Visual Processing Flashcards
What are photoreceptors and where are they located?
Photoreceptors are light-sensitive neurons located in the retina.
What are the two main types of photoreceptors in the retina?
cones and rods.
How do photoreceptors respond to stimuli?
with graded membrane potentials instead of firing action potentials.
What is the structure of cones and rods?
Both cones and rods have outer segments with disk-like layers, inner segments, and a synapse
How does light affect photoreceptors?
When light hits photoreceptors, pigment molecules change shape, triggering a chemical cascade that hyperpolarizes the cell, reducing its release of glutamate.
What pigment is found in rods?
rhodopsin
What is the appearance of the fovea?
a central pit in the macula, densely packed with cones.
Where is the blindspot and why is it called a blindspot?
The blind spot occurs when the optic nerve exits the eye
there are no photoreceptors in this region.
What type of lighting conditions are cones mainly used in, why, and what is their job?
Cones are less sensitive and function in bright light, distinguishing colours.
How do rods adapt to darkness?
Rods rebuild their stores of rhodopsin over approximately 30 minutes in a process called dark adaptation.
How are cones and rods distributed in the retina?
Cones are concentrated in the fovea, while rods are mainly found in the peripheral retina, making peripheral vision more sensitive to light.
What is a receptive field in the visual system?
It refers to the set of photoreceptors influencing cells in the retina.
What is the difference between on-center and off-center bipolar cells?
On-center cells are excited by light in the center and inhibited by light in the surroundings, while off-center cells are the opposite.
How do bipolar cells respond to uniform lighting?
Bipolar cells do not respond to uniform lighting because the effects of the center and surroundings cancel out, reacting only to contrast.
What is the function of retinal ganglion cells? (3)
receive input from bipolar cells
detect contrast
transmit visual information via action potentials to the brain.
How is visual information compressed before reaching the brain?
The retina condenses input from 126 million photoreceptors into about 1 million ganglion cells
Where is the optic chiasm located, and what happens there?
The optic chiasm is where optic nerve fibres cross, with nasal retina fibers crossing to the opposite side of the brain, while temporal fibers do not.
what is the job of photoreceptors?
They convert light energy into electrical energy in cells through phototransduction.
how many cones does the retina have?
6 million cones
how many rods does the retina have?
120 million rods.
what pigments are found in cones
cones have three different pigments corresponding to different types of cones.
what is the job of the fovea and why?
It is used for detailed vision and has the highest visual acuity.
What type of lighting conditions are rods mainly used in?
Rods are more sensitive, functioning in dim light but are bleached out in bright conditions.
why is visual information compressed before reaching the brain?
reducing redundancy to transmit information efficiently.
what does the outer layer contain in cone and rod structures?
visual pigments
what does the inner layer contain in cone and rod structures?
nucleus and organelles
what does the synapse in cones and rods release?
glutamate.
