Neurology | Gross Anatomy of the Spinal Cord and Spinal Nerves

hi ninja nerds in this video we're going to talk about the gross anatomy of the spinal cord and the spinal nerves let's go and get started all right ninja so what we have to do first is we have to talk about the spinal cord right and its associated spinal nerves now before we do that i just want to make a little quick division over here you guys remember that the spinal cord and the brain are part of what nervous system your central nervous system right so if i were to say here central nervous system if

we were to break that up into two components what are the two components the upper part here is the brain and the bottom part here which we're going to focus on a lot is our spinal cord right so that's a part of our central nervous system but guess what the central nervous system is intimately connected with the peripheral nervous system guess what the part of the peripheral nervous system is these spinal nerves so if you guys remember the peripheral nervous system is composed of two components a sensory component and a motor component but both of

these sensory and motor component whether it be somatic or visceral meaning autonomic they both are going to be involved in making up our spinal nerves so we are literally talking about this spinal cord and spinal nerves as two different systems but intimately connect with one another okay first thing that we have to understand with the spinal cord is where does it start where does it end that's the basic anatomy so in order to do that you guys know we have up here our brain right so here's our cerebrum this whole bad boy up here is

going to be the cerebrum then from your cerebrum what else do we have here we have our cerebellum here right so the mini cerebrum then here we have our brain stem so what is this i'm just going to annotate brainstem what are the different components midbrain pons medulla now in this back part here you have two little fossas right what are those different fossas if you guys remember from our skull anatomy video we have your anterior cranial fossa our middle cranial fossa and our posterior cranial fossa all this big here this little scoop here coming

in this posterior cranial fossa is a big old hole in the skull what is that big hole in the skull called it's called the foramen magnum so this is that hole which we see the spinal cord exiting out of what is this hole here called it is called the foramen magnum now the spinal cord exits out of the skull via the foramen magnum and it starts right below that so what we say is we correlate the beginning of the spinal cord with this first vertebrae what is that first vertebrae well if you guys remember what

are the vertebrae in the neck called we call those cervical vertebrae so this first vertebrae here is c1 your first cervical vertebrae that's the start of the spinal cord it extends down all the way to about what vertebrae well here's the end instead of counting every single vertebrae what i'm going to do instead is i'm going to be smart i'm going to start at my sacrum and i know that right above here's my sacrum right so this big bone here is called my sacrum if i go 1 up i have l 5 l 4 l

l3 l2 l1 generally anywhere between l1 to l2 is about where the spinal cord terminates so we know the spinal cord starts at the level of c1 we know it extends all the way to about l1 l2 the next thing we need to know about the spinal cord here is that there's different segments okay there's different segments of the spinal cord what are the different segments well if you guys remember all the vertebrae what are the different vertebrae cervical thoracic lumbar sacral and then we have also our coccyx right the segments of the spinal cord

have those same names so here in green what is this segment here called this is our cervical segment of the spinal cord so what is this green one here called this whole green section here is the cervical segment of the spinal cord beautiful pretty simple there then the next segment here extending from this blue portion to this blue portion what is this guy this one right here is going to be our thoracic segment so this is our thoracic segment beautiful keep going down you guys already know this it's going to be pretty self-explanatory we got

lumbar segment so we have our lumbar segment and then after that what is the next segment of the spinal cord and this purple color here this is our sacral segment of the spinal cord and then last but not least we have this small little orange section here that we're going to represent as the coccygeal segment the coccygeal segment of the spinal cord now this is the respective aspects of the spinal cord but remember that spinal cord is a part of our central nervous system the nerves that are coming off the spinal cord and leaving that's

a part of our peripheral nervous system so we should know that these are our spinal nerves so we talked about the segments of the spinal cord which is a part of our central nervous system now let's talk about these spinal nerves coming off of the spinal cord which is a part of a peripheral nervous system these things coming out moving between the vertebrae are called your spinal nerves how many spinal nerves are there in these different segments that's important common questions come up well in the cervical segment there's a total of eight now here's the

