Lecture 9 - Vision Flashcards
Define sensation
Receiving information about a certain stimulus
Define perception
Conscious experience and interpretation of information that was sensed
How do receptor neurons detect physical stimuli?
With receptor proteins that are specific to different stimuli
Define sensory transduction
Process by which sensory stimuli get transformed into receptor potentials
Define receptor potential
Graded change in membrane potential of a sensory neuron caused by sensory stimuli
Define sensory neuron
Specialized neuron that detect particular sensory stimuli
Do all sensory neurons generate action potentials?
No, not all sensory neurons have axons or generate action potentials, but all of them release neurotransmitter
In what fashion do small sensory neurons release neurotransmitter?
In graded fashion, the more depolarized the neuron is, the more neuotransmitter will be released
What’s the name of receptor proteins that are sensitive to light?
Opsins
Name all opsin proteins used to detect light
Rhodopsin, red, blue, green cone opsins
How many opsins does one photoreceptor cell contain?
Each photoreceptor cell can only contain one type of opsin
How many photoreceptor cells do humans have?
Four, rod cells that express rhodopsin, and red, green and blue cone cells that express red, green, and blue cone opsins respectively
What is a photoreceptor cell?
Sensory neuron responsible for vision. These cells convert electromagnetic energy from visible light into receptor potentials
Define Opsin
Light sensitive protein
How do opsins gain their sensitivity to light?
By binding to a molecule of retinal
What type of receptors are opsins in our eye that transduce visual info
They are inhibitory metabotropic receptors
Define retinal
A molecule made from viatmin A that binds to opsin proteins
What happens when light reaches retinal?
Retinal reacts to light and changes its shape, launching a signaling cascade of G-proteins
How does retinal return to its initial form?
An enzyme comes in and uses ATP to bring the electron to a low energy state, thus forcing retinal to go to its initial state
What wavelength is visible light?
Between 380 and 760 nm
What are gamma rays and how do they interact with physical matter?
Gamma rays have extremely short wavelength and usually don’t interact with physical matter because of that
What happens if gamma rays hit an electron in a body
If an electron is hit by gamma rays, it will leave the atom entirely, creating positively charged ions which are very unstable.
What do positively charged ions do to balance themselves?
They will try to grab electrons from neighboring cells, leading apoptosis or blocking of cell destruction, leading to cancer
What happenes to electrons in the visible light wavelength?
Photons get absorbed by electrons causing electrons to enter higher energy state
What allows us to see ful spectrum of color?
Presence of red, blue and green cone opsins
Where are most cone opsins concentrated?
In the center of the eye
Where are rods mostly concentrated?
In the peripheral vision
How do three cone opsins work?
By relative activation, some opsins are activated less, some more to create a certain color
What are three perceptual dimensions of light and color?
Brightness, Saturation (purity in terms of composite wavelength), Hue (color)
Define protanopia
Absence of red cone opsins, people with this condition have trouble differentiating color in green-yellow-red spectrum, but have normal visual acuity since red cone cells get filled with green cone opsin
Define deuteranopia
Absence of green cone opsins, visual acuity is not affected, since green cone cells get filled with red cone opsins
Define tritanopia
Absence of blue cone opsin. Blue cone cells do not compensate for that loss, but visual acuity is not affected since blue cone cells are not sensitive to light
Define Achromatopsia and the cause
True color blindness that is usually cause by malfunctioning of G-protein signaling cascade that is shared between all of the opsins
What type of cells does fovea mostly contain?
Fovea primarily contains cone cells
Why are images in the center of our FOV usually very clear?
In the fovea, there is no compression of information, photorececptors (primarily cones) converge to downstream collections of neurons that do not decrease drastically, ensuring good image quality
Why are images less clear in our peripheral vision?
Photoreceptors (primarily rods) converge to fewer and fewer downstream collections of neurons, the information gets compressed leading to poor resoluton, but high detection of light and general shapes
What allows to hide the presence of a blind spot and the fact that our peripheral vision is color blind?
Rapid eye movement with the help of psychological processes that complete the images
Define Saccadic eye movement
Rapid eye movement that is scattered all over the place
Define Pursuit movement
Focused type of eye movement that allows us to keep a clear image of a moving object
What is an unusual property that photoreceptors have?
Apart from potassium leak channels, photoreceptors also have leaky sodium ion channels which are open in the dark when cells are at rest. In the dark, sodium constantly enters the cell through these channels depolarizing the membrane to -40mV
What do photoreceptors do in the depolarized state?
They continuously release glutamate
When are photoreceptor cells more depolarized and release more glutamate?
During the night, for when light hits photoreceptors, opsin receptor proteins change shape and launch a g-protein cascade that hyperpolarizes the cell
What are the two types of bipolar cells?
OFF bipolar cells and ON bipolar cells
How do OFF bipolar cells function?
They are more depolarized by glutamate since they express ionotropic glutamate receptors. Since photoreceptor cell constantly releases glutamate in the dark, OFF bipolar cells are more active in the dark than light
How do ON bipolar cells function?
Bipolar On cells have inhibitory metabotropic glutamate receptors hence they are uncommonly inhibited by glutamate. They are more active in presence of light than darkness
What does receptive field refer to?
it refers to the area of visual space where light is capable of changing the activity of a neuron
