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321 - Physiology > Lecture 9 - Vision > Flashcards

Lecture 9 - Vision Flashcards

1
Q

What is visible light?

A

The small portion of the electromagnetic spectrum that we can see

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2
Q

Scotopic

A

Function of eye in very low light

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3
Q

Mesopic

A

At threshold of cone vision, low light

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4
Q

Photopic

A

Eye function under well lit conditions, colour vision (mainly cones)

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5
Q

What is the purpose of a third eyelid?

A

-Keeps eye moist
-Removes irritants
-Shield eyes

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6
Q

What is the function of the cornea?

A

-Refracts light towards the retina
-Protects against dirt/debris
-Sensitive (blink reflex)
-Protects against infection
-Filters UV light

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7
Q

Where does most light refraction occur?

A

Cornea

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8
Q

Function of the lens?

A

-Filters some UV light
-Accommodation for far and near vision
-Finely focuses light

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9
Q

Function of the retina?

A

-Light detection
-Signal processing through 10 cell layers
-Signal transmission
-Adaptation

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10
Q

What kind of pupils do predators usually have and why?

A

Vertical pupils - good for depth perception and distance without moving head

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11
Q

What kind of pupils do prey usually have and why?

A

Horizontal pupils - Enhances light from front and behind and enhances ground view

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12
Q

What is cyclovergence?

A

The ability to keep eyes level to the ground as an animal bends its head to monitor environment while grazing

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13
Q

Where does the dorsal oblique muscle pull the eye?

A

Diagonal downwards

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14
Q

Where does the ventral oblique muscle pull the eye?

A

Diagonal upwards

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15
Q

Where does the medial rectus pull the eye?

A

Towards the midline

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16
Q

Where does the lateral rectus pull the eye?

A

Towards the lateral side

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17
Q

What is accommodation?

A

The process of bending (refracting) light rays to focus them on the retina

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18
Q

When is accommodation required and when is it not required?

A

Required - Viewing close objects
Not required - viewing far objects

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19
Q

Do horses use accommodation?

A

No, they may have a unique retinal structure

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20
Q

What does activation of the parasympathetic nervous system do to pupils?

A

It constricts pupils and promotes accommodation (near vision)

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21
Q

What does activation of the sympathetic nervous system do to pupils?

A

It dilates pupils and flattens the lens (far vision)

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22
Q

What happens when the ciliary muscles contract?

A

The suspensory ligaments become slackened, causing the lens to become more rounded.

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23
Q

How many layers is the retina organized into?

A

10 layers

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24
Q

What is the 1st layer of the retina?

A

Pigment epithelium

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25
Q

What is the 2nd layer of the retina?

A

Photoreceptor layer

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26
Q

What is the 3rd layer of the retina?

A

Outer limiting membrane

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27
Q

What is the 4th layer of the retina?

A

Outer nuclear layer (nuclei of photoreceptors)

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28
Q

What is the 5th layer of the retina?

A

Outer plexiform layer

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29
Q

What is the 6th layer of the retina?

A

Inner nuclear layer

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30
Q

What is the 7th layer of the retina?

A

Inner plexiform layer

31
Q

What is the 8th layer of the retina?

A

Ganglion cell layer

32
Q

What is the 9th layer of the retina?

A

Nerve fiber layer

33
Q

What is the retina like?

A

An ogre (it has layers)

34
Q

What 5 cell types accomplish visual processing?

A

-Photoreceptors
-Horizontal cells
-Bipolar cells
-Amacrine cells
-Ganglion cells

35
Q

What do photoreceptors do?

A

Transduce light (photons) into electrical signals (action potentials)

36
Q

What do Horizontal Cells do?

A

Enhance contrast and edge detection (detects visual changes)

37
Q

What do Bipolar Cells do?

A

Intermediate cells that project to Ganglion Cells

38
Q

Which cells do photoreceptors synapse with?

A

Bipolar Cells

39
Q

What do Amacrine cells do?

A

Interconnect bipolar, ganglion cells and other amacrine cells to refine the visual signal

40
Q

What do Ganglion Cells do?

