Chapter 50

Question 1

What are the layers of the retina? (remember your pneumonic)

Answer 1

• Inner limiting membrane
• Layer of optic nerve fibers
• Ganglion
• Inner plexiform
• Inner nuclear
• Outer Plixiform
• outer nucear
• Rods and cones
• Pigmented epithelium

Question 2

What are the four functional segments of the rods and cones?

Answer 2

• Outer segment
• Innter segment
• Nucleus
• Synaptic body

Question 3

What is contained in the outer segment?

Answer 3

• Light sensitive photochemical (rhodopsin in rods)
• layered discs

Question 4

What is contained within the inner segment?

Answer 4

Cytoplasmic organelles:

-mainly mitochondria

Question 5

What is the major purpose of the pigmented layer of the retinal epithelium?

Answer 5

-prevents light reflection which increases visual acuity

Question 6

What two compounds together make rhodopsin?

Answer 6

Scotopsin and retinal

Question 7

What is the affect of light exposure to rhodopsin?

Answer 7

-The cis-retinal is converted to all trans-retinal and then separates from scotopsin

Question 8

What causes night blindness?

Answer 8

-Vitamin A defficiency

Question 9

How does a lack of Vitamin A cause night blindness?

Answer 9

-Limits the amount of retinal and therefore rhodopsin that can be synthesized and then decreases low light (purple) vision.

Question 10

Where is vitamin A stored and how can a deficiency be restored?

Answer 10

• the liver
• IV vitamin A

Question 11

What is the membrane polarization of Rods in the light? How about when it is dark?

Answer 11

• Light: hyperpolarized
• Dark: Depolarized

Question 12

What is the flow of effects when light striked a rhodopsin molecule?

Answer 12

Rhodopsin exposed to light–> Activated rhodopsin (all trans-retinal)–> activates transducin–> activates cGMP phosphodiesterase–> decreases cGMP–> closure of cGMP gated Na channels–> Decreases Na influx–> hyperpolarization

Question 13

Is the polariazation state of the rod dependant on the amount of light striking it?

Answer 13

• Yes
• The more light, the more hyperpolarized.

Question 14

What enzyme converts activated rhodopsin back to rhodopsin and reverses the whole excitatory process?

Answer 14

-Rhodopsin kinase

Question 15

Are rods or cones more sensitive?

Answer 15

Rods (30-300 times)

Question 16

What is the light adaptation?

Answer 16

• When moving from dark to light:
• the rods will be exposed to light and rapidly convert their retinal to vitamin A ehich reduces the concentration of photosensitive pigments

Question 17

What is the dark adaptation?

Answer 17

When moving from light to dark:

-retinal and opsins are coverted back to light sensitive pigments (rhodopsin) and Vitamin A is converted back into retinal (to form rhodopsin)

Question 18

Which adapts more quickly to light and dark? Which achieves the greatest sensitivity to light?

Answer 18

• The cones adapt quickly but briefly
• The rods achieve a greater sensitivity (the tortise wins the race)

Question 19

What cones are stimulated by what color?

Answer 19

• blue pigment cones= blue light
• Red pigment cones= red light
• Green pigment cones= green light

White light= all 3 equally

Question 20

What does the overlap in cone sensitivity allow?

Answer 20

-allows for the detection of mixed color

Question 21

What is protonope?

Answer 21

• lack of or loss of RED cones
• shortened visual spectrum at the long wavelengths

Question 22

What is the name for green color blindness?

Answer 22

• Deuteranope
• normal visual spectral length, missing green component

Question 23

What is the inheritance pattern of color blindness?

Answer 23

• X linked recessive
• so mostly in males

Question 24

Which are the only retinal neurons that transmit visual signals via action potentials?

Answer 24

Ganlgion cells through the optic nerve.

Question 25

What are the 5 main type of neural cells located within the retina?

Answer 25

• Photoreceptive cells (rods and cones)
• Horizontal cells
• Bipolar cells
• Amacrine cells
• Ganglion cells

Question 26

Where are horzontal cells and where do they transmit?

Answer 26

• outer plexiform layer
• transmit signals from the rods and cones to the bipolar cells

Question 27

What is the location and function of bipolar cells?

Answer 27

• Transmit signals from the rods and cones to the ganglion cells and the amicrine cells
• between the outer and inner plexiform layer

Question 28

What is the major function of the amicrine cells?

Answer 28

-lateral inhibition

Question 29

What do ganglion cells do?

Answer 29

-transmit signals from the retina to the brain

Question 30

What is the output of horzontal cells?

Answer 30

• always inhibtory
• provide lateral inhibition

Question 31

How are amicrine cells directionally senstive?

Answer 31

-They respond to a spot of movement in a specific direction across the retina

Question 32

What are some characteristics of X ganglion cells?

Answer 32

• most numerous
• small fields so fine detail
• resposnible for color vision

Question 33

What are some characteristics of Y ganglion cells?

Answer 33

• largest and highest velocity
• wide spread retinal areas

Question 34

What is the main purpose of the Y ganglion cells?

Answer 34

-to alert the brain to a new visual stimulus and gives clues as to where to move the eyes

Question 35

Why are ganglion cells located laterally to the sopt of light inhibited? (off)

Answer 35

-the “on” ganglion cell laterally inhibits those around it, increasing contrast

Question 36

What type of bipolar cells transmit a direct, excitatory signal?

Answer 36

-depolarizing bipolar cells

Question 37

Why type of bipolar cells transmit a lateral inhibitory signal?

Answer 37

-hyperpolarizing bipolar cells

Question 38

How do the ganglion cells start to distinguish color?

Answer 38

-some cone colors excite the depolarizing ganglion cells while other inhibit it (hyperpolarizing ganglion cells). (comon with red and green)