Anatomy & Physiology Nervous System Part 3: Spinal Cord & Nerves

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

This is the next nervous system lesson specifically on the spinal cord and nerves.0002

If you will look at the nervous system as a giant flow chart, that have to do with the brain, spinal cord, and all the nerves, this is a good representation.0007

For the top here in the orange box is the central nervous system which is the brain and the spinal cord.0017

That communicates with the peripheral nervous system with all the nerves extending from the spine and from the cerebral area, from the cranium.0025

These working conjunctions have to do with sending and getting signals up to them.0035

There are 2 main divisions in terms of tracks that the neurons run along.0042

There is the motor or the efferent division and the sensory or the afferent0047

Sensory has to do with your senses.0052

Those are the signals that are going from the peripheral nervous system up into the spinal cord and brain.0055

It is the opposite with motor.0060

Motor having to with movement and initiating with those responses from out of the nervous system.0062

The way that I keep afferent and efferent straight is I think of it alphabetically in terms of the brain being on top.0068

A has to do with going up to with the brain, afferent is all this sensory signals.0080

Efferent is going down, going out.0087

The other way you can remember it is that the end goal of an afferent signal is the effector which starts0090

with the same beginning, whatever is affected, a muscle, gland, or an organ by that motor signal.0096

Motor nerves fibers and sensory nerves fibers, sometimes they are contained in other nerves and0106

sometimes they are nerves that are called mixed because they have both afferent and efferent tracks.0112

When you look at the spinal cord as a whole, the spinal cord has a motor or efferent section and sensory or afferent section.0119

Make sure you keep those straight.0131

When you look at how the motor part of it is working in terms of initiating action in your body, the somatic portion is all the things you have conscious control over.0136

When I move my fingers, arm, legs, those have to do with somatic or voluntary motor neurons because I have elected to consciously do that.0150

The other side of that is autonomic.0162

Autonomic think of it as automatic.0165

It is a slightly different word but it basically means the same thing but automatic without you having to think about it.0169

The autonomic part of the motor division is all of those activities that happen without you thinking about it.0175

For instance your heart rate, you do not have to think about beating your heart.0183

Your breath rate, you can consciously choose your breathing but you do not have to.0187

The blood vessels, another one is sweating, you do not have to think to make yourself sweat.0195

It happens when you need it to, same with digestion.0203

All of those things are regulated by the autonomic branch of the peripheral nervous system specifically it is the motor branch of the PNS.0207

When you look at the autonomic part, there are 2 main divisions.0217

I will go over in more detail later in this lesson.0221

The sympathetic with have to do with fight or flight response when there is danger.0224

The opposite of it which is parasympathetic which is more like rest and digest.0228

All of these fit together to make your nervous system do what it does.0233

The spinal cord, this particular part of the CNS is how the brain is connected to body and the body is connected to the brain.0238

When we look at the white versus gray matter, it is flipped compared to the brain.0248

Remember in the brain, gray matter is superficial and white matter is deep.0255

It is the opposite here.0260

This is one of those horizontal or transverse portions and you can see that along the superficial portions of it is very white and the deepest part is gray.0261

is white and the deepest parts is gray.0268

Once you go through the medulla oblongata, it flips.0272

It actually make sense that a large proportion of the spinal cord is white matter because if you remember from previous lessons,0276

white matter is because of having a lot of those myelinated axons.0282

Those Schwann cells or oligodenrocytes in certain parts give it that white appearance.0288

It is the signaling part.0294

The spinal cord is very much a signaler.0295

The central canal is the deepest part, the most central part, it is a perfect name central canal.0298

It is a tiny hollow tube down the spinal cord where you are going to have cerebral spinal fluid.0305

There are also cerebral spinal fluid along the outside of the spinal cord.0312

The spinal cord itself travels through the foramen magnum of each vertebra.0316

Together with foramina of the vertebra contained the spinal cord.0322

When you get down to the lumbar region, those little holes are proportionally smaller.0328

The spinal cord eventually branches outside of that and almost looks like a horse’s tail down0336

at the bottom of your back if you are look at all the extensions of the spinal cord coming out.0343

Because of that they call it the cauda equina which in Latin means horse tail.0347

The spinal cord branches out significantly to the point where it does not look like a compacted cord anymore when you get passed the mid pack.0353

When we look at more detail at what is going in the spinal cord, you have a motor side and sensory side.0366

You can call it motor tracks and sensory tracks.0376

The motor or going out of the nervous system, the commanding of muscles and other tissues, that is more on the anterior side.0378

