Midterm 2 Lecture 8 Flashcards
what are Sensory Receptors Cells (also known just as Sensory Receptors)
specialized neurons that detect a specific category of physical events
how do what are Sensory Receptors Cells accomplish their task
accomplish this task with receptor proteins that are sensitive to specific sensory stimuli, specific features of the extracellular environment
what are the receptor proteins that Sensory Receptors have
the presence of specific molecules (via chemical interactions) – physical pressure – temperature – pH (acidity, basicity) – electromagnetic radiation (photons)
what does the protein that senses the presence of specific molecules (via chemical interactions) do
• smell, taste (except for sour), hunger, thirst, nausea, pain
what does the protein that senses physical pressure sense
• touch, stretch, vibration, acceleration, gravity, balance, hearing, thirst, pain
what does the protein that senses temperature proteins sense
• heat, cold, pain
what does the protein that senses pH (acidity, basicity) sense
• sour taste, suffocation, pain
what does the protein that senses electromagnetic radiation (photons) sense
• vision, sunburn
do all organisms sense the same things
Some non-human animals have other senses, such as the ability to detect electrical and magnetic fields, humidity, and water pressure.
what is Sensory transduction
Process by which sensory stimuli are transduced (converted) into receptor potentials
(how the organism senses stuff)
what are Receptor potential
Graded change in the membrane potential of a sensory neuron (sensory receptor cell) produced in response to sensory stimuli
what are Sensory Receptor (Cell)
Specialized neuron that detects a particular category of physical events (sensory stimuli).
E.g., photoreceptor (cells) transduce light into receptor potentials
what is the order of sensory transduction
Sensory transduction
Receptor potential
Sensory Receptor (Cell)
do all sensory receptor cells have action potentials
Not all sensory receptor cells have action potentials, but they all release neurotransmitter.
The sensory receptor cells that do not have action potentials tend to release neurotransmitter in what fashion
a graded fashion, dependent on their membrane potential. The more depolarized they are, the more neurotransmitter-filled vesicles they release
what are Photoreceptor (cell)
The sensory receptor (cell) responsible for vision. Located in the retina, photoreceptor cells transduce the electromagnetic energy of photons into receptor potentials.
Each photoreceptor cell contains how many types of opsin protein.
one
Since humans have 4 different types of opsin proteins, we have how many types of photoreceptor cells
we have 4 different types of photoreceptor cells
what is Opsin
A type of protein that, in conjunction with retinal, is responsible for the transduction of visual information (i.e., light). The opsins found in humans are all inhibitory metabotropic receptors. Rod photoreceptor cells express the rod opsin (rhodopsin). Cone photoreceptor cells express one of the cone opsins (red, blue or green).
what is Retinal
Small molecule (synthesized from vitamin A) that binds to opsin proteins. In mammals, retinal is the actual molecule that absorbs the energy of photons. The type of light that retinal can interact with is dependent on the opsin protein that retinal is bound to.
Visible light refers to electromagnetic energy that has a wavelength between 380 and 760 nm. We detect this light using four kinds of photoreceptor cells , what are they
1 rod cell & 3 cone cells
what is the fovea
the area that cones detect light/color in the centrea
The three cone opsins are sensitive to different wavelengths of light: explain the blue cone
blue cone opsins are most sensitive to short wavelengths
The three cone opsins are sensitive to different wavelengths of light: explain the green cone
green cone opsins are most sensitive to medium wavelengths
The three cone opsins are sensitive to different wavelengths of light: explain the red cone
red cone opsins are most sensitive to long wavelengths
The amount that any one cone will be activated depends on what
both on the wavelength of the light and the amount of it (its intensity). If shown three colors separately (blue, green, and red) at the same intensity, people often say the green light is brighter. This is because green cone opsins are the most sensitive to light
what is Trichromatic Coding
colour is made up of three colours (Red, blue and green), when the overlap the can look like a different colour when really they are juts a mixture of 2-3 of the colours
Our perception of light and color has three dimensions to it: what are they
Brightness
Saturation
Hue
what is Brightness
– intensity
(luminance, amount)
what is Saturation
– purity (in terms of
composite wavelengths)
aka is it more white or the colour… think about the cone)
what is Hue
– dominant wavelength (color)
If brightness is 0%, what happens
your image will be all black. Hue and saturation have no impact if there is no brightness
If saturation is 0%, what happens
you are in the middle of the color cone where there is no color (equal contribution from all wavelengths) which means you have a black and white image
what are the 3 types of colour blindness
Protanopia
Deuteranopia
Tritanopia
what is Protanopia
Absence of the red cone opsin (1% of males). Visual acuity is normal because red cone cells get filled with green cone opsin.
