Exam 2

Question 1

Shape of Rods

Answer 1

large and cylindrical

Question 2

Shape of cones

Answer 2

small and tapered

Question 3

Distribution of Rods and Cones on Retina

Answer 3

Fovea consists soley of cones

Peripheral retina has both rods and cones

More rods that cones in periphery

Question 4

Photopigment of Rods

Answer 4

Rods contain rhodopsin

Rhodopsin mediates dim light vision and thus is extremely sensitive to light.

Rhodopsin is a G-protein coupled receptor, and is the most abundant protein in the rod cells found in the retina (Figure 1). It functions as the primary photoreceptor molecule of vision,

Question 5

Photopigments of Cones

Answer 5

Cones contain different forms of iodopsins

Question 6

Specialization of Rods

Answer 6

Rods specialized for motion, dim light

Question 7

Specialization of Cones

Answer 7

Cones specialized for color, detail, and bright light

Question 8

Opsins

Answer 8

light-sensitive GPCRs found in photoreceptor cells on the retina

Opsins convert photons of light into an electrochemical signal through the process called phototransduction

Question 9

Phototransduction

Answer 9

The process of the opsins converting photons of light into an electrochemical signal

Question 10

What neurotransmitter does rods release in darkness?

Answer 10

rods release glutamate when its dark

Question 11

What happens when opsins are struck by light?

Answer 11

Opsins including rhodopsin and iodopsins change shape and cause a biochemical cascade that closes the Na+ ion channel.

By closing this Na+ channel, Na+ ions can no longer enter the cell. This causes the cell to hyperpolarize (become more negative). This inhibits action potentials as the potential membrane becomes too negative and is below the excitation threshold. This causes the action potentials from the rods to stop.

When the rods can no longer send action potentials, less glutamate is released.

As a result, the next cells in the neural chain (bipolar cells) lose their inhibition and become active, sending signals about light to the brain.

Question 12

At what wavelength (nm) do Rod pigment absorb the best?

Answer 12

500 nm

Question 13

What are the three kinds of cones?

Answer 13

Small Cones (S) - 419 nm (dark blue)

Medium Cones (M)- 531 nm (light greenish-yellow)

Large Cones (L) - 558 nm (yellow)

Question 14

Relative Abundance of Long, Medium, and Short wavelength cones

Answer 14

Long and medium wavelength cones are more abundant that short wavelength cones.

Question 15

Number of Rods in Retina

Answer 15

120 million rods

Question 16

Number of Cones in Retina

Answer 16

6 million

Question 17

Blind spot

Answer 17

The place in the eye where the optic nerve leaves the eye

Question 18

Why can we not see our blindspot?

Answer 18

We don’t see the blindspot because the other eye covers the blind spot of the other.

The blindspot is located at the edge of the visual field.

The brain “fills in” the spot

Question 19

Color Vision Deficiency

Answer 19

A group of conditions that impacts how an individual perceives color

Dichromat
Monochromat
Anomalous

Question 20

Ishihara plates

Answer 20

displays of colored dots used to test for the presence of color deficiency

The plates are colored so that trichromats perceive a pattern, but people with color deficiency cannot