 Hey everybody, Dr. O here, in this video we're going to cover the basic structure and function of the synapse. So we've covered the rest of the neuron, now we're at the end where the electrical signal is usually going to become a chemical signal. There actually are two types of connections that can occur between electrically active cells. There are electrical synapses where one cell is directly connecting another. But in this video we're going to talk about the chemical synapse because by far more common or more important. So we're going to focus on the chemical synapses here. So the synapse is going to be this place where one neuron can communicate with another cell. Now notice in this picture both the pre-synaptic and post-synaptic cell are neurons, but a pre-synaptic neuron can also stimulate any type of muscle. So skeletal muscle, cardiac muscle, smooth muscle, glands, and fat as well. So you'll see that the first cell, the cell with the synaptic knob is going to be the pre-synaptic neuron, the one released in the neurotransmitter. Whatever cell is receiving the signal will be called the post-synaptic cell, but in this case it is a neuron. So between these two cells we see this space. They're not actually touching each other. The space is called the synaptic cleft. And to crop, so we have an electrical signal that needs to create a chemical signal, which are neurotransmitters, that's going to cross the synapse and then create an electrical signal in the post-synaptic cell. So it's actually pretty cool. So the synaptic knob there at the end of the axon terminal, or at the end of the axon, is full of these synaptic vesicles. And inside of them is the neurotransmitter. Now what neurotransmitter it is depends on the cell. Like I did a video on the neuromuscular junction and that would be the neurotransmitter acetylcholine, but it could be any neurotransmitter. And the response that it has is going to depend on the receptors on the post-synaptic cell. All right, so we did the basic terminology. We covered the pre-synaptic neuron, the post-synaptic cell. We talked about the synaptic cleft. We talked about the synaptic knob with those synaptic vesicles in it. And we covered what a neurotransmitter was, a chemical messenger that crosses a synapse. If it's the same chemical, but it's in your bloodstream, it'd be called a hormone. But here they're called neurotransmitters. Let's go ahead and look at how they work. So number one, we have that electrical signal. The actual potential is going to arrive at the axon terminal there at the end at the synaptic knob. And then number two, voltage-gated calcium channels open and then calcium is going to enter the axon terminal. At the same time, this calcium entry is causing these neurotransmitter, these synaptic vesicles, to release their neurotransmitters. So calcium is what causes neurotransmitters to be released from a neuron into the synapse. So now calcium is flooding across the synaptic cleft. So we get to step four. Sorry, calcium is led to the neurotransmitters that are going to flood across the synaptic cleft. So number four, neurotransmitter diffuses across the synaptic cleft and binds to ligand-gated ion channels on the post-synaptic membrane. So again, the receptor type and the function, the result, are going to be dependent on the neurotransmitter involved. Number five, so there you see the neurotransmitter actually binding and then leading to the greater potential there at the post-synaptic cell and the cell is doing what it's supposed to do. Then step six is how this stops. So as soon as neurotransmitters are released, they're going to start to be actively reabsorbed and some of them are going to be destroyed by enzymes like, for example, with a neuromuscular junction, I taught you how the enzyme acetylcholinesterase is actually going to break down acetylcholine. So some neurotransmitter is going to be destroyed. Some is going to be reabsorbed and some is just going to flutter away. And now the neurotransmitter concentration has dropped low enough where this will stop. So that's how synapses work, how they turn on and then how they turn off. Let me give you one example of this idea of reuptake dose that's pretty important. So drugs like Prozac, they're classified as SSRIs or selective serotonin reuptake inhibitors. What that means is that drug doesn't actually increase the amount of serotonin being produced. What it does is it slows its reabsorption. So you do have more serotonin in your synapses affecting your post-synaptic cells, but it's because they've slowed this reuptake, this reabsorption. So things like the reuptake and enzymatic destruction or degradation are very important. All right, that's the basics of how a synapse works. I hope this helps. Have a wonderful day. Be blessed.