Cells of the Nervous System: Study with Video Lessons, Practice Problems & Examples

Neurons vs. Glial Cells

In this video, we're going to be talking about the 2 main types of cells in our nervous system, starting with neurons. So, neurons are specialized cells that communicate with each other via electrochemical signals. Neurons are the cells in our nervous system doing all of the actual communicating or signaling. Now, we also have glial cells, the singular of this being glia, and glial cells perform all different types of functions. They help to insulate neurons, support neurons, like they literally hold them up and hold them in place, nourish neurons, and generally support neuronal health.

Now I always think of neurons as kind of like the star of the show, and they tend to get a lot of attention because they're the ones actually communicating, but glial cells are doing a lot of the really important behind-the-scenes work to keep your brain nice and healthy and functioning, and running smoothly; they do a lot to support neurons. Now, as of the recording of this video, we believe that there's about a 1 to 1 ratio of neurons to glia, although that can change a bit depending on which part of the brain you are looking at. So if you look at our little image here, we have a whole bunch of cells all hanging out together, and these two yellow cells represent our neurons. And then all of these other cells, the ones that are kind of holding on to the neurons and weaving in between them, the red, the purple, and the blue, all represent different types of glial cells. Now, for this course, you don't need to know the different types of glial cells but be aware that there are different types and that those different types do have different functions, but in this course, we're going to be focusing quite a bit more on those neurons.

So I will see you in our next video to talk about neuronal anatomy and the actual structure of a neuron. See you there.

Cells of the Nervous System Example 1

Okay, so for this example, we're going to be reading through these statements and then associating these statements with either neurons or glial cells. Let's get started. So "a" reads housekeeping cells and if we're thinking about housekeeping tasks we're thinking of like cleaning, organizing, maybe supporting, nourishing other cells and that is going to be the role of our glial cells, right? Glial cells are doing a lot of work to keep our neurons nice and healthy. So we'll put an "a" in our glial cell box.

"B" is to send electrochemical signals and that is the job of our neurons, right? So we'll put a "b" in the neuron box. Neurons are cells that are completely specialized just for electrochemical communication, that is their entire function. "C" reads cell in the nervous system and that is true of both neurons and glial cells. So we will put a "c" in each of their boxes.

And then finally, "d" is to provide insulation. That is another function that glial cells perform in order to keep our neurons nice and healthy and functioning properly. So we'll put a "d" in the glial cell box. Alright, so there you have it and I will see you in the next one. Bye bye!

True or False: if false, choose the answer that best corrects the statement.

Neurons are the only important cell type in the nervous system.

• A. True.
• B. False; both neurons and glial cells are important for nervous system function.
• C. False; there are hundreds of cell types in the nervous system, and all of them are important.
• D. False; glial cells are the most important cell type for nervous system function.

Types of Neurons

This video, we're going to be talking about different types of neurons. So neurons can be grouped into 3 functional classes, and what I mean by functional classes is that we are literally grouping them based on their function. So we're not grouping them based on physical characteristics or anything like that, we're just thinking about what actual task or function they have within the nervous system. So based on this classification, we end up with 3 types of neurons: sensory neurons, motor neurons, and interneurons. So sensory neurons essentially just receive sensory information from all over the body and then they convey those signals to the CNS.

So you have sensory neurons all over your body, in your fingertips, your arms, your legs, your toes, etcetera, and they're going to be conveying information about, you know, touch, pressure, pain, temperature, etcetera, up to the CNS to basically tell your brain, like, what your environment is like and what is happening in your environment at any given moment. So those are our sensory neurons. Now, we also have motor neurons and motor neurons are going to be carrying signals from the CNS, so from the brain and spinal cord, to the muscles to produce movement. Okay. So motor always refers to movement, right?

So those motor neurons are helping us to actually enact movement within our muscles. And finally, we have interneurons, and interneurons are going to basically connect sensory neurons, motor neurons, and other interneurons. So I always think of, like, interneurons as being, like, in between other types of neurons. But just to give you a sense of how these can all kind of work together, let's just say you are walking around and you step on some blocks. Not the most pleasant sensation.

Right? And so we have a sensory neuron on the bottom of our foot and that neuron is going to convey information about pain up to our CNS or up to our spinal cord. So this blue line here represents a sensory neuron. K. So now we have information entering our CNS that, like, hey, we are in pain.

That information will travel through an interneuron. So right here this interneuron is connecting our sensory neuron and our motor neuron, here in purple. That's our motor neuron. And our motor neuron is basically going to send a signal from the CNS, here at the spinal cord, going to send a signal down right to the muscle of the thigh to say, hey, let's pick up our leg and let's stop that pain sensation from happening. So that is an example of how those three types of neurons might work together.

