Peripheral Nervous System, Spinal Nerves PDF

All right, this is the first recording for the peripheral nervous system, spinal nerves. We are going to really start out with reviewing kind of what we already know and apply it to where we're going. So spinal nerve intro here. So spinal nerves, we've actually talked a lot about them in terms of wh...

All right, this is the first recording for the peripheral nervous system, spinal nerves. We are going to really start out with reviewing kind of what we already know and apply it to where we're going. So spinal nerve intro here. So spinal nerves, we've actually talked a lot about them in terms of where our information coming from the central nervous system and then going to the central nervous system is running within, right? So we have that somatic motor and somatic sensory and so forth, right? So we first need to identify or further identify some of these different portions here of these structures. So the spinal nerves themselves are going to arise from the central nervous system as rootlets, right? So this is going to happen at each spinal level, right? Each spinal routine or body level and we'll have several spinal nerves either coming out of the anterior portion or the posterior portion. They are going to come together to form roots, right? So these rootlets will come out and form roots. These are going to have either motor if it's going to be in the anterior portion or sensory information going through them, right? So rootlets, the roots here and here are going to carry specific types of information. Then they're actually going to come together here, right? So this is going to be the next portion. This is the actual spinal nerve that we talk about. Note that we have some familiar structures, right? We're going to have that anterior horn and posterior horn of gray matter. Here's our white matter for the spinal cord. Here are our dural layers that cover, meningeal layers that cover the spinal cord. And here we have our posterior root ganglion, right? Which reminds us that this is a sensory side, right? Recall that the nerve cell bodies are going for the anterior motor unit is going to be in the anterior horn, right? They're going to have nerve cell bodies and they're going to send information out. Well, in comparison, in our sensory route, we are going to have our cell bodies into the dorsal roots, one's going to travel that way, and one aspect is going to travel the other direction, right? So a little bit of a different organization, okay? So again, like I said, that spinal nerve is going to be after these two roots come together. So the specific portion of this right here, that is the spinal nerve. And because it's where the two roots come together, this is going to carry mixed information, which means it's going to carry sensory and motor here. And then we're going to have another division. We are going to divide these into a rami for plural or a ramus. We're going to have a posterior ramus going posteriorly and an anterior ramus going anteriorly. This portion here is going to be part of our autonomic nervous system, which we'll get to in block four, right? Here we can see those neuron cell bodies and their associated axons shown here for our sensory and motor as well, right? When we talk about our peripheral nerves, sometimes we will say this is a sensory nerve or a motor nerve, and in real life, in reality, they're going to carry both sensory and motor most of the time, but usually can be defined by their primarily carrying motor or primarily carrying sensory, so just keep that in mind. All right, so here's our gross anatomy. We're going to have our anterior and posterior horns. We can think of those as our motor and sensory horns sending out these rootlets, right? So if it's on the anterior portion, this is going to be our anterior rootlets versus our posterior rootlets here. Then we're going to have our posterior root versus our anterior root. Our posterior root ganglion tells us what is posterior, right, and what is sensory. And then this specific small portion where they come together before we split into the rami is the spinal nerve, right? That spinal nerve is then going to give off a posterior smaller root, much smaller. We're going to see why here in a little bit, and a bigger anterior or ventral ramius here. So sorry, I called them roots. This is a posterior rami, dorsal rami, or ventral or anterior rami. All right, so like I said, this is going to happen at each level, right? So each of our spinal cord levels from C1 to C8, remember there's an extra one thrown in there, T1 to T12, and so forth, right? So the posterior rami that we talked about that are smaller that we can see right here, they are going to go posterior and supply the vertebral column, the apaxial muscles, and the overlying skin, right? So this is the portion that is going to travel with that portion of the somite, specifically that portion of the myotome, right? These nerves are going to travel with that apaxial muscles, portion of the myotome posteriorly here, right? So we're going to pull those roots along. These roots aren't going to separate and form nerve plexuses. What does that mean? That means that they're going to come out as a single nerve, and it's not going to join up with other nerves, right? So we're going to see this really nicely patterned organization. The anterior rami are the spinal nerves, all right? So here's the bigger one that is not surprisingly going to do the apaxial muscles and the skin overlying that. So really the rest of our body outside that smaller portion of the back or that midline portion of the back and those associated muscles, right? And we can see that here is representative of our anterior roots, our roulette roots come together with spinal nerve and then the rami is going to send those nerves, those axons into the anterior aspect of this dermatome and be pulled anteriorly to form those muscles, right? In the trunk, as we can see here, here we have our anterior rami, the little posterior tine ones are here. Our anterior rami are going to be separate, stay separate nerves and become our intercostal nerves, right? So nicely organized here for us. In our limbs or for our limbs as well as really our neck, we're going to have different plexuses. A plexus is a network, right? So a network of nerves will come together and they are going to form different plexuses in specific