big thing we're looking at a sagittal section we're only looking at one half okay so in this case we'd be looking at like the left half there's also the right half so there's eight pairs so eight pairs of spinal nerves okay sweet next thing thoracic segment there's going to be 12 pairs of spinal nerves okay and then we keep going down what else do we have here we have the lumbar segment lumbar segment how many how many spinal nerves are there five we're going to make a little kind of easy way to remember all this

in a second five pairs of spinal nerves sweet sacral segment five this is actually pretty self-explanatory right we're gonna get there in a second so again we got sacral segment this is going to be five pairs of spinal nerves and then last but not least here we have our coccygeal segment and this only makes up one pair of spinal nerves so this is one pair of spinal nerves now let's add all that up okay you have eight cervical pairs twelve thoracic pairs five lumbar five sacral one coccygeal pair that's eight plus twelve is twenty twenty

plus five is twenty five twenty five plus another five is thirty thirty one our total number of spinal nerves here is going to be a whopping 31 pairs of spinal nerves beautiful okay easy way that i like to remember this is just there's a little modification you can remember the number of spinal nerves based upon this little easy way based upon the vertebrae you eat breakfast at seven lunch at 12 dinner at five you have a big drink and a small dessert now we said seven cervical vertebrae well why are there eight eighteen spinal nerves

then okay because zach you said that should kind of correlate let me explain why here so now the the reason why there's eight pairs of spinal nerves and not seven pairs based upon the vertebrae is because the first cervical spinal nerve exits above its respective vertebrae so here's c1 vertebrae look where the c1 spinal nerve is it's above it so here's your c1 spinal nerve then c2 c3 c4 c5 c6 c7 c8 now if we go down the corresponding vertebrae here here's where it's just a little bit different as we move our way down here's

c2 c3 c4 c5 c6 c7 vertebrae here's t1 vertebrae the eighth cervical spinal nerve actually moves above the t1 vertebrae then look what happens as we move into the thoracic segment and down it's all the same from the point starting at the thoracic segment the thoracic spinal nerves and all the other associated ones where does it move here's your t1 spinal nerve what is it moving in with respect to its corresponding vertebrae it's moving below its corresponding vertebrae so the cervical segment is the only segment where the spinal nerves are moving above their vertebrae and

then from the thoracic spinal nerves down those spinal nerves are moving below their corresponding vertebrae that's why there's eight cervical spinal nerves okay that's that one modification so eight pairs of spinal nerves 12 that should make sense because there's twelve vertebrae five lumbar vertebrae five pairs of spinal nerves now i said that there's one sacral vertebrae one sacral bone embryologically embryologically the sacrum actually if you kind of looked at it here if you kind of looked at the sacrum here it used to be five individual bones embryologically that fuse together so technically if we look

at this one bone we have one two three four five individual bones they all fuse together and these little fusing points when you look at the bone is called your transverse ridges so again embryologically there is one bone but it was five individual bones so that's why you have five pairs of spinal nerves okay coming from the sacral segment okay beautiful so now we understand the cervical segments of the spinal cord we understand i'm sorry we understand the segments of the spinal cord we understand their corresponding spinal nerves next thing we need to know is

two other anatomical terms so if you look here at the bottom of the spinal cord here at the bottom of the spinal cord where we said it ended around l1 l2 there's a special name for the end of the spinal cord because it comes to a kind of a pointy edge that point there this part here is called your conus medullaris your conus medullaris and again that's usually around l1 maybe l2 where the spinal cord ends the next thing here is if you take and wrap around okay all these nerves these spinal nerves that are

coming off of the spinal cord around the end of the spinal cord technically from l2 all the way to coccygea one this whole bundle of spinal nerves coming off the end of the spinal cord that has a special name that's called the cauda equina it's called the kata equina let me explain where they got that kind of term from if you imagine here we're looking at the back looking at the dorsal aspect of the spinal cord here's our dorsal aspect of the spinal cord okay here is our conus medullaris okay if you look at this

