Studied by 0 peopleWhat is a Stimulus?
This is any input light, sound, touch taste gravity movement
What is processing give an example?
What the brain does with the information
ex. simple: touching a hot pan
complex: taking an exam
What is a behaviour, give examples?
anything you do in response
removing your hand for the hot pan
filling in the circle for answer A
What are. the step necessary for the brain to do work?
Stimulus
Processing
Behaviour
What is action potential?
an electrochemical wave driven by the movement of ions along their electrical and concentration gradients
What are Neurons?
cells, containing the same complement of organelles: (cytoskeleton, DNA) etc as other cells
They also have features that make them distinct, dendrites, axon, synapse
What are Dendrites?
processes near the cell body
receive input form other neurons
What is an axon?
the main conducting unit of the neuron
connects one cell to the next
conveys information by propagating en electrical signal (the action potential)
What is a synapse?
used to communicate signals from one neuron to another
the action potential is converted into a chemical signal
the chemical connections of the axon (pre-synaptic) of one neuron to the dendrites (post-synaptic) of another
What is a concentration gradient?
molecules move from area of high concentration to areas of low concentration, until they are evenly distributed
you can have diffusion in a wide open space
you can also have diffusion if there is a barrier with a hole in it ex. cell membrane
How may concentration gradient be affect by a channel
if you have a channel in a membrane, the molecules will be able to move from high concentration to low concentration but they will do so more slowly
Concentration gradient in neurons
HIGH concentration of sodium (Na+) outside the cell
Low concentration of Na+ on the inside of the cell
concentration gradient for Na+ goes into the cell
What is an ion
a molecule that carries a positive charge
, ex. sodium
What is voltage and what does it look like in relation to particles?
it is a force that moves oppositely charged particles toward each other
it also moves similarly charged particles away from each other
Charged particles can be either positive or negative
Being charged means that they experience a force when they are around other changed particles
How is voltage created?
you need to separate opposite charges
separating charges creates voltage or “potential energy” or “potential difference”
voltage is a force so that if you release the charges they will move toward one another
What is a current?
the electricity or flow of charge that happens when there’s a voltage
Describe the electrical gradient within a neuron
there are positively charge ions outside of the cell and negatively charged anion inside the cell, with a membrane separating them, which creates voltage
adding a channel to the membrane allows charged particles to flow through
What negatively charged particles are inside the cell and what is the voltage?
proteins and ions
voltage around -70mV
Why are channels important for the function of a neuron?
they are a key part to how neurons work
they open at different times in response to different changed in the cell, ex. some way open when the cell is more positive or when the cell is more negative
Ion channels
some channels just for Na+ ( nothing else can flow through them
they only let Na+ go one way: IN
specific for particular ions and directions
Na+ channel
normally closed at a very low voltage, when its very negative inside
-70mV inside = closed
though bringing the voltage up channels will open (above -70mV)
once the channel opens Na+ will rush in being pushed by both the concentration gradient and electrical gradient
the charge on the inside will increase
once the voltage gets really high (eg. +40mV) the Na+ channels close, this is know as the refractory period
Channels and voltage
wether a channel is open or close can depend on voltage
What is the refractory period
when the voltage on the inside of the cell gets really high the channel will shut
these channels go “offline” for a little while because they need to reset
during this time you cannot get them open
Is K+ inside or outside of the neuron?
it is set up the opposite way from Na+
Lot of K+ inside
concentration gradient for K+ goes out
How does K+ flow out?
the concentration gradient
less voltage holding K+ in
the K+ channel may open due to a lower voltage than that of Na+
Steps of the diffusion for K+ and Na+
Na+ channels open, Na+ begins to enter the cell
K+ channels open, K+ begins to leave the cell
Na+ channels become refractory, no more Na+ enters cell
K+ continues to leave cell causes membrane potential to return to resting level
K+ channels close, Na+ channels reset
Extra K+ outside diffuses away
What is a sodium potassium pump?
it uses energy (ATP) to move K+ in and Na+ out until everything is back to normal
starting the whole process over again
Why is energy (ATP) important in with the diffusion of K+ and Na+ across the cell membrane?
Similarly to potential energy with gravity or a battery, you put energy in to create the separation
then you get movement when you release it
Then you need energy to create the separation again
Do all channels open at once?
no
ex. like popcorn popping, at first you hear a few popcorn popping which leads to a flood of the popping popcorn
How does action potential diffuse down the axon?
Na+ comes in
Na+ diffuses from the channel
Adjacent areas get more positive
Opens adjacent channels
More Na= comes in
Na+ diffuses from the channel
Adjacent area gets more positive
Opens adjacent channels
more Na+ comes in
Can action potential travel in multiple directions?
on each cell action potential travel in one direction
from the cell body to the synapse
Why doesn’t action potential flow backwards?