Motor we are going to use red and that is why there is this little ventral root here that has to do with the sending out of those motor signals.0387

That is on the anterior or ventral side of the spinal cord and the sensory also known as the afferent part,0401

the coming in of signals into the spinal cord is on the posterior or dorsal side.0412

Remember efferent and afferent.0419

Afferent is the sensory part going up to the brain and efferent is going out.0422

I am also going to color coordinate this, efferent is the motor side of it.0429

Afferent is the sensory side.0435

When we look at the sequence of how a signal goes through, motor is going out and sensory is coming in.0438

There are also nerves that have both.0448

When we look at what is this afferent sequence is doing, this is coming form some sensory nerve that is taking information to the CNS.0451

This one is the efferent side that is commanding the tissue to do something and together in this case it looks like they come together in one nerve.0463

In other cases you are not going to see that.0476

The reason why I have this here is you sometimes do have nerves that have both tracks in them.0478

There are other nerves that are one or the other.0484

When we look at what is going on inside of these tracks, motor inter sensory basically means if you have a signal coming into the body,0486

let us say something touches your skin and then you want to have the sensation of that come to the spinal cord and brain0499

so you can react to it, the sensory part is the coming in.0509

then you have something called intra neurons which will connect the sensory and motor parts together.0515

It is like the goal between the middleman.0521

The intra neuron you are going to find a lot of that in the spinal cord.0523

It is what connects the sensory to the motor.0527

Your ability to react to stimulus or sensation has to do with the sensory communicating0529

with an intra neuron that commands certain motor neurons transmitters to send out signal so I can react to it.0537

The dorsal root and ventral root comes back into this red and blue portion.0545

The dorsal root is the back side which should be blue.0550

The ventral root is red.0554

The spinal meninges you are also going to have that layer of connective tissue sheeting and enveloping the spinal cord as you do with the brain in previous lessons.0557

Along the outside of this, you are going to have the meningal layers.0570

The average adult spinal cord is about 45cm long, that is the length.0576

In terms of width, it is 14mm.0582

It is pretty thin.0587

I think it is thinner with most people would think.0591

It is going to be slightly wider on average up towards the top.0593

As you go down the spinal cord, as you go posterior, you have a lot of nerve branches coming off.0599

It is like a freeway where there is a lot of off branch coming off, taking cars off their destinations.0605

By the time you get from the cervical part of the spinal cord down at the thoracic, on average in that region it is going to be less wide.0612

But the area that it has the widest portion only 14mm.0621

When we look at the different parts of the autonomic branch of the peripheral nervous system there are the sympathetic and the parasympathetic.0626

They are opposites.0636

Right not I am in the more sympathetic mode.0637

The camera is not threatening and neither are you.0640

There is no reason why my heart rate need to be fast and my breath to be fast, and my skeletal muscle prepare to react.0643

In the case that something threatening does happen you want your body to initiate a response and enable you to live longer and get rid of that threat.0651

It is either you are fleeing, that is the flight part or you are fighting back.0661

In the sympathetic branch gets initiated, your heart rate, blood pressure, and breath rate, are going to go up.0666

Think about walking through a forest and seeing a bear or seeing some kind of a wild tiger,0674

you want to be able to get away from that particular animal if you can, to make yourself live longer.0680

The pupil dilating the reason of that is if something threatening happens, what is going to tend to happen is your pupils will expand.0688

Your pupil is just the opening that lets the light in to they eye.0696

Why is that happen?0703

The more light you let into your eyes, the more you can judge your surroundings to properly figure out what is going on and how to react to what you are seeing.0705

Digestion is going to decrease and here is why.0715

It takes a lot of blood flow into the abdominal region to move digestive fluid through and to absorb it.0718

If I see a threatening thing in my environment that I need to react to, I am going to put digestion on hold.0726

I am going to get that blood flow into my arms and legs primarily so I can fight it.0732

Digestion is going to tend to decrease.0739

However, on a cellular level specially in muscle fibers the metabolism, the break down and building up of ATP, by breaking down glucose and building up ATP.0741

As a result of that breakdown is going to allow you to use your muscles a lot more in that instance.0756

Though digestion decreases in terms of moving stuff into your digestive tract, on a cellular level metabolism is going to go up.0762

Sweating is going to increase because the more muscular activity you are doing, the more heat you are going to generate in and you are going that heat via sweat.0772

Parasympathetic is the exact opposite.0780

There is no rhyme for it.0782

Instead of fight or flight, it is rest and digest, which is no rhyme.0784

Your heart rate, blood pressure, and heart rate, are going to drop.0789

You are getting relaxed.0794

There is nothing threatening so why will your heart rate and blood pressure go through the roof?0796