coming off of the end of the spinal cord is all of those spinal nerves from what points technically the points here for the cauda equina are from uh generally l2 to the coccygeal one spinal nerves all of these spinal nerves that are coming off that end that is your cauda equina okay so that's where caught equina is actually means horse tail so caudle means tail equina means horse so it's horse tail kind of looks like a horsetail from that view okay so we now know the divisions of the nervous system we know with what makes

up the central nervous system component here which is our spinal cord and the spinal nerves that are going to be a part of that peripheral nervous system we know the basic segments two more things that we have to talk about here you see how there's some bulbous portions here in the spinal cord you see right here we have this bulbous portion here and this bulbous portion here this one's primarily in the cervical region and it's enlarged so we call this bulbous portion here this here we call the cervical enlargement it's called the cervical enlargement now

the cervical enlargement technically from the spinal cord segment uh it extends from about c5 to t1 there's obviously a reason that we should know the cervical enlargement it's enlarged our bulbous because it has more gray matter within those ventral horns of the spinal cord we'll talk about what they are for right now i just want you to associate ventral gray horn with skeletal muscles so they supply the skeletal muscles since this is in the upper aspect of the spinal cord these will be going to the skeletal muscles of your upper limbs that's why it's more

bulbous there so this is associated with upper muscles okay beautiful then you come down here we have another bulbous segment guess what that bulbous segment is called and it's in the lumbar kind of region here this is called our lumbar enlargement and the lumbar enlargement is actually going to extend from spinal cord part l2 down to about s3 spinal cord segment okay this is bulbous for the same reason it has a lot of ventral gray matter that ventral gray horn has a lot more gray matter gray matter in the ventral gray horn is associated with

skeletal muscles of the lower limbs that's why it's more bulbous in that portion so it's associated with lower limb muscles okay beautiful now that we understand that we can move on here to taking cross sections we understand kind of the basic overview of this kind of spinal cord and spinal nerves now what we're going to do is we're going to take cross sections at each one of these segments look at them and understand some basic anatomy then what we'll do is is we'll kind of look at the spinal nerves and look at their anatomy okay

so let's go ahead and start over here all right so we talked about the segments of the spinal cord we talked about the basic concepts of the spinal nerves now what i want to do is i want to take cross sections at each one of those segments of the spinal cord and just go over a specific relationship that you have to understand let's say that we take a look at the cross sections all here right there's one there's two relationships i want you to understand as we descend from cervical to coccygeal one of the things

i want us to understand is what is happening to the white matter so we're going to write here white matter okay what is happening to the white matter as we go down from cervical to coccygeal the second thing i want us to look at here is what is happening to the gray matter as we move from that cervical portion of the spinal cord down to the coccygeal segment i'm going to already tell you what what the difference is and then we're going to make sense of why there is that difference the white matter as you

go so again here we're going to go from cervical down to the coccygeal segments as we work our way down the white matter here is going to decrease so there's going to be decreasing white matter and we'll explain why and the same concept here with the gray matter as you go from the cervical segment of the spinal cord down to the coccygeal segment it the gray matter is going to increase there's going to be an increase in this gray matter beautiful okay let's explain why let's start with the white matter and the gray matter will

kind of work itself out through that explanation here's what i want you to remember white matter what is it carrying it's carrying information that goes up right ascending information sensory information and it's also going to carry descending information down which could be motor information let's explain why those ascending and descending information is higher up in the cervical and less of it is here in the coccygeal let's use an example here here we have the coccygeal segment right we're going to have here picking up some sensory information from the coccygeal segment okay which is you know

if we're saying that's usually near the coccyx the tailbone right here it's going to have the sensory information move in here right and whenever the information from the coccygeal segment moves in here it goes to the most medial aspect here so the most medial aspect here's our kind of like midline portion here in this dorsal column and then it comes up right so it's going to ascend all the way up here through all the portions of the spinal cord as we're going up right and this is eventually going to send sensory information up to your

