Understanding the Peripheral Nervous System

What's up? Time Talks Med here. Let's talk about the peripheral nervous system. This video is going to be an overview of the peripheral nervous system. So all I've done is gather the information that will help you build a general mind map around this topic. So if you're new to the peripheral nervous system, I highly recommend you to watch this video before you start studying any plexuses or nerves. With that being said, what we're going to go through is first talk a little bit about what is considered the peripheral nervous system. We're going to go through the classification of the peripheral nervous system, where we'll be talking a little bit about the differences between motor and sensory nerves, and the differences between autonomic and somatic nerves. Then we will make a simple outline of the spinal nerve. We're first going to make an external scheme of the spinal nerve, and then make an internal scheme of the spinal nerve. Awesome! So, what is considered the peripheral nervous system? I guess at this point And since you're studying the peripheral nervous system, you already know that the brain and the spinal cord are considered the central nervous system. That means that all the nerves that go out from the brain and the spinal cord are considered the peripheral nervous system. So what do you call the nerves that exit the brain and the spinal cord? Nerves that exit the brain, within the cranium, they're called the cranial nerves, and nerves that exit the spinal cord, they're called spinal nerves. Easy. It's enabled bidirectional communication between the central nervous system and the rest of the body, which is referred to as the periphery. There are 31 pairs of spinal nerves originating from the spinal cord, and 12 pairs of cranial nerves from the brainstem, giving a total of 43 paired nerves forming the basis of the peripheral nervous system. Awesome. So, that is what is considered the peripheral nervous system. Peripheral nerves. and spinal nerves. But now, how do we classify the nerves within the periphery of our body? The peripheral nervous system is broken into two systems, right? A sensory system and a motor system. The sensory system, or the afferent system, are peripheral processes of the pseudo-unipolar neurons of the spinal ganglions, and they convey impulses to the central nervous system. You know, there can be somatic sensor fibers, and visceral sensory fibers. Somatic sensory fibers take impulses from the exterior receptors of the skin, sensing cutaneous sensations of pain and temperature, touch and vibration and pressure. And they also take impulses from proprioceptors, localized in muscles and joints and ligaments, or in the periosteum of bones via spinal nerves and some cranial nerves as well, sensing proprioception. The motor system or the efferent system, takes impulses from the central nervous system to the periphery. Now, we can actually break the motor system into two parts. One is called somatomotor, which is a part of the somatic system, and this one is under voluntary control. So, in other words, if I want to have my biceps brachii contract, I have voluntary control over that, right? So, we call that somatomotor. Whereas, My heart, or my GI tract, or any different parts of my actual viscera, those aren't under voluntary control. Thank goodness they're not, they're under involuntary control. So, the involuntary control is a part of the visceral motor. They call this the autonomic nervous system, which means that it stands by itself. Okay. Now, the autonomic nervous system, there's three traditional branches of it. Most people know it as the sympathetic nervous system, the parasympathetic nervous system, and the last one, most people don't consider it, they forget about this one, but the enteric nervous system. The enteric, an example of it, are the myenteric and the submucosal plexuses located in the walls of the digestive organs, which are part of the enteric nervous system. The sympathetic and parasympathetic fibers come from the lateral part of the spinal cord, and they come from specific areas within the spinal cord. The segments C8 to L2 are responsible for the sympathetic nerve response, while the segments S2 to S4 give parasympathetic nerve response. And here's a quick way to remember this. S stands for stress, to remind you that the sympathetic neurons are responsible for the fight or flight response, or stress response, and what it does is that it causes a sudden increase of hormones that boosts your body's alertness and heart rate, sending extra blood to the muscles. So all of this is gonna come from fibers that leave your spinal cord between the C8 and L2 segments. The P in parasympathetic stands for peace, which is rest and digest. When the parasympathetic nervous system is activated, it slows the heart and breathing rates, lowers the blood pressure and promotes digestion. Our body enters the state of relaxation, and this relaxation breeds recovery. All of those things come from fibers that emerge between S2 to S4 spinal segments. Alright, now I want to share some clinical facts regarding the motor neurons which will help you understand the symptoms a person may experience having damage to the motor neurons at different levels. So, from the clinical point of view, there are two types of motor neurons, upper motor neurons and lower motor neurons. The upper motor neurons are located in the cerebral cortex, and the lower motor neurons are located in the anterior horns of the spinal cord and in the nuclei of the cranial nerves. If there's, you know, damage to the lower