Recap Visual system 1

Question 1

Just to clear up:

• Rods are most important for …
• Cones are most important for …

Answer 1

• Rods are most important for seeing in the dark, since they’re most sensitive to light.
• Cones are most important for visual acuity and shape.

Question 2

How can rods and cones signal difference intensities of light?

Answer 2

Rods and cones hyperpolarize when they sense light. When the intensity of the light changes, this is also seen in a change in membrane potential (there’s a graded response of the membrane potential to a graded change in light).

Question 3

What is dark current?

Answer 3

Dark current is where the cGMP-gated sodium channels (cation channels) on rods and cones are open, since there is no light present. This results in the depolarization of rods and cones

Question 4

Which second messenger is important in light transduction?

Answer 4

cGMP.

• When the concentration of cGMP increases due to the absence of light, cation channels are open. This causes depolarization of the rods and cones.
• When the concentration of cGMP decreases due to the presence of light, cation channels close. This causes hyperpolarization of the rods and cones.

Question 5

What is the connectivity pattern in rods and cones to bipolar cells?

Answer 5

• Many rods are connected to one bipolar cell.
• One cone is connected to one bipolar stal.

Question 6

Which cells in the retina are able to generate action potentials?

Answer 6

On- and off-center ganglion cells