Anatomy & Physiology Nervous System Part I: Neurons

Hi and welcome back to www.educator.com.0000

This is the first lesson on the nervous systems and this is about neurons.0002

Neurons are the basic cell of the nervous system.0006

The brain alone has a hundred billion neurons.0009

Besides the brain, you have the spinal cord and the other nerves.0013

You got billions of neurons in your body.0017

About 25% of your neurons are concentrated on your brain alone.0020

There is a lot of going on there.0026

There are 3 basic functions for us to summarize.0028

The first one is the sensory reception.0031

Those are the neurons that are receiving in what your body is experiencing outside of your body.0034

What your neurons notice within your body, they can sense that and tell your brain.0040

Besides you got the other direction, the motor stimulation.0046

The motor stimulation, it is going from the brain, spinal cord, out.0050

That controls your muscles, glands, organs, all stuff.0052

Any action your body does is controlled by neuron and that is motor stimulation.0060

Processing, these are the in between neurons.0066

You have a sensory signal going from the central nervous system, you have intraneurons.0070

It is the one connecting the sensory to the motor going back out.0077

That is the processing portion.0081

In your cerebral cortex, there is a lot of processing going on.0084

The form = function this is any much tissue of the body, whatever it looks like that corresponds to whatever function they have.0092

You are going to see that in the next slide.0104

This neuron is a classic looking neuron.0106

This is your typical form for a typical function of a neuron.0110

You have up here the receiving end of the neuron and you have here the end that is sending the signal to whatever cell is beyond it.0116

It could be another neuron or muscle cell or sweat gland.0126

When we look at the basic neuron anatomy, there are few parts you have to keep in mind.0131

The cell body is this part right up here.0137

The cell body is where you have most of the organelles that you see in a typical cell.0142

This green dot is the nucleus.0146

You can see ribosomes, mitochondria, etc.0149

The dendrites look like little tree branches.0153

The little tiny extensions extending beyond it you can call it dendritic branches.0157

Those dendritic branches they are on the receiving end.0169

They have a signal molecule that docks there and then initiates the signal into the neuron as a whole.0173

The axon hillock is the connection portion between the cell body of the neuron and the axon.0179

Right here that is a thicken portion that connects the cell body and the axon.0190

The axon is this classic long part.0196

I am drawing a purple line through those yellow sheets.0202

The axon is typically long for sending the electrical signal to some other part of the nervous system.0207

The axolemma on the axon is basically the modified plasma membrane.0216

If you are going to zoom in this purple part here that border you can call the axolemma.0224

And lemma means sheets or husk.0231

It is like a husk of a corn that surrounding that axon.0236

Lemma means husk.0241

Axolemma border of the axon.0244

Myelin sheets, these yellow wrappings are made up of myelin.0246

Myelin is 80% lipids and 20% proteins.0253

It is mostly fatty when we look at the structure of it.0257

The nickname of it is in the peripheral nervous system is Schwann cells.0261

Each of these is its own separate cell.0268

The orange dot is the nucleus of each one and they are made up of myelin.0272

Picture that my arm here is the neuron.0277

Here you got the cell body, dendrites with the dendritic branches.0279

Here is the axon.0283

Imagine that they are socks wrapped around my arm, the socks wrapped around my forearm here would be the myelin sheets.0284

The function of these, we will get into that more in the future.0296

It has to do with insulation and increasing the speed of electrical conduction.0300

Nodes of ranvier are here.0307

They are parts of the axon that are exposed.0313

Right here you have a Schwann cell that is covering the part of the axon but in between of this two Schwann cells,0318

there is an exposed axon section that is the nodes of ranvier.0325

Axon terminals are right here.0329

Another name I have heard for the ending here are axon buttons.0337

It is the ending of the axon, the termination of the axon.0344

Here are these little axon terminals and it has neurotransmitter released from there.0352

If we were to zoom in to one of these axon terminals, concentrated at the end here you are going to see synaptic vesicles.0359

Inside of the synaptic vesicles are little signaling molecules called neurotransmitters, these little black dots.0379

What happens is when you got electric signal travelling down the axon, at the end of the axon terminals these little vesicles are waiting to be stimulated.0389

When stimulated they are then fused with the end of the axon button and end up dumping these neurotransmitters into the synapse.0398

They end up traveling to the next neuron or to whatever the neuron is affecting.0409