A

Produce final signal that is propagated to the brain

41
Q

What is convergence?

A

Where lots of rods converge on fewer bipolar cells, which converge on even fewer ganglion cells for processing

42
Q

If there is decreased convergence, we can detect _________ detail

A

Greater

43
Q

What is the fovea?

A

An area of high visual acuity

44
Q

Do most veterinary species have a fovea?

A

No; they have an area of high visual acuity around the central retina, but with no distinct fovea

45
Q

What is the tapetum lucidum?

A

A reflective layer of cells behind the retina to reflect light back into the photoreceptors when in low light conditions

46
Q

What is the drawback of having a tapetum lucidum?

A

Reduced visual acuity (because the extra reflection bends the light)

47
Q

What protein is involved in the activation of rods?

A

Rhodopsin (vitamin A derivative)

48
Q

How are rods activated?

A

Light causes a conformational change in rod cells, which leads to hyperpolarization of the rod cells by closure of Na+ channels

49
Q

Where are rods and cones usually located on the retina?

A

Rods - Peripheral retina
Cones - Central retina

50
Q

Which cones do dogs have?

A

Green-yellow
Blue

51
Q

Which cones do horses have?

A

Red
Blue

52
Q

What is Occipital and Association Cortices responsible for?

A

Perception of objects

53
Q

How are objects represented on the retina?

A

Inverted. Brain turns them right side up

54
Q

What occurs through the lateral geniculate - visual cortex pathway?

A

Conscious perception

55
Q

What does the retino-tectal pathway control?

A

-Pupillary reflexes
-Reflex orientation of the eye

56
Q

What does the retino-hypothalamic pathway control?

A

Circadian rhythms and seasonal changes

57
Q

Where are images from the left visual field processed?

A

Right occipital cortex

58
Q

Where are images from the right visual field processed?

A

Left occipital cortex

59
Q

What is the pathway of an action potential for simple processing?

A

Optic nerve –> lateral geniculate –> optic radiations –> occipital cortex in area VI

60
Q

What is the pathway of an action potential for complex processing?

A

Optic nerve –> lateral geniculate –> optic radiations –> occipital cortex in area V2, 3

61
Q

What does binocular vision provide?

A

-Stereopsis (depth perception)
-Binocular summation

62
Q

What type of animal (role in ecosystem) has greater binocular vision?

A

Predators. Eyes are placed forward

63
Q

Why do prey animals tend to have eyes placed on the side of their head?

A

To better detect predators with a maximum field of view

64
Q

What do simple cells in the visual cortex respond to?

A

Lines placed in certain areas of the visual field at certain orientations

65
Q

What do complex cells in the visual cortex respond to?

A

Edges or lines in a particular orientation no matter where they are in the visual field

66
Q

What is the visual stream for WHERE something is?

A

Occipital lobe –> parietal lobe

67
Q

What is the visual stream for WHAT something is?

A

Occipital lobe –> temporal lobe

68
Q

What occurs in cataracts?

A

-Cloudiness of the lens
-Scatters light so that it cannot be focused on the retina

69
Q

What occurs in glaucoma?

A

Increased intraocular pressure

70
Q

What occurs in conjunctivitis?

A

Inflammation of the thin mucous membrane of the eyelid

71
Q

What is the Menace Response Pathway

A

Reflex blinking that occurs following a fast movement of an object

-Tests integrity of cranial nerve pathways (2-optic and 7-facial)

72
Q

Which cranial nerves are involved in the palpebral reflex?

A

Trigeminal (5) and facial (7)

73
Q

What is the pupillary reflex?

A

Reduction in pupil size in response to light
–> Response is consensual
–> Controlled by parasympathetic pathway

74
Q

What is the Dazzle reflex?

A

Strong light causes immediate closing of the eyelids.
–> Controlled from subcortical areas of the brain
–> Useful when pupillary reflex is difficult to evoke
–> Can also cause 3rd eyelid protrusion, blinking, and head movements

321 - Physiology (52 decks)

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