motor neurons, how do you think that will look like? Well, if there's a damage to the lower motor neurons, which is from the anterior horn of the spinal cord, the patient is going to have a flaccid paralysis, meaning the muscle tone is gonna be decreased, called hypotonia, there's gonna be partial or complete impairment of the voluntary movement, called paresis or plesia, And the tendon reflexes are gonna be weakened or completely absent, called hyporeflexia or areflexia. Okay, so flaccid paralysis is a lower motor neuron damage. What if there's a damage to the upper motor neurons, damage to the motor neurons in the actual brain? If there's a damage to the upper motor neurons, the patient will most probably experience a condition called spastic paralysis. It occurs as a result of lesions in the cerebral motor cortex, or from damage to the axons of the upper motor neurons that descend from the cortex to the spinal cord. What are some conditions that may cause this? This may rise after an ischemic insult, seen in strokes, or if there's a perinatal hypoxia that can occur from complicated labor. Spastic paralysis manifests as partial or contrived labor. complete impairment of the voluntary movements. So we also get paresis or plagia here as well. But this time, we get an increased muscle tone, so hypertonia, and signs of spasticity, so hyperreflexia, and irritative pyramidal signs, including Wabinski's sign. Cerebral palsy is a classical example of an upper motor neuron disorder. To suture nerves, a special microsurgical technique is used to apply stitches to the perineurium of the individual fascicles. Alright, I hope that made sense. Now that we know a little bit about what nerves are considered the peripheral nervous system, and a little bit about the classification system of the peripheral nervous system, basically what types of neurons and systems are involved, let's now go ahead and make a scheme of the spinal nerve, because this is very very important to know when you want to study the peripheral nervous system. Ok, so here we got a model of the brain and the spinal cord, with spinal nerves leaving from it. If we now take a section of one spinal nerve, together with the spinal cord, we will see this. So what we can see here from this scheme is a spinal cord and a spinal nerve. Now, if we go ahead and zoom in a little bit on the spinal nerve, we can see that the spinal nerve consists of rootlets, or roots, that connect the peripheral nervous system to the spinal cord. Those rootlets meet and form the trunk of the spinal nerve. And notice here that we see the intervertebral foramen between the trunk and the roots of the spinal nerve. That means that the roots of the spinal nerve are located within the vertebral canal, and the trunk is just outside of the vertebrae, formed just as it passes the intervertebral foramen, leaving the vertebral canal. Alright, let's go ahead and talk a little bit about the spinal rootlets first. In order to do that though, we need to remind ourselves that the grey matter of the spinal cord is composed of anterior horn, containing cell bodies of the somatomotor neurons, or motor fibers. There's a posterior horn, containing bodies of the somatosensory neurons. We got a lateral horn on specific areas of the spinal cord, containing cell bodies of the visceromotor. or the autonomic nervous system. And then we got intermediate zone, containing cell bodies of the visceral sensory neurons. The roots of the spinal nerve are divided as the anterior spinal root, containing fibers that exit the spinal cord, and the posterior spinal root, containing fibers that primarily enter the spinal cord. Notice that the posterior spinal root have a ganglion called the spinal ganglion. Now what is a ganglion? A ganglion is a is just a group of cell bodies. In the peripheral nervous system, which is outside of the central nervous system, so outside of the brain of the spinal cord, you're gonna have different types of cell bodies clustered together forming a ganglion. And if it's located within the vertebral canal, like this one is, it's then called spinal root ganglia, which has the cell bodies of afferent nerves entering the spinal cord. So, that's really the external scheme of the rootlets. Let's now talk a little bit about the trunk of the spinal nerve and its branches. When the spinal nerves leaves the spinal canal, it divides into the posterior branch, which innervates the back. It divides into the anterior branch, which innervates the anterior part of the trunk and the limbs. There's a meningeal branch that goes back into the vertebral canal to innervate the spinal meninges. Another thing we can see here is a ganglion on the side here, called ganglia of the sympathetic trunk, or simply paravertebral ganglia. So we got another ganglia now. Remember if the ganglia are located within the vertebral canal, it's called spinal ganglia. If it's located on the side of the vertebral canal, it's called chain ganglia or paravertebral ganglia. If it's located in the front, they're called prevertebral ganglia. But this one highlighted in blue is a chain ganglia, or paravertebral ganglia, or ganglia of the sympathetic trunk. Many names for this one. The chain ganglia will connect to each other, forming a sympathetic chain. And these are part of the autonomic nervous system. And I will make an own dedicated video for the autonomic nervous system, but just keep in mind, on the side of the vertebral column, there will be a chain of neurons for the sympathetic nerve connections. formed by the paravertebral ganglions connected to each other, as well as connected