It is a waste of energy in that case.0800

The opposite is going to happen in your pupils.0802

They are going to constrict.0804

If I am resting in a room just chilling and the light go down, my pupils are going to open up a bit.0806

In general, your pupils tend to be more constricted when you do not need them to be dilated to assess what is threatening.0815

Digestion is going to increase.0822

You will be able to digest better when you are relaxed and chilling.0824

A way that can be a problem is if I eat something quickly and I get it into my stomach and it is gradually going into my small intestine,0829

and then 10 minutes later I realized that I am late for class or late for an appointment and then I start running, I am going to get cramps.0840

That is the way that my body is telling me you just inhaled all of those food and you got it into the stomach and intestine,0846

you have all the blood flow there to help digest it and now you are asking the body to get a bunch of blood flow into your skeletal muscles.0853

What is it going to be?0861

When they say that you should wait 30min after eating before you go swimming, that is the reason why.0862

You are giving your body an opportunity to do some of the digestion and then after you have done a lot of that then you can go for your run or do your activity.0867

It depends on the person and how much you eat.0878

Increased salivating that is paired with the digestion part of it.0880

It makes sense that you would salivate more in this particular instance, the parasympathetic part then sweat.0885

When I say increased sweating with sympathetic, sweating is going to decrease and salivating is going to go up.0892

Conversely, when you activate the sympathetic branch you are going to get decreased salivation as well.0898

Reflexes, we know them very well.0905

Reflexes are the slings that happen automatically without you having to think about it consciously.0909

These are rapid automatic responses to particular stimuli.0915

A single reflex can be studied via the reflex arc, the back and forth of sensing that stimulus and the reaction to it.0918

Number 1 stimulus arrives.0928

It could be something touching your body or your skin.0929

Sensory neuron activation those are the afferent neurons going to the CNS.0934

Processing of info is oftentimes it goes all the way up to the brain, this part of the CNS.0941

There are some reflexes that bypass the CNS altogether which is pretty amazing.0948

That is located primarily in parts of the digestive tract.0955

If you ever asked a trivia question name a part of the body where a reflex in terms of the sensing and reaction to it bypasses the CNS altogether?0959

It is in the digestive part, in the gut.0971

That is why some people say that the gut is almost like a second brain because it can regulate all that stuff reacting to what is going on in itself.0974

Typically the processing is part is the inter neurons, the neurons in the CNS helping connect the sensory to the motor.0984

Number 4 is motor neuron activation.0993

It is the sending out of the signal quickly to whatever effector it is going to, whether to muscle, gland, parts of your digestive system.0996

The response is contraction of muscle or sweating.1006

A little bit different types of reflexes.1011

These are all opposites of each other.1015

Innate and acquired are opposites.1017

Innate is you are born with it.1020

A reflex that you are born with is something as simple as tracking an object with your eyes.1023

Even babies at a younger age do this.1028

You hold something in front of their face and their eyes just follow it.1031

It is something very natural and that reflex is around from birth.1034

Acquired reflexes would be something like when you are driving a car and you have a reflex to something that happens.1038

Your reflex is to mutely turn the wheel left or you see the red lights in front of you and you step on the break.1045

That is something that does not take very long to react to because it is a reflex.1053

That is acquired.1057

You are not born knowing to slam on the breaks when those red lights happen.1059

Somatic versus visceral.1063

Somatic means bodily.1066

These are those reflexes that happen naturally and you do not have to think about it.1069

Somatic reflex is something like that knee test also called the patellar reflex test.1076

The doctor, if they are testing your reflexes and that little hammer hitting your patellar tendon it is that tendon that connects the knee to the other part of the leg.1084

When they hit that part, what is happening is they are elongating the tendon with respect to the muscle attached to.1095

When that elongation happens, your body’s reaction is for the muscle in your thigh tends up.1102

That is supposed to happen very quickly.1111

They do that test to test your reflexes.1113

A visceral reflex would be something like if a light is shined into one eye, what is going to tend to happen is your pupil1115

is going to get constricted because that amount of light you do not need that much into your eye.1125

We are going to lessen the window into which the light comes into the eye.1130

The amazing thing is that if you are shining a light into the right eye your left pupil should constrict as well at the same time and amount.1135

That is a visceral reflex.1144

Monosynaptic versus polysynaptic.1145

It is polysynaptic it has to do with how many synapses are involved in the reflex.1148

