3. Brain to Neuron (w2) - Lecture notes 3 PDF

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Lecture 3: From Brain to NeuronBrain componentsVentriclesFluid-filled cavities in the brain containing cerebrospinal fluid (CSF)Cerebrospinal fluid (CSF) : what is it?- CSF is found in ventricles, between meninges and around brain cells. - CSF is produced in the ventricles. Made from ependymal cells...

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Lecture 3 : From Brain to Neuron Brain components Ventricles Fluid-filled cavities in the brain containing cerebrospinal fluid (CSF)

Cerebrospinal fluid (CSF) : what is it? -

CSF is found in ventricles, between meninges and around brain cells.

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CSF is produced in the ventricles. Made from ependymal cells that line the inside of ventricles. -

It can flow between the ventricles and the meninges through the brain tissue to diff cells.

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The CSF circulates throughout the brain over the course of the day.

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CSF is produced by cells that line the ventricles and found in the ventricles, spinal cord and around brain cells.

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CSF is made of high sodium and small concentration of potassium

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Has the correct ion concentrations etc. to support cell function.

Cerebrospinal fluid (CSF): what does it do? -

Cushions the brain (so if u bang it, it manages itself.

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Flushes unwanted products from the brain into the blood vecells -

Ex: broken down proteins such as beta amyloids (if these accumulate, u see alzheimer’s disease)

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Sets environment for the brain cells -

Concentration of molecules such as glucose and ions affect how the neurons work so CSF regulates the environment to help the neurons work well.

Meninges The meninges are membranes surrounding the brain and the spinal cord 1. Dura -> the tough outer membrane a. Lies under the skull (or in some cases, there could be a blood sinus) 2. Arachnoid a. CSF flows between the arachnoid and the pia 3. Pia -> next to the brain surface a. Has blood vessels in it b. The blood vessels go across the surface and dive down into the cortex of the brain. i.

The blood vessels dive down and branch out into a dense network of capillaries

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Blood supply (aka capillary) Brain needs lots of energy -

2% body mass, 20% of the body’s resting energy (is the most energy-consuming part if not doing physical exercise)

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But it can't store very much energy so it needs a constant supply of blood.

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Therefore, has specialised dense network of blood vessels to provide the brain with the amount of energy it needs

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The brain is highly vascularized = (lots of blood vessels put densely inside it)

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The neurons are very close to each other

Circle of willis -

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Since it needs so much blood, it has 4 main arteries that feed in the form of a circle.

Activity -

If an area of the brain is active, the blood vessels dilate and increase blood flow to that specific brain area

Stroke -

When experiencing a stroke, blocked cerebral blood vessels starve the area supplied by that vessel. -

If one artery gets blocked or damaged, you have 3 more to keep it going.

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Strokes can affect different blood vessels which demonstrates the functions of different areas of the brain

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Because the brain’s energy delivery is so important, neurons can signal to blood vessels to dilate locally to allow an increase in blood flow to particular regions -

This is why fMRI scans can pick up increases in blood flow to individual areas when performing certain tasks.

Brain Cells Cells perform different functions because of the different proteins they express.

Brain cell types: 1.) Neurons (aka nerve cells) -

The key informational transmitting brain cell -

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Transmit and process info -

using electrical signals within them

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and chemical signals between them.

There are many diff neuron types -

Diff types of neurons = diff types of computations that they do.

Parts of a neuron Dendritic tree (Gossip house) -

Receive most of the input

Soma (Main body) -

Aka the “Cell body”

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Contains the nucleus with the genetic info (ex: DNA)

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Has organelles to do diff functions -

To keep the cell healthy though

Axon (talker) Output from the neuron -

Takes info and passes it on till the axon terminal -

Axon hillock -

is where the decision is made weather or not to fire an action potential

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Axon terminal

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Myelin sheath

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Where the signal is passed on

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Wrap each axon

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Made from oligodendrocytes .

2.) Glial cells Central nervous system a.) Astrocytes i.)

Support and regulate ions

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Star shaped

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Govern the exchange of materials between neurons and capillaries (blood vessels)

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Anchor the neurons to the blood supply

b.) Microglial cells i.)