to the spinal nerves through the white rami communicants containing myelinated axons going to the sympathetic ganglion, we call these preganglionic fibers, and the gray rami communicants. Now the question is, why is it gray? Because it contains fibers that are not myelinated. It contains fibers that originate from the sympathetic ganglions and goes into the spinal nerve containing postganglionic fibers that are unmyelinated. Okay, so now we've got a general idea of the different parts of the actual spinal nerve. Let's try to schematically draw all the types of neurons that go within the spinal nerve. One type of fiber that go within the spinal nerve is the somatomotor fibers, or simply motor fibers, that that originate from the anterior horn of the spinal cord, and go out to different nerves within the periphery of our body, to regulate the movement and tension in skeletal muscles. This one is efferent, it leaves the spinal cord, so it goes through the anterior horn of the spinal nerve. So that was the somatomotor fibers. Another efferent nerve that leaves the spinal cord are the visceromotor fibers, or the preganglionic fibers. that leave the spinal cord from C8 to L2. And what they do is that they join the ganglia of the sympathetic trunk via the white rami communicans. So the white rami communicans exit only at the levels of the spinal cord where the intermedio-lateral cell columns is present, so between C8 to L2. Remember the intermedio-lateral nuclei are responsible for the sympathetic outflow of neurons. So they're responsible for carrying preganglionic nerve fibers from the spinal cord to the paravertebral ganglion. The preganglionic nerve fibers will synapse with the postganglionic sympathetic fibers within the paravertebral ganglia, which will go back into the spinal nerve through the gray rami communicans. These postganglionic nerve fibers don't necessarily have to go through the gray rami communicans though, Some fibers can leave the ganglia independently as well. We also have the pre-ganglionic parasympathetic fibers as well. They're not related to the sympathetic trunk, so they don't synapse in the ganglia of the sympathetic trunk. But again, we will talk more about this in detail when we talk about the autonomic nervous system. Alright, so two types of fibers that leave the spinal cord through the anterior root are the somatomotor and the visceromotor fibers. Then we get somatosensory fibers, which transfers information from mechanoreceptors, exteroreceptors, propioreceptors and thermoreceptors of the body's surface. So in other words, these fibers take in information like touch, pressure, vibration, temperature, itch and tickle and pain. And since we have somatosensory fibers, we also got viscerosensory fibers, which transfers information about body receptors and chemoreceptors and receptors inside the internal organs, sensing wall tension, special receptors for visceral pain and chemical stimuli. So these fibers will go together and enter the posterior root of the spinal nerve. where they're going to have their neural body within the spinal ganglion. And then they will go into the spinal cord to synapse with the nuclei, primarily in the posterior horn. So these are primarily the fibers that go within the spinal nerve. Now within the posterior branch of the spinal nerve you will find postganglionic fibers, you will find somatomotor fibers, and somatosensory fibers as well. The posterior branches are thinner and shorter than the anterior branches. And they're going to innervate the muscles of the back and neck and provide sensory innervations for the skin of the neck and back and the butt. Some important examples of these nerve branches, especially the posterior branch of C1, are called suboccipital nerves. It's purely motor nerve for the suboccipital muscles and the semispinalis capitis. The posterior branch of C2 is called the greater occipital nerve, which innervates the skin of the posterior region and the deep muscles of the back in the neck region. The posterior branch of C3 is called the occipital nerve, which is purely a somatosensory nerve innervating a narrow area of the skin medial to the greater occipital nerve. Posterior branches of L1 to L3 are called the superior clunial nerves, which provide somatosensory innervation of the superior gluteal regions, and the posterior branches of S1 to S3 are called the middle clunial nerves, providing somatosensory innervation of parts of the gluteal region. So that's really the posterior branch. Now, the anterior branch of the spinal nerve is longer and thicker than the posterior branch, and they provide motor innervation of muscles of the anterior abdomen, the thorax and the neck, and they also provide sensory innervation of the skin on the anterior aspect of the abdomen and the thorax. What's unique with the ventral branches of the spinal cord though, is that they form plexuses. Between C1 to C4, we got the cervical plexus. Between C4 to T1, they form the brachial plexus. where we got the lumbar plexus between T12 to L4, and the sacral plexus between L4 to S4. Notice that there's a gap between T1 and T12. Those anterior branches don't form plexuses. They leave as thoracic nerves, innervating the intercostal spaces primarily. So that was really the overview of the peripheral nervous system I wanted you to have a general idea of. In the next few videos, we will go through each of these plexuses shown here, and we will animate them, highlight the most important things, and make an easy mind map that will help you remember them quite easily. With that being said, see you next time.

