaylses to other visual areas.

24
Q

What is the main function of V2?

A

Depth perception which is detected by analyzing the disparities between two eyes

25
Q

What is the main function of V3a?

A

Identification of motion occuring

Answers the question: “Is motion happening? Yes or no?”

26
Q

What is the main function of V4?

A

Complete processing of color inputs. Lesions here are known to cause achromatopsia - unilateral lesions may go unnoticed by patients

27
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
28
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

Example: watching a cat run across a yard or watching a ball move through the air

29
Q

What type of input do ocular dominance columns respond to?

A

Colums that span all 6 layers of the cortext. Each column will prefer input from either the right or left eye but not both

30
Q

What type of input do the orientation columns respond to?

A

Each orientation column responds various angles. They span all 6 layers of the cortex

31
Q

What are blobs of the primary visual cortex responsive to?

A
  1. Span all 6 layers of the cortex
  2. Organized region of nreurons that are sensitive to color
  3. All 3 color-coding cones are required for accurate color detection.
32
Q

What are Melanopsin Ganglion (MG) cells

A

Non-image-forming-light-responsive cells. They provide light-sensing information for regulation of circadian rhythm

33
Q

Where do melanopsin ganglion cells project to?

What color are they sensitive to?

A

Project to hypothalamic suprachiasmatic nucleus, the neuroendocrine effector in the pineal gland which produces melatonin in a rhythmic pattern

Sensitive to blue wavelength light

34
Q

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

A

Circadian rhythms

35
Q

What is the function of the dorsal pathway?

A

The “Where pathway”. Completes motor acts based on visual input.

Watching a baeball being pitched at you so you can swing the bat at the right time

36
Q

Direction of the dorsal pathway

A

From primary visual cortex and goes to the parietal/frontal cortex

V1 –> V2,V3 –> V5/MT –> Parietal/frontal lobe

37
Q

What is the function of the ventral pathway?

A

Interprets images (recognizing or copying shapes, forms, faces) and complex patterns.

The WHAT pathway

38
Q

Direction of the ventral pathway

A

From primary visual cortex to the inferior temporal cortex

V1 –> V2 –> V4 –> Temporal lobe

NeuroEndo Exam 3 (16 decks)

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