Exam 3: L4 Vision

Question 1

Development of Eye:

The eye develops as an outpocket of the ________

• ectoderm (……)
• neural crest(…..)

Answer 1

Development of the Eye:

The eye develops as an outpocket of the diencephalon

• Ectoderm (neural retina and iris, lens corneal epithelium)

optic disc is neural retina and iris

-neural crest

Question 2

***Basic Anatomy of the Eye:

What are the basic three layers of the eye

Answer 2

Basic Anatomy of the Eye:

Three Layers:

1. Sclera (outermost, fibrous outer coat, helps keep shape, muscles insert here)
2. Choroid (vascular layer)
3. Retina (interior layer)

Question 3

*****Corneo-Schlera Layer:

Explain the corneo schlera layer

Answer 3

Schlera: tough, outer coat, “white part of the eye”

Cornea has 5 layered structure: Epithelium, Basement Layer, Substantia Propria, DM, Endothelial Layer

Cornea isn’t very vascular, gets O2 from outside air or aquous humor

Question 4

*****Uveal (Choroid Layer):

Ciliary Body: muscles

___________ contracts circular fibers to release tension to rounden out the lens, makes you see up close

Uveal/Choroid layer is where _______ is created

Answer 4

Uveal/Choroid Layer

Ciliary body: muscles

PARASYMPATHETIC contracts the circular fibers to release tension and rounded out the lens, makes you see up close

Uveal/Choroid layer is where aquoeous humor is created

Question 5

If you have little to no pigment in the fluid in your iris you have _____ colored eyes

Answer 5

If you have little to no pigment in the fluid in your eyes you have blue colored eyes

Question 6

Trabecular Network and Canal of Schlem:

Fluid being made in the anterior chamber is filtered through before it gets to the ______

Then it goes around the iris and gets dumped into the _____

Drainage of fluid important in maintaining pressure in front of lens to maintain shape of cornea

Answer 6

Trabecular Network and canal of schlem:

Fluid being made in anterior chamber is filtered through before it gets to canal of schlem

Then it goes around the iris and gets dumped into the venous system

Drainage of fluid important for maintaining eye pressure

Question 7

Glaucoma:

Explain angle open vs angle closed

Answer 7

Angle Open: tribicular network is open, something else is blocking it or the TN isn’t working fast enough to drain it

Angle Closed: quick increase in pressure from posterior chamber, pushing iris off the lens and blocking fluid from entering the trabicular network

Question 8

****Iris:

The constrictor muscle of the pupil (_________) consists of a band of ________ oriented smooth muscle fibres in the pupillary aspect of the stroma. Like the smooth muscle of the ciliary body, the sphincter pupillae is innervated by the ________. The deep layer. The dilator pupillae muscle is innervated by the ______

PSNS causes _____

SNS activation causes _____

Answer 8

Constrictor muscle of the pupil (sphincter papillae) consists of band of circually oriented smooth muscle fibers. The sphincter papillae is innervated by the PSNS

Deep layer: radially oriented muscle, dilater pupillae muscle is innervated by the SNS

PSNS activation causes circular muscle fibers to contract to constrict pupil

SNS activation causes radial muscle to contract, causing pupil dilation

Question 9

*****Lens

The ciliary muscle is innervated by the _____ only

This causes the lens to ____

Answer 9

Lens:

The ciliary muscle is innervated by the PSNS only

This causes the lens to thicken

Question 10

Blood Supply:

What are the two blood supplies to the eye?

What is the pathway/progression of the vessels?

Where is the avascular zone in the eye?

Answer 10

Two blood supplies in the eye: retinal and corneal arteries

Progression:

Internal Carotid—-> Opthalamic—-> Retinal & Corneal

Avascular zone in eye: fovea

Question 11

Area of the eye where there is no photoreceptors?

(also the place where the retinal artery and optic nerve enter)

Answer 11

Optic disc is where the artery and optic nerve enter

it has no photoreceptors in it

Question 12

TopHat:

Dillator pupillae is innervated by what?

