Vision Physiology II Flashcards
Retina is the ___ _______ portion of the eye
Retina is the light sensitive portion of the eye
The retina
- Contains ____ for color vision
- Contains _____ for night vision
- Contains ____ _______
The retina
- Contains cones for color vision
- Contains rods for night vision
- Contains neural architecture
Melanin is located in the ____ layer of the retina
pigmented
Melanin prevents ____ _____ and stores ______
Melanin prevents light reflection and stores Vitamin A
Vitamin A is exchanged back and forth through the ___ ______ of the ____ segments of the rods and cones
Vitamin A is exchanged back and forth through the cell membranes of the outer segments of the rods and cones
What is a precursor to photosensitive chemicals of the rods and cones?
vitamin A
Fovea is a small area at the____of the retina (1 sq mm) that is capable of ___ and ____vision.
Fovea is a small area at the center of the retina (1 sq mm) that is capable of acute and detailed vision.
The center of the fovea (central fovea) contains only ____
The center of the fovea (central fovea) contains only cones
What is the area of greatest acuity?
the central fovea
Major functional segments of rods or cones:
- Outer segment: ____ ______photochemical
- Inner segment: ____ _____
- Nucleus
- Synaptic body: connects to subsequent _____cells
Major functional segments of rods or cones:
- Outer segment: light sensitive photochemical
- Inner segment: cytoplasmic organelles
- Nucleus
- Synaptic body: connects to subsequent neuronal cells
Rods and cones contain chemicals that_____ on exposure to light. This ____ the nerve fibers leading from the eye.
Rods and cones contain chemicals that decompose on exposure to light. This excites the nerve fibers leading from the eye.
- When light is absorbed by _____ it immediately begins to decompose
- In the process of splitting away a number of ____ _____ are formed
- _________ excites the rods forming ____ _____ of the optic nerve and transmission of the visual image into the CNS
- When light is absorbed by rhodopsin it immediately begins to decompose
- In the process of splitting away a number of intermediary compounds are formed
- Metarhodopsin II excites the rods forming action potential of the optic nerve and transmission of the visual image into the CNS
Reformation of rhodopsin:
- Rhodopsin is broken down into _____+ ______
- Metabolic energy converts all-trans retinal to _______, catalyzed by_________
- 11-cis retinal automatically recombines with _______ to form rhodopsin
Reformation of rhodopsin:
- Rhodopsin is broken down into all-trans retinal + scotopsin
- Metabolic energy converts all-trans retinal to 11-cis retinal, catalyzed by retinal isomerase
- 11-cis retinal automatically recombines with scotopsin to form rhodopsin
Role of vitamin A for the formation of rhodopsin:
- All-trans retinal conversion to _______(form of Vitamin A)
- All-trans retinol converted to______
- Catalyzed by ______
- 11-cis retinol converted to ______which can combine with scotopsin to form new rhodopsin
Role of vitamin A for the formation of rhodopsin:
- All-trans retinal conversion to all-trans retinol (form of Vitamin A)
- All-trans retinol converted to 11-cis retinol
- Catalyzed by isomerase
- 11-cis retinol converted to 11-cis retinal which can combine with scotopsin to form new rhodopsin
Rods under No light conditions=______
Outer segment of rod:
- _____-gated channels allow influx of _____
- In the dark, cGMP levels are _____
Inner segment of rod:
- _____pump
- ___- leak channels
-____ mV is resting state
Reduced _____
Rods under No light conditions=DARK CURRENT
Outer segment of rod:
- cGMP-gated channels allow influx of Na+
- In the dark, cGMP levels are high
Inner segment of rod:
- Na/K pump
- k- leak channels
-40 mV is resting state
Reduced electronegativity
Rods under LIGHT conditions:
- _____ in the outer segment is exposed to light, becomes activated, and decomposes
- cGMP-gated sodium channels ____
- ____ influx of Na+
- Na+ continues to be pumped via ____ pump from ____ ____
- More Na+ ____
Increased Negativity: ______
Rods under LIGHT conditions:
- Rhodopsin in the outer segment is exposed to light, becomes activated, and decomposes
- cGMP-gated sodium channels close
- Reduced influx of Na+
- Na+ continues to be pumped via Na/K pump from inner segment
- More Na+ leaves
Increased Negativity: HYPERPOLARIZATION
Mechanism for Light to Decrease Sodium Conductance
- Light activates______
- Stimulates _______
- Transducin activates ______ that breaks down cGMP
- Reduced cGMP ____ cGMP-gated sodium channels
- Photoreceptors _____
Mechanism for Light to Decrease Sodium Conductance
- Light activates Rhodopsin
- Stimulates G-protein transducin
- Transducin activates cGMP PDE that breaks down cGMP
- Reduced cGMP closes cGMP-gated sodium channels
- Photoreceptors hyperpolarize
What is responsible for keeping Na+ channel in the outer segment of the rods open?