So if you're new to the peripheral nervous system, I highly recommend you to watch this video before you start studying any plexuses or nerves. With that being said, what we're going to go through is first talk a little bit about what is considered the peripheral nervous system. We're going to go through the classification of the peripheral nervous system, where we'll be talking a little bit about the differences between motor and sensory nerves, and the differences between autonomic and somatic nerves. Then we will make a simple outline of the spinal nerve. We're first going to make an external scheme of the spinal nerve, and then make an internal scheme of the spinal nerve.

Awesome! So, what is considered the peripheral nervous system? I guess at this point And since you're studying the peripheral nervous system, you already know that the brain and the spinal cord are considered the central nervous system.

That means that all the nerves that go out from the brain and the spinal cord are considered the peripheral nervous system. So what do you call the nerves that exit the brain and the spinal cord? Nerves that exit the brain, within the cranium, they're called the cranial nerves, and nerves that exit the spinal cord, they're called spinal nerves. Easy. It's enabled bidirectional communication between the central nervous system and the rest of the body, which is referred to as the periphery.

There are 31 pairs of spinal nerves originating from the spinal cord, and 12 pairs of cranial nerves from the brainstem, giving a total of 43 paired nerves forming the basis of the peripheral nervous system. Awesome. So, that is what is considered the peripheral nervous system. Peripheral nerves.

and spinal nerves. But now, how do we classify the nerves within the periphery of our body? The peripheral nervous system is broken into two systems, right?

A sensory system and a motor system. The sensory system, or the afferent system, are peripheral processes of the pseudo-unipolar neurons of the spinal ganglions, and they convey impulses to the central nervous system. You know, there can be somatic sensor fibers, and visceral sensory fibers. Somatic sensory fibers take impulses from the exterior receptors of the skin, sensing cutaneous sensations of pain and temperature, touch and vibration and pressure. And they also take impulses from proprioceptors, localized in muscles and joints and ligaments, or in the periosteum of bones via spinal nerves and some cranial nerves as well, sensing proprioception.

