Source: Video and Images Created by Amanda Soderlind
Welcome to this lesson today on neurotransmitters. Today we will be discussing the role of neurotransmitters in relaying signals throughout the nervous system.
So an action potential will stimulate the release of neurotransmitters. And neurotransmitters are basically the chemical form of a signal. So we'll get a little bit more into this when I show you an example in just a moment here.
But first, we are going to explain how neurons communicate. So we're going to be explaining today specifically how neurons communicate with muscle fibers in order to set the stage for muscle contractions. So basically, these are the steps that occur in order for that to happen. It explains how neurons can communicate with these muscle fibers.
So an action potential will flow along the axon of a motor neuron to a neuromuscular junction. And a neuromuscular junction is basically the area where a neuron and a muscle fiber come close to one another. And then the neurotransmitters will diffuse across a gap known as a synapse. So remember, the neurotransmitters are the chemical form of whatever signal is being carried.
So these neurotransmitters will diffuse across the synapse or this gap between the axon endings of the neuron and the muscle fiber plasma membrane. So we call these the presynaptic and postsynaptic cells. So this gap between the axon ending of the neuron separates the axon ending of that neuron from the muscle fiber. So the synapse is that gap in between.
So the cell that's before the synapse is called the presynaptic cell. And the cell that is after the synapse is called the postsynaptic cell. So the neurotransmitters will carry that information from the presynaptic cell across the synapse to the postsynaptic cell. From there, those neurotransmitter molecules will bind to receptor proteins on the postsynaptic cell. So they'll bind to these receptor proteins.
In this case we'll use a cell membrane of a muscle fiber for example. So they'll bind to these receptor proteins on that muscle fiber and allow channels to open. And ions can then diffuse through those channels and an action potential can occur.
Neurotransmitters can either excite or inhibit activity in a target cell. So basically, whether they excite or inhibit is determined by the amount of the neurotransmitter, the type of the receptor, among other factors. But exciting signals will drive a membrane toward an action potential, while inhibiting signals will do the opposite.
So let's take a look at a diagram here so you can understand this a little bit more in detail. So what we have here is a picture of a neuron. So we're going to say that this is a motor neuron. So the information will travel along the axon to the axon endings. So right here we basically have just zoomed in on an axon ending.
And then we have in here our synaptic vesicle. And these synaptic vesicles are what contain neurotransmitters. And then we're going to call this line right here-- we're just going to say that this is our muscle fiber.
So this would be our presynaptic cell. And this would be our postsynaptic cell. So this area in here, this gap in between them, is the synapse. So the neurotransmitter is going to carry information from this presynaptic cell across the synapse to the postsynaptic cell, which is the muscle fiber in this example.
So if we zoom in a little bit more, we're going to say that this is the plasma membrane of this muscle fiber. And we have these proteins that are embedded in the plasma membrane. And on those proteins we have this binding site. So this is the binding site for neurotransmitters.
Now you'll notice when the binding site is empty, when there's nothing there, we have these ion channels are closed. But when a neurotransmitter binds to the binding site, it causes that ion channel to open so then ions can flow through the plasma membrane and then allow for an action potential to occur. So the neurotransmitters are carrying information from the presynaptic cell to the muscle fiber, binding on these sites, allowing the ion channels open and allowing an action potential to occur. So this is the way in which neurons can communicate with muscle fibers. But neurons can also communicate with other neurons or with gland cells as well.
So we're going to take a moment to talk about Botox. And Botox is a type of injection that people get to smooth out facial wrinkles. And it's actually made from a bacterium.
And what it does is it blocks the release of acetylcholine so that the muscle contractions that produce wrinkles will stop temporarily. And acetylcholine is a type of neurotransmitter. So people get this in order to stop or slow down facial wrinkles. So that's what Botox is and the role that it has in muscle contractions.
So this lesson has been an overview on neurotransmitters.
The chemical form of a signal that is sent between neurons and muscle cells, gland cells or other neurons.
The gap between a neuron and a gland cell, muscle cell and another neuron.
The cell at a synapse that stores a neurotransmitter for release.
The cell at a synapse to which the neurotransmitter binds.
Signals that trigger an action potential to happen.
Neurotransmitters that inhibit or prevent action potentials.
A bacterial toxin that is often used to smooth facial wrinkles by stopping the release of the neurotransmitter acetylcholine.