21 - Bio

What 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?

1. Stimulus
2. Processing
3. 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+

1. Na+ channels open, Na+ begins to enter the cell
2. K+ channels open, K+ begins to leave the cell
3. Na+ channels become refractory, no more Na+ enters cell
4. K+ continues to leave cell causes membrane potential to return to resting level
5. K+ channels close, Na+ channels reset
6. 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