After Na+ flows in and makes the inside positive the Na+ channels in that patch close
Na+ channels won’t open again for a little while, they have to reset
Even though Na+ diffuses in both directions inside the cell it can only open channels that haven’t recently opened
it can only move forward
How can we measure action potential?
by the voltage
How can we manipulate action potential?
either by altering the chemistry or by altering the voltage
What can alter the speed at which action potential moves?
this depends on:
size
structure
of the neuron
What is a Loligo?
a large axon
action potentials were first studied using these
worked on by two scientists, (Hodgkin and Huxley)
who did measurements to figure out how action potential works
Why was using a Loligo important to Hoagkin and Huxley
it was big and easy to work with
they were measuring electrodes, in order to do this they needed to put in a tiny piece of metal, the size of this axon allowed them to do so
Do larger axon conduct action potential faster or slower then a smaller axon and why?
Faster
charge travels faster in large axons before leaking out
Big neurons can space channels and pumps further apart
recreate the action potential fewer times
less work for the Na+/K+ pump to do
When would a squid use their large axon?
to convey signals for critical reflexes
where information needs to get to the muscles quickly
What is a Schwann cell (Myelination)?
seen in many vertebrates
this wraps the axon
this insulates the axon, preventing Na+ and K+ from leaking out or in
enables the cell to hold the charge for longer
i.e the positive charge from the influx of Na+ can travel farther down the axon
used as a “solution”(instead of) bigger axons
Does the Myelin (Schwann cell) wrap the entire axon in one piece?
No
Rather there are many Schwann cells that wrap the axon
What are the “Nodes of Ranvier”
in between Schwann cells
At these nodes there are lots and lots of channels and pumps
How does Myelination increase the rate of action potential along the axon?
instead of having to open channels along every single cm of the axon
the action potential can “skip” rapidly from one node to the next, regenerating just at he nodes instead of at all the areas in between
Multiple Sclerosis
an autoimmune disease that results in damage to and breakdown of the myelin
patience show impaired movement and other deficits because signals are no longer travelling quickly or efficiently
Does the action potential regenerate at different strengths"?
no
“all or none”
you either have one or you don’t
“0s and 1s”
How does action potential change at the synapse?
The all-or-nothing action potential gets turned into a graded more complex response
Pre-synaptic vs post
before the synapse (axon terminal), after the synapse (dendrites)
Describe how the synapse works
action potential leads to the release of neurotransmitter from the terminal of the pre-synaptic cell
It travels across the space between the pre-synaptic cell and the post-synaptic cell
Its binds to receptors on the post-synaptic cell
binding to receptors leas to all kinds of things
What will the neurotransmitters control
They modulate the cell’s activity
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
Are all receptors the same?
No, there are different receptors for all of different kinds of substances
different receptors do different things
some are just channels
some activate second messenger systems, they aren’t channels though they activate many “down stream pathways”, ex dopamine
What are second messenger systems?
they aren’t channels though they activate many “down stream pathways”, ex dopamine
they activate pathways that can affect activity of proteins (like channels) gene transcription, mRNA translation and more, because of this they have more longterm effect on the neuron’s activity
How can we change the response of a post-synaptic cell?
this is caused by the many different chemicals used (and therefore different receptors)
What are inhibitory inputs?
reduce action potential
What are excitatory inputs?
increased action potential
What are modulatory inputs?
alter the effects of other inputs
What inputs does a neuron typically receive?
excitatory inputs
inhibitory inputs
modulatory inputs
post-synaptic cell and inputs
its sums up the inputs and produces a response
it could fire an action potential (or not)
It could fired one or many spikes
it could fire immediately or a little later
What causing the “sprinkling of sodium” inside the cell?
this may be due to inputs
not all input will result in an act potential
they may just alter the potential a little bit
with enough of these inputs an action potential may be cause
synapse + action potential = ?
synapse can turn action potential into a graded and complicated response
networks of neurons
hundred or thousands or neurons working as a group
how you scale up from one cell to a network in complicated, because of how synapses work, and because of the convergence of multiple inputs
They are not just the passing of a signal from one cell to the next, but the signal changes in the process
functional neuroanatomy
information comes in through a specialized receptor
then is goes through a relay station called the thalamus (for vision, it’s called lateral geniculate nucleus)
Then it goes to more outer brain areas like the cortes, lots of the processing happens in the cortex
Once the information is processed, the output of the cortex goes back down to areas that will execute
Sensory Inputs
They process sensory input
they turn external information into action potentials
Information gets taken apart at the sensory receptors, then progressively assembled at high stages in the brains (the thalamus and cortex)
Sensory input - Vision
Photoreceptors in your retina turn light into action potentials
the pattern of action in visual cortex recreates the visual scene
Sensory input- Hearing
hair cells in you cochleas turn sound waves into action potentials
the pattern of action potentials in your auditory cortex indicates what and where a sounds is
Sensory Inputs - Smell
Olfactory receptors in your nose turn odours into action potentials
olfactory cortex and other cortical and memory areas (hippocampus) identify smell
How does processing work
Many sub-cortical (under the cortex) regions monitor your current and previous internal state (hypothalamus, preoptic area amygdala, nucleus accumbens, septum, ventral, pallidum, hippocampus)
Cortical regions provide top-down information on what you should or can do, decision-making
Cortex
refers to the outermost part of the brain
It is a layered structure: the cells are organized into layers and columns
does a lot of high-level processing
Integrates information from multiple sources
it’s where your brain recreates the sensory world
it’s where you brain makes decisions and plans movements
the cortex has lots of connections to other parts of cortex as well as to underlying structures
Who did some of the first drawings of the cortex?
