in this video we're taking a look at a cross section of a spinal cord in a previous video we looked at the different regions of the spinal cord the cervical thoracic Lumbar and sacral but now we're going to zoom in on a little cross section on the spinal cord and talk about signals coming in and out like in a reflex arc as well as signals going up and down to the brain and back out we're also going to take a look at some of the anatomy of the spinal cord cross section so spinal cord cross-section anatomy and physiology let's jump to the Whiteboard and get started so let's start by drawing a cross section of the spinal cord right here it's like we've taken this long thin spinal cord and we've sliced a little section of it we've zoomed in on that and we're going to talk about what's happening in that little cross section that little cross section of the spinal cord is going to have a couple branches coming off either side those branches are going to form a spinal nerve where they come together right here so I have one pair of spinal nerves drawn on here but you're going to have 31 pairs of spinal nerves that come out of the spinal cord in all the different sections of that spinal cord to orient yourself in the diagram a little bit here we have the anterior or front side of the spinal cord and at the top of my diagram of the posterior or back side of the spinal cord so it's kind of like the person's facing us right now now another word for our posterior side is dorsal in other words for anterior side is ventral so we're going to use the words dorsal and ventral a lot in our diagram here so where that spinal nerve branches as it enters the spinal cord we're going to have something called the dorsal root and then on the ventral side or anterior side will have the ventral root though that's come together we already said is a spinal nerve so each spinal nerve coming into the spinal cord is going to Branch off into a dorsal root and a ventral root the dorsal root is going to be where signals come into the spinal cord the ventral root is going to be where signals go out of the spinal cord a little bit later in the video we're going to map out some neurons on here and take a look at where those signals are traveling but for now just know the signals go in through the dorsal and out through the ventral root now I've got all this drawn basically the same color but there's really two types of nervous tissue that are going to exist in the spinal cord we're going to have some white matter and we're going to have some gray matter and so on the diagram I've got it as kind of a lighter yellow and a darker yellow the darker yellow color here will be the gray matter and the lighter colored yellow is the white matter so we've got white matter in here and down in there and then in this central part right there we're going to have all of the gray matter so what's the difference between white matter and gray matter what causes this to be white versus gray well white matter is going to have myelinated neurons the axons are the long projections that come out of the neuron they're going to be covered in these myelin sheaths these things are kind of wrapped around the axon in a bunch of spots that's going to speed up the signal or the action potential that travels down the neuron so anywhere we have white matter we're going to have myelinated neurons that can send signals pretty quickly and wherever we have gray matter we're going to have unmyelinated neurons that don't have those special myelin sheets that speed up the signals that they send it's interesting here in the spinal cord the gray matter is kind of in the central part with white matter around it whereas our brain is the opposite we've got the gray matter on the outside of the cortex we've got the white matter kind of on the inside of the the brain it makes it easy to get confused where the white matter and the gray matter is and the fact that the white matter is surrounding the gray matter as well as the fact that our nerves that are coming in are white matter that's going to include us in that the signals coming in from the rest of the body are going to be on myelinated axons and think about it they got to travel pretty far like if I touch something and signals have to be sent from my finger all the way down my arm to my spinal cord that's a long distance where not a lot really has to happen besides that signal just to get there really quickly and so we have those myelinated neurons that can send that signal really fast well unmyelinated neurons in between and then when signals go back out like when I tell my arms to move there's going to be myelinated neurons they're going to send the signals back out to the muscles of my arms I'm getting a little bit ahead of myself we're going to draw that out in just a minute but first let's take a look at some anatomy of the spinal cord here and talk about a couple regions that are in the spinal cord cross-section for sake of my diagram not getting too busy I've drawn a smaller cross section down in here so that gray matter is going to be divided up into three sections that we call the horns and so we've got the dorsal horn which is on the dorsal side we have a lateral horn so this is kind of sticking off to the side lateral means to the side and then we have a ventral horn so we've got a dorsal lateral and ventral horn as part of that gray matter of the spinal cord and we've got these two kind of creases that go into the spinal cord and so on the ventral side we have what we call the ventral median fissure ventral because it's anterior or ventral side median because it's kind of in the middle of the spinal cord it's not lateral it's medial and then fissures whenever we have some sort of like crevice that's uh coming in on the dorsal side we have kind of the same thing we've got the dorsal median sulcus it's on the dorsal side it's medial and it's a sulcus it's an