The motor system or the efferent system, takes impulses from the central nervous system to the periphery. Now, we can actually break the motor system into two parts. One is called somatomotor, which is a part of the somatic system, and this one is under voluntary control. So, in other words, if I want to have my biceps brachii contract, I have voluntary control over that, right? So, we call that somatomotor.

Whereas, My heart, or my GI tract, or any different parts of my actual viscera, those aren't under voluntary control. Thank goodness they're not, they're under involuntary control. So, the involuntary control is a part of the visceral motor. They call this the autonomic nervous system, which means that it stands by itself.

Okay. Now, the autonomic nervous system, there's three traditional branches of it. Most people know it as the sympathetic nervous system, the parasympathetic nervous system, and the last one, most people don't consider it, they forget about this one, but the enteric nervous system. The enteric, an example of it, are the myenteric and the submucosal plexuses located in the walls of the digestive organs, which are part of the enteric nervous system. The sympathetic and parasympathetic fibers come from the lateral part of the spinal cord, and they come from specific areas within the spinal cord.

The segments C8 to L2 are responsible for the sympathetic nerve response, while the segments S2 to S4 give parasympathetic nerve response. And here's a quick way to remember this. S stands for stress, to remind you that the sympathetic neurons are responsible for the fight or flight response, or stress response, and what it does is that it causes a sudden increase of hormones that boosts your body's alertness and heart rate, sending extra blood to the muscles. So all of this is gonna come from fibers that leave your spinal cord between the C8 and L2 segments. The P in parasympathetic stands for peace, which is rest and digest.

When the parasympathetic nervous system is activated, it slows the heart and breathing rates, lowers the blood pressure and promotes digestion. Our body enters the state of relaxation, and this relaxation breeds recovery. All of those things come from fibers that emerge between S2 to S4 spinal segments. Alright, now I want to share some clinical facts regarding the motor neurons which will help you understand the symptoms a person may experience having damage to the motor neurons at different levels.

So, from the clinical point of view, there are two types of motor neurons, upper motor neurons and lower motor neurons. The upper motor neurons are located in the cerebral cortex, and the lower motor neurons are located in the anterior horns of the spinal cord and in the nuclei of the cranial nerves. If there's, you know, damage to the lower motor neurons, how do you think that will look like? Well, if there's a damage to the lower motor neurons, which is from the anterior horn of the spinal cord, the patient is going to have a flaccid paralysis, meaning the muscle tone is gonna be decreased, called hypotonia, there's gonna be partial or complete impairment of the voluntary movement, called paresis or plesia, And the tendon reflexes are gonna be weakened or completely absent, called hyporeflexia or areflexia. Okay, so flaccid paralysis is a lower motor neuron damage.

What if there's a damage to the upper motor neurons, damage to the motor neurons in the actual brain? If there's a damage to the upper motor neurons, the patient will most probably experience a condition called spastic paralysis. It occurs as a result of lesions in the cerebral motor cortex, or from damage to the axons of the upper motor neurons that descend from the cortex to the spinal cord.

What are some conditions that may cause this? This may rise after an ischemic insult, seen in strokes, or if there's a perinatal hypoxia that can occur from complicated labor. Spastic paralysis manifests as partial or contrived labor.

complete impairment of the voluntary movements. So we also get paresis or plagia here as well. But this time, we get an increased muscle tone, so hypertonia, and signs of spasticity, so hyperreflexia, and irritative pyramidal signs, including Wabinski's sign.

Cerebral palsy is a classical example of an upper motor neuron disorder. To suture nerves, a special microsurgical technique is used to apply stitches to the perineurium of the individual fascicles. Alright, I hope that made sense.