People with this inherited condition have trouble distinguishing colors in the green-yellow-red section of the spectrum.
Simple mutations in of the red cone opsin (1% of males) produce less pronounced deficits in color vision.
what is Deuteranopia
Absence of the green cone opsin (1% of males). Visual acuity is normal because green cone cells get filled with red cone opsin. People with this inherited condition have trouble distinguishing colors in the green-yellow-red section of the spectrum.
Simple mutations in of the green cone opsin (6% of males) produce less pronounced deficits in color vision.
what is Tritanopia
Absence of the blue cone opsin (1% of the population). Blue cone cells do not compensate for this in any way, but the blue cone opsin is not that sensitive to light anyway, so visual acuity is not noticeably affected
what is The cornea
is the outer, front layer of the eye. It is transparent and admits light
what is The conjunctiva
is a mucous membranes that line the eyelid
turns into the sclera at the back of the eye
what is The sclera
is opaque and does not permit entry of light
what is The iris
is a pigmented ring of muscles
what is The lens
consists of several transparent layers. The shape of the lens can change to allow the eye to focus, a process known as accomodation
what is The pupil
regulates the
amount of light entering the eye. It is an opening in the iris
what are the types of Movement of the Eye
Saccadic and Pursuit
what is Pursuit
Pursuit movements allow us to maintain an image of a moving object
what is Saccadic movements
– rapid, jerky shifts in your gaze from one point to another. Our eyes scan a scene by making saccadic movements.
The interior lining (furthest back part) of the eye is the what
retina
The interior lining (furthest back part) of the eye is the retina. The retina contains what
photoreceptors
In humans, photoreceptors are classified as what
rods or cones
Rods are very sensitive to what
light (i.e. vision in the dark).
Cones are not particularly sensitive to what
light
Cones are not particularly sensitive to light, but because there are three different kinds of them, each sensitive to different wavelengths, the cones can do what
encode color vision
Light passed through the lens and crosses what
the vitreous humor, a clear, gelatinous fluid.
The central region of the retina is the what
fovea
The central region of the retina is the fovea. It contains a high density of what
photoreceptors and thus mediates acute vision
Site of blind spot is where
Site of blind spot is the optic disk
Site of blind spot is the optic disk what is this
point at which the optic nerve exits through the back of the eye. It has no receptors
give locations and response characteristics of photoreceptor cones
most prevalent in the central retina; founding fovea
sensitive to moderate-to-high levels of light
provide info about hue
provide excellent acuity
give locations and response characteristics of photoreceptor rods
most prevalent int he peripheral retina; not found in the fovea
sensitive to low levels of light
provide only monochromatic info
provide poor acuity
he fovea primarily contains cone cells, each of which connects to what
a single downstream collection of cells (a bipolar cell which in turn connect to a single ganglion cell).
he fovea primarily contains cone cells, each of which connects to a single downstream collection of cells (a bipolar cell which in turn connect to a single ganglion cell). Thus, photoreceptors in the fovea can register the exact location of the input. This enables what
high resolution, color vision
In the periphery, collections of photoreceptors (primarily rods, which use the opsin rhodopsin) converge onto fewer and fewer what
downstream collections of neurons (bipolar and ganglion cells)
In the periphery, collections of photoreceptors (primarily rods, which use the opsin rhodopsin) converge onto fewer and fewer downstream collections of neurons (bipolar and ganglion cells). Although precise location and shape of input is heavily impeded, the periphery enables what
the perceptions of faint lights and general shapes (low resolution).
Peripheral Vision has low what
low Spatial Frequency
explain low Spatial Frequency
Images deficient in high frequency information look unfocused but we can still make out the form
People have poor visual acuity in their peripheral vision where most of light perception is mediated by rod cells.
The high visual acuity needed for reading is only possible in the fovea, which is primarily where the cone cells are located.
explain Transduction of light into receptor potentials
Photoreceptor cells do not have action potentials.
They release glutamate in a graded fashion dependent on their membrane potential. The more depolarized they are, the more glutamate-filled vesicles they release.
Photoreceptor cells have sodium ion channels in their membrane which are open in the dark (when the cells are at rest).
