Hi this is Peter from AnatomyZone, and in this brief tutorial we are going to take a look at the basic structure of the neuron.

Nervous tissue is composed of two different types of cells, you've got neurons, and you've got glial cells. So on the right hand side of the screen you can see these various different glial cells interacting with the neuron. But I'm going to focus on the structure of the neuron in this tutorial.

 

Neurons are the basic structural and functional unit of the nervous system, whereas glial cells play a supportive role.

 

Cell Body

Just like any other cell in the body, the cell body of the neuron contains the nucleus, and other major organelles. So within the nucleus, you've got chromosomal DNA, and you also might have a small nucleolus. And then outside of the nucleus, you've got the cytoplasm, which occupies the rest of the intracellular space.

 

Now one thing to mention about the cytoplasm of the neuronal cell body, is that it contains something called Nissl granules. So I'm just drawing these on in black. These Nissl granules consist of rough endoplasmic reticulum, and ribosomes, and they're responsible for manufacturing proteins in a similar way to the endoplasmic reticulum and the Golgi apparatus. These can be visualised when stained with basophilic dyes. So these Nissl granules are quite prominent in the neuron, because of the highly metabolic nature of these cells.

 

And then we've also got structural proteins within the nerve cells. You've got these neurofilaments, which are assembled into the larger neurofibrils. So I'm just drawing these on here - these are the neurofilaments.

 

And finally within the cell body worth mentioning is the neurotubules, so these neurotubules are responsible for cellular transport - bringing stuff to and from the cell body. So I'm drawing these on in blue.

 

Dendrites

The next thing to mention with regard to the structure of the neuron is these extensions which you can see coming off the cell body. These are known as dendrites, and they are highly specialised structures, responsible for receiving information from other neurons at synapses, which are the junctions between different neurons.

 

Axon

Next, coming off from the cell body and extending the length of the neuron, is the axon. So each neuron has one axon which projects to the target cells. And this axon that you can see at the end, has these several branches. So the axon can branch several times to many other cells. Now the axon is very important because this is where the nerve impulse propagates down, from the cell body to the end of the axon, and then this nerve impulse can be transmitted across a synapse to the next neuron in the sequence. So this nerve impulse propagates through the dendrites, into the cell body, and then down the axon into the axon terminal, and then the impulse can be transmitted to the next neuron. This direction of information flow is known as the polarity of the neuron.

 

Axon Hillock

Where the cell body tapers to become the axon, this is known as the axon hillock. I've just outlined that in red. This is where the axon emerges from the cell body, and it's the initial part of the axon, so it's also referred to as the initial segment. At this point of the axon hillock, the cytoplasm is then referred to as axoplasm.

 

Myelin Sheath

The next structure we'll look at is the myelin sheath. I've just animated that on to the diagram. This myelin sheath essentially acts as insulation for the nerve, so it prevents the electrical impulse that is generated from escaping from the neuron, and allows the impulse to flow more effectively.

 

Nodes of Ranvier

Between the myelin sheaths, you can see these gaps, which I'm outlining in green. So these gaps are known as the nodes of Ranvier, known after the man who first described and defined them. These nodes of Ranvier are crucial in allowing the propagation of the nerve impulse down the axon, and what they do is allow a sort of jumping conduction of this nerve impulse. The nerve impulse can kind of hop, from one node to the next, down the axon until it reaches the end of the axon at the axon terminal, and this type of jumping conduction is known as saltatory conduction, or conduction by saltation.

 

Axon segment

Each different segment that is coated by myelin is known as an axon segment.

 

Axon terminal

Now coming to the end of the axon, the end is known as the axon terminal, and as you can see it has several of these branches, which then form connections with other neurons.

 

Synaptic Bouton

Where the branch ends, the end point of that axon branch is known as the synaptic bouton, or the terminal bouton. The terminal bouton is also referred to as the presynaptic junction, because it is this area of the axon immediately before the synapse. So the synapse is this junction between one neuron and the next, and this is where information is transmitted from one cell to the next.

 

Synapses

So if you look up here at the top of the diagram again, you can see the axon endings of one nerve cell interacting with the dendrites of another. This kind of junction would be called an axodendritic junction. But you also have different types of synapses, like axosomatic, so the axons would interact with the cell body. And you've also got axoaxonic synapses. So I'll talk about synapses and action potentials in another tutorial, but those are the basic structures of the neuron.

 

In the next tutorials, we will take a look at glial cells. We will take a look at different types of neurons and their classification, and we will also take a look at synapses and action potentials.

 

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