3 lecture 6 Flashcards
how do Neurons send signals
using the highly controlled movement of ions along their concentration and electrical gradients
ions pass through specialized channels in the membrane
channels are proteins that open and close based on the voltage
Energy used to return the system back to where it started
what does action potential read as
The action potential will read as 0 until the cell that it is measuring has a voltage which at that point it will read as 1, then when it passes it will reach 0 again
what s the synapse
The connection between the terminal of one cell and the dendrite on the next cell is known as the synapse
what happens at the synapse
At the synapse, the electrochemical wave or action potential is converted into a chemical signal
This chemical signal is released by the terminal of the sending cell (the pre-synaptic cell) and taken up by the receiving cell (post-synaptic cell)
what are the steps of synapse
1) Voltage gated calcium channels in the terminal open
2) Calcium helps release neurotransmitters from the cell
3) Transmitter diffuses across the space between cells, then binds to receptors on the dendrites of a nearby cell
4) This binding to receptors does ALL KINDS OF THINGS
There are many (many) kinds of neurotransmitters and neuroactive substances, what do they do
These all modulate a cell’s activity
They can affect the probability and timing of action potentials
–how much input will be needed to fire
–when the cell will fire relative to that input
–how many action potentials will be produced And so on
what are the types of neurotransmitters
excitatory
inhibitory
modulatory
what are 2 things to keep in mind about neurotransmitters
There are many (many) kinds of neurotransmitters and neuroactive substances
There are receptors for all of these different kinds of substances
what is the neurotransmitter we will be focusing on
GABA
what are EXCITATORY transmitters
We’ve talked about action potentials or spikes as being the currency of the brain –and there are lots of chemicals that can result in more spikes being produced (these chemicals are EXCITATORY transmitters)
must a spike always be produced?
But it turns out that it can be just as important to not produce a spike as to produce one
INHIBITION is really important too
what is a seizure
For example, seizures are just one consequence of a burst of too much excitatory activity
what does GABA do
GABA is the main neurotransmitter ensuring that there isn’t just an action potential free-for-all going on in the brain
Rather than exciting a cell to produce a spike, GABA inhibits a cell and prevents a spike (or makes a spike harder to produce)
Often it does so by making the inside of the cell MORE negative
–e.g. instead of -70mV, it might lower it to -90mV
This means that instead of just needing a little nudge to get an action potential started, a cell might need a shove –i.e. the cell will need more or stronger input
how does GABA do it
GABA receptors are chloride channels, the let chloride flow into the cell
Chloride is negative (Cl-)
When chloride enters the cell because of its concentration gradient, it lowers the resting potential
what is Multisensory integration
This is the ability to pull together information from more than one sense at the same time
We actually do this all the time, without really thinking about it
But you can see the evidence of it when we do something called the McGurk Effect
what animal uses a lot of Multisensory integration
the owl– for hunting
They are very good at localizing prey based on sound
They then orient to the prey (with their eyes) and swoop in to catch it
how do owls do it
To do this, they have to have two maps in their brain, each recreating the world around them –one is a map based on the auditory or sound information
–one is a map based on the visual information
Not only do they have to have these maps, but they have to be in register
–a location in the auditory map should correspond to the same location in the visual map
This takes a lot of practice to get the maps to line up properly
but eventually they do and owls become amazing hunters
what happens if we mess up one of the maps
Work by Eric Knudsen at Stanford has looked in detail at these maps
How do they get set up, that is, how does the brain not only create the maps but get them to correspond to each other
He also studies what happens if you alter the sensory input or the maps
For example, by putting prism goggles on the owls
The prisms shift where the target appears to be
Thus, if there’s a mouse straight ahead, it will look like it’s a few degrees to the right or left, depending on which glasses the owl is wearing
This means that the auditory and visual maps are not longer in register
So the owl has to learn (again) how to relate the sound and the visual signal
–it turns out that they can do this too, even if they are learning to do so as adults
why is GABA critical for owls
GABA is critical for how the brain can create that second map
how does GABA inhibit the maps
It turns out that the brain doesn’t write over or erase the old maps
The old ones are there, they are just silent, inhibited, while the new map is formed That inhibition is done by GABA
If you block GABA, both the old and new maps are present at the same time
When the prisms are taken off, GABA inhibits the new maps and the old ones are active again