Alright. So those are the different types of neurons in the nervous system, and I will see you guys in our next video. Bye bye.

Cells of the Nervous System Example 2

Okay, so for this example, we have 2 pathways here tracking a signal through the nervous system and we're going to be filling in the blanks with the words sensory or motor. So for this first pathway, we are starting in the brain and then traveling to the spinal cord so we're starting off in the CNS then we're going into some type of neuron and then following that a muscle fiber contract. And so if it is enacting some kind of motor response it must have been a motor neuron, right? Alright, so for this next pathway we are starting off with some kind of sensory stimuli. Let's just say we touch a hot stove that goes to some type of neuron and then that signal travels to the spinal cord and then the brain, so up to the CNS.

And so, if we are receiving some type of sensory stimuli that must have been a sensory neuron. Alright, so those are two examples of signals that can get sent in the nervous system and I'll see you guys in the next one. Bye bye.

Which of the following statements are true about interneurons?

I) Interneurons can be found in the spinal cord.

II) Interneurons only connect to motor neurons.

III) Interneurons can connect sensory and motor neurons.

• A. I & II only.
• B. I & III only.
• C. II & III only.
• D. I, II, & III.

Anatomy of a Neuron

This video, we're going to be going over the anatomy of a neuron and all neurons pretty much have the same basic parts. So, all neurons have a soma or a cell body. This is going to be similar to any other cell body that you've ever learned about in a bio class. It will contain the nucleus and the organelles of these cells. So it contains the DNA and any of the biochemical machinery needed to keep the neuron alive.

So if we're looking at our neuron here, this kind of large portion of it with that nucleus right in the center is going to be our soma. Okay, so that is our cell body, it's keeping our cell alive, and all neurons also have structures called dendrites and dendrites are going to be the part of our neuron that receives chemical messages from other neurons. Okay. So they are going to be receiving signals from other neurons and most neurons will have multiple dendrites, not all but most. So you can see here kind of coming off of our soma, we have all of these structures and all of these are dendrites.

So basically each of these dendrites is going to be making a connection with a neighboring neuron and when that neuron sends a signal the dendrites are going to be receiving that message, basically. Now, all neurons also have an axon and the axon is going to be the part of the neuron that sends messages to other neurons. Okay. So this is a really important takeaway point, is that dendrites receive signals and axons send signals. Now, unlike with dendrites, neurons have 1 axon.

However, that one axon can have multiple branches at the end and those are called axon terminals. So if we are looking at our diagram here you can see coming off of our soma we have this very long structure here that is our axon. And you can see our axon is covered in those kind of like bluish gray blobs. Don't worry about that yet, we'll talk about that in a future video. But you can see at the end our axon is branching off and each of those branches is called an axon terminal.

Now axon terminals end in what we call terminal buttons. So at the end of each axon terminal is kind of like a little bulbous structure, and those terminal buttons contain something called vesicles, which are very similar to, like, sacs and those vesicles, or those sacs, are filled with neurotransmitters. So if we are looking at our axon terminals you can see we have these kind of like little bulbous structures at the end of each one. Each of those would be a terminal button. Okay?

And if we were to kind of zoom in on a terminal button and open it up we would see all of these little sacs and those sacs are the vesicles. And those little triangles inside the vesicles would represent the neurotransmitters. So just to give you, like, a very general sense of what a typical neural signal might look like, we would basically be receiving a message from other neurons over here, via our dendrites. We would receive a message that would travel down the dendrite, down the soma, and then our neuron would fire something called an action potential. We'll learn all about those very soon.

So that is basically an electrical signal that will then travel down our axon, down the axon terminal to the terminal button, which would trigger the release of neurotransmitters, which would then send the message to any neighboring neurons. Okay? So we are receiving information over here on the dendrite end and then we are sending that signal to neighboring neurons over there on the axon end. Alright, so that is the basic anatomy of a neuron and I will see you guys in our next video. Bye bye.

Cells of the Nervous System Example 3

Okay, so for this example, we're going to be marking different parts of the anatomy of our neuron. First, we're going to put an X on the soma, also known as the cell body. The soma is this kind of large structure right here that contains all the biochemical machinery to keep our neuron alive. Next, we're going to draw a box around the axon. Our neuron has one axon, right, and the axon does technically include the axon terminals, so we're going to include those in our box there.

Next, we're going to circle any dendrites, and neurons have multiple dendrites, right? So I'm not going to be super precise with this, I'm sure that you'll get the idea, but all of these structures here branching off of the soma are dendrites. Then finally, we're going to draw an arrow in the direction a neuronal signal would move. The signal is received, it's coming in through our dendrites, right? So it's going to start kind of over here and then it's going to travel down the neuron, down through the soma, down the axon to the axon terminal.

