Lecture 22: Physiology of the Visual System

Question 1

What is rod-mediated vision called?

What is it called when rod-vision is lost?

Answer 1

Scotopic vision

Night Blindness

Question 2

What is cone-mediated vision called?

Answer 2

Photopic Vision

Question 3

What is mesopic vision called?

Answer 3

Rods and cones are both activated

Question 4

Which retinal cells are horizontally oriented?

Answer 4

Horizontal cells

Amacrine cells

Question 5

Which retinal cells are vertically oriented?

Answer 5

Receptor cells (Rods and cones)

Bipolar cells

Ganglion cells

Question 6

What do rods and cones converge to?

Answer 6

Rods/Cones –> Bipolar Cells –> Amacrine Cells

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

Question 7

In the retina, where are rods most abundant?

Where are cones most abundant?

Answer 7

Rods - Just off center

Cones - Directly center (fovea)

Question 8

What NT is released by rods/cones?

Answer 8

Glutamate

Glutamate is constantly released despite dark/light

Question 9

What visual conditions cause higher glutamate release?

Answer 9

Dark Current

Darkness: cells are constantly depolarized, releasing GLU

Question 10

What visual conditions cause lower glutamate release?

Answer 10

Bright light

Light causes hyperpolarization –> less release of GLU

Question 11

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

When are they activated?

Answer 11

mGluR6: Gi GPCR

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

Question 12

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

When are they activated?

Answer 12

AMPA (non-NMDA)

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

Question 13

What NT causes depolarization of a ganglion cell?

Answer 13

Glutamate

Question 14

Where are ganglion cells found?

What do ganglion cell axons form?

Answer 14

Inner Plexiform Layer

Fibers of Optic Nerve

Question 15

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

What NT is released?

Answer 15

Amacrine cell

GABA or glycine (inhibitory)

Question 16

What is the purpose of on and off center cells?

Answer 16

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

Question 17

What does the lateral genicular body do?

Answer 17

• 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 18

What does the superior colliculus do?

Answer 18

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

Question 19

What tract is associated with the superior colliculus?

Answer 19

Tectospinal

Question 20

What does the pretectum do?

Answer 20

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

Question 21

What does the hypothalamus do?

Answer 21

• 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

Question 22

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

Answer 22

• 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

Question 23

What does the accessory optic nuclei do?

Answer 23

• 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.

Question 24

What is the major function of V1?

Answer 24

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

Question 25

What is the main function of V2?

Answer 25

Depth perception

• Analyzes disparity between two eyes

Question 26

What is the main function of V3a?

Answer 26

Identification of motion occuring

Question 27

What is the main function of V4?

Answer 27

Complete processing of color input

Question 28

What type of input do ocular dominance columns respond to?

Answer 28

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

Question 29

What type of input do the orientation columns respond to?

Answer 29

Each orientation column responds various angles

Question 30

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

Answer 30

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

Question 31

What is the difference between achromatopsia and color blindness?

Answer 31

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

Question 32

Where do melanopsin ganglion cells project to?

What color are they sensitive to?

Answer 32

Project to suprachiasmaatic nucleus

Sensitive to blue

Question 33

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

Answer 33

Circadian rhythms

Question 34

What is the function of the ventral pathway?

Where does it begin and travel to?

Answer 34

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

Question 35

What is the function of the dorsal pathway?

What part of the visual cortex does it pass through?

Answer 35

Completes motor acts based on visual input

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