These synaptic vesicles hold those little neurotransmitters until they are stimulated and they are usually calcium.0417

The synapse is the space.0427

Right where I drew the little black dots, those are the synapse.0430

The synapses there are 2 main varieties.0434

One of them is the electrical synapse0436

Electric synapse would be if this is the axon terminal of one neuron here is the cell body of the next.0439

If they are physically attached to each other by protein there is no space in the synapse.0449

It is just the connection of the two.0454

If this is the one that is sending the signal this is the pre synaptic neuron and this is the post synaptic neuron.0457

The way that they stimulate each other is just simply electrical signal from the axons of these stimulates this one.0464

That is not as common in the nervous system.0472

What tends to be more common is here is the endings of the axon and here is the cell body of the next one,0474

there is a space between the pre synaptic and post synaptic neurons.0480

That space is called chemical synapse.0487

It is chemical synapse because the chemicals found in it are these neurotransmitters, these little black dots that I have mentioned before.0490

If you were looking at a chemical synapse here you might see something like this.0497

Here is the cell body of the post synaptic neuron, little dendritic branches coming out and you can see that there are little spaces in here.0504

That is the synapse.0516

The amazing thing is some neurons have thousand of synapses with neighboring neurons.0518

If you consider all those different connections, the potential for those connections in the brain,0526

you can see how a hundred billions of neurons can give you a lot of variety in terms of the neural pathways.0531

A hundred billion neurons times a thousands of synapses, it is amazing to think about.0537

Like I said the form = function.0543

The forms of neurons can vary greatly.0547

Here are some examples.0550

This one here on the far left, this is a classic looking neuron from the cerebellum.0552

If you take slices through the back of the brain the cerebellum, when you look at a microscopic level you have these amazing sets of dendritic branches.0559

It looks like a crowded tree with tiny little branches all through out.0573

This shows you that you can have all kinds of signals coming up to this.0577

There are so much on the receiving end.0585

Here is the cell body down here and there is the axon.0587

This is part of the cerebral cortex, the outside of the brain.0592

This is a simpler, average looking neuron.0596

Here is the cell body, dendrites, axons, and axon terminals.0600

Looking back at the human brain, here is how you are able to smell, odoring molecules or smell odors would drift here,0606

stimulate these particular neurons and you have a relay station here, mitrocells assisting in getting the signals into these fibers.0619

These are extension of neurons especially axon portions that when come together to be olfactory nerves0629

which is just giant bundle of axons located up there that allow you to smell.0638

These are just 3 examples and there are a lot more.0644

Neurons can vary in their form based on the functions that is needed.0648

Action potential describes how electric signal is transmitted along the neurons.0653

How does it get from the dendrites connected to the cell body, down the axon to the axon terminals?0667

How does it happen?0674

It is action potentials.0675

These are electric changes along the neurons membrane that allows signaling to occur.0676

The 2 main contributors are Na+ and K+ also known as sodium and potassium.0681

These are both charged ions, both known as cations.0687

They are both big players in how these little electrical waves occur.0693

It is all or none activity meaning you cannot have stimulates a neuron.0699

You are either stimulating it or not?0705

It is at rest or it is sending signals.0708

What you can vary is how many signals is it sending in a second?0711

Is it sending 200 signals?0716

Is it sending 1 or 2?0718

This is a little graph that depicts what happens in an action potential.0719

Typically the average neuron is at rest when it is -700725

This is in millivolts.0729

A -70 the neuron is just chilling.0733

You can see here that there is a failed initiation meaning there is a tiny bit of a signal from a neighboring neuron0736

maybe a few neurotransmitters that dock but not enough to get it going.0743

You can see that there is a little hump but it not go all the way.0747

Once you reach threshold that is the level when it its going to happen.0751

Once you reach threshold it is going.0756

Threshold at -55 you are going to get depolarization.0759

Depolarization is where it gets more positive.0764

You are going to see in the next few slides how that happen.0767

Basically a lot of sodium enters the cell and gets it all the way to +40.0769

Some textbook says +30 but if you are using textbook where you are learning from me, please follow along whatever the textbook says.0776

I have seen textbook says +30 and I have seen other say +40 as this little graph does.0784

Following depolarization, it goes back down to where it came from repolarization.0790

The opposite occurs, instead of a bunch of positive of sodium coming into the axon, potassium leaves.0795