So that is the direction that our signal would be moving in this case. All right, I will see you guys in our next one. Bye-bye!

_________ are responsible for sending chemical messages, and the ________ are responsible for receiving them.

• A. Soma: Axons.
• B. Soma: Dendrites.
• C. Axons: Soma.
• D. Axons. Dendrites.

The Myelin Sheath

This video, we're going to be talking about the myelin sheath. So, in the nervous system, many axons, not all but many, are coated in something called a myelin sheath which is basically a layer of fatty tissue that covers and insulates the axon. If you look at our image here, all of these little clumps that are forming on the axon represent our myelin sheath. And the main purpose of the myelin sheath is to help the electrical signal move down the axon faster and with less resistance, and by faster, I mean pretty fast. So a myelinated axon can actually conduct a signal at over 200 miles per hour, which is so cool, right?

So myelin really, really speeds up the process. And when we say that myelin insulates the axon, I mean that it literally acts the way that insulation would in real life. You know how if we have a wire, we'll often insulate it in like rubber or plastic, and that insulation basically prevents the electricity from leaking, which allows it to get conducted faster down the wire, and that's really how myelin works as well. So, we have an electrical signal traveling down our axon, and the myelin is going to cover that axon up and basically prevent leakage of that signal, which allows the signal to get conducted faster down the axon. So that is the main purpose of myelin.

Now, as I mentioned, not all neurons in the nervous system have myelin on them. Myelin is particularly important for, like, long-distance signaling. And remember, neurons are very tiny, so long distance doesn't necessarily need to be huge. This could be, like, from the left side of the brain to the right side of the brain, for example, or, you know, a signal going from our brain down to our toes needs a lot a little extra help. Right?

Because that's a further distance that that signal has to travel, so it has to travel a little bit faster. So those are the kind of situations where myelin is particularly important. Now, myelin is actually made up of glial cells. So you may remember seeing this image, and you may have noticed how the way that the glial cell is kind of holding on to the axon there looks quite a bit like this. So you don't have to know what type of glial cell myelin is made of, but just be aware that it is made of glial cells.

And despite that really common analogy of this being similar to like insulation on a wire, myelin is not continuous. It actually forms in clumps, and those clumps have little gaps between them, and the gaps are called the nodes of Ranvier. They were named after the French pathologist who discovered them. So in our image here, all of these little gaps represent the nodes of Ranvier. And I always remember this because to me Ranvier kind of looks like the word ravine, and I just picture them as like little ravines in between those little clumps of myelin.

At this level, you don't have to know the purpose of the nodes of Ranvier or how they work, just be aware that they are there. So big takeaways here, myelin coats axons specifically. It helps to conduct the electrical signal faster down the axon. Myelin forms in clumps and has little gaps between those clumps. Alright.

I will see you guys in our next video. Bye bye.

Cells of the Nervous System Example 4

Okay, so for all the statements below, we're going to go through and just circle any statement that accurately describes myelin. So A is, "made of glial cells," and that is correct, right? We know that myelin is made up of glial cells, so we'll circle that one. B is, "keep neurons from changing temperature," and that one's tricky because myelin does insulate the neuron, right? But it's not that kind of insulation.

It's not the insulation made to keep something warm, it's insulation designed to basically contain an electrical current. So B is not really accurate. C is that the spaces between myelin are called the nodes of Ranvier, that is correct. D is that it helps electrical signals be conducted more quickly, and that is true. The insulation that myelin provides is to basically stop the electrical signal from leaking out, which allows it to be conducted more quickly, so we'll circle that one and then E is that it is a layer of fatty tissue that wraps around dendrite.

That is not correct; it is a layer of tissue that wraps around axons, right? So, we do not see myelin on dendrites; myelin only appears on axons. Alright, so it looks like the correct choices here are A, C, and D, and I'll see you guys in the next one. Bye bye!

The neurodegenerative condition Multiple Sclerosis (MS) is characterized by the degradation of myelin wrapping in neurons in the brain and spinal cord. Patients with MS can experience vision loss, muscle weakness, and emotional changes. Which of the following could explain these changes in MS patients?

• A. Loss of myelin prevents efficient neural communication.
• B. Loss of myelin prevents the release of chemical messengers between neurons by blocking vesicles.
• C. Loss of myelin prevents the movement of important cell-sustaining proteins from the soma.
• D. Loss of myelin causes near-instant neuronal death.

Myelin is not continuous for the length of the axon. What structures are formed by the gaps in myelin?

• A. Dendritic terminals.
• B. Axon terminals.
• C. Nodes of Ranvier.
• D. Glial gaps.