Retinal Phototransduction Flashcards
What structure does the following statement describe?
A spherical and avascular, white dense connective tissue that covers the globe posterior to the cornea.
Sclera
Which structure provides a strong tough external framework to protect the delicate optic and neural structures?
sclera
What structure does the following statement describe?
A mechanically strong and transparent connective tissue that covers the anterior 1/6 surface of the eye
Corea
What is the post powerful focusing element of the eye?
The cornea
What structure does the following statement describe?
A specialized epithelial tissue that is responsible for fine-tuning the image that is projected on the retina
the lens
Where is the lens of the eye located?
Inside the eye, surrounded by aqueous humor
What stabilizes the lens and allows for accommodation?
Elastin based zonular fibrils
What do these three structure compose?
Choriod, ciliary body, iris
Uveal tract
What structure does the following statement describe?
Capillary bed nourishing the photoreceptors and outer retina.
choroid
What structure does the following statement describe?
A structure composed of the ciliary muscle, controlling the refractive power of the lens, and a vascular component, that produces the aqueous humor filling the anterior chamber
Ciliary body
What structure does the following statement describe?
Colored portion of the eye, seen through the cornea
Iris
What does the Iris contain?
It contains 2 sets of muscles with opposing actions that allow the size of the pupil to be adjusted.
What is the anterior chamber?
Volume behind the cornea and in front of the lens. It is filled with aqueous humor
What is the posterior chamber?
region between the vitreous and the lens
What structure does the following statement describe?
Clear watery liquid that nourishes the cornea and lens and produced by the ciliary body
Aqueous humor
What structure does the following statement describe?
Thick gelatinous substance filling the space between the back of the lens and the surface of the retina
Vitreous humor
What structure does the following statement describe?
Contains neurons that absorb light and process visual information in the images and send that information to the brain
Retina
What is the macula?
Oval spot containing a yellow pigment
What is the fovea?
Small depression at the center of the macula (has high spacial acuity)
What structure does the following statement describe?
Whitish circular are where retinal axons leave the eye and travel through the optic nerve to targets in the midbrain and thalamus
Optic disk
Where do blood vessels supplying the inner retina enter the eye?
optic disc
What is the blood supply to the eye?
Ophthalmic artery (anterior segment and retinal system)
What are cataracts?
Clouding of the lens that affects vision. There is a disruption of the order of the organization of the lens cell fibers or aggregation of the proteins within them can destroy transparency of the cell
What are the symptoms of cataracts?
hazy vision, poor night vision, glare and faded colors
What is the treatment for cataracts?
surgical removal of the cloudy lens and replacement with an artificial lens
What is glaucoma?
A group of diseases that damage the eye’s optic nerve and can result in vision loss (peripheral at first)
Is glaucoma reversible?
No, it is not
What are the types of glaucoma?
Normal tension, open- angle, closed- tension
What is a major risk factor for glaucoma?
Elevated eye pressure, thin cornea, abnormal optic nerve anatomy, high blood pressure
Describe the structure of the retina
Organized layers of neurons (3 nuclear layers, 2 plexiform layers, 1 fiber layer)
1) Ganglion layer
2) Inner plexiform layer
3) Inner nuclear layer
4) Outer plexiform layer
5) Outer nuclear layer
What are teh 5 types of neurons in the retina?
Photoreceptors, horizontal cells, bipolar cells, amacrine cells, ganglion cells
Where is pigmented epithelium found and what is its function?
It is found behind the photoreceptors and acts as a backstop for light and maintains phototransduction machinery of photoreceptors by recycling photoreceptor discs
How does neurotransmission occur in the retina?
cells along the vertical path release glutamate
cells mediating lateral information transmission release GABA or glycineric
What is vertical information flow?
Photoreceptors —-> bipolar cells —–> ganglion cells
What is lateral information flow?
Mediated by horizontal cells and amacrine cells
What are the two types of photoreceptros in the retina?
Rods and cons
True or False:
Photoreceptors are ciliated cells
True
What are the structural components of the photoreceptors?
Outer segment (has phototransduction machinery)
Inner segment (has cell organelles)
Synaptic terminal (contacts bipolar and horizontal cells)
Neurotransmitter (glutamate)
How do receptors respond to light?
with graded hyperpolarizations
What is circulating current?
Na and Ca in through cGMP gated channels and K in through channels. COmbined action depolarizes the cell to a steady -40
What happens to the inward cationic current when the photorecetpors are exposed to light?
The Na and Ca channels are closed but the K channel remains open and this hyperpolarizes the cell
What does teh phototransduction cascade provide for?
High amplification which allows rods to respond to absorption of a single photon
What is phototransduction?
Process by which light is converted into electrical signals
Describe the process of pigment activation?
