Midterm 2

Question 1

What is the function of the iris?

Answer 1

Adjust pupil size

Question 2

What is the cornea?

Answer 2

Specialized transparent tissue

Question 3

What is the aqueous humor?

Answer 3

Liquid that supplies nutrients to cornea and lens

Question 4

What is the ciliary body?

Answer 4

Muscle that adjusts refractive power of the lens; ciliary processes produces fluids

Question 5

What is the function of the retina?

Answer 5

Contains neurons that transducer sensory signals and transmit electrical signals to central targets in the brain

Question 6

What is the function of the optic disk?

Answer 6

Area where blood vessels enter the eye and retinal axons leave the eye

Question 7

What are 5 classes of neurons in the retina?

Answer 7

1. Photoreceptors
2. Bipolar cells
3. Horizontal cells
4. Amacrine cells
5. Ganglion cells

Question 8

What is phototransduction?

Answer 8

Process by which absorption of light by photopigment

Question 9

What is the process for phototransduction?

Answer 9

1. Photon of light is absorbed by chromophore retinal, coupled ti GPCR-opsins
2. Absorption of light causes changes in retinal configuration (cis to trans)
3. Changes in retinal configuration activates transducin
4. Transducin activates PDE, which hydrolyzes cGMP reducing cGMP level
5. cGMP channels are closed
6. Hyperpolarization

Question 10

What are the roles of retinal pigment epithelium?

Answer 10

1. Phagocytose oldest disks are the tip of the outer segment

2, Regerneration of photopigment after exposure to light

Question 11

What is the retinoid cycle in photoreceptors?

Answer 11

1. Light absorption by cis-retinal
2. Photoisomerization of retinal
3. Trans-retinal dissociates from opsin and is converted to trans-retinol
4. Trans-retinol is transported into pigment epithelium and converted to cis-retinal
5. cis retinal is transported back into the outer segment where it recombines with opsins

Question 12

What are the specialized vision aspects of rods and cones?

Answer 12

• Rods have high sensitivity to light, low resolution (night vision)
• Cones have low sensitivity to light, high resolution (day vision)
• Cones are responsible for color vision

Question 13

What is the range of luminance for rods and cones?

Answer 13

Rods = scotopic and mesotopic
Cones = mesotopic and photopic

Question 14

How do rods improve detection of light and signal?

Answer 14

Convergence improves detection of light, but reduces a spatial resolution.
Amplification contributes to detection of signal

Question 15

Where is cone receptor density the highest?

Answer 15

Highest at the center of macula (in the fovea)

Question 16

How many photopigments does the human retina have?

Answer 16

4

Question 17

Where are the genes for cone pigments located?

Answer 17

Localized on X chromosome (Red and green) and on chromosome 7 (blue)

Question 18

What is protanopia?

Answer 18

Loss of long-wavelength sensitive cones = difficult to discriminate between green and red

Question 19

What is deuteranopia?

Answer 19

Loss of medium-wavelength sensitive cones = difficult to discriminate between red and green

Question 20

What is the difference between on-center and off-center ganglion cells?

Answer 20

• “on” responds to onset of small bright light and offset of and annulus light
• “off” responds to offset of bright light and onset of annulus light

Question 21

What determines the difference between on- and off-center cells?

Answer 21

• “on” responds to decreased glutamate by becoming depolarized
• “off” responds by becoming hyperpolarized

Question 22

What do horizontal cells to in terms of surround response?

Answer 22

modulatory inputs generate the surround response

Question 23

What are characteristics of M, P and K ganglion cells

Answer 23

• M: larger receptive fields than P, M axons have faster conduction velocity than P cells, respond transiently to visual stimuli, do not transmit info about color because contain same classes of cones in center and in surrounds
• P: cells respond in sustained fashion, convey color info because receptive field centers and surrounds contain difference classes of cones
• K: might contribute to color vision as they receive info from S cones

Question 24

What is binocular visual field?

Answer 24

Consists of two symmetrical visual hemifields

Question 25

What is contralateral visual field?

Answer 25

Represented by axon of ganglion cells that originate in both eyes

Question 26

What does the LGN do?

Answer 26

Receives input from both eyes, responses are similar to retinal ganglion cell responses

Question 27

What are the different layers of LGN?

Answer 27

• Magnocellular (large neurons)
• Parvocellular (small neurons)
• konicellular (small neurons)

Question 28

What is optic radiation?

Answer 28

Portion of internal capsule that comprises the axons of lateral geniculate neurons that carry visual info to striate cortex

Question 29

What is the architecture of primary visual (striate) cortex?

Answer 29

• LGN neurons primarily synapse on layer 4 of striate cortex
• laminar organization of visual cortex serves to segregate populations of neurons that are having distinct patterns of connections

Question 30

What are ocular dominance columns?

Answer 30

Stripes of neurons in the visual cortex that respond to input from one eye or the other

Question 31

What are the characteristics of neurons along the radial axis?

Answer 31

1. Have receptive fields centered on the same region of visual space
2. Exhibit similar orientation preferences
3. orientation preference that progressively shift

Question 32

Where do retinal ganglion cells project to?

Answer 32

• Pretectum
• Hypothalamus
• Superior colliculus
• Thalamus (LGN)