The synapse

So, last week, we met a drawing of a neurone, which showed its characteristic structures, which looked something like this. And when we did that, we came to the conclusion that if you have repeatable structures, they must be there for a reason. They must have a function. And we’re going to start to look at the function of some of these parts of the neurone today. So here, what we can see is that we have to two neurones drawn. And the process that we’re going to look at is the process by which one neurone can communicate with another. And that’s by this process here.

So we’re going to focus on this point, and think about the actual processes going on here, to allow these two neurones to communicate with each other. So I’m going to draw a diagram below here, which shows that in greater magnification.

So here is the terminal of this cell.

And here is the membrane of the dendrite of this, the second cell. Now, this whole structure is known as a synapse, and as such, the cell but provides the terminal is known as the pre-synaptic cell, or pre-synaptic neurone. And the one that is after this part of the structure is known as the post-synaptic cell, or post-synaptic neurone. So what happens here to allow you this cell to communicate with this one? If we look closely within the terminals, we can see what look like little packages, vesicles. And we know from studies involving chemical analysis that there are molecules contained within these vesicles.

Now, these chemicals contained within these vesicles can act as signalling molecules, and these can signal to this cell. But clearly, to do that, they need to get out of our pre-synaptic terminal. And what happens, it is believed, is that these vesicles fuse with the membrane, thus releasing their cargo into this space. Now, this space is called the synaptic cleft. And as I have drawn it is actually a little inaccurate, in terms of scale, because this is a tiny, tiny space. So the chemicals do not have much distance to travel. So what triggers the release of these chemicals and this fusing of these vesicles with the membrane?

The answer is activity in the axon, going to the terminals, and changing something about how this pre-synaptic terminal is working. And that something is the electrical activity that we met earlier on this week. OK. So we can see that the chemicals can be released, but how does this cell know that they are there? And the answer is that it contains in its membrane specific, what we might describe as, docking stations. So that these molecules can dock here in the docking station. If enough of these chemical molecules dock with enough of these, then this cell will know a message has been sent to it. And what I’ve just described here are the principles of what we call neurotransmission.

What we’re going to go on to look at next is the variety of chemicals involved in this, and the different places in the brain where those chemicals are found.