Mono means one and poly means many.1155

If there is a lot of process that needs to happen, it is going to happen quickly but if there is a lot of steps1157

in terms of numerous synaptic events it is going to be polysynaptic rather than monosynaptic.1163

Cranial versus spinal means is it just with the cranial nerves or is it also with the spinal nerves?1170

Which one is it?1177

Something like that knee jerk is definitely going to be spinal because the nerve associated with that connects to the spinal cord rather than to the cranium.1178

When we look at a nerve whether it is a sensory, motor, or mixed nerve, there are some parts to keep in mind.1188

If you remember the structure of a muscle from previous lessons there are a lot of same terminology here, same prefixes and same terms.1198

Remember epi, peri, and endo, these prefixes were found in muscle anatomy.1208

Instead of epimysium it is epineurium.1215

The epineurium is the outermost, superficial connective tissue that is keeping a nerve in tact.1219

The fascicle is the same term as in muscles.1226

In muscles the fascicle contain the muscle fibers and this sometimes each one is called a fascicules.1229

I just like saying fascicle.1239

A fascicules contains a bunch of neurons.1241

It depends on the nerve sometimes thousands and thousands.1245

The perineurium is the connective tissue that is separating each fascicle from each other similar to how it is in the muscle.1249

The neuron is the actual cell that is contained in the fascicles.1257

We can pull one of those out.1263

Endoneurium is the tissue separating individual neurons from each other within one fascicle.1265

That is the basics of nerve anatomy.1273

You can also see that blood vessels are going to be found there too.1276

That is not color coded very well in here but you would see in most diagrams red dots and blue dots1281

because you have little arterials and venial taking oxygenated and deoxygenated blood to the parts of the nerve.1287

They are made up of cells too so they need nourishment and need that waste taken away too.1295

That is a nerve.1300

Some examples of nerve, I am not going to all of them because they are so many but one of the classic nerves that you will hear about is the vagus nerve.1302

Vagus means wonderer.1311

The reason why they call it the wonderer nerve is because the vagus nerve when it branches off from the CNS it splits up and goes to a lot of areas within the torso.1314

It has a lot to do with blood vessels and organs within this part of the body.1327

One of the many functions is sections of the vagus nerve go to the aorta and the carotid artery.1333

It has to do with the communication with the chemo receptors with the CNS.1341

As your blood gets more sealed with it, if I inhaled oxygen and exhale CO2, if it has been several seconds since I have taken a new breath,1346

right now I as I am talking I am inhaling I am getting a build up of CO2 in my blood stream making it more acidic.1359

I just breathe in so I can exhale again.1366

The reason why the vagus nerve is important in that sense is the chemoreceptors in the walls of the carotid artery that sense that increase in acidity.1370

If that did not happen your body will not know it is time to take another breath because we got to get more O2 and get some CO2 out of the body to reduce that acidity.1381

That is part of the mechanism of this breathing.1391

That is one of the many things the vagus nerve has to do what is in the body.1393

The sciatic nerve is another classic nerve a lot of people have heard about.1397

That goes back to the posterior part of the pelvic curvature and down the leg.1402

You can see it goes to the buttocks and down each leg.1412

You may have heard the term sciatica that has to deal with irritation and swelling with respect to this nerve.1415

Various health conditions can make it so that not only it is hard to move the legs but you get a numbness,1423

tingling pain associated with this nerve getting pressure on it.1432

Surgeries are one of the things that can relieve sciatica.1437

Medications can help too.1441

The radial nerve has to do with the radius.1443

Remember that the radius is on the thumb side of the forearm.1446

It is one of the major nerves that is going to your arm.1449

Facial nerves has to do with moving all the facial muscles and that branches off numerous little extensions1451

from the nerve to coordinate the different muscle movements to the face.1461

Finally the 2 major optic nerves that come to the eye.1466

There is a little bit of criss cross that happens so that the majority of information from the right eye goes to the left occipital lobe and vice versa.1470

Those are some classic nerves.1479

Spinal cord medical terms.1482

Two things you might have heard of and I will explain in a little bit about is a lumbar puncture1485

or spinal tap is a way of withdrawing some cerebral spinal fluid to do some certain test.1489

That is one of the way that meningitis is diagnosed.1494

If you go the hospital with symptoms of meningitis they want to test for certain if you have that infection going on.1498

If you stick a needle into one of those cartilaginous pads between the vertebrae, you can go just deep enough to withdraw1506

the CSF without going into deeper meningal layers because you do not want get to the spinal cord.1519

If you puncture the spinal cord, it can cause paralysis.1526

That is one way that you can withdraw fluid tap.1529

The reason why they do it down here is because the epidural space that is on the more superficial side of this cavity is greater here.1534