cortex same thing here at the sacral division it's the same concept i'm going to take that sensory information maybe from uh you know the actual genital area or the perennial area and i'm going to take that sensation and i'm going to send that into my my area here the spinal cord and it's going to move just a little bit laterally here and then it's going to ascend upwards through all these different spinal cord segments working its way to the cortex and you guys already get the point here same thing with the lumbar it's going to

take its information in here move just a little bit laterally to that segment and continue to ascend and then thoracic here it's going to take its portion here the sensory information here from maybe from the trunk take that sensory information here move a little bit laterally and then ascend and then finally you're going to pick up sensations from maybe from the upper limbs from the neck that's going to move in here and then ascend upwards what's happening to the sensory information okay these ascending tracks as we go up they're getting thicker you're taking more sensory

information up as you ascend that is one of the reasons why the white matter is going to be a lot thicker it's the same concept with the descending pathways as motor pathways are going down it's just flipped if you look here the cervical it would be going down here same thing it would continue right so the cervical would come here and then it would exit out right but all the other fibers would also continue so you would also have the thoracic fibers coming here and it would continue here and then eventually what will happen it'll

exit out you would have the same concept here if we followed the next one which is the lumbar it's going to move a little bit more laterally here and it's going to come down it's going to continue and then it's going to exit out and if we were to continue we'll do one more just for the sake of it but the whole concept is the same you have descending motor information coming here it's going to continue down continue down here and then obviously come to the sacral portion here and then exit out the whole concept

is that the descending pathways are there's more of them in the cervical region and more ascending information in the cervical region than as we go lower the concept is straightforward the other thing is that is the gray matter there's going to be less white matter as you go down so the gray matter is going to occupy more space also think about the mass of the muscles in the lower extremity they're bigger so you've got bigger muscles down there fatter muscles you're going to need more motor supply from that ventral gray horn that's why the gray

matter is a little bit bigger as you go lower okay so that describes the relationship here now that we described the relationship of these cross sections now let's move over here and talk about some basic anatomy of these cross sections all right so now we're going to do is we're going to take a look at these cross sections and just describe some of the basic anatomy of this spinal cord cross section so first thing we have to talk about is some basic concept here you see how all of this portion of the spinal cord is

this dark black color there's a reason why this dark black color of the spinal cord is called our gray matter okay it's called our gray matter and then all of this white spots here this is called our white matter now we have to have a basic histological understanding of what in the heck is the difference between gray rider and white matter let's come over here to this neuron because it's very important so when we talk about the structure or the kind of anatomy of a neuron there's pretty much just two real components okay technically you

could say three but we're just going to focus on two components one component of the neuron is just going to be this big structure here called our cell body okay so there's two components of this this is going to be our cell body which is this big structure here and then you're also going to have these little things coming off of the cell body what are these called these are called your dendrites okay they're little extensions that are receiving signals from maybe other neurons then you're going to have this portion of this the actual neuron

coming from the cell body down to this little terminal bulb here this right here is called your axon okay so from this here all the way to this here is your axon and then there's these little like fatty sheets these little lipid protein fat sheaths that are surrounding the axon that insulate it and allow for conduction of these action potentials down the neuron what are these bad boys these are called your myelin sheaths and these are basically lipid and fatty protein content and they're actually formed by specific types of cells you guys know if we

talk about the structures that myelinate axons in the cns we're referring to the oligodendrocytes they're the ones that form that myelin that wrap around the neurons if we're talking about the myelin sheaths formed by formed around neurons in the peripheral nervous system we're talking about the schwann cells okay now that we've covered the basic anatomy here okay of the neuron what i want you to remember is that the myelin sheath gives off kind of a whitish more appearance to the neuron so because of that this entire axon because of the myelin sheaths this is referred