Now that we know a little bit about what nerves are considered the peripheral nervous system, and a little bit about the classification system of the peripheral nervous system, basically what types of neurons and systems are involved, let's now go ahead and make a scheme of the spinal nerve, because this is very very important to know when you want to study the peripheral nervous system. Ok, so here we got a model of the brain and the spinal cord, with spinal nerves leaving from it. If we now take a section of one spinal nerve, together with the spinal cord, we will see this. So what we can see here from this scheme is a spinal cord and a spinal nerve. Now, if we go ahead and zoom in a little bit on the spinal nerve, we can see that the spinal nerve consists of rootlets, or roots, that connect the peripheral nervous system to the spinal cord.

Those rootlets meet and form the trunk of the spinal nerve. And notice here that we see the intervertebral foramen between the trunk and the roots of the spinal nerve. That means that the roots of the spinal nerve are located within the vertebral canal, and the trunk is just outside of the vertebrae, formed just as it passes the intervertebral foramen, leaving the vertebral canal. Alright, let's go ahead and talk a little bit about the spinal rootlets first. In order to do that though, we need to remind ourselves that the grey matter of the spinal cord is composed of anterior horn, containing cell bodies of the somatomotor neurons, or motor fibers.

There's a posterior horn, containing bodies of the somatosensory neurons. We got a lateral horn on specific areas of the spinal cord, containing cell bodies of the visceromotor. or the autonomic nervous system.

And then we got intermediate zone, containing cell bodies of the visceral sensory neurons. The roots of the spinal nerve are divided as the anterior spinal root, containing fibers that exit the spinal cord, and the posterior spinal root, containing fibers that primarily enter the spinal cord. Notice that the posterior spinal root have a ganglion called the spinal ganglion. Now what is a ganglion?

A ganglion is a is just a group of cell bodies. In the peripheral nervous system, which is outside of the central nervous system, so outside of the brain of the spinal cord, you're gonna have different types of cell bodies clustered together forming a ganglion. And if it's located within the vertebral canal, like this one is, it's then called spinal root ganglia, which has the cell bodies of afferent nerves entering the spinal cord. So, that's really the external scheme of the rootlets.

Let's now talk a little bit about the trunk of the spinal nerve and its branches. When the spinal nerves leaves the spinal canal, it divides into the posterior branch, which innervates the back. It divides into the anterior branch, which innervates the anterior part of the trunk and the limbs. There's a meningeal branch that goes back into the vertebral canal to innervate the spinal meninges. Another thing we can see here is a ganglion on the side here, called ganglia of the sympathetic trunk, or simply paravertebral ganglia.

So we got another ganglia now. Remember if the ganglia are located within the vertebral canal, it's called spinal ganglia. If it's located on the side of the vertebral canal, it's called chain ganglia or paravertebral ganglia. If it's located in the front, they're called prevertebral ganglia.

But this one highlighted in blue is a chain ganglia, or paravertebral ganglia, or ganglia of the sympathetic trunk. Many names for this one. The chain ganglia will connect to each other, forming a sympathetic chain.

And these are part of the autonomic nervous system. And I will make an own dedicated video for the autonomic nervous system, but just keep in mind, on the side of the vertebral column, there will be a chain of neurons for the sympathetic nerve connections. formed by the paravertebral ganglions connected to each other, as well as connected to the spinal nerves through the white rami communicants containing myelinated axons going to the sympathetic ganglion, we call these preganglionic fibers, and the gray rami communicants.

Now the question is, why is it gray? Because it contains fibers that are not myelinated. It contains fibers that originate from the sympathetic ganglions and goes into the spinal nerve containing postganglionic fibers that are unmyelinated. Okay, so now we've got a general idea of the different parts of the actual spinal nerve. Let's try to schematically draw all the types of neurons that go within the spinal nerve.

