Week 10 - Vision - finished

Question 1

What are the 3 layers of the eye?

Answer 1

Outermost sclera
Choroid
Innermost retina

Question 2

Where does the light enter the eye and through what structures?

Answer 2

Anteriorly through the cornea and lens to be focussed on the retina where the visual perception begins

Question 3

What is the function of the cornea and the lens together?

Answer 3

A simple converging lens meaning the image reaches the retina both reversed and inverted.

Question 4

How much does the lens contribute to the refractive power of the eyes? Where does the rest of the refractive power come from?

Answer 4

15%

The majority of the eyes refractive power comes from the cornea, the lens further aids this process by changing it’s shape, this process is known as accommodation

Question 5

Are the cells of the retina PNS or CNS cells?

Answer 5

The CNS, because of their development from the optic vesicle of the diencephalon.

Question 6

What are the 5 basic cell types within the retina? List them from innermost to outermost

Answer 6

Ganglion cells
Amacrine cells
Horizontal cells
Bipolar cells
Photoreceptors

Question 7

Where does visual processing begin?

Answer 7

At the photo receptors at the retina

Question 8

What are the cells from innermost to outermost that light has to pass through before it gets to the photoreceptors?

Answer 8

Ganglion cells
Amacrine cells
Horizontal cells
Bipolar cells

Question 9

What are photoreceptors responsive to?

Answer 9

Light

Question 10

What is the basic pathway through the retina in terms of impulse?

Answer 10

Photoreceptors to the bipolar cells to the ganglion cells which are the cells of the optic nerve

Question 11

What are the ganglion cells basically cells of?

Answer 11

The optic nerve

Question 12

What are the 4 cells layers in the retina other than photoreceptors sensitive to?

Answer 12

The chemical change in the photo receptors when they are exposed to light. Before the light reaches the photoreceptors, these cells are unresponsive

Question 13

What gives a higher degree of differentiation in vision?

Answer 13

Placing greater emphasis on differences in intensity rather than absolute intensities.

Question 14

What are the 2 key classes of photoreceptors?

Answer 14

Rods and cones

Question 15

How mich to rods outnumber cones?

Answer 15

20-1

Question 16

What are rods sensitive to?

Answer 16

Light

Question 17

When do rods function best?

Answer 17

In dim light or low light conditions (our night vision)

Question 18

Do rods function much during the day?

Answer 18

No

Question 19

What kind of information do rods give us?

Answer 19

Information about gross shape and form

Question 20

Where are rods most highly concentrated?

Answer 20

Around the periphery of the retina

Question 21

Does the fovea contain rods or cones or both?

Answer 21

Cones only

Question 22

What kind of information do cones give us?

Answer 22

Detailed nformation about vision and colour

Question 23

What is the fovea?

Answer 23

The area of highest visual acquity

Question 24

How much of the information sent to the primary visual cortex comes from the fovea?

Answer 24

Almost half

Question 25

What factors make the fovea the area of highest visual acquity?

Answer 25

Increased by the displacement of all other retinal cells and their axons. Blood vessels are also displaced at the fovea where the cells receive nutrients via diffusion

Question 26

What kind of output do rods and cones have? When does this output get inhibited?

Answer 26

They have tonic or basal glutamate output. It gets inhibited my exposure to light.

Question 27

What are technically the second order neurons in the input of visual information?

Answer 27

The bipolar cells

Question 28

What makes bipolar cells fire?

Answer 28

They fire in response to decreased glutamate output from the rods and cones

Question 29

What bipolar cells receive information from rods?

Is this input large or small (do they receive input from a few or many rods)? What does this mean for the visual information that is processed here?

Answer 29

Rod bipolar cells

Rod bipolar cells receive input from several rods giving them a large receptive field, this decreases the clarity of the visual input but increases their sensitivity to light.

Question 30

What bipolar cells receive information from the cones?

Is this input large or small (do they receive input from a few or many cones)? What does this mean for the visual information that is processed here?

Answer 30

Cone bipolar cells.

Cone bipolar cells typically receive inputs from fewer cone cells, usually around one or two; this helps to maintain high visual acuity

Question 31

What are the 3rd order neurons of the visual system?

Answer 31

The ganglion cells

Question 32

Where do the axons of the ganglion cells leave the retina?

Answer 32

Through the optic disc and form the optic nerve

Question 33

Where do the axons of the ganglion cells become myelinated?

Answer 33

Once they exit the retina and become the optic nerve

Question 34

Describe the visual pathway:

Answer 34

Hemidecussation of visual information via the optic chiasm.

Only information from the nasal half of each retina decussates.

Axons of the ganglion cells terminate at the lateral geniculate nucleus.

From the lateral geniculate nucleus information travels back to the calcarine cortex in the optic radiations.

Each radiation is divided into a superior and inferior loop which travel separate courses back to the cortex.

This is protective measure to reduce the impact of a lesion in the pathway

Question 35

Describe the direct and indirect pathways of the visual system

Answer 35

Information from the photoreceptors can reach these output cells via two pathways the direct/vertical pathway or the indirect/horizontal pathway.

The direct pathway is that outlined above; photoreceptors -> bipolar cells -> ganglion cells.

The indirect pathway involves greater processing and includes the horizontal and amacrine cells, in this pathway processing still begins with the photoreceptors. Photoreceptors -> bipolar cells -> horizontal cells -> bipolar cells -> amacrine cells -> ganglion cells.

These two pathways are typically functioning simultaneously.