locations. And that's what we're going to dive further into, right? And this is going to be our peripheral innervation. And then our distribution is going to follow these patterns. All right, so this is a super review, right? So the functional categorization of these spinal nerves going to our different locations in our body, right? We're going to have somatic motor and visceral motor. Somatic motor is going to do the muscle movements that we think about, right? Those somatic motor fibers are going to be processed specifically in our multi-axon neurons, right? So there we can see that there. And then in comparison, our visceral motor is going to be some multi-axonal neurons. Our visceral motor is going to be, oop, I said somatic motor. Our visceral motor is actually going to send all that information to the muscles in our body, right? So autonomic stuff. And this is going to be our glands, so even those in our skin, our salivary glands, our pancreas, our smooth muscle in our GI tract, and also our heart, right? So visceral motor is our organ motor. That is also going to travel through these fibers, right? These spinal nerves that we talked about. They are going to synapse in their own ganglia, right? So we're going to have a whole other set of ganglia that are going to have, or be associated with their autonomic nervous system here, right? And they're going to be in this multipolar motor neuron. Sorry, I call them multi- axonal. And they are going to be, and we're going to have pre-synaptic fibers and post-synaptic fibers that are going to be associated with where they transition into that next set of nerves, so we'll talk about that in block four. Our somatic sensory, right, and our visceral sensory. So somatic sensory is going to be our general sensory system that we, you know, we feel things with. We have different types. We have x-thera receptors that cover our pain, temperature, touch, pressure from the skin. So basically, most of those spinal cord pathways that we talked about, right, dorsal colon pathway, spinal thalamic pathway. And then we have our proprioceptive information coming in. And it's considered somatic because it's coming from the body, right? Where we are in space. Where's, where's our body in space? And that's going to be coming from that spinal cerebellar pathway, right? In terms of sensory. Somatic sensory fibers are going to be processed in those uni- axial or uni-polar neurons, right, that have their cell bodies in one location, right? Our dorsal root ganglia, which we can see up here, and then sending fibers in two different directions. Visceral sensory is going to travel with our, our visceral motor. It's just going to be sending information the complete opposite direction. So instead of going this way, we're going to have fibers going this way. They are going to synapse in different locations. But when we do the autonomic nervous system, we're going to kind of fly by sensory because it's going to travel the same routes. Just the information is going the opposite direction. This is going to transmit also our visceral pain. So if you've heard of appendicitis causing pain in certain areas, it's going to go through this track or this pathway. And then visceral reflexes and so forth, right? So things that happen in terms inside our body that we don't have to have really control over. All right, dermatomes and myotomes. We've already covered this when we talked about our muscles, muscle development. And so here it is again, that's why we group these two sections together, right? So it's the segment of skin that we can see here or muscles that are supplied by a single spinal nerve, right? So we'll have that vertebral body. We'll have our posterior and anterior roots come out. And there we'll have our single spinal nerve come out and serve or provide information to and from one location. We know it's more complex in our arms and our legs, not only to rotation, but also because these are going to come from plexuses, right? Nerve plexuses, okay? Knowing these can help us identify or indicate potential damage to a spinal nerve in a location, right? They're also going to play a role in referred pain. And again, we'll get to this in the fourth block. So referred visceral pain is when you feel pain in your skin, but it's really coming from an organ. So these are the areas that we would test. We're not gonna do face and scalp yet, cuz we haven't covered the cranial nerves. But in the cervical spinal nerves, so these ones up here, those individual ones that will come out to form a plexus, will be tested in the neck, the shoulders, superior thorax, a majority of the upper limb. So you can see that here, all this yellow. Thoracic is really gonna be our torso with our thorax and our abdomen here. But a little bit on the medial aspect of our upper limb. And then our lumbar, sacral, and coccygeal, our lumbosacral and coccygeal nerves will innervate the skin of the pelvis, gluteal region, and the whole lower limb, right? And you can see these maps when really kind of laid that out for you. All right, development of the dermatomes and myotomes. We already know this, we're gonna talk about it again. Here's that lovely limb rotation happening. And you can see from that limb rotation, how these dermatomes get a little bit twisted as they move along, all right? So somites from that paraxial mesoderm, right? Form those derma- myotomes, as well as that sclerotome, but we're talking about muscles right now, all right? And that derma-myotome can be further divided or will be further divided into the dermatome and the myotome. Those spinal nerves, here's our developing neural two, which is really our spinal cord sending out motor and sensory innervation. Notice that right here, it's all motor, so that's gonna be a root. This is all sensory, that's going to be a root. Then they come together right here in our spinal nerve. Then they're going to go out that posterior or dorsal ramus with mixed fibers. And then going out that anterior ventral ramus with mixed fibers, right? So these are gonna go to the hypaxial muscles, the anterior stuff. And versus the apaxial muscles here, our back really, right? And so that's how our muscles are innervated by specific levels of the spinal nerves, right? This is gonna happen all the way from C1 down to the lowest sacral vertebrae, actually, all right? And we are going to go over nerve plexuses in the second recording.