Exam 3: L4 Vision Flashcards
Development of Eye:
The eye develops as an outpocket of the ________
- ectoderm (……)
- neural crest(…..)
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
***Basic Anatomy of the Eye:
What are the basic three layers of the eye
Basic Anatomy of the Eye:
Three Layers:
- Sclera (outermost, fibrous outer coat, helps keep shape, muscles insert here)
- Choroid (vascular layer)
- Retina (interior layer)
*****Corneo-Schlera Layer:
Explain the corneo schlera layer
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
*****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
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
If you have little to no pigment in the fluid in your iris you have _____ colored eyes
If you have little to no pigment in the fluid in your eyes you have blue colored eyes
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
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
Glaucoma:
Explain angle open vs angle closed
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
****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 _____
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
*****Lens
The ciliary muscle is innervated by the _____ only
This causes the lens to ____
Lens:
The ciliary muscle is innervated by the PSNS only
This causes the lens to thicken
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?
Two blood supplies in the eye: retinal and corneal arteries
Progression:
Internal Carotid—-> Opthalamic—-> Retinal & Corneal
Avascular zone in eye: fovea
Area of the eye where there is no photoreceptors?
(also the place where the retinal artery and optic nerve enter)
Optic disc is where the artery and optic nerve enter
it has no photoreceptors in it
TopHat:
Dillator pupillae is innervated by what?
Tophat:
Dillator pupillae: radial muscles, SNS
Remember, the constrictor pupillae, circumference stuff is PSNS
TopHat:
Define these various terms:
Hyperopia
Myopia
Astigmatism
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
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 _____
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
Visual perception occurs in the cortex but processing begins in the retina:
Vision occurs in two stages:
1.
2.
Vision occurs in two stages
- Light enters eye and is converted into electrochemical signal by photoreceptors (transduction)
- These signals are relayed to visial nuclei and cortices, where integration and perception take place
What two things does the pigmented epithelial layer (outer back of the eye do)?
Note: pigmented epithelial layer is right under photoreceptors.
Pigmented Epithelial Layer:
craddling tips of photoreceptors, it has two functions:
- metabolic function to give blood to the photoreceptors
- makes back of the eye black (to avoid a bunch of light reflection)
****Explain the path of light vs the path of neural info
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)
****Fovea:
The fovea only has _____ (NO _____)
What is the other significance of the fovea?
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
****Rods and Cones:
Explain which one has:
higher sensitivity,
more photopigment per cell
higher amplification
Rods and Cones
- Rods are more sensitive than cones, rods are specialized for nighttime vision (cones are for daytime vision)
- Rods have more photopigment per cell (captures more light)
- Rods also have higher amplification
*****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
Rods and Cones:
- Rods have lower temporal resolution (slower)
Cones have higher temporal resolution (faster)
- Rods: sensitive to scatered light / transient stimulation
Cones: sensitive to direct, axial stimulation
- Rods saturate in daylight, cones are only saturated in intense light
*****Rods and cones:
Explain the acuity and convergence of pathways in both
Then explain which one is achromatic vs chromatic
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
IMPORTANT:
In both rodes and cones there are NO ______
The first ____ actually occurs in the ganglion cell
In both rods and cones there are NO Action potentials
The first action potential occurs in the ganglion cell
Photoreceptors (both rods and cones) are arranged into three distinct regions:
- outer segment: consisting of
- inner segment: consisting of
- synpatic terminal which synpases with ___ cells
Photoreceptors are arranged into three distinct regions:
- 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
- synpatic terminal which synpases with bipolar cells
Explain the resulting cascade when light hits a rod:
- Light stimulation of rhodopsin activates G protein called ______
- Activated G protein then activates cGMP dependent ______
- ____ then cleaves cGMP, reducing its concentration
- Reducing the concentration of cGMP then results in ____ of Na channels
When light hits a rod:
- Light stimulation of rhodopsin activates G protein called transducin
- Activated G protein transducin activates cGMP dependent PDE
- PDE then cleaves cGMP, reducing its concentration
- Reduction in concentration of cGMP then closes Na channels
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
cGMP levels drop
HYPERPOLARIZES the outside segment of the photoreceptor
Each of the Na channels in the outer segments of rods needs how many cGMP to remain open?
Each Na channel needs 3 cGMP to remain open
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
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
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
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
Ganglion Cell Properties:
Ganglion cells are ________ , and information from the bipolar cells only modulates this activity
Ganglion cells only report ______ to the CNS
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.
Information is processed in the retina in two general ways:
Direct
Indirect
Explain both
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,
Types of synpases in the retina:
- Electrical (explain this one)
- Chemical:
- ribbon
- basal (no vesicles, or specialized zone, only uses Ca, unknown mechanism)
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
What are Muller cells?
Tips of the photoreceptors are supported by ______
Muller cells are like glia, they are like support cells
Note: tips of photoreceptors are supported by pigmented epithelium
Ganglion cells:
Explain M type vs P type
Which one goes with rods vs cones
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
What is the visual pathway of sensory processing from the retina all the way to the cortex?
Retina–> optic nerve –> optic chiasm—> optic tract–> lateral geniculate nucleus (thalamus) —>visual cortex
*****Visual pathways:
Upper fibers via the _____ lobe
Lower fibers via the _____ lobe
Upper fibers via parietal lobe
Lower fibers via the termporal lobe
“lower your temper”
**** 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
Up down right and left all get switched
Lower fibers of optic radiation course through the temporal lobe via Meyer’s Loop
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 _______)
Lateral Geniculate:
M type ganglion cells to magnocellular area (1 and 2)
P type ganglion cells to parvocellular are (3-6)
Visual Cortex:
Layer ___ (the input layer) is greatly expanded in the visual cortex
Visual cortex:
Layer 4, the input layer is greatly expanded in the visual cortex
If you cut the optic chiasm, what kind of visual defecit will you have?
Cut optic chiasm: tunnel vision
Bitemporal hemionopsia
Dorsal/parietal pathway ____ an object is
Ventral/temporal pathway: ____ an object is
Dorsal/parietal pathway: where an object is
Ventral/temporal: what an object is
VHAT is that?
Where is the door
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
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
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 “______”
CNS can only focus on one thing at a time
either see one cup or two faces
this is called winner takes all
Cortex prefers to group things
This is because it is the ____, ____ way to process the data
Grouping occurs because this is the easiest and fastest way to process data
Define the various Monocular cues: use only ___ eye
- previous familiarity
- interposition
- linear and size perspective
- shadows and illumination
- motion parallax
Monocular cues: use only one eye
- Previous familiarity (viewer knows info about sizes and shapes of certain object)
2, interposition (objects hidden by others are far away)
- linear and size perspective (parallel lines seem to converge as they get far away)
- shadows and illumination (brighter = closer)
- motion parralax (closer objects move faster)
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 ____
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