When that positive ions leaves, brings it back down to negative.0803

Enough of it leaves to get it back below what was the original resting potential goes down to about -90 and comes back to resting.0807

You can see that if you look at the time this is in milliseconds.0818

In just a few milliseconds is one action potential.0822

Think about of how many you can get in a second of time.0825

Like I have said it is an electrical wave.0828

You will see that in the next few images that I will show you.0831

A neuron at rest, the average neurons have a potential of about -70 millivolts at rest.0836

More negative ions are inside of the axon than in the outside0842

The reason why it is important to realize is because that is why it is -70.0846

This is an axon, pretend this is an axon without myelin sheets.0854

That exist, there are lots of axons in the nervous system where we are not going to see those wrappings.0865

It is just a pure, bare axon from the cell body over the terminals.0870

In other areas that you are going to see those wrappings.0877

Let us pretend we are not looking at those wrappings right now.0880

This is just the axolemma and these are little proteins.0882

Gauged protein channels which me may have learned in biology.0888

They involve transport of ions back and forth and usually it is involving ATP to do that.0893

To start off it is more negative.0900

I am going to draw negative signs here on the inside of the axon.0904

Here this is the intercellular part and here is extracellular side.0908

I could draw a few negatives here because there are going to be negative ions.0930

There are 4 charged ions, there are chlorine ions, etc.0935

Definitely a lot more on the inside.0939

How you get the -70 millivolts.0941

When we look at the amount of sodium and potassium, you can see a lot more sodium outside.0943

Like I said earlier, the way you get that negative depolarization is because a lot of sodium is coming in.0951

I am going to draw a gigantic Na+ here and I am going to write a tiny Na+ on the inside.0955

You are going to get some sodium on the inside of the axon but proportionally concentration wise you are going to have a lot more inside.0964

Conversely there is a lot K+ on the inside.0972

I am going to draw a tiny K+ on the outside just to show you there is some there but this is where they are most abundant when a neuron is at rest.0979

Keep that in mind when we talk about how action potential is initiated and what happens next.0990

Here are the steps on how you get action potential coming to perish on.0996

Here is going to be our graph.1002

I know that people who are in the math will be bugged by the fact that I am doing this but just bare with me.1006

I am going to draw -70 millivolts above the x axis, normally negative number would be below but for the sake of this example it is better this way.1013

Our range is from -70 to +30.1030

Resting potential is right here.1036

Here is time in milliseconds and this is millivolts on the y axis.1039

Those are our milliseconds.1047

Here is our neuron specifically on the axon.1053

This is a 3 dimensional structure but we are looking at 2 dimensional here but1061

the picture that you are going to see on how this works is 2 dimensional so bare with me.1071

Threshold reach, as we look before with the cell body, threshold all it takes is getting enough of the situation to dock at the dendrites,1076

to have the electrical signal be initiated to the axon.1087

That is going to get you up to -55 approximately and you are going to go from there.1091

Imagine that just to the left of the image here you got the axon hillock, cell body, and there are enough of signals docking here and get it going.1096

Depolarization we are going to use red to depict depolarization.1108

That is sodium moving inwards from the extracellular space.1113

That is depolarization in red.1119

That is when you have a whole bunch of sodium going in.1126

It is started with negative millivoltage on the inside.1132

Once a bunch of positives come in, your net charge will be more positive.1138

It is going to go until you get +30.1144

If you are asking what if it just goes to +10?1146

It is regulated in a way where it is going to go all the way up to that.1149

It is predictable how much sodium goes in to get it to that point.1153

Once depolarization finishes, this little sodium channels once you get it to +40 they are going to deactivate.1158

They are going to close.1167

That is going to initiate the other one, the potassium ones to open.1169

Let us use blue for the potassium part of it that is known as the repolarization.1173

Repolarization is going to get you all the way down there.1179

We have a bunch of potassium inside, once this happens you get a bunch of that Na+ inside that is going to trigger a bunch of potassium ions to leave.1184

One thing to keep in mind, this is just action potential for just this part of the axon.1202

The action potential is to initiate another action potential and another action potential.1209

That is why it is good to picture it as an electrical wave.1215

The electrical wave finishes here and initiates at the next one.1217

Once you have repolarization happening here you are going to start off to get that threshold being reached at the next one1222

and depolarization is going to happen right after it.1230

It is nice to think of it as a wave because it happens up and down the next place.1233

