Physiology of the Visual System (Pierce)

Question 1

What are the synaptic connections of rods and cones

Answer 1

Rods/Cones –> Bipolar Cells –> Ganglion Cells

Question 2

What NTs is released in the synapse between:

1. Photoreceptor + Bipolar cell
2. Bipolar cell + Ganglion cell

Answer 2

1. Glutamate
2. Glutamate

Question 3

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

Answer 3

Rod system

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

Question 4

What photoreceptor has the most acuity

Answer 4

Cones

1 cone + 1 bipolar cell + 1 ganglion cell

Question 5

In the retina, where are rods most abundant?

Where are cones most abundant?

Answer 5

Rods - 20 degrees away from fovea

Cones - Center of fovea

Question 6

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

Answer 6

Darkness

Question 7

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

Answer 7

Light

Question 8

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

Answer 8

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

When bound to NMDA, AMPA or Kainate it is excitatory

Question 9

What receptor is expressed by Bipolar cells

Answer 9

mGluR6

Question 10

What is the function of mGluR6

Answer 10

Closes cGMP-gated Na⁺ channels.

This allows a typically excitatory NTs like Glutamate to act inhibitory

Question 11

What receptor is expressed on the ganglion cells

Answer 11

Normal NMDA or non-NMDA receptors

Gluatamate acts as a typical excitatory NTs.

Question 12

Explain what happens in photoreceptors in conditions of darkness

Answer 12

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

Question 13

Explain what happens to photoreceptors in conditions of light

Answer 13

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

Question 14

What are the direct targets of the retina

Answer 14

Lateral geniculate nucleus/body (LGB)

Superior Colliculus

Pretectum

Hypothalamus

Accessory Optic Nuclei (AON)

Question 15

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

Answer 15

Lateral geniculate nucleus/body (LGN/LGB)

Question 16

What does the lateral genicular body do?

Answer 16

• 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.

Question 17

What is the function of the Superior Colliculus?

Answer 17

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

Question 18

What tract is associated with the superior colliculus?

Answer 18

Tectospinal Tract

Question 19

What does the pretectum do?

Answer 19

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

Question 20

Function of the hypothalamus as a direct target of the retina

Answer 20

• 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

Question 21

Where does the retinohypothalamic tract originate and terminate

Answer 21

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

Terminate: Supraoptic, suprachiasmatic & paraventricular nuclei of the hypothalamus

Question 22

What does the Accessory Optic Nuclei (AON) do?

Answer 22

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

Question 23

What is the major function of V1?

Answer 23

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

Question 24

What is the main function of V2?

Answer 24

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

Question 25

What is the main function of V3a?

Answer 25

Identification of motion occuring ## Footnote *Answers the question: "Is motion happening? Yes or no?"*

Question 26

What is the main function of V4?

Answer 26

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

Question 27

What is the difference between achromatopsia and color blindness?

Answer 27

* Achromatopsia: cones work fine but there is damage to cortical areas * Color Blindness: improper functioning of cones

Question 28

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

Answer 28

* 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*

Question 29

What type of input do ocular dominance columns respond to?

Answer 29

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

Question 30

What type of input do the orientation columns respond to?

Answer 30

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

Question 31

What are blobs of the primary visual cortex responsive to?

Answer 31

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.

Question 32

What are Melanopsin Ganglion (MG) cells

Answer 32

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

Question 33

Where do melanopsin ganglion cells project to? What color are they sensitive to?

Answer 33

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

Question 34

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

Answer 34

Circadian rhythms

Question 35

What is the function of the dorsal pathway?

Answer 35

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*

Question 36

Direction of the dorsal pathway

Answer 36

From primary visual cortex and goes to the parietal/frontal cortex V1 --\> V2,V3 --\> V5/MT --\> Parietal/frontal lobe

Question 37

What is the function of the ventral pathway?

Answer 37

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

Question 38

Direction of the ventral pathway

Answer 38

From primary visual cortex to the inferior temporal cortex V1 --\> V2 --\> V4 --\> Temporal lobe