So peripheral nervous system, everything outside the central nervous system, everything outside of the brain spinal cord. So we're talking nerves, ganglion, receptors, all those wonderful things that have been kind of alluded to. And we've started talking a little bit about some peripheral nervous system stuff, because those two systems are connected or two divisions are connected.
So it's kind of hard not to eventually talk about them both. So the peripheral nervous system connections to our body, to our internal environment, or the central nervous system. If you recall way back when we talked about the divisions of the nervous system, integration happens in the central nervous system, so it doesn't really have any additional divisions. The peripheral nervous system.
Sensory input, motor output, both of those are taken care of by the peripheral nervous system. So we have to divide that out into more divisions. Oops, that's not the one I want.
This is the one I want. So let's remind ourselves how that's organized. Because, I mean, it is organized in that thing, but it's kind of crazy. So peripheral nervous system is divided into one and one.
Motor and Sensory. Yep. Sensory and Motor divisions, also known as the afferent division and the efferent division.
Afferent carrying towards, efferent carrying away. Reference point being the central nervous system. Then depending on where information is coming from or where we're sending information, we can further divide it into somatic and visceral sensory divisions. And then motor into...
division and. Now the autonomic nervous system can be further divided into the sympathetic and parasympathetic division. I'm going to go ahead and introduce them now. So this will be chapter 14. We'll focus on just this part of the peripheral nervous system autonomic.
So when we get into like reflexes and stuff, we're going to be focusing on the somatic motor divisions. Autonomic is its own whole chapter all to itself because it's so awesome. So hopefully that looks familiar, other than the new part there with our sympathetic and parasympathetic divisions.
So the main organ of the peripheral nervous system are nerves. Let me see an example of one here. And this looks an awful lot like how the arrangement of what other structure we've looked at. Sure does.
Bundles and bundles and bundles again. And the connective tissue sheets that help organize them sound very similar. So nerves, main organ of the peripheral nervous system.
Bundles of bundles of bundles. So the whole nerve is surrounded by the epineurium. The whole structure, the nerve consists of a bunch of fascicles.
They've returned. The perineum surrounds an individual fascicle. And that fascicle is a bundle of axons.
So that's where all those individual circles are. And each axon is surrounded by, bless you, an endoneuron. And if myelin is present, the endoneuron will surround that myelin also, as we see here.
So a nerve contains the axons of a whole bunch of neurons. So nerves and organ, a neuron is a cell. And here's just an actual micrograph of a neuron.
Let's see. Nerves are not all alike. You can classify them according to the direction their transmitting impulse is.
So all those neurons inside that nerve, are they carrying sensory input to the central nervous system? Are they taking motor output from the central nervous system out to an effector? So it gives us three classifications, mixed, sensory, and motor nerves.
Mixed nerves are the most common. They're going to contain neurons that carry motor information and neurons that carry sensory information. Let's see... Sensory nerves only contain neurons that carry sensory input to the central nervous system.
Those are specific classifications to a neuron. So this, and it can be interneurons, because interneurons are only in the central nervous system, and we're talking about stuff in the peripheral nervous system. Okay, so these contain parts of motor neurons and parts of sensory neurons in that mixed nerve, but no interneurons because those are only in the central. Sensory motor nerves only contain neurons that carry motor output to effectors. They are not very common.
In fact, they've found that most motor nerves still carry some kind of sensory input. But for our purposes, we'll look at the three classifications. Well, that's really all we're looking at, defining them. Any questions about that?
The next part, talking about regeneration of nerve fibers, I'm actually going to skip to save us a little time because I'd rather spend more time on the harder stuff that's coming up. and time reviewing the harder stuff. There will be a peripheral nervous system, autonomic nervous system worksheet that will ask you questions about this. Okay? So answer it for the worksheet.
That's how you're covering it. But I will not ask you any questions on the test about this since we're not going to talk about it in here. Okay? So you'll probably see on your worksheet.