Hypopolarization is when you have slight more positive leaving the inside of the axon then you need to have to get pass -70 millivolts.1239

It goes down a little further to -70 about to -90.1255

Then it evens out again, you get back to resting.1262

Those little switching happens where you get going back to resting so that right away it is ready again to be stimulated.1268

You can have hundreds of action potentials happen in just a second or two.1278

It is amazing to think about.1283

Resting, depolarization, repolarization going back down, hypopolarization, back to resting potential.1284

Here is another image that shows this.1296

Here is the intercellular space and here is the extracellular space, you can see that initially the sodium is coming in.1302

These little orange hexagons are coming into this little area here that fits them and that dumps them on the inside.1314

What are these little purple things?1326

Those have to do with ATP.1328

It have to do with using ATP to power these little protein channels.1330

The potassium does the exact opposite.1335

Potassium is going to end up leaving.1338

You could see that this little yellow ovals come in here and that are dumped out.1341

You see that because of the action potential you have the increase of sodium here and increase of potassium in the opposite direction.1347

That is how you get that up and down of depolarization and repolarization.1356

Saltatory conduction that terms come from the Spanish word salta meaning to jump.1360

Saltatory conduction is the jumping in electrical signal in axon.1369

This happens every second of everyday in your life in your body.1373

Anywhere you have an axon that is covered by Schwann cells or the other one is oligodendricytes.1377

Oligodendricytes tend to be more in the central nervous system, the brain and spinal cord.1384

In some parts of your peripheral nervous system you have this Schwann cells.1391

Whether you are in the brain, spinal cord, or nerves going through out your body you are going to see these little sheets,1396

this little covering around the axon.1402

Think of it this way, if you have those little wrappings what it does is1404

instead of the electrical signal the action potential having to go along every little portion of the axon.1412

If I have a wrapping and here, you have those little nodes of ranvier1419

and salutatory conduction means the action potential jumps from node to node and that speeds up the signal.1425

Another function of this is just insulation.1434

It is a protection and insulating of the axon.1437

Primarily that jumping is going to speed up the electrical signal.1440

That is very important.1445

Saltatory conduction you get that jumping of the electrical signal all the way to the axon1446

until you inevitably get to the axon terminals where you have synaptic vesicles waiting.1452

They are waiting to get that signal to the next neuron or whatever is right after that pre synaptic neuron.1457

I love this image because they are showing how oligodendricyte covers these axons on some neuron within the central nervous system.1462

They are showing you what it looks like on the inside of the axon.1471

It easy to forget that there are intracellular things beside just charged particles like sodium and potassium.1475

Here they are showing you they have micro tubule and micro filament.1482

If you remember from biology those are important parts of the cyto skeleton.1486

The cyto skeleton you are going to find that in a specialized modified cell like a neuron.1490

Synapse and neurotransmitters.1497

Like we have mentioned before synapses are the spaces between neurons or a neuron and whatever after that synapse.1502

Neurotransmitters are molecules that drift across synapses.1511

That is the case in chemical synapses when they are right on each other.1516

More often you are going to have a tiny space between a pre synaptic and post synaptic neuron.1522

This is s great picture of it.1528

Here is that little button at the end of an axon terminal.1529

One here that would be action terminal.1534

Two this is a modified plasma membrane of a muscle called sarcolemma.1536

Three, is a synaptic vesicle.1544

If we zoom into that, what is inside of that vesicles are tiny neurotransmitters.1549

There are a lot of different neurotransmitters in your body and they have slightly different functions and rules.1557

In this particular example we are going to talk about acetylcholine also abbreviated as ACH.1564

That is a classic abbreviation for acetylcholine.1571

It has very important function is the central nervous system.1574

Here we are going to talk about the peripheral nervous system.1577

What does it do to your arms, torso, legs?1580

When you have this nerve coming off your spinal cord and going to your muscle, you are going to have ACH being that initiator.1584

If you ever wonder what makes my muscle contract?1592

ACH is that signal that goes form the neurons to the muscles to actually make it contract.1595

These little things here these are receptors that have perfect fit for ACH.1602

ACH is like a key that fits into the lock.1611

Number 4, without ACH fitting there it is not going to stimulate the muscle.1614

Number 5, is labeling a mitochondrion.1620

How would ACH actually leaves a neuron and go toward to its destination and how would it function?1623

