The Visual System

Question 1

What is sensation?

Answer 1

Bottom-up processing where sensory receptors receive and relay outside stimuli

Question 2

What is perception?

Answer 2

Top-down processing where the brain organizes and interprets information by putting it into context. We filter out most of the sensory info we collect.

Question 3

How can you reduce pain?

Answer 3

Drugs (NSAIDs, opioids), rub, cold, acupuncture, massage, hypnosis

Question 4

How can Capsaicin be perceived as pain or heat?

Answer 4

Capsaicin binds to receptors causing the channel to open below 98.6 degrees and gives a sensation of heat. Prolonged activation depletes substance P (a neurotransmitter for pain/heat)

Question 5

What is thermoreception?

Answer 5

The sence by which we perceive temperature

Question 6

True or False. Thermoreception and pain have the same pathways.

Answer 6

True.

Question 7

What is light?

Answer 7

Electromagnetic radiation visible to our eyes, travels in waves. This includes wavelength, frequency and amplitude.

Question 8

Describe how the eye functions like a camera lens (visual mechanics)

Answer 8

Light enters the eyes and is focused on the retina. Retinal photoreceptors transduce light energy to electrical energy.

Question 9

What percentage of nerve fibers are from the fovea? Where are the other nerve fibers found in the eye?

Answer 9

50%

Retina

Question 10

What is the optic nerve?

Answer 10

Axon bundles from retina to brain

Question 11

What is reflection?

Answer 11

Bouncing of light rays off of a surface

Question 12

What is absorption?

Answer 12

Transfer of light energy to a particle or surface (paint)

Question 13

What is refraction?

Answer 13

Bending of light rays from one medium to another

Question 14

How does diabetic retinopathy effect the eyes?

Answer 14

The first stage is non-proliferative diabetic retinopathy (NPDR) and has no symptoms - 20/20 vision

It can be detected by fundus photography - microaneurysms seen (microscopic blood-filled bulges in the artery walls)

Question 15

What are the two types of photoreceptors?

Answer 15

Rods and cones

Question 16

Describe visual phototransduction

Answer 16

Light is converted into electrical signals in photoreceptor cells. Occurs through a photopigment (opsin) - membrane-bound protein (G protein) bound to Retinal (Vitamin A).

Causes conformational change once hit by photo - starts signal transduction cascade (channel closes)

Question 17

What color(s) do blue cones absorb?

Answer 17

Violet and blue

Question 18

What color(s) do rods absorb?

Answer 18

Violet, blue, green, yellow and some orange

Question 19

What color(s) do green cones absorb?

Answer 19

Blue, green, yellow and some orange

Question 20

What color(s) do red cones absorb?

Answer 20

Some blue, green, yellow, orange and red

Question 21

How does frequency impact how we see color?

Answer 21

The hue

Question 22

How does amplitude impact how we see color?

Answer 22

The brightness

Question 23

How many cones do humans have? What is this called?

Answer 23

3 types of cones; trichromats

Question 24

How is an image formed by the eye?

Answer 24

Light is refracted by the cornea. The cornea collects and bends light so it converges on the back of the eye.

Question 25

What is focal distance?

Answer 25

Distance from the reflective surface to the retina.

Question 26

What focuses light on the retina?

Answer 26

The lens

Question 27

The fovea comprises less than 1% of retinal size but takes up over _____ of the visual cortex in the brain.

Answer 27

50%

Question 28

What are some regional differences in retinal structure?

Answer 28

The central retina has more cones and greater acuity. The peripheral retina has a higher ratio of rods and cones and a higher ratio of photoreceptors to ganglion cells, and is more sensitive to light.

Question 29

Describe the visual pathway in the retina.

Answer 29

Ganglion cells --> Bipolar cells --> Photoreceptors (deepest layer, converts light into impulses)

Question 30

Why is the visual system set up "backwards"?

Answer 30

Retina contains cones to sense the colors, red, green and blue. Rods, much more light-sensitive than cones, but which are color-blind. Light travels through a mass of neurons before it reaches the light-detecting rods and cone cells. High density (very refractive) glial cells can guide light.

Question 31

What is myopia? How is this corrected?

Answer 31

A common visual defect known as near-sightedness, which occurs when the focal point falls in front of the retina With a concave lens

Question 32

What is hyperopia? How is this corrected?

Answer 32

A common visual defect known as far-sightedness, which occurs when the focal point falls behind the retina. With a convex lens.

Question 33

What is accommodation?

Answer 33

The process by which the eye adjusts the shape of the lens to keep objects in focus.

Question 34

What happens when the ciliary muscle is relaxed?

Answer 34

The ligaments pull on and flatten the lens.

Question 35

What happens when the ciliary muscle contracts?

Answer 35

It releases tension on the ligaments and the lens becomes more rounded.

Question 36

What is presbyopia?

Answer 36

Old eye. It is a loss of elasticity in the lens. The cornea is less able to change shape due to the rigid and increased size of the lens.

Question 37

What is binocular vision?

Answer 37

The coordinated use of both eyes to make a single mental impression.

Question 38

What is macular degeneration?

Answer 38

Progressive destruction of macula, common eye condition in older people.

Question 39

What is retinitis pigmentosa?

Answer 39

A group of inherited diseases causing retinal degeneration (photoreceptor cells, rods and cones die )

Question 40

What is visual acuity?

Answer 40

The ability to distinguish two nearby points.

Question 41

What is a visual angle?

Answer 41

Distances across the retina described in degrees

Question 42

``` Fovea Visual Field: Photoreceptor: Functions: Ganglion ratio: ```

Answer 42

Front Cones Color and acuity 1:1

Question 43

``` Peripheral retina Visual field: Photoreceptor: Functions: Ganglion ratio: ```

Answer 43

Edges Rods Night and motion Many: 1