by Jason Amores Sumpter
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neurotransmitters are the signaling molecules of neurons but on their own they don't really do much. They need receptors in order to exert their effects and they're going to exert their effects when they bind to receptors. Now a single neurotransmitter will have many different types of receptors that it combined and it is the type of receptor it binds to that determines the effect of the neurotransmitter. So I'm making this distinction because I don't want you to think, oh this neurotransmitter has X effect. No this neurotransmitter binding to this particular receptor will have X effect. Now neurotransmitters have to be removed from the synapse after they've been released in order to have action potentials come in as discrete signals. You don't want to just pile up neurotransmitter in the synapse and leave it there because then you're not gonna be able to tell the difference between one signal and another. So Euro transmitters are removed by either re absorbing them and this is going to be a main job of glial cells. They're going to often be responsible for re absorbing neurotransmitters. So essentially sucking them up into those cells and removing them from the synapse or neurotransmitters can be degraded. They'll just be broken down in the synapse so that they can't bind to the receptors anymore. Now the first neuro transmitter I want to talk about is acetylcholine. Not because it's the most important but because it was the first one to be discovered by Otto Louie who actually believe it or not woke up in the middle of the night from a dream and in his dream, he had figured out how he was going to run an experiment on a frog heart to determine whether or not neurotransmitters existed more or less and guess what rest is history? His dream came true, so to speak. Now. Acetylcholine is a neurotransmitter used by the peripheral nervous system as well as the central nervous system and it does or it binding to its various receptors has a variety of different effects. So I'm not even going to try to generalize there, There is no generalizing here. In fact, to illustrate that point even better, let me tell you about the difference acetylcholine has if the neuro muscular junction versus heart. So the neuro muscular junction is the connection between motor neurons and muscles. It's basically a synapse, but technically because it's not between two neurons, it's considered a junction instead of a synapse. This is getting into nitty gritty jargon stuff that you don't need to worry about for your purposes. Please feel free to think of this as a synapse Now it is that connection between motor neurons and muscles and the receptors. There are going to be ion a tropic receptors, you don't need to worry about memorizing this name, just know that these are ion tropic receptors that will allow in ions. Acetylcholine actually has an excitatory effect at the neuro muscular junction and causes muscle contraction conversely in heart muscle as opposed to skeletal muscle. Acetylcholine has an inhibitory effect. So you see, really can't generalize with neurotransmitters, it excites one type of muscle inhibits contraction in in a different type of muscle. Now, acetylcholine will also have an inhibitory effect in some parts of the parasympathetic nervous system, which is a division of the peripheral nervous system. Now, acetylcholine is removed from the synapse by degrading it with the enzyme said a colonist race, another class of neurotransmitters is rather are the amino acids. These are amino acids which include glutamine, glycerine and Gabba. Gabba is what everyone calls it because its name is gamma amino butyric acid and no one wants to say that or write that. So Gabba, it is please don't even worry about memorizing that name. Just know Gabba. So glutamate is going to be the major X excitatory neurotransmitter of the central nervous system that is, its binding to receptors often leads to excitation of the post synaptic cell. Whereas Gabba is the major inhibitory neurotransmitter of the central nervous system. So it's binding to its receptors will generally lead to hyper polarization of the post synaptic membrane. No Xanax is a very common drug prescribed for anxiety. It is part of a class known as Benzodiazepines. Don't worry about that, saying it if you're curious and it will actually act on Gaba receptors technically it will act on a receptor called Gaba a Now, you know what else acts on this receptor ethanol. Now, the reason I bring this up is because lots of people like to mix ethanol and Xanax and that's a really bad idea and I'm going to explain why biochemically now ethanol stimulates these Gaba receptors. It almost acts like Gaba. So when ethanol comes in contact with these Gaba receptors they respond as if Gaba had been bound. Right? So ethanol stimulates those receptors. Xanax has an interesting effect on them. See these Gaba a receptors, their ion channels right there, chloride or this is a chloride ion channel. What Xanax is actually gonna do is keep the channel open longer so it modulates the effect of this channel. It causes it to become more effective at its job basically. So the reason you really don't want to combine ethanol and Xanax is because ethanol stimulates the receptor and Xanax causes it to stay open longer. This is an inhibitory neuro transmitter. It will depress various systems of the body and can actually lead to death. So please, next time you see someone do this, tell them not to because it's a very bad combination. Mono means are another class of neurotransmitter and they contain an amine and an aromatic ring and that's because they're derived from the aromatic amino acids or the amino acids that contain aromatic rings. There are three major types of Monami sorry, there are three uh types of mono means that I want you guys to know those are serotonin dopamine and norepinephrine serotonin is a well, it's the major transmitter of the enteric nervous system which is the nervous system around your gut. So very important there in the central nervous system though it's involved in feelings of happiness and I don't really want to try to make any more specific statements about serotonin. However, I will leave you with this. The drug known as ecstasy chemical name M. D. M. A. Acts on serotonin pathways and serotonin receptors and I just bring it up because it's street name is ecstasy, you know, and this neurotransmitter is involved in feelings of happiness. Hopefully you can put the connection together. Dopamine is actually a technically a cata cola mean which is a subcategory of mono means dopamine is involved in reward pathways of the brain and actually dopamine is going to be uh the neurotransmitter that people focus on when talking about addiction and a lot of illicit drugs will actually uh stimulate these dopamine reward pathways which reinforces that addiction now nor epinephrine is also a cata cola mean and it acts as both a hormone and a neurotransmitter and it's used as a neurotransmitter in the sympathetic nervous system. So acetylcholine is the neurotransmitter of the parasympathetic nervous system. Norepinephrine is the neurotransmitter of the sympathetic nervous system and we'll talk more about those uh different divisions of the peripheral nervous system in a different lesson Now neuro peptides are peptide neurotransmitters and they include things like substance P neuro peptide Y, ghrelin and endorphins. Now I only really want you to be aware of endorphins though Ghrelin actually comes up in our lesson on uh the endocrine system because it is a hormone as well as a neuro peptide that is involved in appetite. Now endorphins, these the ones I want you to really know about these are endogenous opioids meaning there opioids produced by the body, that's what endogenous means. Now generally speaking they're going to be involved in suppressing pain signals and inducing a sense of euphoria. Now the term opioid here hopefully jumps out at you because there's a whole class of drugs called opioids that stimulate these same receptors that endorphins do and that's why opioids are a major class of painkiller drugs right now I mentioned earlier nitric oxide, that's a gas that can act as a neurotransmitter and it doesn't obey those pre to post synaptic transmission rules. It diffuses widely and kind of just goes whichever way it wants. Now the last thing I want to talk about here are neurotoxins. We've talked about neurotransmitters but neurotransmitters aren't the only things that bind to these receptors. Right. In fact we've mentioned that this drug ecstasy interacts with serotonin receptors. So there are also poisons that can interact with these receptors. And neurotoxins are poisons that are destructive to nerve tissue. Now here, I have a picture of a very angry looking puffer fish. Right? And puffer fish considered a delicacy in sushi restaurants is very dangerous to eat because it contains tetrodotoxin. This is a neurotoxin that prevents action potentials. This neurotoxin blocks those sodium channels, so tetrodotoxin prevents action potentials from being fired and can very easily lead to death. That's why it takes a very skilled chef to prepare puffer fish. They have to make sure they, you know, don't cut into the areas that contain tetrodotoxin and remove the portions of the meat uh and you know, get them away from all those toxins. So with that, let's call it a day, See you guys next time.