The Eye

Front 1

the eye itself is surrounded by accessory structures:

Back 1

1. eyelids (palpebrae) that seperate the palpebral fissue

2. eyelashes

3. tarsal glands or meibomian glands

4. lacrimal apparatus:

lacrimal gland

lacrimal canuncle w/ lacrimal canaliculi lacrimal sac and naso lacrimal duct

Front 2

conjuctiva

Back 2

epithelium covering the inner eyelid and outer surface of the eye

extends to the edges of the cornea.

Front 3

lacrimal apparatus

Back 3

produces, distributes, and removes tears

Front 4

posterior cavity or vitreous chamber

Back 4

filled with gelatinous liquid called vitreous humor or vitreous body

Front 5

anterior cavity

Back 5

located in front of the lends and divided into two chambers (anterior and posterior).

filled with aqueuos humor

Front 6

excessive fat behind the eye causes the eye to bulge forward (may be caused by hyperthyroidism)

Back 6

exophthalmos

Front 7

Cranial nerve that activates the lateral rectus

Back 7

abducens nerve (VI)

Front 8

cranial nerve that activates the superior oblique

Back 8

trochlear nerve (IV)

Front 9

cranial nerve that activates the inferior rectus, the superior rectus, the inferior oblique, and the medial rectus

Back 9

occulomotor nerve (III)

Front 10

3 main layers (tunics) to the wall of eye organ

Back 10

1. outer fibrous tunic

2. middle vascular tunic

3. inner nervous tunic

Front 11

outer fibrous tunic

Back 11

sclera, cornea, limbus

Front 12

middle vascular tunic

Back 12

iris, ciliary body, choroid

Front 13

inner nervous tunic

Back 13

retina

Front 14

choroid

Back 14

majority of the sclera and is very vascular

contains many melanocytes near the border with the sclera

Front 15

near the anterior portion of the eye, the choroid develops into the

Back 15

ciliary body

Front 16

ciliary body is composed out of the

Back 16

ciliary smooth muscles that extend inwards toward the lens

Front 17

the lens attaches to the ciliary body via ______ _______. It keeps the lens in front of the iris and centered.

Back 17

suspensory ligaments

Front 18

The ______ extend as a flap of tissue beyond the ciliary body and provide a central opening for light to enter the eyeball (the pupil)

Back 18

Iris

Front 19

Vascular tunic (uvea) is composed out of two layers

Back 19

radial dilator muscles and circulator constrictor muscles

Front 20

contraction of the two layers of muscles (uvea) results in

Back 20

pupil dilation or pupil constriction

Front 21

circular constriction contraction is under the _________ influence (makes pupil smaller)

Back 21

parasympathetic

Front 22

radial dilator contraction is under ________ influence (makes pupil larger)

Back 22

sympathetic

Front 23

RETINA:

consists of:

function:

Back 23

is the innermost of the eye wall

consists of the pigmented part and a neural part

preventing light from bouncing back and also providing biochemical feedback to the light receptors in the retina

Front 24

the neural part is the actual retina with the light receptors:

rod

cones

Back 24

rods: do not discriminate color-good for gray shades-highly sensitive to light-good for dim light vision

cones: discriminate color-require higher light intensities

Front 25

retina extends anteriorly only as far as the __________

Back 25

ora serrata

Front 26

1. rods and cones synapse with _________, which synapse with ___________, and their axons form the _________.

Back 26

bipolar cells

ganglion cells

optic nerve

Front 27

axons of the ganglion cells leave the eye at the ____ _____ (contains no light receptors; reason for blind spot)

Back 27

optic disc

Front 28

______ _______ is a depression in the retina where no rods occur.

Back 28

macula lutea

Front 29

________ ________ is the center and has the highest levels of cones; provides the sharpest vision

Back 29

fovea centralis

Front 30

________ and _______ divide the anterior cavity of the eye into posterior (vitreous) cavity and anterior cavity

Back 30

ciliary body

lens

Front 31

anterior cavity further divided:

Back 31

anterior chamber in front of eye

posterior chamber between the iris and the lens

Front 32

aqeous humor circulates within the anterior eye cavity

made by the:

passes through the:

Back 32

ciliary body and diffuses through the walls of the anterior chamber

canal of schlemm and re enters circulation

Front 33

vitreous humor fills the posterior cavity

Back 33

not recycled

permanent fluid

Front 34

blockage of canal of schlemm

Back 34

blockage of this drainage pathway may result in an increase in ocular pressure resulting in GLAUCOMA

Front 35

the lens:

Back 35

helps to focus light on the retina by refracting (bending) as it passes through lens

Front 36

the lends is made from slender, elongated cells fill with trasparent proteins called

Back 36

crystallins

Front 37

loss of transparency of lens

Back 37

cataract (cloudy lens)

Front 38

refraction

Back 38

light changes direction when it passes from one medium to another medium with different density

most of refraction occurs when light passes through the cornea

when light is not centered on the retina, we end up with blurry vision

Front 39

accomodation is the process

Back 39

where the shape (thickness) of the lens is adjusted to keep the focal distance constant

the lens becomes fatter when we try to focus on a near by object and thinner when the object is distant

Front 40

accomodation is executed via the _____ nerve by action on the ciliary body

Back 40

CN III

Front 41

contraction of the ciliary muscles causes

Back 41

relaxation of the ligaments and bulging of the lens

Front 42

relaxation of the ciliary muscles results in a pull on the

Back 42

suspensory ligaments, which in turn flattens the lens

Front 43

visual physiology

Back 43

relates to understanding how we actually see images

Front 44

the rods and cones are responsible for

Back 44

picking up the information in visible light (the photons)

Front 45

our rods and cones are sensitive to visible light only

Back 45

400-700 nm

Front 46

functional characteristics of rods:

Back 46

very sensitive to dim light

best suited for night vision and peripheral vision

perceived input is in gray tones only

pathways converge, resulting in fuzzy and indistinct images

Front 47

functional characteristics of cones:

Back 47

need bright light for activation (low sensitivity)

have one of three pigments that furnish a vividly colored view

nonconverging pathways result in detailed, high resolution vision

Front 48

visual pigments are located in the

Back 48

membranes of the membraneous discs pigments

Front 49

the visual pigment is called

Back 49

rhodpsin

Front 50

rhodosin is a molecule made from

Back 50

opsin (larger protein)

retinal (smaller visual pigment)

Front 51

retinal is a derivative of

Back 51

vitamin A

Front 52

in cones, the opsin protein is slightly different, accounting for the

Back 52

color sensitivity of the cones

Front 53

rhodopsin, the visual pigment in rods, is embedded in the membrane that form

Back 53

discs in the outer segment

Front 54

rhodopsin is made from

Back 54

retinal, which is the vitamin a derivative

opsin, a larger protein part

Front 55

retinal has two different configurations

Back 55

trans form

cis forms

Front 56

trans form

Back 56

molecule has a straight tail

Front 57

cis form

Back 57

molecules has a bent tail

Front 58

light energy converts retinal from the _____ to the ______ form

Back 58

cis to the trans form

Front 59

the conversion from the cis to the trans state is at the basis of

Back 59

photoreception

Front 60

steps in photoreception:

Back 60

1: light energy converts retinal from the cis form to the trans form: this now activates the OPSIN part of rhodopsin

2: OPSIN activates the enzyme TRANSDUCIN ( G-protein complex): transducin activates a phosphodiesterase-which breaks down cGMP levels

3: phosphodiesterase thus reduces cGMP levels: this reduces the numbers of Na channels that are opens: it results in hyperpolarization

4: the membrane potential drifts about -70 mV. this reduces the number of neurotransmitters at the synapse with the bipolar cells

Front 61

PhotoReception is a

Back 61

graded response: the higher the intensity of light, the greater the hyperpolarization and the less the amount of N.T released