Santiago Ramon y Cajal
Cortex function
different subdivisions, some are concerned with sensory input (figuring out what or where a stimulus is)
some are concerned with memory or recognition or decisions or language
some are concerned with determining how to respond assembling a behaviour or motor response
What is white matter?
directly underneath the cortex
filled with axons going to and from the cortex
this is called white matter because the myelin on the axons make them appear white
Hippocampus
memory
Amygdala
emotion
Hypothalamus
regulates body function
What allows you to execute a behaviour?
motor cortex, basal ganglia and cerebellum are important for learning and altering movements
they allow you to assemble a motor plan to enable you to execute a behaviour
electroencephalography (EEG)
uses electrodes to measure electrical activity along the scalp
What are the pros and cons of electroencephalography (EEG)
Pros: Non-invasive People can move around during recording (for example, there are studies of people playing the guitar)
Cons: Electrodes are outside the brain, Means you can say when a change in activity happens, but hard to determine exactly where
What is Positron Emission Tomography PET
Person eats radioactively labeled sugar (fluorodeoxyglucose or FDG)
Sugar gets picked up by active cells (because busy cells need energy to run the Na+/K+ pump!)
Cells will give off radiation that can be detected by the scanner
This means that active regions will give off a lot of radiation and “light-up” on the scanner
What are the pros and cons of What is Positron Emission Tomography PET?
Pros: Better resolution than the EEG and can see deeper brain structures
Cons: 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 are Functional Magnetic Resonance Imaging fMRI?
Like PET, also involves a scanner, but this time it uses magnets
Scanner applies magnetic fields to the brain then measures the energy emitted by different brain areas as they return to their normal, unmagnetized states
How is fMRI able to use magnets?
cells take up oxygen from the blood
blood returns to the lungs to get more oxygen
blood without oxygen is more magnetic than oxygenated blood
Areas that are more metabolically active (e.g use more oxygen) emit different signals than less active areas
What are the pros and cones of fMRI?
pros: compare activity across the whole brain to different stimuli
no radioactive sugar
Cons: once again, participants can’t move around much
What is Electrophysiology
uses electrodes to measure 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
mostly done on animals
high resolution: you can find out what a single cell is doing during behaviour
What are examples of measuring the brains activity indirectly?
PET
fMRI
look at which area use more energy or oxygen and therefore more active
What are examples of measuring the brains activity directly?
electrophysiology
EEG
directly measure action potentials
Gene and protein expression
Label mRNA or proteins with radioactivity, dye or antibodies attached to fluorescent tags
look at the expression under the microscope
you can do this by making a very thin brain slice and then reconstructing it, now we can do this with the entire brain by making it clear
What are the pros and cons of gene and protein expression?
Pros:
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 abut changes or differences in particular molecules or cell types
Cons:
you have to take the brain out to look a it
can’t measure the brain during behaviour
can only have one “treatment” pre individual, compare expression between groups
How do you know what a brain area does?
Look at when its active ( EEG, PET, fMRI, etc)
or manipulate activity in a brain then look at behaviour
How can we manipulate activity in the brain?
Increase the activity of cells: stimulate cells using electricity or lights
Decrease the activity of cells: lesion or kill cells or block cell activity with drugs, e.g tetrodotoxin is a poison (from puffer fish) that blocks sodium channels which means it blocks action potentials
modulate the activity of cells: block or stimulate receptor chemical like serotonin, dopamine, norepinephrine
How do we increase the activity of cells:
stimulate cells using electricity or lights
How do we decrease the activity of cells
lesion or kill cells or block cell activity with drugs, e.g tetrodotoxin is a poison (from puffer fish) that blocks sodium channels which means it blocks action potentials
How do we modulate the activity of cells?
block or stimulate receptor chemical like serotonin, dopamine, norepinephrine
Memory
a behavioural change caused by experience
What does a memory look like in the brain?
a change in the number or strength of synaptic connections
What leads to the formation of a memory
changes in the activity of neurons or circuits can lead to changes in synaptic connections
Describe the spines the denrites. Are the spins always present?
tiny extensions on the dendrites
make neurons look bumpy
spines and synapses are dynamic: they comes and go, appear and disappear
Depends on the input (action potentials) to the synapse
if there’s a lot of input they might increase in size or become stable (less likely to disappear)
If there’s only a little or no input they might shrink or disappear
What activity can increase the number of stable spines?
Learning
Where in the brain should we look for memory?
anywhere there is synaptic plasticity (changes to spines and synapses), everywhere in the brain
there are part of the brain that seem to be dedicated to storing particular kinds of memories
Where is episodic memory formed?
the hippocampus
What are episodic memories?
abut autobiographical events
things that happened to you
generally tend to involve: what, where and when
What are semantic memories?
things you remember but didn’t experience
ex. you remember that John Edmonstone taught Charles Darwin taxidermy
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