This model represents a somatic motor neuron. This motor neuron is structurally classified as multipolar because there are many projections coming off of the nucleus. Sorry, the soma.
Multipolar neurons are going to be motor neurons or they will be interneurons. Now interneurons are only found in the central nervous system gray matter. So if you look at this particular motor neuron, we have myelin around the axon and since myelin is present, it can't be in gray matter. Myelination makes structures considered white matter. So this cannot be an interneuron, so it's a motor neuron.
Now The parts of the motor neuron that we're going to cover is the soma, which is another name for cell body. We have the nucleus, and we have these little blue roughened areas. These are analogous to rough ER, but we call them nizzle bodies, and their function is to produce proteins. Off of the soma, we are going to have a lot of thickened projections. These thickened projections are the dendrites, and they will receive information from other neurons.
And the dendrites are going to have ligand or mechanical gates on them. Since this is a motor neuron, it will be ligand. Mechanical gates are only on sensory neurons. Now, communicating with the soma are going to be synaptic end bulbs from a previous neuron, so a presynaptic neuron. In real life, these synaptic end bulbs do not touch the soma ardendrites.
There is a small cleft between them, but in this particular model, so we don't lose them, they are glued together. Now, off of the soma, we're going to see this cone-shaped area. This cone-shaped area is known as the axon hillock, and this is really important because this is where your trigger zone is.
The trigger zone is where we have lots and lots of sodium voltage gates, and this is where an action potential will begin as long as we hit threshold negative 55. We'll also see some neurofibrils, which are basically structural fibers to help keep and support the neuron shape. Off of the hillock, we have our initial segment of the axon. And then here, this pink fiber, when cut open, or when we see the whole fiber intact, this is the axon.
The axon is going to be covered by myelin, which is protein lipids wrapped around the axon multiple times for protection, but more importantly, to speed up action potentials. Since this is a motor neuron and it's myelinated, and this motor neuron is in the peripheral nervous system, the myelin is formed by Schwann cells. So what we're seeing here is a Schwann cell nucleus.
Here's another Schwann cell nucleus. It takes many Schwann cells to myelinate a single axon in the peripheral nervous system. So the Schwann cells will wrap around the axon, forming multiple layers, which is the myelin sheath. Now Schwann cells are just like every other cell in your body.
They will have their own cell membrane, and their outer layer is known as the neurolemma. So the Schwann cells outer layer of the myelin sheath is the neurolemma. lemma. So the one that you can actually touch on the outside is the neurolemma. Now you'll notice that not every part of the axon is myelinated.
We'll see that we have indentations. Indentations right here and right here. Those indentations are areas that lack myelin and they're called node of Ranvier.
And since the myelin blocks the voltage gates from working on the axon, the action potential will jump from one node to another node, and this speeds up action potential. So it speeds up conduction speed, and jumping from a node to another is called saltatory conduction. Now because the myelin and the Schwann cells are delicate, they're going to be covered by the endoneurium, which is just a connective tissue layer, and this is going to be analogous to the endomycin that you covered in your muscle cell.
chapter. And so neurolemma is analogous to sarcolemma. If you look real closely in the axon, you'll also notice that there are some more neurofibrils, again, with help with structure and support. So quick review, motor neuron, somatic, meaning that it's going to a skeletal muscle.
It is multipolar in structure and motor in function. So it sends information to glands and muscles. to bring about an action. We have our soma, which is another term for cell body.
We have the blue rough area, which is the nizzle bodies. Dendrites with ligand gates. Synaptic end bulbs from a presynaptic neuron, a neuron previous to this one, communicating with this neuron, but in real life they don't touch. There's a synapse.
We have our hillock, which is this cone-shaped area that contains the trigger zone. Then we have our axon. The axon is covered by myelin sheath formed by Schwann cells.
The outer layer of the Schwann cell, its membrane is the neurolemma and it's protected by the endoneurium. And then areas without myelin are known as the node of Ranvir. First, he has to be completely complete.