Vision Sensory System

Question 1

What is light with regards to reception by the eye?

Answer 1

The visual signal.

Question 2

What are the three criteria that “perceiving” a visual signal requires?

Answer 2

1) The eyes capable of detecting, focusing, and responding to light
2) The appropriate neural pathways
3) Brain regions to interpret the signal

Question 3

Define visual perception.

Answer 3

The ability to detect light and interpret it.

Question 4

What is the purpose of rod and cone cells?

Answer 4

To convert visually transduced light into electrical signals.

Question 5

Where are rods and cones located within the eye?

Answer 5

The retina.

Question 6

Name the steps of visual perception starting with light passing through the threshold.

Answer 6

1) Threshold passage
2) Transduction by receptors
3) Conduction by afferent neurons
4) Processing by brain
5) Perception

Question 7

Define wavelength (l).

Answer 7

The distance between successive peaks of EMR.

Question 8

Between what wavelengths can the human eye perceive and what is this portion of the EMR called?

Answer 8

400-750 nm.

Visible spectrum.

Question 9

What distinguishes one color from another when an eye receives a light input?

Answer 9

Different wavelengths are what dictates the color perceived.

Question 10

What portion of the EM spectrum can snakes “see”?

Answer 10

Infrared light.

Question 11

When light passes through a concave medium, what happens?

Answer 11

The light is refracted to diverge relative to the original vector.

Question 12

When light passes through a convex medium, what happens? What is effective formed?

Answer 12

The light is refracted to converge to form a focal point.

Question 13

What is a focal point? (EMR)

Answer 13

The point at which light vectors converge and intersect.

Question 14

Define what focal length is and what surfaces it is often associated with.

Answer 14

Focal length is the distance from a CONVEX surface to the focal point of light passing through the original medium.

Question 15

With respect to light, which of its characteristics is responsible for why we can see objects that do not emit light? How can this property be defined?

Answer 15

Reflection is responsible for why we can see objects. Reflection is when light waves strike and bounce off surfaces we see.

Question 16

When light bounces off of a surface, why do we see objects in different colors?

Answer 16

Different objects will absorb non-perceived wavelengths of the light striking it.

Question 17

Define refraction.

Answer 17

Refraction is when light passes through transparent mediums of varying density.

Question 18

Briefly given an overview of the eyes organization.

Answer 18

The eye is a 3 layered fluid filled ball that is divided into 2 chambers.

Question 19

What does Layer-1 of the eye consist of? (3 items)

Answer 19

1) Sclera (outer layer)
2) White connective tissue capsule around eye
3) Clear cornea at the front

Question 20

What does Layer-2 of the eye consist of? (4 items)

Answer 20

1) Choroid
2) Iris
3) Ciliary muscle
4) Zonular fibers

Question 21

What is the suspensory ligament composed of?

Answer 21

Ciliary muscle and zonular fibers.

Question 22

What does Layer-3 of the eye consist of? (2 items)

Answer 22

1) Retina

2) Photoreceptors

Question 23

What are the two chambers of the eye and where are each located in the eye?

Answer 23

1) Aqueous humor (anterior)

2) Vitreous humor (posterior)

Question 24

Define the function of the iris and what components of it accomplish this function.

Answer 24

Regulates the size of the pupil via circular and radial muscles. Therefore, determines the amount of light that enters the eye.

Question 25

What is the optic nerve and what is its function?

Answer 25

Axons of ganglion neurons in the retina that carry info to the brain.

Question 26

How does pupil size change relative to light intensity?

Answer 26

Bright light = smaller pupil diameter Low light = bigger pupil diameter

Question 27

In weak light, which muscles are responsible for pupil size increasing? What kind of nerves are these muscles stimulated by?

Answer 27

Outer radial muscles are responsible for pupil size increase and they are stimulated by parasympathetic nerves.

Question 28

In strong light, which muscles are responsible for pupil size decreasing? What kind of nerves are these muscles stimulated by?

Answer 28

Inner circular muscles are responsible for pupil size decrease and they are stimulated by sympathetic nerves.

Question 29

The kind of surface is the cornea and lens?

Answer 29

Convex.

Question 30

Where does the focused light from the cornea and lens travel to next?

Answer 30

The retina.

Question 31

How is visual information that reaches the retina oriented?

Answer 31

It is reversed from right to left and is upside down.

Question 32

When viewing a distant object, what kind of lens is required for refraction? Why?

Answer 32

A flattened lens is required for weak refraction because light rays are nearly parallel when they arrive.

Question 33

When viewing a near object, what kind of lens is required for refraction? Why?

Answer 33

A rounded lens is required for strong refraction because light rays are still strongly diverging when they arrive.

Question 34

Define optical accommodation.

Answer 34

The normal ability of the lens to adjust its curvature to view near and far objects.

Question 35

How is focus related to lens shape for distant and near objects?

Answer 35

For distant objects, focus is enhanced by a flattened lens. For nearby objects, focus is enhanced by a rounded lens.

Question 36

What two anatomical structures contribute to form a flattened lens? How are they behaving?

Answer 36

Ciliary muscles and zonular fibers. Ciliary muscles are relaxed and zonular fibers are tensioned.

Question 37

What two anatomical structures contribute to form a rounded lens? How are they behaving?