Here is the answer.1637

If you look at these how this neurotransmitters functions and how they move across a synapse, there are 4 steps.1638

Number 1, action potential depolarizes synaptic knob.1647

This synaptic knob I have been calling it axon button.1651

It is the same basic thing.1655

Action potential, you are going to get action potential happening all the way down the axon to the end here like a wave of electricity1657

and that is going to cause calcium also labeled as Ca2+ because it is a charged ion, it has +2 charge unlike Na and K that have +1 charge.1664

Calcium is not just in your bones.1682

It is not just for giving your bones all that matrix and hardness that gives them most of their mass.1684

Calcium is also very important in making neurotransmitters drift across a synapse.1692

Once you have that wave electricity down here it stimulates calcium to move these little synaptic vesicles to the edge1697

and it causes them to fuse with the edge and dumped through exocytosis, the little transmitters in that synapse.1708

They just drift across through passive transport.1718

I do not want you to think that ATP is forcing them across.1720

The synapse is very tiny and all it takes is just a bunch of diffusion and drifting of these neurotransmitters across.1725

Those little black dots are going to symbolize the neurotransmitters and they are going to dock to those little receptors.1735

Next up ACH binds those receptors on the post synaptic membrane like I have demonstrated in the previous drawing.1746

Once those little black dots come into contact here and this is definitely not doing this just 6, you only see just 7 of this little protein receiving the neurotransmitters.1755

There are going to be hundreds, probably thousands on the average motor end plate,1770

which means you have a motor signal coming to that muscle and you have the reception of that signal there that end plate.1778

Once the ACH binds to those receptors that ACH is going to initiate muscle contractions.1786

In future lessons you are going to learn about how a muscle contracts once that signal is received.1793

You got to get of ACH to stop the initiation of the muscle contraction.1799

If ACH stays there contraction is going to keep happening.1804

You want to get rid of it eventually.1807

A lot of times there is an enzyme hanging there and ready to be used when you want to get rid of that signal.1809

In this case, it is called acetyl cholinesterase and it gets rid of those little black dots, which is ACH and once that is broken down the signal stops.1816

If you want it to be happening again dump more ACH out of that little synaptic knob or axon button.1833

That is how neurotransmitters functions across a synapse.1840

When it comes to one neuron stimulating another it has a lot to do with inhibition and excitation.1843

Inhibition is the turning of the signal and making neuron stop doing what it is meant to do.1852

Excitation is the exact opposite.1857

It makes those action potentials happen more and more.1860

Neurotransmitters some of them can do both depending on where they are located.1863

Some neurotransmitters are only inhibitory and others are only excitatory.1867

The sum of 2 or more neurotransmitters in an area dictates the result.1872

Here is an example of that.1877

We are going to talk about pre synaptic inhibition first.1879

Let us say this is pre synaptic neuron that is going to stimulate this neuron here.1882

This will be called post synaptic neuron1896

and it is going to have little dendritic branches that is going to increase the reception of the signal and here is the synapse.1899

What you can have here is another neuron off to the side that can affect whether or not this pre synaptic neuron is going to send the signal across.1908

Let us say you got action potentials going along here and all you need is calcium to make these little synaptic vesicles dump their neurotransmitters across.1921

You can have this particular neuron send signals here to turn off this process.1936

If you have this ability here for these neurotransmitters to prevent calcium for making this fuse and make exocytosis that is called inhibition.1948

You are not going to get neurotransmitters dock in here on the post synaptic neuron.1958

That means you are turning off the ability of this neuron to effectively stimulate this one.1966

The opposite can be true.1972

You can actually have pre synaptic facilitation which is a form of exciting this particular neuron.1975

The opposite can happen.1986

We can have a lot of neurotransmitters coming from this particular synaptic knob1987

or axon button getting this stimulated and causing these synaptic vesicles to fuse there1995

by dumping the little neurotransmitters here and docking on these little proteins on the receiving end.2007

That would cause the electrical stimulation and the action potentials to carry along this particular neuron.2017

You have both sides of those and it is into summation.2025

If I have one little neuron here and one neuron here and this one is producing an inhibitory effect and this one is producing excitatory or facilitating effect.2028

Whichever won is doing more is going to win.2040

If you have significantly more inhibition coming from here than excitation from here chances are2044

this particular neuron is not going to be throwing enough neurotransmitters over here to initiate action potentials.2049