to as our white matter and then the cell body and dendrites which are not myelinated make up our gray matter pretty straightforward concept beautiful done now let's talk about some other components here of this spinal cord what are some of the anatomical names for all of this stuff so pretty straightforward this is our gray matter right here right and it forms horns in the back forms forms in the front and then a little horn here okay this horn here in the posterior portion how do i know it's the posterior portion because this little line right

here there's a name for this this is called our posterior median sulcus okay and this gray horn pointing towards the posterior end is called our posterior gray horn pretty original right so it's called our posterior gray horn then this horn here which is going to be in the anterior surface how do i know it's anterior well this whole this little fissure here this is called our anterior median fissure and so this gray matter here in the anterior ventral surface here is called our anterior or ventral gray horn beautiful okay then we have white columns okay

you see all these white columns their white columns are named based upon their position with respect to the gray matter so look at this white column it's posterior to the gray matter so we call this our posterior white column or another better name for it as we call the dorsal white column but you know they give special names to this white columns instead of calling them white columns we call them the dorsal finiculus then this is the lateral white column because it's on the lateral sides of the gray matter this is our lateral funiculus and

the last one here is this guy here these are ventral this white column is ventral to the what to the gray matter so this right here is called our ventral funiculus okay one more structure here you see these little bulbs here that are coming off the sides here they're in between the posterior gray horn and the ventra gray horn these are called your lateral gray horns we're going to write this over here because i want to make a note about it so again these things here on the side are called your lateral gray horn there's

a reason why i want us to know this this lateral gray horn is only found in one specific place in the spinal cord and it's found between t1 2 l2 okay this is basically where you have two different things okay the lateral gray horn is only present in t1 to l2 and it consists of the pre-ganglionic pre-ganglionic motor neurons of the sympathetic nervous system that's what i want you to know with respect to the lateral gray horn it is only present in t1 to l2 which contains preganglionic motor neurons of the sympathetic nervous system beautiful

we covered the basic anatomy here now let's go down and talk about the basic function of these different structures here it's going to be very straightforward very basic okay in your posterior horn since we covered that first i'm going to shade this in red okay the reason why i'm going to shade this in red here is that this posterior gray horn is responsible for containing sensory neurons that's all i want you to know when someone says what do you associate with posterior gray horn i want you to say sensory neurons are associated with the posterior

horn and i'm going to shade in this ventral gray horn this ventral gray horn here is going to be containing what it's going to can be containing neurons for the motor system so this is going to be containing motor neurons okay motor neurons and if you really want to be specific this is technically more of these semantic motor neurons so we'll put here ventral gray horn is technically somatic motor neurons because we already talked about what's in that lateral gray horn which is the motor neurons of the sympathetic nervous system okay the next thing is

we have all these white columns these white columns are containing things like tracks and we'll basically describe what a track is but that's sending sensory information containing accessing sensory information up to the brain and same thing in these lateral and ventral white columns you can have both ascending and descending tracks and we'll talk about this in more detail when we talk about white matter of the spinal cord but for right now all i want you to know is that their job the white columns is to send sensory information up and to send descending motor information

down that's all i want you to know okay that covers the basic aspect there now what i want you to also realize is that we give special names to these neurons okay what's in that that's just the cell bodies and dendrites in this kind of gray matter we call that bundle of cell bodies here in the central nervous system these kind of cell bodies here we call these a group of cell bodies so cell bodies a bunch of them and the cns is called a nucleus the same thing these are the axons right within that

white matter they're sending sensory information up or descending information down a bundle of these axons in the central nervous system is called a tract okay so again a bundle of axons okay axon bundles in cns is referred to as a tract beautiful that's all i want you guys to know here for right now okay now let's discuss since we talked about the spinal cord let's talk about some of the spinal nerves okay so now what i want to do is basically talk about the basic anatomy of the spinal nerve now so we talked a lot

