Visual system

Question 1

What is the blind spot? Why is it not visible in your visual field?

Answer 1

Exit of the retina for ganglion cells forming the optic nerve. The corresponding portion of the retina is rid of photoreceptors. Not perceivable because visual processing “fills” the “empty” portion of the visual field.

Question 2

What are the five retinal cell types? From the bottom of the retina to the top, place the cell types in order.

Answer 2

Ganglion cells
^^
Amacrine cells
^^
Bipolar cells
^^
Horizontal cells
^^
Photoreceptors

Question 3

What are “nuclear” layers of the retina referring to? “Plexiform” layers?

Answer 3

Retinal cell bodies
Synapses

Question 4

True or false: there is an even number of rods and cones.

Answer 4

False: much more rods.

Question 5

In what portion of the retina do we find most cones and almost exclusively cones?

Answer 5

Fovea.

Question 6

Why does light hyperpolarize photoreceptors?

Answer 6

Light indirectly causes the transformation of cGMP into 5’GMP -> no more cGMP to keep open the cGMP-gated cation channels -> no more cation flowing in -> neuron hyperpolarizing.

Question 7

How is the intensity of light translated in the visual system?

Answer 7

By the AP frequency of the ganglion cells.

Question 8

From what does arise on/off-center/surround receptive fields?

Answer 8

Lateral inhibition on photoreceptors by horizontal cells.

Question 9

Why are receptive fields larger outside of the fovea?

Answer 9

More photoreceptors feed to one single ganglion cell.

Question 10

Retinal ganglion cells are mostly from what type?

Answer 10

Midget ganglion cells

Question 11

Provide the following information about midget ganglion cells:

Type of cones they have as input;
The information they provide;
Size of their receptive field;
Pathway they are belonging to.

Answer 11

M (green) and L (red) photoreceptors;
Ratio between amount of red and green in light + ration of brightness overall;
Small receptive field;
P-pathway (parvocellular).

Question 12

Provide the following information about parasol ganglion cells:

Type of cones they have as input;
The information they provide;
Size of their receptive field;
Pathway they are belonging to.

Answer 12

M (green) and L (red) photoreceptors (but convey ACHROMATIC signal);
Movement and changes in illumination;
Large receptive field;
M-pathway (magnocellular).

Question 13

Which ganglion cell type is good at detecting edges? Why this type?

Answer 13

Midget ganglion cells because their on-center/off-surround receptive fields allow them to detect contrast in brightness.

Question 14

What are the three main types of ganglion cells?

Answer 14

Midget, parasol and bistratified.

Question 15

Provide the following information about bistratified ganglion cells:

Type of cones they have as input;
The information they provide;
Size of their receptive field;
Pathway they are belonging to.

Answer 15

S, M and L photoreceptors;
Ratio between amount of blue and yellow (red/green) in light;
Large receptive field;
K-pathway (koniocellular).

Question 16

What ganglion cells are particularly concentrated in the fovea?

Answer 16

Midget.

Question 17

Why someone with only one cone type would be color blind?

Answer 17

Color perception arises from contrast between different wavelengths (captured by different cone types).

Question 18

Complete the sentence with the words below:

-ipsilaterally
-contralaterally

For each eye, nasal visual information is sent ____ and visual temporal information is sent ____.

Answer 18

For each eye, nasal visual information is sent contralaterally and visual temporal information is sent ipsilaterally.

Question 19

How many layers does contain the lateral geniculate?

Answer 19

6

Question 20

The layers of the LGN receive ipsilateral or contralateral inputs from both eyes. Describe the distribution.

Answer 20

Layers 1, 4, 6 get input from contralateral eye.
Layers 2, 3, 5 get input from ipsilateral eye.

Question 21

What layers of the LGN form the m-pathway? The p-pathway? The k-pathway?

Answer 21

M-pathway: 1-2.
P-pathway: 3-4-5-6.
K-pathway: in-between layers.

Question 22

Bottom portion of optic radiation corresponds to the ____ visual field. Top portion of optic radiation corresponds to the ____ visual field.

Answer 22

Bottom portion of optic radiation corresponds to the upper visual field. Top portion of optic radiation corresponds to the lower visual field.