indentation in nervous tissue so the gray matter has these horns we've got the dorsal median sulcus the ventral median fissure and then the white matter we can divide up into three sections as well that we're going to label dorsal lateral and ventral and we're going to call that the dorsal funiculus the lateral funiculus and the ventral funiculus a funiculus is just a bundle of neurons that are going to send signals up and down and they're surrounded by some connective tissue and more specifically the talking about these regions in the spinal cord in the white matter so the dorsal finiculus here the lateral funiculus here and then the ventral funiculus down and the ventral side finally you'll notice on diagrams there's this little kind of tiny Circle right in the middle of the gray matter that little circle in the middle of the gray matter is called the central canal and it's filled with cerebral spinal fluid if you were to follow that little Canal all the way up into the brain it would connect to the ventricles of the brain where the cerebral spinal fluid is produced and so that's how nutrients and stuff will get between the brain and the spinal cord it's going to go through this little Canal that's filled with cerebrospinal fluid so not about sending signals but rather about sending nutrients where they need to go along the spinal cord in the brain so there was some anatomy of the cross-section of the spinal cord now let's talk a little bit about what's happening in this cross section of the spinal cord let's take a look at the physiology here so I'm going to draw in a few neurons I'm going to start with a sensory neuron a sensory neuron is going to be any neuron that's sending signals toward the brain so it could be that I touch something and the Signal's traveling along my arm into my my spinal cord our sensory neuron will have a signal coming in through here it's going to pass by a cell body and then through the rest of the axon into the gray matter we'll draw some arrows to show the direction of that signal and this is all in white matter so we must have myelinated axons so I'm going to draw that in there these are all the myelin sheaths that are going to insulate that neuron and make that signal travel faster through that sensory neuron and you'll notice where that cell body is under sensory neuron we've got this kind of Bulge in the dorsal root that's called the dorsal root ganglion and the reason that bulges out like that is because this is where all of the cell bodies of all of the many Sensory neurons that are coming through there those cell bodies are all bunched up in this area right there so it has to bulge out to make room for all of those cell bodies dosal root ganglion the sensory neuron cell bodies if you ever run across the other ganglia throughout the nervous system just know that those are where the cell bodies of neurons are located once that signal reaches the end of the sensory neuron it's going to synapse with something called an interneuron now the interneuron is completely located in the gray matter here so it's not going to contain any myelin and it's going to transmit a signal from that sensory neuron down to the next neuron which is going to be a motor neuron now not every reflex arc that we're drawing here is going to have a interneuron there's some reflex arcs that go directly from a sensory neuron to a motor neuron and back so just a two neuron reflex arc and here I'm drawing a three neuron reflex arc so that we can talk about all the types of the neurons that we have so that signal is going to be traveling down this direction back out of the spinal cord so it's going to be going through the anterior root remember we said signals come in through the dorsal and then out through the anterior root and we're back in the white matter so we're going to have a myelinated neuron that can send those signals really quickly that whole Loop there is called a reflex arc and to give that example again let's say I touch a hot stove the signal has to travel through the sensory neuron to my spinal cord through an interneuron and then back out through a motor neuron that's going to tell my arm to jerk back because I just touched something hot even before that signal of touching the hot stove gets all the way up to my brain that reflex art can happen and tell my arm to move back really quickly before I even have time to register consciously what just happened hence it's a reflex but if I do touch a hot stove with my hand that signal is going to make it up to my brain if I touched it with my foot or my leg that signal would not get up to my brain because of my spinal cord injury but if I touch it with my arm that signal makes up to my brain I haven't drawn that yet so I need to draw that into the diagram that's where the interneuron comes in that interneuronic will also send a signal somewhere else in this case it's going to send that signal up to the brain now it's going to cross over to the other side of the spinal cord whenever it does this so that sensory neuron is going to send its signal all the way up through here it's going to synapse with the interneuron that's going to continue the reflex arc but it's also going to send a signal across and then up through one of these ascending tracks of the spinal cord so the signal can make it all the way up to my brain and I can register what just happened so what is all of this white matter in this section here the section there in the section there those three Funiculi those are going to be where the ascending going up and the descending going down tracks of the spinal cord are signals have to travel from the brain down through the spinal cord and out signals also have to travel from our body parts like when we touch something to the spinal cord and back up those signals will travel through ascending tracks we're not going to name all of the ascending and descending tracks but I do want