Retinal Information Processing

Question 1

Molecules called visual pigments are made in the _____ and stored in the _______ where they are incorporated into the membrane

Answer 1

inner segment ; outer segment

Question 2

Chromophore

Answer 2

Captures light photons and is the part of a molecule responsible for its color.

Question 3

Bipolar Cells

Answer 3

The intermediary between the photoreceptors and the ganglion cells

Question 4

How do photoreceptors pass their information onto bipolar cells?

Answer 4

Via graded potentials which vary in size instead of an all or nothing action potential

Question 5

The relationship between glutamate and cell Synapse

Answer 5

Amount of glutamate present in the photoreceptor- bipolar cell synapse at any one time by inversely proportional to the number of photons being absorbed by the photoreceptor

Question 6

Information Pathway of a Photon

Answer 6

1) A photon is captured by one of the photoreceptors and is absorbed by a visual pigment
2) The energy of the photon is transferred to the chromophore portion of the molecule in a process known as photoactivation
3) Hyperpolarization triggers the reduction of glutamate molecules released in the synapse 4) Finally, this change alerts the bipolar cells that a photon has been captured
5) Since the trigger is a reduction in glutamate concentration, the magnitude of reduction is used as an indicator of how many photons are absorbed

Question 7

Lateral Inhibition

Answer 7

The phenomenon in which a neuron’s response to a stimulus is inhibited by the excitation of a neighboring neuron

Question 8

Role of horizonal cells

Answer 8

Play a role in lateral inhibition and send their information down the pathway to the ganglion cells

Question 9

Where do amacrine cells receive info?

Answer 9

Amacrine cells do not receive information from the photoreceptors, instead communicating with bipolar cells and other amacrine cells

Question 10

Bipolar to Ganglion Cell Tranmission

Answer 10

The bipolar cells transmit the signals from the photoreceptors or the horizontal cells, and pass it on to the ganglion cells directly or indirectly (via amacrine cells)

Question 11

Where do bipolar cells receive input?

Answer 11

Either from rods or cones but not both

Question 12

Difference between diffuse bipolar cells and midget cells

Answer 12

Diffuse BC: Cells that get information from multiple different photoreceptors

Midget BC: Cells that get information form a single cone

Question 13

Lateral Geniculate Nucleus (LGN)

Answer 13

A structure in the thalamus that receives input from the retinal ganglion cells and has input and output connections to the visual cortex

Question 14

How many layers does the LGN have?

Answer 14

6 layers
top four are parvocellular -two layers from each eye
bottom two are magnocellular - one layer from each eye

Question 15

Where do layers 1 & 2 (magnocellular layers) receive input from?

Answer 15

Large neurons receive input from m ganglion cells in the retina which means they receive input from diffuse bipolar cells

Question 16

Where do layers 3-6 (parvocellular layers) receive input from?

Answer 16

smaller cells that receive input from retina’s P ganglion cells which means they recieve input from midget ganglion cells

Question 17

Receptive Field

Answer 17

Region of retina in which visual stimuli influence the neuron’s firing rate

Question 18

ON Centre Ganglion Cell Firing Rate

Answer 18

Increases its firing rate when a light is turned on in the center of its receptive field and decreases its firing rate when light is turned on in the surround

Question 19

OFF Centre Ganglion Cell Firing Rate

Answer 19

Decreases their firing rates when a light is turned on in a spot in the center of its receptive field and increases when light is turned on in a spot in the surround

Question 20

What is the size of the receptive field determined by?

Answer 20

The size of the receptive field is determined by how many photoreceptors are converging into the ganglion cell
- More photoreceptors = larger receptive field

Question 21

How do retinal ganglion cells act as a filter?

Answer 21

Retinal ganglion cells act as a filter by responding best to stimuli that are just the right size and less to stimuli that are larger or smaller

Question 22

What are ganglion cells most and less sensitive to?

Answer 22

Sensitive to differences in the intensity of light in the centre and in the surround, and they are less affected by the average intensity of light

Question 23

How do the receptive fields of P and M cells differ?

Answer 23

1) Receptive fields of P cells is always smaller than M cells at all eccentricities
2) M cells are more sensitive and better able to detect visual stimuli than P cells under low light conditions, however the smaller receptive fields on P cells result in greater acuity than M cells

Question 24

The magnocellular pathway carries information about?

Answer 24

Large, fast things (low spatial frequency, high temporal frequency) and is colorblind

Question 25

The parvocellular pathway carries information about?

Answer 25

Information about small, slow, colorful things (high spatial frequency, low temporal frequency

Question 26

Difference in firing rate between P and M Ganglion Cells

Answer 26

1) P cells have a sustained firing rate over the course of stimulus presentation
2) M cells have a transient firing rate, it gives a brief burst and then returns to
spontaneous firing even when the stimulus is present

Question 27

What signals do P and M cells signal different information to the brain?

Answer 27

• P cells provide information about mainly the contrast in the retinal image
• M cells signal information about how the image changes over time

Question 28

Intrinsically photosensitive Retinal Ganglion Cells (ipRGCs)

Answer 28

Refer to ganglion cells that do not receive info from photoreceptors

Question 29

What are the first photoreceptors to mature in the retina and therefore are the first to send light driven signals to the brain?

Answer 29

Intrinsically photosensitive Retinal Ganglion Cells (ipRGCs)