Vision Physiology II

Question 1

Retina is the ___ _______ portion of the eye

Answer 1

Retina is the light sensitive portion of the eye

Question 2

The retina

• Contains ____ for color vision
• Contains _____ for night vision
• Contains ____ _______

Answer 2

The retina

• Contains cones for color vision
• Contains rods for night vision
• Contains neural architecture

Question 3

Melanin is located in the ____ layer of the retina

Answer 3

pigmented

Question 4

Melanin prevents ____ _____ and stores ______

Answer 4

Melanin prevents light reflection and stores Vitamin A

Question 5

Vitamin A is exchanged back and forth through the ___ ______ of the ____ segments of the rods and cones

Answer 5

Vitamin A is exchanged back and forth through the cell membranes of the outer segments of the rods and cones

Question 6

What is a precursor to photosensitive chemicals of the rods and cones?

Answer 6

vitamin A

Question 7

Fovea is a small area at the____of the retina (1 sq mm) that is capable of ___ and ____vision.

Answer 7

Fovea is a small area at the center of the retina (1 sq mm) that is capable of acute and detailed vision.

Question 8

The center of the fovea (central fovea) contains only ____

Answer 8

The center of the fovea (central fovea) contains only cones

Question 9

What is the area of greatest acuity?

Answer 9

the central fovea

Question 10

Major functional segments of rods or cones:

• Outer segment: ____ ______photochemical
• Inner segment: ____ _____
• Nucleus
• Synaptic body: connects to subsequent _____cells

Answer 10

Major functional segments of rods or cones:

• Outer segment: light sensitive photochemical
• Inner segment: cytoplasmic organelles
• Nucleus
• Synaptic body: connects to subsequent neuronal cells

Question 11

žRods and cones contain chemicals that_____ on exposure to light. This ____ the nerve fibers leading from the eye.

Answer 11

žRods and cones contain chemicals that decompose on exposure to light. This excites the nerve fibers leading from the eye.

Question 12

• When light is absorbed by _____ it immediately begins to decompose
• In the process of splitting away a number of ____ _____ are formed
• _________ excites the rods forming ____ _____ of the optic nerve and transmission of the visual image into the CNS

Answer 12

• When light is absorbed by rhodopsin it immediately begins to decompose
• In the process of splitting away a number of intermediary compounds are formed
• Metarhodopsin II excites the rods forming action potential of the optic nerve and transmission of the visual image into the CNS

Question 13

Reformation of rhodopsin:

• Rhodopsin is broken down into _____+ ______
• Metabolic energy converts all-trans retinal to _______, catalyzed by_________
• 11-cis retinal automatically recombines with _______ to form rhodopsin

Answer 13

Reformation of rhodopsin:

• Rhodopsin is broken down into all-trans retinal + scotopsin
• Metabolic energy converts all-trans retinal to 11-cis retinal, catalyzed by retinal isomerase
• 11-cis retinal automatically recombines with scotopsin to form rhodopsin

Question 14

Role of vitamin A for the formation of rhodopsin:

• All-trans retinal conversion to _______(form of Vitamin A)
• All-trans retinol converted to______
• Catalyzed by ______
• 11-cis retinol converted to ______which can combine with scotopsin to form new rhodopsin

Answer 14

Role of vitamin A for the formation of rhodopsin:

• All-trans retinal conversion to all-trans retinol (form of Vitamin A)
• All-trans retinol converted to 11-cis retinol
• Catalyzed by isomerase
• 11-cis retinol converted to 11-cis retinal which can combine with scotopsin to form new rhodopsin

Question 15

žRods under No light conditions=______

žOuter segment of rod:

• _____-gated channels allow influx of _____
• In the dark, cGMP levels are _____

žInner segment of rod:

• _____pump
• ___- leak channels

ž-____ mV is resting state

žReduced _____

Answer 15

žRods under No light conditions=DARK CURRENT

žOuter segment of rod:

• cGMP-gated channels allow influx of Na+
• In the dark, cGMP levels are high

žInner segment of rod:

• Na/K pump
• k- leak channels

ž-40 mV is resting state

žReduced electronegativity

Question 16

žRods under LIGHT conditions:

• ž_____ in the outer segment is exposed to light, becomes activated, and decomposes
• žcGMP-gated sodium channels ____
• ž____ influx of Na+
• žNa+ continues to be pumped via ____ pump from ____ ____
• žMore Na+ ____

žIncreased Negativity: ______

Answer 16

žRods under LIGHT conditions:

• žRhodopsin in the outer segment is exposed to light, becomes activated, and decomposes
• žcGMP-gated sodium channels close
• žReduced influx of Na+
• žNa+ continues to be pumped via Na/K pump from inner segment
• žMore Na+ leaves

žIncreased Negativity: HYPERPOLARIZATION

Question 17

Mechanism for Light to Decrease Sodium Conductance

1. Light activates______
2. Stimulates _______
3. Transducin activates ______ that breaks down cGMP
4. Reduced cGMP ____ cGMP-gated sodium channels
5. Photoreceptors _____

Answer 17

Mechanism for Light to Decrease Sodium Conductance

1. Light activates Rhodopsin
2. Stimulates G-protein transducin
3. Transducin activates cGMP PDE that breaks down cGMP
4. Reduced cGMP closes cGMP-gated sodium channels
5. Photoreceptors hyperpolarize

Question 18

žWhat is responsible for keeping Na+ channel in the outer segment of the rods open?

