Visual Processing

Question 1

What are photoreceptors and where are they located?

Answer 1

Photoreceptors are light-sensitive neurons located in the retina.

Question 2

What are the two main types of photoreceptors in the retina?

Answer 2

cones and rods.

Question 3

How do photoreceptors respond to stimuli?

Answer 3

with graded membrane potentials instead of firing action potentials.

Question 4

What is the structure of cones and rods?

Answer 4

Both cones and rods have outer segments with disk-like layers, inner segments, and a synapse

Question 5

How does light affect photoreceptors?

Answer 5

When light hits photoreceptors, pigment molecules change shape, triggering a chemical cascade that hyperpolarizes the cell, reducing its release of glutamate.

Question 6

What pigment is found in rods?

Answer 6

rhodopsin

Question 7

What is the appearance of the fovea?

Answer 7

a central pit in the macula, densely packed with cones.

Question 8

Where is the blindspot and why is it called a blindspot?

Answer 8

The blind spot occurs when the optic nerve exits the eye

there are no photoreceptors in this region.

Question 9

What type of lighting conditions are cones mainly used in, why, and what is their job?

Answer 9

Cones are less sensitive and function in bright light, distinguishing colours.

Question 10

How do rods adapt to darkness?

Answer 10

Rods rebuild their stores of rhodopsin over approximately 30 minutes in a process called dark adaptation.

Question 11

How are cones and rods distributed in the retina?

Answer 11

Cones are concentrated in the fovea, while rods are mainly found in the peripheral retina, making peripheral vision more sensitive to light.

Question 12

What is a receptive field in the visual system?

Answer 12

It refers to the set of photoreceptors influencing cells in the retina.

Question 13

What is the difference between on-center and off-center bipolar cells?

Answer 13

On-center cells are excited by light in the center and inhibited by light in the surroundings, while off-center cells are the opposite.

Question 14

How do bipolar cells respond to uniform lighting?

Answer 14

Bipolar cells do not respond to uniform lighting because the effects of the center and surroundings cancel out, reacting only to contrast.

Question 15

What is the function of retinal ganglion cells? (3)

Answer 15

receive input from bipolar cells

detect contrast

transmit visual information via action potentials to the brain.

Question 16

How is visual information compressed before reaching the brain?

Answer 16

The retina condenses input from 126 million photoreceptors into about 1 million ganglion cells

Question 16

Where is the optic chiasm located, and what happens there?

Answer 16

The optic chiasm is where optic nerve fibres cross, with nasal retina fibers crossing to the opposite side of the brain, while temporal fibers do not.

Question 17

what is the job of photoreceptors?

Answer 17

They convert light energy into electrical energy in cells through phototransduction.

Question 18

how many cones does the retina have?

Answer 18

6 million cones

Question 19

how many rods does the retina have?

Answer 19

120 million rods.

Question 20

what pigments are found in cones

Answer 20

cones have three different pigments corresponding to different types of cones.

Question 21

what is the job of the fovea and why?

Answer 21

It is used for detailed vision and has the highest visual acuity.

Question 22

What type of lighting conditions are rods mainly used in?

Answer 22

Rods are more sensitive, functioning in dim light but are bleached out in bright conditions.

Question 23

why is visual information compressed before reaching the brain?

Answer 23

reducing redundancy to transmit information efficiently.

Question 24

what does the outer layer contain in cone and rod structures?

Answer 24

visual pigments

Question 25

what does the inner layer contain in cone and rod structures?

Answer 25

nucleus and organelles

Question 26

what does the synapse in cones and rods release?

Answer 26

glutamate.