The Visual System

Question 1

cornea

Answer 1

the transparent covering of the eye that lets light in. Not only does it protect the eye but also focus the light on the retina at the back of the eye

Question 2

pupil

Answer 2

black area, controlled by circular sphincter muscles (iris)

When the environment is dark, the pupil enlarges to let more light in; when the environment is bright, the pupil becomes smaller to let less light in

Question 3

iris

Answer 3

circular, colored area of the eye. It controls the amount of light that enters the eye by making the pupil large or small

Contains 2 sets of smooth muscles:
- Pupillary dilator muscle
- Pupillary constrictor muscle

Responsible for dilating or constricting the pupil

Question 4

sclera

Answer 4

the white portion of the eye. Tougher layer of the eye

Question 5

conjunctiva

Answer 5

Thin, clear layer of mucous membrane that covers the front of the eye (except cornea) and lines the inside of the eyelids

Secretes mucus to lubricate the eye keeping bacteria and foreign material from getting behind the eye

Question 6

lacrimal glands

Answer 6

produce watery portions of tear. Located at the top outer edge of each eye

Question 7

lacrimal glands

Answer 7

produce watery portions of tear. Located at the top outer edge of each eye

Question 8

what cells does the retina contain?

Answer 8

photoreceptors

Question 9

photoreceptors are…

Answer 9

Each photoreceptor is attached to a nerve fiber. All nerve fibers are bundled together to form the optic nerve

Convert image into electrical impulses, which are carried to the brain by the optic nerve

Question 10

what is the most sensitive area in the retina?

Answer 10

“the area centralis”

Question 11

layers of the posterior eyeball

Answer 11

1. Outer: sclera
2. Middle: choroid
3. Inner: retina

Question 12

Macula lutea

Answer 12

a dark area, situated at the posterior pole of the eye, also called as a “yellow spot” or “area centralis”

*Primary function: photopic vision

Question 13

Fovea centrali

Answer 13

a central depression in the macula thickness. MOST sensitive part of the retina

Question 14

what are the 2 main photoreceptors within the retina?

Answer 14

1. rods: dim light, peripheral vision
2. cones: bright light, high acuity color vision

Question 15

Visual of retina

Answer 15

highest concentration of cones is in the fovea or fovea centralis

Question 16

cones

Answer 16

• responsible for fine detailed and color vision
• Clustered near the center of the retina, called the fovea
• There are 5 million cones in the average retina

Question 17

rods

Answer 17

• Responsible for low light and peripheral vision
• They are present everywhere in the retina EXCEPT the fovea
• There are 125 million rods in the average retina

Question 18

Do animals see one or more color (s)?

Answer 18

Dogs, cats, and most mammals only have 2 color receptors. They’re missing the one that detects the one that detects red. So, it’s true dogs don’t see many colors, but they are not colorblind! They only see shades of blue and yellow

*Birds have 4 kinds of cones

Question 19

3 types of cones

Answer 19

1. red
2. blue
3. green

Question 20

Color Blindness

Answer 20

• based upon or defects in the red and green cone pigments
• Inheritance in males
• A genetic disorder

Question 21

Trichromats

Answer 21

normal color vision

Question 22

Dichromats

Answer 22

have 2 types of cones

*most animals are dichromats

Question 23

Monochromats

Answer 23

have 1 type of cone system

Question 24

why do females rarely get colorblindness?

Answer 24

colorblind chromosome is mostly “X” females are carriers of the color-blind gene. Male have “XY”, hence the likelihood for males to only get the color-blind gene

Question 25

what are 5 major retinal cell types

Answer 25

1. Photoreceptor cells (rod or cone)
2. Bipolar cells (neuron)
3. Horizontal cells
4. Amacrine cells (interneuron), and
5. Ganglion cells

Question 26

Sequence of events involved in the phototransduction

Answer 26

• Activation by the affects Na+ channels, through transducing, a G protein that controls formation of cyclic GMP
• In the dark, there is a constant release of the neurotransmitter (glutamate). In the light, hyperpolarization causes a reduction in the release of glutamate

Question 27

what molecule is extremely sensitive?

Answer 27

rhodopsin

Question 28

Range of light sensitivity of rods and cones

Answer 28

• As long as the light is of low intensity, rods quickly regenerate rhodopsin, and the retina continues to respond to light stimuli
• High light intensity, rhodopsin is bleached quickly as rhodopsin can be produced = rods nonfunctional
  - If this happens, cones take over

Question 29

what cranial nerves control extrinsic eye muscles?

Answer 29

(III) oculomotor: medial rectus, superior rectus, inferior rectus, inferior oblique

(IV) trochlear: superior oblique

(VI) abducens: lateral rectus

Question 30

Strabismus

Answer 30

“cross-eyed” is a condition where the eye rotates medially or laterally. Usually due to congenital weakness of eye muscles

Question 31

is it the rectus or obliques that permit the eye to move up and down?

Answer 31

obliques

Question 32

Accommodation

Answer 32

Curvature of the lens to bring other objects into focus

Question 33

ciliary muscle

Answer 33

• Changing the shape of the lens is done
• is relaxed when the light rays from an emmetropic eye (normal vision) are brought into focus on the retina

Question 34

what happens when ciliary muscles deteriorates?

Answer 34

with age, it results in presbyopia-loss of accommodation

Question 35

Presbyopia

Answer 35

a farsightedness caused by loss of elasticity of the lens of the eyes

Question 36

normal vision

Answer 36

the lens focuses the visual image on the retina

Question 37

myopia

Answer 37

or near-sighted, short sighted. The lens focuses the distant images in front of the retina. Myopia corrected by a diverging lens

Question 38

hyperopia

Answer 38

or far-sighted. Closer images are focused “behind” the retina. Hyperopia corrected by a converging lens

Question 39

The aperture controlling the amount of light entering the eye is called:

Cornea
Lens
Pupil
Ciliary muscle

Answer 39

pupil

Question 40

Changing the shape of the lens is done by the_____

Ciliary muscle
Iris muscle
Eyeball

Answer 40

Ciliary muscle