Front 62

step 1 of PhotoReception

Back 62

opsin activation occurs

Front 63

step 2 of PhotoReception

Back 63

opsin activates transducin and transducin activates phosphodiesterase

Front 64

step 3 of PhotoReception

Back 64

cyclic GMP levels decline and gated sodium channels close

Front 65

step 4 PhotoReception

Back 65

rate of neurotransmitter release declines

Front 66

how does the brain receive info of the light stimuli

Back 66

the N.T released by the photoreceptors are inhibitory neurotrasmitters (glutamate): they thus cause IPSPs in the bipolar cells (hyperpolarization)

the bipolar cells in turn reduce frequency of stimulation to the ganglion cells

the reduction in N.T release induced by the light stimuli thus reduces the amount of IPSPs

the removal of inhibition equates with stimulation

Front 67

In the dark:

Back 67

1. cGMP gated channels open, allowing cation influx; the photoreceptor depolarizes

2. voltage gated Ca channels open in synaptic terminals

3. neurotrasmitter released continuously

4. neurotransmitter causes IPSPs in bipolar cell-hyperpolarization occurs

5. hyperpolarization closes voltage gated Ca channels-inhibiting neurotransmitter release

6. no ESPSs occur in ganglion cells

7. no action potentials occur along the optic nerve

Front 68

due to the open Na channels, the rod experiences a

Back 68

"dark current" that keeps the cell depolarized

Front 69

in the light:

Back 69

1. cGMP-gated channels are closed, so cation influx stops; the photoreceptor hyperpolarizes

2. voltage gated Ca channels close in synaptic terminals

3. no neurotransmitter is released

4. lack of IPSPs in bipolar cell results in depolarization

5. depolarization opens voltage gated Ca channels-neurotransmitter is released

6. EPSPs occur in ganglion cell

7. action potentials progogate along the optic nerve

Front 70

light responses closes Na channel due to the cGMP breakdown and the rod experiences

Back 70

hyperpolarization

Front 71

after light stimulation, retinal is in the

Back 71

TRANS form and does not spontaneously convert back to the CIS form

Front 72

shorly after light stimulation, rhodopsin actually breaks down into _______ and _______. Also called bleaching effect

Back 72

retinal and opsin

Front 73

photoreceptors cannot function with damaged rhodopsin. before it can become an active molecule again, it needs to be

Back 73

glued back together: occurs only if retinal is in the CIS position. this occurs in the "dark" and requires enzymes and ATP

Front 74

dark adapted state

Back 74

when exposed to the dark long enough, all photoreceptors are loaded and ready.

our visual system is then in highly sensitive state and receptive to small amounts of light

Front 75

light adapted state

Back 75

when moving from a dark area to a bright area, all photoreceptors become bleached and thus reduce the immediate sensitivity to a series of additional light stimuli

Front 76

white light

Back 76

spectrum of all different colors

Front 77

in an object absorbs all color

Back 77

it appears black

Front 78

the color of an object is determined by the

Back 78

wavelength it reflects (what it doesnt absorb)

Front 79

there are three different kinds of cones:

Back 79

1. blue cones (16%)

2. green cones (10%)

3. red cones (74%)

Front 80

color blindness

Back 80

is the inability to perceive certain colors. it occurs when one or more of the classes of cones becomes non functional

Front 81

most convergence occurs with the

Back 81

rods

Front 82

about a thousand rods converge on a single ganglion cell that monitor a certain portion of the visual field

Back 82

M cell

Front 83

since rods are more effective in dim light, M cells provide information about the fact that light

Back 83

has arrived in a certain area

Front 84

cones show little

Back 84

convergence

Front 85

ganglion cells that monitor cones are called

Back 85

P cells

Front 86

P cells

Back 86

are active in bright light and provide info about detail, color from a specific area

Front 87

M Cells provide...

Back 87

grainy fuzzy pictures with low resolution, blurry details

Front 88

P cells (cones) provide..

Back 88

high resolution fine grained sharp and clear detail

Front 89

visual pathways in the CNS

Back 89

axons from the ganglion cells meet up at the optic disk and exit the eyeball

they proceed as the optic nerve towards the diencephalon.

the optic nerves cross over at the optic chiasm and become the optic tracts

the optic tract proceeds to the laterate geniculate nuchleus in the thalamus

Front 90

in the laterate geniculate nucleus

Back 90

information is passed on via the projection fibers called OPTIC RADIATION to the visual cortex of the occipital lobe

Front 91

the Binocular Zone is the

Back 91

overlapping zone seen by both eyes, which is important for depth perception