Answer 18

cGMP

Question 19

Light activated rhodopsin activates what?

Answer 19

žG-protein transducin

Question 20

What deactivates the activated rhodopsin?

Answer 20

rhodopsin kinase

Question 21

žReceptor potential is proportional to the logarithm of the ____ ______

•Very important for discrimination of the ____ _____

Answer 21

žReceptor potential is proportional to the logarithm of the light intensity

•Very important for discrimination of the light intensity

Question 22

žthe sensitivity of the retinal automatically adjusts to the __ ____

Answer 22

žthe sensitivity of the retinal automatically adjusts to the light level

Question 23

žColor vision is the result of activation of ____

Answer 23

cones

Question 24

What are the three types of cones?

Answer 24

blue, green, and red

Question 25

What is the protein that exists in cones?

Answer 25

Photopsin

Question 26

Color blindness * Lack of a particular type of \_\_\_\_\_ * žGenetic disorder passed along on the \_\_\_\_\_\_ * žOccurs almost exclusively in \_\_\_\_\_ * žMost color blindness results from lack of the ___ or ____ cones * •Lack of \_\_\_\_cone, protanope * •Lack of _____ cone, deuteranope

Answer 26

Color blindness * žLack of a particular type of **_cone_** * žGenetic disorder passed along on the **_X chromosome_** * žOccurs almost exclusively in **_males_** * žMost color blindness results from lack of the **_red_** or **_green_** cones * •Lack of **_red_** cone, protanope * •Lack of **_green_** cone, deuteranope

Question 27

žtransmit signals in the outer plexiform layer and synapse with bipolar cells and horizontal cells

Answer 27

rods and cones

Question 28

žtransmit signals horizontally in the outer plexiform layer from rods and cones to bipolar cells

Answer 28

horizontal cells

Question 29

žtransmit signals vertically from rods, cones, and horizontal cells to the inner plexiform layer and synapse with ganglion cells and amacrine cells

Answer 29

bipolar cells

Question 30

žtransmit signals from bipolar cells to ganglion cells

Answer 30

amacrine cells

Question 31

žtransmit output signals from the retina through the optic nerve into the brain

Answer 31

ganglion cells

Question 32

žELECTRONIC CONDUCTION (signal transduction in retina) * Direct flow of ____ \_\_\_\_\_, NOT action potential * Always ____ \_\_\_\_\_proportional to _____ \_\_\_\_ * The only cells that have action potentials are\_\_\_\_\_ cells –Send signals all the way to the brain

Answer 32

žELECTRONIC CONDUCTION (signal transduction in retina) * Direct flow of **_electric current_**, NOT action potential * Always **_graded response_** proportional to **_light intensity_** * The only cells that have action potentials are **_ganglion_** cells –Send signals all the way to the brain

Question 33

žRods and cones release \_\_\_\_\_

Answer 33

glutamate

Question 34

\_\_\_\_\_ cells release aminobutyric acid, glycine, dopamine, acetylcholine and indolamine

Answer 34

amacrine cells

Question 35

Output of horizontal cells is always \_\_\_\_\_

Answer 35

inhibitory

Question 36

Horizontal cells prevent the lateral spread of light excitation on the retina, which is called

Answer 36

lateral inhibition

Question 37

Horizontal cells have an \_\_\_\_center and an\_\_\_\_ surround, which is essential for transmitting \_\_\_\_\_borders in the visual image.

Answer 37

Horizontal cells have an **_excitatory_** center and an **_inhibitory_** surround, which is essential for transmitting **_contrast_** borders in the visual image.

Question 38

Three types of ganglion cells: žW cells (40%) receive most of their excitation from \_\_\_\_cells; sensitive to ____ \_\_\_\_ in the visual field žX cells (55%) ___ receptive field, ____ retinal locations, may be responsible for the ____ of the visual image itself, always receives input from at least one \_\_\_\_, may be responsible for _____ transmission žY cells (5%) \_\_\_receptive field respond to\_\_\_\_ _____ in the visual field

Answer 38

Three types of ganglion cells: ## Footnote žW cells (40%) receive most of their excitation from **_rod_** cells; sensitive to **_direction movement_** in the visual field žX cells (55%) **_small_** receptive field, **_discrete_** retinal locations, may be responsible for the **_transmission_** of the visual image itself, always receives input from at least one **_cone_**, may be responsible for **_color_** transmission žY cells (5%) **_large_** receptive field respond to **_instantaneous changes_** in the visual field