If you go up into the thoracic cervical parts, it is much more narrow.1546

There is not as much as CSF, it is more dangerous to take fluid from those parts.1551

Epidural block this is done for numerous reasons but one of the common ones is if a woman1556

is getting into labor and does not want to feel the pain of child birth as much.1564

An epidural block is the opposite of the spinal tap because they are injecting some anesthesia, some medications that is going to reduce the pain.1568

Wherever they inject that pain medication you are going to be numbing the nerves that branch off from just that portion.1579

If you inject it in the lumbar area, you are covering the area where the labor pains are going to be felt normally.1587

Epidural block is done prior to birth to minimize the pain of child birth.1598

Once again they do not want to go deep with that particular injection because you got some spinal cord damage.1604

For some spinal cords and nerve disorders and conditions.1609

The first one is meningitis and it is cause by bacteria, fungi, or viruses.1613

It has to do with infection and inflammation of that wrapping around the spinal cord and brain.1619

Oftentimes it is fatal if you do not get rid of the bacteria, fungi, or virus that is causing it.1625

Shingles is like chicken pox back with the vengeance.1631

The reason why I say that is chicken pox is caused by virus and it is happening less and less in kids these days because of the chicken pox vaccines.1636

When people my age and older who have had chicken pox as a kid, sometimes when chicken pox is done the virus is not entirely destroyed in your body.1644

Some of the virus go to a dormant state also known as the lisogen exyco which you can remember from earlier biology.1654

It will stay at dormant state for years and then all of a sudden one day when you are a little bit older it comes back with vengeance.1661

Something stimulates it to come back and re attack parts of the skin and instead of it being the pox, it is a rash and it tends to be concentrated somewhere in the torso.1668

It is very painful and it is way worse than chicken pox that is why it is said as the virus back with vengeance.1683

The shingles eventually goes away and the severity can be almost unbearable.1689

Cerebral and nerve palsy usually has factors when the person is born with that are affecting1697

the nerves in the cerebral area or in the nerves that are coming off of the spinal area.1707

The palsy has to do with a reduction in proper motor control of certain areas and there are a lot of different palsies.1714

It varies from person to person.1720

Hypesthesia is a fancy way to say that it is a reduction in the sensation that someone experiences.1724

If someone does not have the average sensitivity that your eye would have when your skin is touched, you can call that hypesthesia.1733

A severe form of that would be someone who does not experience pain.1744

They do not get that sensation at all.1748

When I have described this to people in the past they would say that would be awesome.1751

I love it not to experience pain.1755

No it would not because pain is a way that your body is told that is something is wrong.1757

Something is harming it and something bad is happening into your body.1764

It is a signal that can save your life.1770

Hypesthesia can vary.1773

Sometimes it is just swelling next to a nerve that is reducing sensitivity the person experiences.1775

Sometimes it is something the person is born with.1782

Multiple sclerosis affects millions of people.1785

There are probably genetic and environmental factors that had to do with it.1789

It impacts slightly more women than men.1793

In general what multiple sclerosis is it is describing the reduction in the myelination that is happening on nerves of the body.1795

Not just in the nerves within the CNS as well.1807

There are areas where you are supposed to have the Schwann cells and oligodendrocytes1810

and they are supposed to be insulating the axon and helping increase the electrical signaling speed.1815

In a lot of MS cases you will get that reduction overtime.1822

There are a lot of signs that happen.1827

It tends to be around the persons 30 and 40’s that tends to obvious.1830

In some of those people it gets worse and worse as time goes on.1837

There are treatments and medications that can delay the effects of MS and currently there is no cure.1840

Paraplegia and quadriplegia have to do with being paralyzed from somewhere mid back down.1847

It is impacting the legs and quadriplegia is some kind of damage to the spinal cord that impacts all of the limbs.1856

Someone who is in a wheelchair who is able to use their arms, they probably have some accidents1864

and it varies that has impacted some part of their lumbar, spinal, or thoracic spine.1870

That injury cut off the ability of the brain and spinal cord to signal past to that point of injury and to get signal coming up past the point of injury.1878

Generally it is going to impact the motor and sensory tracks of that spinal cord section and everything past it.1891

Quadriplegia means if you have a neck break in the cranial part of the spinal cord that is bad enough.1898

It can permanently damage part of the cervical spinal cord and that is taking those signals not only to the arms but all the way down the spinal cord.1905

Those also have no cure but there is hope that there will be a cure for this type of paralysis.1917

Thank you for watching www.educator.com.1923