Here are some examples of neurotransmitters.2056

There are a lot of neurotransmitters in the nervous system and here are some of the main ones.2060

Norepinephrine also known as noradrenaline and you also have epinephrine known as adrenaline.2065

This is a very common neurotransmitter that you are going to see in the nervous system.2071

It is typically excitatory.2077

It is similar to how ACH is in the nervous system.2078

Remember ACH stimulates muscles to contract2083

Norepinephrine does a lot in the brain to stimulate neuropathways.2086

Dopamine depending to where it is and what part of the brain it is in, it can be excitatory and inhibitory.2091

Here are 2 examples.2098

In terms of how it is inhibitory, in some regions it prevents over stimulation of muscle.2100

It prevents you from doing too much muscular contraction you are not supposed to.2108

If I lay my arms down in this table, I am contracting my triceps brachia to bring my arms down like this.2113

I have stopped my biceps brachia from contracting and they are more relaxed.2124

If I did not have dopamine working with my nerves that are going to my arms I can have a shaking going on.2131

A lot of research in Parkinson’s disease has verified that dopamine plays a role.2140

If you do not have dopamine in certain parts of the brain working effectively, you can have a shaking going on.2145

Where the person does not have as much control as they have used to in terms of extending and arm in a particular way and bringing it in when they want to.2152

That dopamine imbalance has to do with Parkinson’s.2160

In other regions, dopamine can give the brain a sense of reward.2165

This will be on the excitatory side.2169

In other parts of the brain, they do not have to do with muscle control,2171

the time you feel most proud of something you have done like a natural high you get from accomplishing something, thank dopamine.2176

There are times when a drug can give your brain illusion of having a lot more dopamine inside of the brain.2184

That is how cocaine works.2192

Cocaine that particular drug when it is snorted the chemical going to your brain is called dopamine reuptake inhibitor.2194

It means it keeps dopamine in the synapses much longer than it is supposed to.2205

If you do not get rid of dopamine it is going to keep making those neuro pathways activated.2210

Like I have said before, if you get rid of a neurotransmitter like with acetyl cholinesterase breaking down ACH2216

that is one way of getting rid of it but you can also suck them back up.2223

That is called reuptake.2227

If you get dopamine back in the neurons where it is supposed to be when you stop it signaling2228

that is one way to stop it but something like cocaine it is going to prevent the reuptake.2234

It is going docking longer and it gives you artificial sense of happiness, pride, or having a great feeling.2240

That is a part of high of cocaine there are negative aspects of doing that.2248

Serotonin that is an excitatory one.2253

This affects attention and emotion.2256

There are a lot of anti depressant drugs that act upon serotonin.2258

If you are having a serotonin imbalance maybe not enough being let go into your brain or too much2263

that can affect your ability to have your attention focus on something and can affect your mood.2272

Endorphins are those natural transmitters that inhibit pain.2279

When I broke my collar bone in high school, there is a period of time right after breaking it, I did not feel any pain and it is called shock.2285

I was walking around for 20 or 30 minutes with this numbness and my brain is attempting to protect me from feeling all that intense pain from this bone being fractured.2295

It eventually wore off and I have felt the pain later.2307

Endorphins are also interesting when talking about opiates.2310

Opiates being class of drugs, opium, morphine, heroin,2314

These drugs if you look at the active ingredient it mimic the shape of endorphins.2320

If you ever wondered make morphine makes someone in the hospital feel like they are on cloud 9.2327

How it happens is if endorphins are the natural neurotransmitters that make you feel that you do not have pain.2333

Somebody who has an intense surgery or a burn victim, somebody who is an AIDS patient or maybe going through a lot of pain,2342

you want to give them more endorphins that their body willing to dish out.2350

Having morphine drifts intravenously that morphine going to the brain it is like the brain having more endorphins than it naturally have.2355

You are going to prevent that person from experiencing pain they would have experienced otherwise.2365

Somebody who is completely healthy and in no need of morphine they can get easily addicted to it.2370

The more you introduce morphine to your system the more the cells your brain make little receptors to respond to that additional morphine.2378

That is how addiction eventually builds and builds.2387

With addiction you are going to get withdraw all the symptoms if all of a sudden you stop introducing that morphine into your body.2391

Drugs are not something you want to play with.2397

Stick with your natural supplies of neurotransmitter whenever possible.2400

Thank you for watching www.educator.com.2405