Don't panic. But I won't ask you about this on the exam. Okay? All right. What does that bring us to then?
Nerves and nerve plexuses. So back here with our mixed and sensory and motor nerves, that's functional classification. We can also structurally classify them based on what part of the central nervous system are they coming off of.
So there are cranial nerves that are coming off the brain. And there are spinal nerves that are coming off the spinal cord. Cranial nerves, we're going to 100% just talk about those in lab, where they're coming off of identifying and such.
Spinal nerves, we're going to talk about a little bit because they're important for reflexes, we're going to talk about here later, and plexuses. So spinal nerves, there are 31 pairs. See coming down here, 8 cervical, 12 thoracic, 5 lumbar, 5 sacral, and 1 costagel, way down here. All spinal nerves are mixed nerves, so they're all going to contain neurons for motor output and sensory input, carrying that info. Spinal nerves are going to connect to our cord through what are called roots, and we've seen these already.
When we talked about, started looking at spinal cord structure and how those axons are going out or coming back into our cord. Let's go ahead and go to... So interior roots and posterior roots come off the spinal cord and merge, unite to form our spinal nerves. And I'll show a closer picture here in a second. But before we get there, Interior roots, and we saw this when we were talking about how those axons are exiting the cord.
They come off their cell bodies. That might be in the gray matter of our spinal cord. Interior roots contain motor fibers only.
And we saw that. It was only motor neuron axons exiting. Where posterior roots were what only? So we look at a picture here.
I think my root names are over here. Yes, they are. So what do we got here?
Interior root, posterior root. So blue, continuing sensory fibers only. Posterior, anterior root, motor fibers only. They did make the, looks like somatic kind of purple. I'm assuming to differentiate, but they're still both motor in this picture.
So as roots then merge together and form our spinal nerve, we see right here. And it's exiting through those intervertebral foramen, the opening between our vertebrae that we saw previously in lab. But they quickly divide again.
So spinal nerves are actually really short, about 1 to 2 centimeters. Shortly after it comes out of that vertebral column, it branches into what are called rami. And, I'm going to apply directional term side also, posterior and anterior rami, arm, let's see, branches or arms, arm is what rami means or refers to. They're all mixed.
All those, whether it's posterior or anterior, will contain sensory and motor fibers. Remember all spinal nerves, I said were mixed, because we take those motor only, sensory only roots, unite them. So bringing all those sensory and motor fibers together, we branch it back out.
We're not going to separate them out again when we branch after forming that spinal nerve. So what's the point of having a spinal nerve? So then what happens, let's go back to our picture actually to show you what I'm talking about. I think they labeled that over here.
So anterior root, posterior root unite form that mixed nerve then quickly branches into posterior and anterior ran line containing motor and sensory fibers, so they're still mixed. Then what happens? Any questions so far? Posterior rami innervate, generally back structures.
Anterior rami, except for the ones coming off spinal nerves T2 through T12, will form what's called a nerve plexus. So nerve plexus, what's that? So nerve plexus is a network of nerves.
So what's going to happen with these anterior rami of our spinal nerves is they're going to start crisscrossing with each other, merging, separating, then merging again with another branch, bless you. So if we look at a picture here, in a moment, drink here, it'll slow down. So let's zoom in on this one up here. Good old brachial plexus.
Okay, there's four. We'll look more closely at the individual plexuses in lab, so we'll revisit some of this. So brachial plexus is formed from spinal nerve C5 through T1.
Okay, so these here. You can see here they're merging, they're separating, merging, separating, okay? So this is our plexus. And then we'll have particular nerves coming off them going out to innervate the arm. Why?
Why go through all this trouble? Because then when we get to this point, to this nerve going to the arm, it's going to contain fibers from two or three spinal nerves. So if... One of these spinal nerves gets damaged, like maybe this one here. But these are fine.
We'll still have functioning in this nerve, so functioning of that body part. It might be a little different. We'll lose some motor and sensory function, but we won't lose it completely. So that's why.
And we'll stop here because we're out of time.