Answer 37

Ciliary muscles and zonular fibers. Ciliary muscles are contracted via PS nerve firing and zonular fibers are slackened.

Question 38

What determines where light rays converge? (3 items)

Answer 38

1) Cornea 2) Lens shape 3) Eyeball length

Question 39

What is the common name for myopia? What are its characteristics? What is its correction?

Answer 39

Near-sightedness. 1) Eyeball too long 2) Focus in front of retina 3) Can see near objects clearly Concave lenses.

Question 40

What is the common name for hyperopia? What are its characteristics? What is its correction?

Answer 40

Far-sightedness. 1) Eyeball too short 2) Focus behind retina 3) Can see distant objects clearly Convex lenses.

Question 41

What are the 3 layers of the retina and where are they located? (front to back)

Answer 41

1) Ganglion cells (inner/front of retina) 2) Bipolar cells (middle) 3) Photoreceptors and pigmented epithelium (outer/back of retina)

Question 42

What is the macula lutea?

Answer 42

Yellow spot near center of the retina.

Question 43

What is the fovea centralis?

Answer 43

A central pit within the macula that contains the highest density of cones. Cones decrease toward periphery where rods are more abundant.

Question 44

What is the optic disc?

Answer 44

A distinct region where neurons carrying information from photoreceptors exit the eye as optic nerve.

Question 45

What is the complex pathway of light starting with the cornea? (8 steps)

Answer 45

1) Cornea 2) Aqueous humor 3) Pupil 4) Vitreous humor 5) Front surface of retina 6) Ganglion neurons 7) Bipolar cells 8) Photoreceptors

Question 46

What are the two types of photoreceptors?

Answer 46

Rods and cones.

Question 47

What are photopigments and what do they consist of?

Answer 47

Light sensitive pigments within photoreceptors that consist of membrane-bound opsins and light sensitive retinol.

Question 48

What is the purpose of the outer segment of rods and cones?

Answer 48

They consist of folds with photopigments that absorb light.

Question 49

What is the inner segment of rods and cones used for?

Answer 49

Serves as basic cell machinery.

Question 50

What does the synaptic terminal of rods and cones do?

Answer 50

Releases glutamate as a neurotransmitter.

Question 51

What are the 5 main characteristics of rod cells?

Answer 51

1) Specialized for dim light - night vision 2) More photopigments: can detect single photons 3) Saturate in daylight 4) Low acuity - none in central fovea 5) 1 photopigment, rhodopsin

Question 52

What are the 5 main characteristics of cone cells?

Answer 52

1) Specialized for day vision 2) Less photopigments, lower sensitivity 3) Saturate in intense light 4) High density in fovea ---> high acuity 5) Provide color vision: 3 types of cones each with different photopsins

Question 53

What type of sensory cell remains depolarized at rest and hyperpolarized when exposed to adequate stimulus?

Answer 53

Cone cells.

Question 54

In the absence of light, what does the enzyme guanyl cyclase do to keep the membrane of cone cells depolarized?

Answer 54

Guanyl cyclase generates cGMP which opens Na+/Ca2+ channels.

Question 55

In the presence of light, what does retinal do to lead to hyperpolarization?

Answer 55

It dissociates from opsin, which activates cGMP phosphodieterase which causes the closure of ion channels.

Question 56

How are light signals converted to APs? (broad terms)

Answer 56

Interactions of photoreceptors with bipolar and ganglion cells.

Question 57

Why can't photoreceptor and bipolar cells generate APs?

Answer 57

They lack voltage-gated ion channels.

Question 58

What are the first cells to initiate an AP?

Answer 58

Ganglion cells.

Question 59

What are the two ways photoreceptors interact with bipolar and ganglion cells?

Answer 59

On and off pathways.

Question 60

In the absence of light, photoreceptors are depolarized. What does this mean regarding bipolar cells?

Answer 60

It means there is an increased release of glutamate onto the bipolar cells.

Question 61

In the ON pathway, what does glutamate do to lessen neurotransmitter release onto associated ganglion cells?

Answer 61

Glutatmate interacts with metabotropic receptors on bipolar cells to hyperpolarize, dereasing neurotrasnmitter release.

Question 62

In the absence of light on bipolar cells, ganglion cells cannot what in the ON pathway?

Answer 62

Fire action potentials.

Question 63

BE ABLE TO DESCRIBE VISUAL PATHWAYS.

Answer 63

CHACH.

Question 64

Color vision begins with what?

Answer 64

The activation of photopigments in retina.

Question 65

How many types of cones do humans have and what do they respond to? (short to long)

Answer 65

1) short (blue light) 2) medium (green light) 3) longer (red light)

Question 66

What is color-blindness?

Answer 66

A sex-linked recessive genetic disorder where 1 or more cone mechanism is lost.

Question 67

What is the most common form of color blindness?

Answer 67

Red-green color blindness, 1/12 men and 1/200 women.

Question 68

Why is red-green colorblindness more prevalent in men?

Answer 68

The genes involved in mutation are loacted on the X chromosome.

Question 69

What is a cataract?

Answer 69

Cloudiness due to accumulation of proteins in the lens.

Question 70

What is glaucoma?

Answer 70

Intraocular pressure build up and retinal damage leading to irreversible blindness.

Question 71

What is macular degeneration?

Answer 71

Impairment of macula lutea leads to visual degradation in the center of visual field.