Sodium continually enters through these ion channels, which depolarizes the photoreceptor cell membrane to about -40 mV. At this depolarized membrane potential, photoreceptor cells continuously release glutamate.
When the retinal portion of the retinal-opsin complex absorbs light, it causes a conformational change (change in shape) in the opsin receptor protein. This launches a g-protein signaling cascade that closes the open sodium ion channels. The closing of these channels hyperbolizes the membrane to -70 mV, at which point the photoreceptor cell largely stops releasing glutamate.
So, photoreceptor cells are more depolarized and release more glutamate in the dark than in the light.
Like photoreceptor cells, bipolar cells also do not have what
action potentials
Like photoreceptor cells, bipolar cells also do not have action potentials and release glutamate in a graded fashion dependent on their what
membrane potential
There are two main types of bipolar cells what are they
OFF bipolar cell and ON bipolar cells
explain OFF bipolar cells
have ionotropic glutamate receptors, and so they are depolarized by glutamate. Because photoreceptor cells constantly release glutamate in the dark, OFF bipolar cells are more active (more depolarized) in the dark than in the light.
explain ON bipolar cells
only have inhibitory metabotropic glutamate receptors, so they are uncommonly inhibited by glutamate. Thus ON bipolar cells are more active (more depolarized) in the light vs the dark.
And finally, retinal ganglion cells (RGCs) are fairly typical neurons. They are generally excited by what
glutamate and have action potentials
The receptive field of a neuron (whether it is a photoreceptor cell, bipolar cell, ganglion cell, or a visual cell in the cerebral cortex) is what
the area of the visual field in which the presence of a stimulus influences the firing rate of that neuron (i.e. the part of space in which the light must fall for the neuron to be stimulated).
NOT part of the actual brain/person/subject… but rather what they are looking at
To determine where a receptive field for a particular neuron is located what happens
an investigator can shine light in various locations in space while recording from the neuron as an animal focuses on a central fixation point.
To determine where a receptive field for a particular neuron is located, an investigator can shine light in various locations in space while recording from the neuron as an animal focuses on a central fixation point.
If light in a particular spot excites the neuron then that location is part of what
the neurons excitatory receptive field (ON firing). Photoreceptor cells only exhibit ON firing.
To determine where a receptive field for a particular neuron is located, an investigator can shine light in various locations in space while recording from the neuron as an animal focuses on a central fixation point.
If the light inhibits activity, the location is what
is in an inhibitory receptive field (OFF firing).
Neurons downstream of photoreceptor cells respond to light in their receptive field with either what
ON firing or OFF firing
Retinal ganglion cells (RGCs) show opposing changes in neural activity when light is where
in the center versus the surround of their receptive field
ON cells are excited by light where
in the center and are inhibited by light in the surround
OFF cells are excited by light where
in the surround and are inhibited by light in the center.
what is a Bipolar cell
A bipolar neuron located in middle layer of retina, conveying information from photoreceptors to ganglion cells
what is a Ganglion cell –
Neuron that receives visual information from bipolar cells; its axons give rise to the optic nerve, which heads back to the rest of the brain.
what is a Horizontal cell –
Neuron that interconnects adjacent photoreceptors and the outer processes of bipolar cells. They regulate the excitability of photoreceptor cells to adjust light sensitivity.
what is a Amacrine cell –
Neuron that interconnects adjacent ganglion cells and inner processes of bipolar cells. They are many different types of amacrine cells and they have many functions.
explain colour vision and Opponent-Process Coding in Retinal Ganglion Cells (RGCs
Some retinal ganglion cells utilize a opponent-color system
Some color-sensitive RGCs respond in center-surround fashion. There are red-green RGCs and blue-yellow RGCs
Each hemisphere of the brain receives information from where
the contralateral visual field.
The optic nerves join where
at the base of the brain to form the x-shaped optic chiasm
The axons from the RGCs serving the inner half of each retina (medial sides) goes where
cross through the chiasm to the opposite side of the brain.
The axons of the RGCs serving the outer half of the retina (lateral sides) go where
remain on the same side of the brain.
RGCs project directly to where
both the superior colliculi of the midbrain and lateral geniculate nucleus (LGN) of the thalamus.
The superior colliculi control what
fast visually-guided movements
The superior colliculi control fast visually-guided movements. The pathway to the thalamus and then on to the cerebral cortex is involved in understanding what
what the visual information represents.