cGMP
Light activated rhodopsin activates what?
G-protein transducin
What deactivates the activated rhodopsin?
rhodopsin kinase
Receptor potential is proportional to the logarithm of the ____ ______
•Very important for discrimination of the ____ _____
Receptor potential is proportional to the logarithm of the light intensity
•Very important for discrimination of the light intensity
the sensitivity of the retinal automatically adjusts to the __ ____
the sensitivity of the retinal automatically adjusts to the light level
Color vision is the result of activation of ____
cones
What are the three types of cones?
blue, green, and red
What is the protein that exists in cones?
Photopsin
Color blindness
- Lack of a particular type of _____
- Genetic disorder passed along on the ______
- Occurs almost exclusively in _____
- Most color blindness results from lack of the ___ or ____ cones
- •Lack of ____cone, protanope
- •Lack of _____ cone, deuteranope
Color blindness
- Lack of a particular type of cone
- Genetic disorder passed along on the X chromosome
- Occurs almost exclusively in males
- Most color blindness results from lack of the red or green cones
- •Lack of red cone, protanope
- •Lack of green cone, deuteranope
transmit signals in the outer plexiform layer and synapse with bipolar cells and horizontal cells
rods and cones
transmit signals horizontally in the outer plexiform layer from rods and cones to bipolar cells
horizontal cells
transmit signals vertically from rods, cones, and horizontal cells to the inner plexiform layer and synapse with ganglion cells and amacrine cells
bipolar cells
transmit signals from bipolar cells to ganglion cells
amacrine cells
transmit output signals from the retina through the optic nerve into the brain
ganglion cells
ELECTRONIC CONDUCTION (signal transduction in retina)
- Direct flow of ____ _____, NOT action potential
- Always ____ _____proportional to _____ ____
- The only cells that have action potentials are_____ cells
Send signals all the way to the brain
ELECTRONIC CONDUCTION (signal transduction in retina)
- Direct flow of electric current, NOT action potential
- Always graded response proportional to light intensity
- The only cells that have action potentials are ganglion cells
Send signals all the way to the brain
Rods and cones release _____
glutamate
_____ cells release aminobutyric acid, glycine, dopamine, acetylcholine and indolamine
amacrine cells
Output of horizontal cells is always _____
inhibitory
Horizontal cells prevent the lateral spread of light excitation on the retina, which is called
lateral inhibition
Horizontal cells have an ____center and an____ surround, which is essential for transmitting _____borders in the visual image.
Horizontal cells have an excitatory center and an inhibitory surround, which is essential for transmitting contrast borders in the visual image.
Three types of ganglion cells:
W cells (40%) receive most of their excitation from ____cells; sensitive to ____ ____ in the visual field
X cells (55%) ___ receptive field, ____ retinal locations, may be responsible for the ____ of the visual image itself, always receives input from at least one ____, may be responsible for _____ transmission
Y cells (5%) ___receptive field respond to____ _____ in the visual field
Three types of ganglion cells:
W cells (40%) receive most of their excitation from rod cells; sensitive to direction movement in the visual field
X cells (55%) small receptive field, discrete retinal locations, may be responsible for the transmission of the visual image itself, always receives input from at least one cone, may be responsible for color transmission
Y cells (5%) large receptive field respond to instantaneous changes in the visual field