One type of fiber that go within the spinal nerve is the somatomotor fibers, or simply motor fibers, that that originate from the anterior horn of the spinal cord, and go out to different nerves within the periphery of our body, to regulate the movement and tension in skeletal muscles. This one is efferent, it leaves the spinal cord, so it goes through the anterior horn of the spinal nerve. So that was the somatomotor fibers. Another efferent nerve that leaves the spinal cord are the visceromotor fibers, or the preganglionic fibers.

that leave the spinal cord from C8 to L2. And what they do is that they join the ganglia of the sympathetic trunk via the white rami communicans. So the white rami communicans exit only at the levels of the spinal cord where the intermedio-lateral cell columns is present, so between C8 to L2.

Remember the intermedio-lateral nuclei are responsible for the sympathetic outflow of neurons. So they're responsible for carrying preganglionic nerve fibers from the spinal cord to the paravertebral ganglion. The preganglionic nerve fibers will synapse with the postganglionic sympathetic fibers within the paravertebral ganglia, which will go back into the spinal nerve through the gray rami communicans. These postganglionic nerve fibers don't necessarily have to go through the gray rami communicans though, Some fibers can leave the ganglia independently as well.

We also have the pre-ganglionic parasympathetic fibers as well. They're not related to the sympathetic trunk, so they don't synapse in the ganglia of the sympathetic trunk. But again, we will talk more about this in detail when we talk about the autonomic nervous system.

Alright, so two types of fibers that leave the spinal cord through the anterior root are the somatomotor and the visceromotor fibers. Then we get somatosensory fibers, which transfers information from mechanoreceptors, exteroreceptors, propioreceptors and thermoreceptors of the body's surface. So in other words, these fibers take in information like touch, pressure, vibration, temperature, itch and tickle and pain.

And since we have somatosensory fibers, we also got viscerosensory fibers, which transfers information about body receptors and chemoreceptors and receptors inside the internal organs, sensing wall tension, special receptors for visceral pain and chemical stimuli. So these fibers will go together and enter the posterior root of the spinal nerve. where they're going to have their neural body within the spinal ganglion.

And then they will go into the spinal cord to synapse with the nuclei, primarily in the posterior horn. So these are primarily the fibers that go within the spinal nerve. Now within the posterior branch of the spinal nerve you will find postganglionic fibers, you will find somatomotor fibers, and somatosensory fibers as well.

The posterior branches are thinner and shorter than the anterior branches. And they're going to innervate the muscles of the back and neck and provide sensory innervations for the skin of the neck and back and the butt. Some important examples of these nerve branches, especially the posterior branch of C1, are called suboccipital nerves. It's purely motor nerve for the suboccipital muscles and the semispinalis capitis. The posterior branch of C2 is called the greater occipital nerve, which innervates the skin of the posterior region and the deep muscles of the back in the neck region.

The posterior branch of C3 is called the occipital nerve, which is purely a somatosensory nerve innervating a narrow area of the skin medial to the greater occipital nerve. Posterior branches of L1 to L3 are called the superior clunial nerves, which provide somatosensory innervation of the superior gluteal regions, and the posterior branches of S1 to S3 are called the middle clunial nerves, providing somatosensory innervation of parts of the gluteal region. So that's really the posterior branch. Now, the anterior branch of the spinal nerve is longer and thicker than the posterior branch, and they provide motor innervation of muscles of the anterior abdomen, the thorax and the neck, and they also provide sensory innervation of the skin on the anterior aspect of the abdomen and the thorax. What's unique with the ventral branches of the spinal cord though, is that they form plexuses.

Between C1 to C4, we got the cervical plexus. Between C4 to T1, they form the brachial plexus. where we got the lumbar plexus between T12 to L4, and the sacral plexus between L4 to S4.

Notice that there's a gap between T1 and T12. Those anterior branches don't form plexuses. They leave as thoracic nerves, innervating the intercostal spaces primarily. So that was really the overview of the peripheral nervous system I wanted you to have a general idea of. In the next few videos, we will go through each of these plexuses shown here, and we will animate them, highlight the most important things, and make an easy mind map that will help you remember them quite easily.

With that being said, see you next time.

Transcript for:Understanding the Peripheral Nervous System

Transcript for:
Understanding the Peripheral Nervous System