Immune defense

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Surveys the brain for damage and Eats up the damage tissue

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If they get activated too make, it can be damaging (cause inflammation)

c.) Ependymal cells i.) ii.)

Line cavities in the ventricles Create, secrete and circulate CSF

d.) Oligodendrocytes i.)

Wrap and insulating barrier called the “myelin sheath”

Peripheral nervous system a) Satellite cells i)

Surround and support neuron cell bodies

b) Schwann cells i)

Insulate and create myelin sheath

Neuronal signaling How do neurons transmit information? -

Can only send electrical signals at one strength and speed (but can change the frequency of how fast the signals they send are)

History of neuronal signaling Luigi Galvani, 1981: Electricity makes frog’s leg muscle contract His nephew Giovanni aldini, 1802 did this with humans

What is electricity? Electrical currents are flows of charged particles (electrons) Like charges repel, opposite charges attract Currents only flow through materials that conduct electricity Voltage is a measure of how much potential there is for charge to move through a material.

Ohm’s law Current = Potential (volts) x conductance Or Current = potential x resistance

Electricity in nerves Hermann von helmholtz (1849) -

Measured speed of nerve conduction by stimulating frog sciatic nerve and measuring time to constrict muscle -

Nerve conduction =30-40 ms = 1million times slower than electricity flow in a wire.

Action potential Current flowers down nerves as a wave of charge movement causing the voltage to change in the axon “Wave of transient depolarisation that travels down the axon”

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Current flows across the membrane of a cell.

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Current flows into a membrane from a cell, then it goes from one membrane to another, then that new membrane put current into the cell (cycle repeats)

How do cells signal electrically? -

Ion = An electrically charged particle -

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Eg. Na , Cl , Ca2 , K

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Electrical impulse sent by a neuron to pass a message to the next neuron

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Different ions are different sizes -

Affects what volt they can go through the membrane with

Proteins can… … Control gene expression … Produce things (eg. ATP) … Act as channels across cell wall

Membrane of Cells -

Cells are surrounded by a phospholipid bilayer membrane, and due to the hydrophobic tails, water-soluble things cannot pass through. -

This allows a concentration gradient of ions across the membrane.

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Outside the cell: lots of Na+ and Cl-, some Ca2+.

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Inside the cell: lots of negatively charged proteins and K+.

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The cells contain potassium channels to allow K+ both in and out of the cell.

Ion flux (ion flow) at Resting potential Some happens at rest (to set the neuron up to be ready to send an electrical signal) K+ channel -

There is Na+ and Cl_ outside the cell membrane (and a bit of k+)

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There is Protein inside the cell. Protein is negatively charged so the cell = (polarised)

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so it attracts a positive ion.

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In the membrane, there are K+ channels (pores in the membrane that only allow K+ particles)

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K+ goes into the cell through the channel making the inside of the cell neutrally charged (combating the negative protein) -

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However, the movement of the K+ cells causes some K+ to leak out. (through the electrochemical gradient) -

ATP Pump: puts K+ into the cell and sends Na+ out of the cell.

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Now the inside of the cell is electronegative again, so it attracts K+ through the channel again to make it neutral.

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The electrochemical gradient (causing it to go in and out) shows that the environment is in equilibrium (some coming in, some going out)

The voltage of the K+ moving in and out of the K+ channel (equilibrium potential) is -70 millivolts (mV)

Equilibrium potential The voltage at which there is no net flow of an ion (if only 1 channel is open) -

Explains how ions move across the membrane -

The direction in which the ion moves across the membrane -

-> the ion concentration difference inside vs outside the membrane

Membrane potential Set by the electrochemical gradient and permeability of membrane to diff ions (how many channels there are. -

If membrane is only permeable to potassium (K+), (aka only the K+ channel is open), E K+ = -80mV

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If membrane has a K+ channel and ALSO a slight sodium channel : EM = -70mV

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Membrane potential is closer to the K+ equilibrium potential because potassium leak channels are more than the sodium-potassium pump

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So the cell membrane potential will become more positive (aka it will depolarise)

The resting membrane potential changes according to the axon and how many K+ channels it has....