sum u p the information thus far
We have an all-or-none action potential that arrives at a terminal
That electrochemical signal gets turned into a chemical signal that can be more graded and complex than just all-or-none
–you can think of it as an analog rather than a digital signal
what are the reasons for the greater complexity
The diversity of things that can happen when a transmitter binds to a receptor
The post-synaptic cell is integrating inputs from many many cells
Where does that “sprinkling” of Na+ that helps open the Na+ channels comes from
not all of these inputs will result in a spike, they may just alter the potential a little bit, i.e. they provide some or all of that initial “sprinkling” of Na+
what happens when the post-synaptic cell sums up the inputs and determines a response
Once that post-synaptic cell sums up the inputs and determines a response, we’re back to the all-or-none, 1s and 0s, “digital” signal: the action potential
in general, how does information flow through the brain
In general, information comes in the middle/bottom part of the brain (sub-cortical)
It goes through the thalamus, kind of a relay station
It then goes to higher or more dorsal and lateral brain areas like the cortex
And gets processed within the cortex
Then the output of the cortex goes back down to areas that will execute behaviors
One of the first stops for incoming sensory input is the what
thalamus
what is the thalamus
relay station for information coming in and going out
what are the subdivisions of the thamalus
There are many subdivisions of the thalamus,
- -they connect to different parts of the brain
- -are involved in different functions
From the thalamus, signals travel to what
the cortex
what is the cortex
Cortex refers to the outermost part of the brain
In mammals it is a layered structure: the cells are highly organized into layers and columns
what does the cortex do
The cortex does a lot of higher-level processing
In fact, a lot of what the cortex does is to integrate information from multiple sources
–it is where your brain recreates the sensory world –it is where your brain makes decisions and plans movements
Like the thalamus, there are many subdivisions –some are concerned with sensory input (figuring out what or where a stimulus is)
–some are concerned with memory or recognition or decisions, things that aren’t simply reconstructing a stimulus
–some are concerned with determining how to respond, assembling a behavior
how deep does the cortex go
not very deep at all, under it is all grayish area is full of axons
We call it white matter because the myelin on it makes it appear white in sections
They are all of the axons going to and from the cortex –The cortex has lots of connections to other parts of cortex as well as to underlying structures
how do Sensory systems process sensory input
Sensory receptors turn external information into action potentials
Information gets taken apart at the sensory receptors, then progressively assembled at higher stages in the brain (the thalamus and cortex)
how does vision aid with inputs
Photoreceptors in your retina turn light into action potentials
–The pattern of action potentials in your visual cortex recreates the visual scene
how does hearing aid with inputs
- -Hair cells in your cochlea turn sound waves into action potentials
- -The pattern of action potentials in your auditory cortex indicates what and where a sound is
how does smell aid with inputs
–Olfactory receptors in your nose bind to odorants (different receptors for different odorants), generate action potentials –olfactory cortex, and other cortical and memory areas (hippocampus) identify smell
what is processing
what you do with the information
Do you approach a stimulus? Attack it? Run from it? Have sex with it? Eat it? Nurture it? Speak to it? Remember it?Many sub-cortical regions monitor your current and previous internal state (hypothalamus, preoptic area, amygdala, nucleus accumbens, septum, ventral pallidum, hippocampus)
what do Cortical regions do
Cortical regions provide top-down information on what you should or can do, decision-making
what does the hypothalamus so
regulates body funtion
what does amygdala do
emotion
what does hippocampus do
memory
what is behaviour
anything to do with your response
what is included in processing (brain parts)
cerebral cortex hypothalamus amygdala hipocampus basal ganglia, ventral palidum, nucleus accumbens
what is included in behaviour (brain parts)
motor cortex, basal gangliam, cereballum
they are important for learning and altering movements.
They assemble a motor plan to enable you to execute a behavior
what is Electroencephalography EEG
Uses electrodes to measure electrical activity along the
scalp
Pros: Non-invasive
People can move around during recording (for example, there are studies of people playing the guitar)
Cons:
Poor spatial resolution:
activity happens, but hard to determine exactly where
can say when a change in
Also, because the electrodes are on the surface, it’s difficult to say what deeper structures are doing
what is Positron Emission Tomography PET
How it works:
Person or animal eats radioactively labeled sugar (fluorodeoxyglucose or FDG)
Sugar gets picked up by active cells (because busy cells need energy to run that Na+/K+ pump!)
