Chapter 4: Visual System

Question 1

What is the function of the conjunctive?

Answer 1

Membrane that covers the front of the eye

Lines the inside of the eyelids

Question 2

What is the function of the cornea?

Answer 2

Takes nutrients and fluid from the aqueous humour

Question 3

What is the function of the pupil?

Answer 3

Opening that lets light enter the eye and reach the retina

Question 4

What is the function of the iris?

Answer 4

Muscle that gives the eye its color and contraction lets eye adapt to changing light

Question 5

What is the function of the lens?

Answer 5

Focuses light rays onto retina

Question 6

What is the function of the retina?

Answer 6

Converts image formed by light rays into nerve impulses by photoreceptors

Question 7

What bends light?

Answer 7

Aqueous and viteous humor

Question 8

What do rods do?

Answer 8

Let you see shades of grey in low light conditions

Question 9

What do cones do?

Answer 9

Sensitive to color in bright light conditions

Question 10

What are the 3 categories of the opsins?

Answer 10

Blue cones
Red cones
Green cones

Question 11

What is color blindness?

Answer 11

Lesions in part of the visual cortex

Cones containing opsins for seeing red-green absent

Question 12

In what gene is the color blindness on?

Answer 12

x chromosome

Question 13

What are the forms classified from for color blindness and what are they?

Answer 13

From the type of cone affected
Protanopia
Deuteranopia
Tritanopia

Question 14

What is achromatopsy?

Answer 14

Total color blindness

Question 15

What are the 3 layers of the retina?

Answer 15

1. Photoreceptive layer
2. Bipolar cell layer
3. Ganglion cell layer

Question 16

Describe layer 1 of the retina.

Answer 16

• back of eye

- contains cones and rods

Question 17

Describe layer 2 of the retina.

Answer 17

conveys information from photoreceptors to ganglion cells

Question 18

Describe layer 3 of the retina.

Answer 18

Receives visual information from bipolar cells and axons give rise to optic nerve

Question 19

What is the dark current? And what is the membrane potential of the outer segment of rods in the dark?

Answer 19

• When the retina is not stimulated, the photoreceptors continuously flow sodium
• Approx. -30 mV

Question 20

What is the result of dark current?

Answer 20

Light hyperpolarizes photoreceptor cells and causes it to release fewer neurotransmitter molecules into synapse with bipolar cells

Question 21

Where is the fovea located and it’s the function?

Answer 21

• region of retina
• color-sensitive cones only in the fovea
• acute vision of birds and higher mammals

Question 22

What is the optic disk’s location and function?

Answer 22

• location of exit point from retina of fibers of ganglion cells
• responsible for blind spot

Question 23

What is the path of the optic nerve?

Answer 23

1. intersection of optic nerve of eyes at optic chiasm
2. majority of optic tract projects to lateral geniculate nucleus
3. projection from LGN to visual cortex via optic radiation

Question 24

What is the LGN?

Answer 24

• 6 layers
• receives input from only 1 eye (approx. 80%)
• Layer 1-4-6: receive input from contralateral eye
• Layer 2-3-5: receive input from ipsilateral eye

Question 25

what is the receptive field?

Answer 25

Portion of visual field where presence of a visual stimulus will modify the activity of a neuron in a layer of retina or cortex

Question 26

Describe what happens in presence and absence of light for bipolar cells.

Answer 26

Exposure of retina to light: hyperpolarizes rods and cones | Absence of light: neurons that connect rods and cones to ganglion cells actively inhibited by rods and cones

Question 27

What do the ganglion cells do?

Answer 27

Respond by increasing or decreasing the frequency with which they discharge action potentials

Question 28

What do complex cells do?

Answer 28

detect movement

Question 29

What do hyper-complex cells do?

Answer 29

See object's edges and angles

Question 30

What is the role of the visual cortex (V1)?

Answer 30

Sends a large proportion of its connections to V2 and some directly to V5

Question 31

What does the ventral pathway allow and where does it entend to?

Answer 31

- Temporal lobe - Allows to consciously perceive, recognize and identify objects by processing their intrinsic visual properties (shape and color)

Question 32

What does the dorsal pathway allow and where does it project to?

Answer 32

- Parietal lobe | - Visual-motor control over objects by processing their extrinsic properties (size, position and orientation in space)

Question 33

What are the ventral (what) stream disorders?

Answer 33

1. cerebral achromatopsia: complete or partial loss of color vision 2. visual object agnosia: failure to recognize objects by the visual modality alone 3. Pure Alexia: severe - can't read words, numbers, letters, map signs or symbols mild - read abnormally slowly 4. prosopagnosia: face blindness

Question 34

What are the dorsal (where) stream disorders?

Answer 34

1. Akinetopsia: motion blindness 2. Simultanagnosia: inability to sustain attention across different locations in visual field 3. Contralateral neglect 4. Blindsight