Answer 12

Tophat:

Dillator pupillae: radial muscles, SNS

Remember, the constrictor pupillae, circumference stuff is PSNS

Question 13

TopHat:

Define these various terms:

Hyperopia

Myopia

Astigmatism

Answer 13

Hyperopia is farsightedness, so it is the inability to see things close up

Myopia is nearsightedness, inability to see far away

Astigmatism: blurred vision due to unusually shaped cornea

Question 14

Optics of Vision:

The ____ plays a larger quantitative role than the lens in focusing light waves because the waves are refracted more while passing through the _______ than passing through the lens

If the original item was in center of vision: image is formed __________ relative to original source

All adjustments for distance are made by the ____. Such adjustments are called _____

Answer 14

Optics of Vision:

The cornea plays a larger quantatitive role than the lens in focusing light waves because waves are refracted more while passing through the cornea and the fluid of the anterior chambers than passing through the lens

If the original item was in the center of vision: image is formed upside down and reversed right to left than the original source

All adjustments made for distance are done by the lens. Such adjustments are called accomadation

Question 15

Visual perception occurs in the cortex but processing begins in the retina:

Vision occurs in two stages:

1.

2.

Answer 15

Vision occurs in two stages

1. Light enters eye and is converted into electrochemical signal by photoreceptors (transduction)
2. These signals are relayed to visial nuclei and cortices, where integration and perception take place

Question 16

What two things does the pigmented epithelial layer (outer back of the eye do)?

Note: pigmented epithelial layer is right under photoreceptors.

Answer 16

Pigmented Epithelial Layer:

craddling tips of photoreceptors, it has two functions:

1. metabolic function to give blood to the photoreceptors
2. makes back of the eye black (to avoid a bunch of light reflection)

Question 17

****Explain the path of light vs the path of neural info

Answer 17

Path of light and neural info travel in opposite directions

Light: ganglion cell —–>bipolar cell layer —-> photoreceptor layer

Neural info: photoreceptors ——> bipolar cells —-> ganglion cells —–> (optic nerve)

Question 18

****Fovea:

The fovea only has _____ (NO _____)

What is the other significance of the fovea?

Answer 18

Fovea:

ONLY cones, no rods

Fovea is an indentation in very back of eye with everything pushed aside

Gives light MOST DIRECT PATH to photoreceptors with the least amount of diffraction resulting in highest visual acuity

Question 19

****Rods and Cones:

Explain which one has:

higher sensitivity,

more photopigment per cell

higher amplification

Answer 19

Rods and Cones

1. Rods are more sensitive than cones, rods are specialized for nighttime vision (cones are for daytime vision)
2. Rods have more photopigment per cell (captures more light)
3. Rods also have higher amplification

Question 20

*****Rods and Cones:
Explain which one has

• higher temporal resolution (therefore faster)
• what are rods and cones more sensitive to in terms of light patterns
• when are rods vs cones saturated

Answer 20

Rods and Cones:

1. Rods have lower temporal resolution (slower)

Cones have higher temporal resolution (faster)

2. Rods: sensitive to scatered light / transient stimulation

Cones: sensitive to direct, axial stimulation

3. Rods saturate in daylight, cones are only saturated in intense light

Question 21

*****Rods and cones:

Explain the acuity and convergence of pathways in both

Then explain which one is achromatic vs chromatic

Answer 21

Rods:

• low acuity, high convergence of pathways (130:1), ABSENT in fovea
• Achromatic

Cones:

• high acuity, low convergence of pathways especially in fovea
• Trichromatic: red, green, and blue

Question 22

IMPORTANT:

In both rodes and cones there are NO ______

The first ____ actually occurs in the ganglion cell

Answer 22

In both rods and cones there are NO Action potentials

The first action potential occurs in the ganglion cell

Question 23

Photoreceptors (both rods and cones) are arranged into three distinct regions:

1. outer segment: consisting of
2. inner segment: consisting of
3. synpatic terminal which synpases with ___ cells

Answer 23

Photoreceptors are arranged into three distinct regions:

1. outer segment: containing invaginations (rods) and discs (cones) and the photopigments

2, inner segment: cellular machinery for metabolic support and the cilium to communicate to outer part

3. synpatic terminal which synpases with bipolar cells

Question 24

Explain the resulting cascade when light hits a rod:

1. Light stimulation of rhodopsin activates G protein called ______
2. Activated G protein then activates cGMP dependent ______
3. ____ then cleaves cGMP, reducing its concentration
4. Reducing the concentration of cGMP then results in ____ of Na channels

Answer 24

When light hits a rod:

1. Light stimulation of rhodopsin activates G protein called transducin
2. Activated G protein transducin activates cGMP dependent PDE
3. PDE then cleaves cGMP, reducing its concentration
4. Reduction in concentration of cGMP then closes Na channels

Question 25

Within the cascade: PDE starts cleaving cGMP. cGMP is needed to keep open sodium channels, therefore the reduction in cGMP levels, will start to close sodium channels, thereby _______ the outer segment of the photoreceptor

Answer 25

cGMP levels drop HYPERPOLARIZES the outside segment of the photoreceptor

Question 26

Each of the Na channels in the outer segments of rods needs how many cGMP to remain open?

Answer 26

Each Na channel needs 3 cGMP to remain open

Question 27

IN THE LIGHT: -Normally in the dark, the photoreceptors are inhibiting on center bipolar cells. In the light, photoreceptors \_\_\_\_polarize, _____ the inhibition of the on-center bipolar cells. Therefore, the hyperpolarization results in an ____ in spontanoues NT release Due to less inhibition, the on-cell bipolar cells depolarize, resulting in _____ of the on-center ganglion cell

Answer 27

IN THE LIGHT: in the dark, the oncenter bipolar cell is being inhibited by the photoreceptor In the light, photoreceptors hyperpolarize, therefore decreasing the inhibition of on center bipolar cells Due to less inhibition, the on-cell bipolar cells depolarize, resulting in stimulation of the on-center ganglion cell

Question 28

IN THE DARK: In the dark, photoreceptors \_\_\_\_\_\_, thus increasing NT release in the dark the on-center photoreceptor inhibits the bipolar cell from stimulating the ganglion cell

Answer 28

IN THE DARK In the dark photoreceptors depolarize, increasing NT release In the dark, the once center photoreceptor inhibits the bipolar cell from stimulating the ganglion cell

Question 29

Ganglion Cell Properties: Ganglion cells are ________ , and information from the bipolar cells only modulates this activity Ganglion cells only report ______ to the CNS

Answer 29

Ganglion Cell Properties: Ganglion Cells are tonically active, and info from the bipolar cell only modulates this activity Ganglion cells only report CONTRAST to the CNS.

Question 30

Information is processed in the retina in two general ways: Direct Indirect Explain both

Answer 30

Information is processed in the retina in two different ways: Direct: "vertical arrangement" photoreceptor---\> bipolar cell---\> ganglion cell (cones function in this manner) Indirect/horizontal: not direct, through various amacrine cells,

Question 31

Types of synpases in the retina: 1. Electrical (explain this one) 2. Chemical: * ribbon * basal (no vesicles, or specialized zone, only uses Ca, unknown mechanism)

Answer 31

Electrical synpase: ONLY USED IN EXTREME, PROLONGED DARK electrical synapse between rod and cone where rod uses the cone's superhighway pathway Rods open gap junctions with cones

Question 32

What are Muller cells? Tips of the photoreceptors are supported by \_\_\_\_\_\_

Answer 32

Muller cells are like glia, they are like support cells Note: tips of photoreceptors are supported by pigmented epithelium

Question 33

Ganglion cells: Explain M type vs P type Which one goes with rods vs cones

Answer 33

M type: large cell bodies, large receptive fields, RODS P type: small cell bodies, small receptive fields, CONES, high acuity the letter M spreads out When you pee, it is a fine stream

Question 34

What is the visual pathway of sensory processing from the retina all the way to the cortex?

