The Visual System Flashcards by Alyssa Gordon

What is light?

Electromagnetic energy that moves in waves

How well did you know this?

Not at all

Perfectly

The color white is ______

A mix of wavelengths

How well did you know this?

Not at all

Perfectly

A single wavelength is a ______

Color

How well did you know this?

Not at all

Perfectly

The highest frequency color is ____

Blue

How well did you know this?

Not at all

Perfectly

The lowest frequency color is ____

Red

How well did you know this?

Not at all

Perfectly

What is the pupil?

The opening that allows light to enter

How well did you know this?

Not at all

Perfectly

What is the iris?

Two muscles that control the diameter of the pupil

How well did you know this?

Not at all

Perfectly

What is the cornea?

Transparent cover over the eye with a layer of fluid underneath

How well did you know this?

Not at all

Perfectly

What is the sclera?

The white walls of the eye

How well did you know this?

Not at all

Perfectly

What are the 3 parts of the retina?

1.) Optic Disc
2.) Macula
3.) Fovea

How well did you know this?

Not at all

Perfectly

What is the optic disc?

Origin point of retinal blood vessels

How well did you know this?

Not at all

Perfectly

What is the macula?

Region of retina for central vision

How well did you know this?

Not at all

Perfectly

What is the fovea?

Thin central point on the retina

How well did you know this?

Not at all

Perfectly

What is the light’s path through the eye?

Through the pupil onto the lens

How well did you know this?

Not at all

Perfectly

How is the lens held in place?

By zonule fibers attached to the ciliary muscle

How well did you know this?

Not at all

Perfectly

What causes a refraction of light?

Corneal fluid

How well did you know this?

Not at all

Perfectly

What is the purpose of corneal fluid?

To focus light onto the retina at the back of the eye

How well did you know this?

Not at all

Perfectly

What is responsible for light accommodation?

The lens

How well did you know this?

Not at all

Perfectly

Why is the lens important?

To see things closer than ~9 meters away

How well did you know this?

Not at all

Perfectly

What has a smaller refraction power? Lens or Cornea?

Lens

How well did you know this?

Not at all

Perfectly

What are the three cell types that compromise the retina’s direct path for visual processing?

1.) Photoreceptors
2.) Bipolar cells
3.) Ganglion cells

How well did you know this?

Not at all

Perfectly

What do ganglion cells do?

Output to form the optic nerve

How well did you know this?

Not at all

Perfectly

What are the 3 types of retinal cells influenced by?

1.) Horizontal cells
2.) Amacrine cells

How well did you know this?

Not at all

Perfectly

What do rods respond to?

All wavelengths in the visual spectrum; cannot distinguish color

How well did you know this?

Not at all

Perfectly

What do cones respond to?

Specific and unique wavelengths in the visual spectrum

How many rods are in each eye?

90-120 million

How many cones are in each eye?

5-7 million

What are rods and cones comprised of?

Stacks of membranous discs

What is contained in discs?

Photopigments that are sensitive to light

Why can rods not distinguish colors?

All rods have the same photopigments

The fovea has a high density of ______

Cone cells

What is the fovea responsible for?

Precise visual acuity

Why does the fovea have precise visual acuity?

Light can strike the cones without passing through other layers

What is the resting voltage in rods and what is it due to?

-30mV due to dark current

What do the membranous discs in rods contain?

Rhodopsin

What is rhodopsin?

A photopigment that is a combination of opsin and retinal

What is Retinal derived from?

Vitamin A

What is bleaching?

Light striking rhodopsin changes retinal and activates the opsin protein

In bleaching, what color does rhodopsin change to?

From purple to yellow

What happens when opsin is triggered?

Intracellular signals close Na+ channels and hyperpolarize the rod cell

Rods _______ easily

Saturate

In daylight, vision is dependent on ______

Cones

Why does vision depend on cones in daylight?

Cone photopigments require more light to bleach

What colors do cones preferentially respond to?

Blue, green, or red light wavelengths

Light induces _______

Hyperpolarization

What happens when rods and cones are hyperpolarized?

It reduces the amount of glutamate NT released

What happens when there is a glutamate reduction?

Depolarization of bipolar cells, which then excite ganglion cells

Every ganglion neuron has a ________

Receptive field

What is a receptive field?

Area on the retina where light will induce an increase or decrease in ganglion neuron firing rate

What is dark-light adaptation?

Pupil dilation/constriction alters the amount of light striking the retinae. This alters levels of unbleached rhodopsin, which creates changes in retinal circuitry

What is the Retinofugal pathway?

Pathway away from the retina to the brain

What does 'fugal' mean?

To flee from

What 3 things does the retinofugal pathway consist of?

1.) Optic Nerve 2.) Optic chiasm 3.) Optic tract

Where does the Optic nerve travel?

Begins at the ganglion cells, out the back of the eyes and enters through the skull

How does the optic chiasm work?

The nasal half of the ipsilateral eye combines with temporal half of the contralateral eye to create the visual field

Nerve axons from the _______ cross over at the chiasm

Temporal fields

What does decussation mean?

The crossing over of nerve fibers or pathways in the central nervous system to the opposite side

What is the binocular visual field?

The portion that is seen by both eyes

What are the temporal portions of the visual field?

The portion that is unique to each eye

How does temporal portions of the visual field travel?

It crosses over to the contralateral optic tracts at the optic chiasm. It is then processed in the contralateral hemisphere of the brain

What is the optic tract?

Pathways leaving the optic chiasm

What does the optic tract do?

Carries visual field information

What is the main location target of the optic tract?

Lateral Geniculate Nucleus of the thalamus

Where does the Lateral Geniculate Nucleus output to?

The visual cortex in the occipital lobe

What is the pathway of the LGN?

Optic radiation

Where else does the optic tract lead to in the brain?

Hypothalamus and midbrain

What is the role of the hypothalamus in the visual system?

Involved in waking/sleeping in sync with light/dark cycle

What is the role of the midbrain in the visual system?

Influences pupil dilation and some eye movements Also houses the superior colliculus

What is the role of the superior colliculus in the visual system?

Involved in controlling saccadic eye movements

What are saccadic eye movements?

Quick movements of the eyes to center a novel object over the fovea

Which of Brodmann's areas are involved in the visual cortex?

17 and 18

What is the secondary visual cortex?

Involved in visual sensory memory and the ability to relate what is being seen to things that have been seen before

What does farsightedness/hyperopia say about the eyeball?

The eyeball is too short

How do you correct hyperopia?

Convex corrective lens focuses light onto nearer retinae

What does nearsightedness/myopia say about the eyeball?

The eyeball is too long

How do you correct myopia?

Concave corrective lens focuses light onto more distant retinae

What is LASIK?

Surgical reshaping of the cornea to provide proper light refraction onto the retina. The flap of the cornea is cut and cornea is reshaped from the inside by the laser

What does LASIK stand for?

Laser-Assisted In Situ Keratomileusis

What two injuries are often associated with optic nerve injuries?

1.) Multiple Sclerosis 2.) Diabetes Mellitus