to draw it kind of where they are so you can get a sense of that so in light blue here I'm drawing all of the ascending tracks of the spinal cord the interneuron that I happen to draw here was going up toward the brain so it's got to go through one of those ascending tracks so all those light blue sections those are ascending tracks and if you notice those are located in the dorsal funiculus as well as the lateral funiculus they also exist on both sides it's not just the right side here if we have a sensory signal coming through this side over here and it goes through the dorsal root then that would come over to the other side and go up an ascending track here on the left side and up so I just drew the ascending tracks on one side to keep the diagram more simple but it's on both sides and then here in pink I've drawn the descending tracks so these are going to be the sections where signals are going to travel from the brain these are going to be motor neurons going from the brain down through the spinal cord those are going to go down through these different regions that I've labeled here in pink those are all located either in the lateral funiculus or the ventral funiculus so those are all the descending tracks to summarize the physiology here we have two things that are happening primarily we've got reflex arcs or a sensory signal is coming in and then motor signal is coming back out and then we have signals that are traveling up the spinal cord and then down the spinal cord and those signals are going up and down interneurons that are located in these blue sections for the ascending signals and then the pink sections here for the descending signals so let's recap all of that one more time and then I'll give you a chance to practice on your own in our cross section of the spinal cord we have dorsal Roots ventral roots and those are going to be the branches of each of the spinal nerves that are coming into the spinal cord we have two types of nervous tissue we've got white matter which contains myelinated neurons and we have gray matter which contains unmyelinated neurons those myelin sheaths on the myelinated neurons speed up the action potential or the signal that the nerves send some anatomical areas of this cross-section of the spinal cord include the dorsal lateral and ventral horns of the gray matter as well as the dorsal lateral and ventral folliculi of the white matter so dorsal lateral and ventral we have the ventral median fissure and the dorsal median sulcus as well as the central Canal which contains the cerebrospinal fluid that allows nutrients to get throughout the brain and spinal cord the spinal cord is involved in reflex arcs which includes Sensory neurons taking information in like when we touch something those signals will be transmitted along the axon of the sensory neuron past the cell bodies which are located in the dorsal root ganglia remember it's not just one neuron involved here there's actually lots and lots of neurons that go through each of these nerves so that signal travels along the sensory neuron it's going to synapse with an interneuron the interneuron is going to synapse with a motor neuron the motor neuron is going to send the signal out to some muscle in the body to tell some part of my body to move for example if I touch the hot stove signal goes to my spinal cord back out to a muscle my arm I pull my arm back that's the reflex arc it happens very quickly but those signals also need to get up to our brain so that we can consciously tell what's going on and so whenever that sensory signal comes in and synapses with the interneuron the interneuron is going to cross the other side of the spinal cord and send the signal up an ascending trap react to the brain where our brain can consciously register out that's hot our brain can send signals back out through the spinal cord though and it'll send those signals from the brain through from the cortex of the brain up here down through descending tracks which I have here in pink and those neurons will then send signals out through motor neurons to tell our body to move that would be examples of conscious control like whenever I tell my arm to move in some way all right here's a blank diagram the only way to learn this really well is to test yourself so pause the video see if you can label all of the different parts of this diagram as well as explain what's happening in all these different parts of the diagram all right let's see how you did we got the dorsal root and the ventral root those joined together to form a spinal nerve we've got white matter as well as gray matter white matter as myelin gray matter has no myelin we've got the dorsal root ganglia which contained the sensory neuron cell bodies we've got the three horns of the gray matter the dorsolateral and ventral horns we have the three Funiculi the dorsal lateral and ventral Funiculi of the white matter we've got the dorsal median sulcus as well as the ventromedian sulcus and the central Canal which contains cerebrospinal fluid we talked about the reflex arc that contains a sensory neuron which transmits the signal to an interneuron which transmits the signal back out through a motor neuron completing the reflex arc the interneuron can also send signals across and up to the brain signals traveling up to the brain are going to be traveling through ascending tracks and motor signals traveling from the brain out to tell our body parts to move are going to travel through descending tracks like I said before I've got another video where I go over the different regions of the spinal cord cervical thoracic lumbar sacroix ideal and talk about what each of those controls I have lots of other videos planned both on the spinal cord as well as other body systems so if you're looking for some anatomy and physiology content I've got more coming your way soon so do all the little stuff here we'll see in the next video