L1-The Visual System

Question 1

What does the sensory system do?

Answer 1

Allows us to interface with the world.

Question 2

List seven basic characteristics of the sensory system.

Answer 2

1) Specific for a type of energy

2) Transduce (convert) the energy into a code the brain understands

3) Filters the “flood” of information

4) Discriminates between intensities of energy

5) Responds reliably

6) Suppresses extraneous (irrelevant) information

7) Contributes to direction of attention and behavior

Question 3

How are receptors spread around the body?

Answer 3

Receptors must be spread with density related to demand.

(i.e. spatial location of receptors must maximize knowledge of the world in an efficient manner and this topographic information must be understood by the brain)

Question 4

What must receptors be able to respond to?

Answer 4

Receptors must be able to respond to stimulus intensity.

e.g. the visual system needs to be able to distinguish between light and dark.

Question 5

What is the difference between anatomical vs physiological?

Answer 5

Anatomy refers to the internal and external structures of the body and their physical relationships, whereas physiology refers to the study of the functions of those structures.

Question 6

What is the receptive field?

Answer 6

An area of space where stimulation results in a response.

(every receptor has one)

Question 7

Describe the basic sensory visual processing pathway.

Answer 7

1) Photo(receptors) in retinal ganglion cells are transmitted through the optic nerve to the 2) Thalamus (Lateral Geniculate Nucleus/ LGN) which are transmitted through the optic radiations to the 3) visual cortex.

Question 8

What side (left/right) of the visual field is projected by which side (left/right) of the hemisphere?

Answer 8

The right side of the visual field is projected by the left hemisphere of the brain while the left side of the visual field is projected by the right hemisphere of the brain.

Question 9

Descsribe an owl’s eyes

Answer 9

tubes/cylinder rod-shaped eye

Question 10

describe bees’ eyes

Answer 10

5 eyes, 2 large compound eyes (lots of tiny lenses that can detect shapes) and 3 simple or ocelli which detect light but not shapes

Question 11

describe lizard eyes

Answer 11

have 4 cones (RGB+UV range) same in some birds and fish

Question 12

describe rabbit eyes

Answer 12

located laterally, provide 360 view

Question 13

What is the function of the visual system?

Answer 13

to detect, filer and process the visual scene into features which can be analyzed in parallel prior to binding or integration into a whole perception

Question 14

What is the stimulus of the eye?

Answer 14

visible light, contrast and color

contrast - the ultimate reason we see anything because it allows us to distinguish objects from each other to perceive them.

Question 15

What is the hub of the eye?

Answer 15

Retina

photoreceptors go to neurons of retina which have correlation with anatomy of optic nerve, LGN, visual cortex and is best regarded as an outgrowth of the brain?

Question 16

What are the eye’s associated processes?

Answer 16

iris/pupil reaction to light level
fixation - extraocular muscles (looking at a stimulus)
accommodation (focusing by crystalline lens)

Question 17

Sagittal or lateral plane

Answer 17

divides body/object into right and left side

Question 18

transverse/ axial/ cross-sectional plane

Answer 18

divides body/object of regard into superior (upper) and inferior (lower) parts

Question 19

coronal/frontal plane

Answer 19

divides body/object of regard into front and back parts

Question 20

anterior/ rostral =

Answer 20

front

Question 21

posterior/ caudal =

Answer 21

back

Question 22

dorsal =

Answer 22

top

Question 23

ventral =

Answer 23

bottom

Question 24

lateral =

Answer 24

toward the side (R/L)

Question 25

medial =

Answer 25

toward the midline

Question 26

ipsilateral =

Answer 26

same side

Question 27

contralateral =

Answer 27

opposite side

Question 28

superior =

Answer 28

above

Question 29

inferior =

Answer 29

below

Question 30

proximal =

Answer 30

closer to origin of strucutre

(e.g. the elbow is proximal to the wrist)

Question 31

distal =

Answer 31

further from origin of structure

(e.g. the wrist is distal to the elbow)

Question 32

What are the three chambers of the human eye?

Answer 32

1) Anterior chamber
2) posterior chamber (smallest)
3) vitreous chamber (largest)

Question 33

What are the three coats of the human eye?

Answer 33

1) internal nervous layer - retina
2) intermediate vascular pigmented layer - uvea, ciliary body, iris, choroid
3) external, fibrous layer - cornea, sclera

Question 34

What are the four sections of the optic nerve?

Answer 34

1) intraocular
2) intraorbital
3) intracanalicular
4) intracranial

Question 35

What is the function of the optic nerve?

Answer 35

it’s the anterior extension of the white matter of the brain. It carries nerve fibers that are the axons of the ganglion cell layer of retina to the lateral geniculate body then to the visual cortex.

• nerve fibers converge on the optic disk and exit through the lamina cribrosa
  optic nerve fibers are (generally) *non-myelinated within the eyeball but are myelinated posterior to the disc
• optic nerve consists of 500,000 to 1,200,000 axons of approx. 1um diameter
• axons comprising the optic nerve do not posses Schwann cells and can therefore not regenerate

Blood supply
- derived from ophthalmic artery via: branches of central retinal artery and short ciliary arteries

Question 36

describe the internal layer (the retina (sensory layer))

Answer 36

1) photoreceptors are at the back of the retina
2) the retinal photoreceptors are our main interface with visual world

intervening structures of the eye must do one or more of the following to maintain homeostasis:
- nourishment
- waste removal
- protection
- transparency anteriorly
- sharp imagery
- pointing to item of interest in world (fixation)
- teaming with the other eye (binocularity)

Question 37

What is the blind spot?

Answer 37

Rod and cone photoreceptors are differently distributed across the retina where there are 0 receptors at around 15 degrees from the fovea on the nasal side because that is where the optic nerve is located hence resulting in the blind spot.