Pigment, which has opsins (G protein linked receptors with 11-cis retinal) are activated by absorbing a photon and changing the conformation of the retinal. This then activates rhodopsin. Activated rhodopsin can then decrease cGMP levels and close Na and Ca channels
What is dark adaptation?
Restoration of sensitivity after exposure to illumination. It occurs mostly in the pigment epitheloum
Does the following statement describe rods or cones?
High sensitivity and low resolution
Rods
Does the following statement describe rods or cones?
Low sensitivity and high resolution
cones
True of false:
High convergence of cones onto bipolar cells
False. There is a high convergence of RODS into rod bipolar cells. There is 1 cone per 1 bipolar (midget) cells
What is the leading cause of vision loss?
Age related macular degeneration - dry (85%)
Describe wet age related macular degeneration?
abnormal bvs behind retina grow under macula
leak and rapidly damage retina
Describe dry AMD?
retinal pigment epithelium and photoreceptors of macula degenerate
-accumulation of yellow deposit - cell debris
What are the symptoms of age related macular degeneneration? What are some associated risk factors?
Loss of central vision and acuity (cones)
-aging, smoking, inheritance
What type of glutamate receptors are in an on center bipolar cell? in a off center bipolar cell?
on center: inhibitory
-in response to light, decreased glutamate released from photoreceptors causes less of an inhibitory response –> depolarization
off center: excitatory
-in response to light, decreased glutamate released from photoreceptors causes less of an excitatory response –> hyperpolarization
Describe nonproliferative vs proliferative diabetic retinopathy?
nonproliferative: hyperglycema-> pericyte death
- microaneurysms and dot hemorrhages
proliferative - new fragile vessels grrow
-leak blood
Describe an on center bipolar cell:
- ? in the center -
- ? in surroundings
- responds to:
- excitatory in the center - depolarization
- inhibitory in surroundings - hyperpolarization
- responds to light going on
- light against dark background
Describe an off center bipolar cell:
- ? in the center -
- ? in surroundings
- responds to:
- inhibitory in center - hyperpolarize
- excitatory in surroundings - depolarize
- respond to lights going off
- dark spot against light background
Ganglion cell’s firing rate is most affected by what?
receptive fields lying along border of illumination
In an on center ganglion cell describe the effects:
- receptive field in dim light
- illumination on inhibitory surround
- border of illumintation falls on middle of receptive field
- center of receptive field is full illuminated
- portion is in dark area
- spontaneous activity
- reduced discharge
- no change in rate - excitatory and inhibitory cancel out
- only partial inhibition - strong discharge
What determines the on or off center properties of bipolar cells and the ganglion cells they innervate?
glutamate receptors
What type of glutamate receptors are in an on center bipolar cell? in a off center bipolar cell?
on center: inhibitory
-in response to light, decreased glutamate released from photoreceptor
What helps detect the borders of objects?
color
Do rods have a high or low convergence onto rod bipolar cells?
High convergence
What is scotopic vision?
rod only vision (no color)
What is photopic vision?
cone only vision (color)
What is mesopic vision?
rod and cone vision
At low light levels, which photoreceptors are active?
Rods only
What colors are the basis for trichromatic vision, and what enables this to occur?
blue, green, red
opsin sequences of the cones on the disk tune the absorption of light to a particular region of the spectrum
Which opsin types are similar in sequence, which are different?
Rho and S-opsin different
S-opsin and M-opsin different
M and L have few differences
In the cone mosaic, which opsin is the least present, and which opsins is there a large ratio of variability present in different people?
How does this ratio affect color perception?
S-opsin - only 5%
M and L - large differences in ratio present
-no impact on color perception
What occurs in color blindness?
there is a change in number of genes coding for red and green cone opsins
What type of color blindness does this describe: no expression of M opsin?
deuteranopia
What is protanopia?
color blindness: no expression of L opsin
What is tritianopia?
color blindness: no expression of S opsin
-very uncommon
Where are M cells found and what do they do?
in the periphery
they sense motion and are not color sensitive
What word describes the pathway of M cells?
magnocellular
Are M cells large or small, and what does this mean?
large cells that receive input from large number of photoreceptors
What word describes the pathway P cells are involved in?
paravocellular
What are P cells involved in?
High acuity and color sensitivity
Which type of cell P or M has good light and contrast sensitivity and temporal resolution?
M cells
Where are P cells found? How many cells do they receive input from?
fovea
receives input from single bipolar cell which receives input from single cone
What type of cell is a K cell and what is it’s function?
bistratified ganglion cells
-carry short wavelength - blue info
How is color determined in relation to cones?
comparisons btwn two or more cone types
What type of cells are involved in synchronization of circadian rhythms, sleep, learning?
photosensitive retinal ganglion cells