about that spinal cord let's talk about that spinal nerve now and their components so basically you have again you had all that dorsal or posterior gray horn here ventral gray horn here we already know that and you have your white columns well coming off the posterior portion of the spinal cord you have this structure here what is this called this is referred to as your dorsal root it's actually made up of little rootlets that come together to make the root but for the most part dorsal root this part here in the front coming off the

ventral portion of the spinal cord this is called our ventral root pretty self-explanatory right the ventral root and the dorsal root come together and when they come together they form this component here you see how this one comes together here and this one comes together here when they come together and fuse they make another structure here called a spinal nerve beautiful and then the last two components here is that this spinal nerve can actually split off and it can form one that goes on the back part okay so in the back and in the neck

that's called your dorsal raymay of your spinal nerve and then there's another one that moves eventually supplying more of the anterior lateral surface and your trunk your limbs and that is going to be your ventral rami now we're not going to talk about there is some other structures here i'm just going to kind of like quickly draw them in but we discover discuss these in more detail in our video on the autonomic nervous system so if you want to go and look at that anatomy go watch our video there but coming off the ventral rami

you also have these little things called white raymi communicants and grayramicomunicans and they're basically connected to what's called a ganglia and a ganglia by definition is a group of cell bodies in the peripheral nervous system again you want to know more about that go watch our video on the autonomic nervous system okay so we know the basic anatomy of the spinal nerve and basically all these components of it right next thing i want to do is discuss the basic function of the spinal nerve so let's come over here so we have a patch of skin

here right a patch of skin and this patch of skin is going to be let's say damaged for some reason right there's going to be injury to that skin maybe you burned it on something there's little nerves right there's little receptors that can pick up whenever there's damage to the skin there or irritation to the skin and send that information down a neuron the axons of a specific sensory type of neuron that sensory neuron then can either depending upon where the injury is so you guys remember here dorsal rami supplies the back in the neck

and it supplies the skin of the back the skin of the neck the muscles of the back the muscles of the neck things like that and even can supply some of the vertebrae as well whereas the ventral rami supplies the anterior trunk even a little bit of a lateral trunk it's a lateral trunk and it also supplies the limbs both upper limbs and lower limbs so for example if we're just saying whatever this is going to be taking sensory information from maybe the skin of the back of the neck okay the whole point here is

i want you to get is that it's a sensory information it can come through the dorsal ram eye or it could come through the ventral rami let's just for the heck of it we'll show that sensory information could come also via the ventral ram eye so the sensory information moving through the ventral rami and the dorsal rami will also move through the spinal nerve and then from that spinal nerve it'll start moving towards the dorsal root not the ventral root you have to remember that dorsal root then what happens is this sensory neuron has what's

called this little cell body here okay and it's called remember what cell bodies a group of cell bodies in the peripheral nervous system is called it's called a ganglia and this thing right here is a special type of ganglion we call this ganglia our dorsal root because it's in the dorsal root ganglia pretty original right okay it sends its central branch into the dorsal gray horn where it will synapse on some of those cell bodies here in the posterior horn which are associated with sensory neurons then through some interneuron pathways it'll activate motor neurons in

this case somatic motor neurons cell bodies of somatic motor neurons present in the ventral gray horn which will travel through the ventral root from the ventral root it can move through that spinal nerve and guess where it can go it can go through either the dorsal rami but wants to go to some of the muscles of the back and the neck or in this case we can send it through the ventral rami where it can go to the muscles on the anterior lateral surface of the trunk as well as the limbs itself okay so what

i want you to know is that the spinal nerve contains mixed fibers of both motor and sensory fibers this basically describes the basic anatomy and function of the spinal cord and spinal nerves all right ninja nurse so in this video we talk about the gross anatomy of the spinal cord and the spinal nerves i hope this video made sense i hope you guys enjoyed it if you guys did hit that like button comment down in the comment section please subscribe also down in the description box we have links to our facebook instagram patreon account you

guys want to go check that out we truly appreciate it as always ninja nerds until next time [Music] you