Cells release radioactivity (cells release positrons, which collide with electrons and emit a gamma ray or gamma photons)
Gamma photons are detected by the scanner Active regions will give off a lot of radiation and “light-up” on the scanner
This means that active regions will give off a lot of radiation and “light-up” on the scanner
what are the pros of PET
Much better resolution than the EEG and can see deeper structures better
what are the cons f PET
The part where you have to eat radioactive sugar
Also, you can’t move around much in the scanner
Lots of PET studies involve watching or listening to things
what is Functional Magnetic Resonance Imaging fMRI
Also involves a scanner, but this time it uses magnets
Basically, the scanner applies magnetic fields to the brain, then measures the energy emitted by different brain areas as they return to their normal, unmagnetized states
Because deoxygenated blood is more magnetic than oxygenated blood, areas that are more metabolically active (areas using more oxygen) emit different signals than less active areas
what are the pros and cons of fMRI
fMRI offers reasonable resolution (and you don’t have to eat radioactive sugar!) but once again, participants can’t move around much
what is Electrophysiology
Uses electrodes to measure the activity (action potentials) of neurons Can measure one or hundreds at the same time
In humans, this is often done prior to brain surgery
–it can help the surgeon determine where speech and language areas are located and avoid them
but mostly it’s done in animals
what are the pros of Electrophysiology
high resolution, you can find out what a single cell is doing during behavior
what are the cons of Electrophysiology
Cons: difficult to follow networks of cells
what is 2-photon imaging
Fusion of green fluorescent protein (GFP) and a calcium indicator (calmodulin and myosin light chain)
Cells light up, literally, when calcium in present –like when voltage gated calcium channels open
wat are the pros of 2-photon imaging
Can look at many cells at the same time (easier than with electrophysiology)
what are the cons of 2-photon imaging
time course for cells to light up is slightly slower than real action potentials
Also difficult to measure just one action potential
How do we study the brain?
With these measures, can look at real-time changes in activity and relate them to behavior
They measure activity directly –electrophysiology and EEG directly measure action potentials
Or indirectly –PET and fMRI look at which areas use more energy or oxygen and are therefore more active
wha is Gene and protein expression
Label mRNA with radioactivity or dye or
Label proteins with antibodies attached to fluorescent or other tags Look at the expression under the microscope
You can do this by making very thin brain slices and then reconstructing it
or, now, with the entire brain, all at once!
what are the pros of Gene and protein expression
Can look at expression across a wide range of brain areas
(hard to do with electrophysiology) Can look at expression within single neurons
(can’t do with EEG, PET or fMRI)
Tells you about changes or differences in particular molecules or cell types
what are the cons of Gene and protein expression
have to take the brain out to look at it
- -not a real-time measure of what’s going on
- -can only have one “treatment” per individual, compare expression between groups
One type of protein that lets us get information about the activity of particular kinds of cells are those translated from immediate early genes, what is it
examples are EGR1 and cFOS
what are Immediate early genes
These are genes that are rapidly transcribed when cells change their firing pattern
how do Immediate early genes help us
By looking at immediate early gene expression, we can know –whether a cell was active at a particular time, during a behavior or in response to a stimulus
–if we label for other proteins, we can know what kind of cell it was
Here, green cells contain the protein of an immediate early gene called c-fos
–that means that these cells altered their pattern of action potentials in response to a particular stimulus
The red label of for a protein called parvalbumin
The merge is showing us that the c-fos and parvalbumin are expressed in the same cell
How do you know what a brain area does?
Look at when it is active
Manipulate activity within the brain area itself
then look at effects on behavior
Increase the activity of cells
Decrease the activity of cells
Modulate the activity of cells
how do you Increase the activity of cells
–stimulate cells using electricity
–stimulate cells using lights
(this is what we’ll talk about for false memories)
how do you decrease the activity of cells
–lesion or kill the cells in that area
–block the activity of cells using different drugs
like adding GABA or tetrodotoxin
tetrodotoxin is a poison from pufferfish
it blocks sodium channels, which means it blocks action potentials
how do you modulate the activity of cells
–you can change the activity of inputs or outputs to an area –you can change the pattern of action potentials
block or stimulate receptors for neuromodulators like serotonin, dopamine, norepinephrine
give a sumar of thus far
Action potentials and how brain cells communicate Synapses, neurotransmitters and creating a graded signal
Summary so far
How does the brain work, inputs, processing and outputs
How do we study the brain? EEG, PET, fMRI, electrophysiology, gene and protein expression
Finding out what the brain does, ways to manipulate the brain