Answer 34

Retina--\> optic nerve --\> optic chiasm---\> optic tract--\> lateral geniculate nucleus (thalamus) ---\>visual cortex

Question 35

\*\*\*\*\*Visual pathways: Upper fibers via the _____ lobe Lower fibers via the _____ lobe

Answer 35

Upper fibers via parietal lobe Lower fibers via the termporal lobe "lower your temper"

Question 36

\*\*\*\* visual pathway What happens to up, down, right and left processing? Fill in the blank: Lower fibers of optic radiation course through the _____ lobe via ____ loop

Answer 36

Up down right and left all get switched Lower fibers of optic radiation course through the temporal lobe via Meyer's Loop

Question 37

Lateral Geniculate: Processing also takes place within the lateral geniculate (thalamus) Projections from M type ganglion cells projecting to layers 1 and 2 (called \_\_\_\_\_\_\_\_) Projections from P type ganglion cells projecting to layers 3-6 (called \_\_\_\_\_\_\_)

Answer 37

Lateral Geniculate: M type ganglion cells to magnocellular area (1 and 2) P type ganglion cells to parvocellular are (3-6)

Question 38

Visual Cortex: Layer ___ (the input layer) is greatly expanded in the visual cortex

Answer 38

Visual cortex: Layer 4, the input layer is greatly expanded in the visual cortex

Question 39

If you cut the optic chiasm, what kind of visual defecit will you have?

Answer 39

Cut optic chiasm: tunnel vision Bitemporal hemionopsia

Question 40

Dorsal/parietal pathway ____ an object is Ventral/temporal pathway: ____ an object is

Answer 40

Dorsal/parietal pathway: where an object is Ventral/temporal: what an object is VHAT is that? Where is the door

Question 41

Color: The human retina has three seperate cone system (trichromatic) that each overlap Cones do NOT transmit specific wavelength info, but rather increase their response to \_\_\_\_\_\_\_ All photoreceptors respond to variety of wavelengths but respond best to particular wavelength of light We need at least __ different photoreceptor types to perceive color There are no "\_\_\_" cones in the fovea

Answer 41

COLOR: Human retina is trichromatic Cones do not transmit specific wavelength info, but rather increase their response to varying intensities of light We need at least 2 different photoreceptor types to perceive color There are NO blue cones in fovea

Question 42

CNS can only focus on one specific object at a time. Object of focus is in the foreground, everything else is in the background. This is often referred to as "\_\_\_\_\_\_"

Answer 42

CNS can only focus on one thing at a time either see one cup or two faces this is called **winner takes al**l

Question 43

Cortex prefers to group things This is because it is the \_\_\_\_, ____ way to process the data

Answer 43

Grouping occurs because this is the easiest and fastest way to process data

Question 44

# Define the various Monocular cues: use only ___ eye 1. previous familiarity 2. interposition 3. linear and size perspective 4. shadows and illumination 5. motion parallax

Answer 44

Monocular cues: use only one eye 1. Previous familiarity (viewer knows info about sizes and shapes of certain object) 2, interposition (objects hidden by others are far away) 3. linear and size perspective (parallel lines seem to converge as they get far away) 4. shadows and illumination (brighter = closer) 5. motion parralax (closer objects move faster)

Question 45

Stereoscopic cues: using both eyes, objects around the focus points will fall on different parts of the retina: objects that are farther away will project \_\_\_\_\_ objects that are closer will project \_\_\_\_

Answer 45

Stereoscopic cues: using both eyes, objects around the focus points will fall on different parts of the retina: objects that are farther away will focus medially objects closer will project laterally