Understanding Nervous System Cells: Neurons, Communication & Neurotransmitters

the topic of this lecture is cells of the nervous system so what we want to focus on is how cells

in our nervous system communicate with one another so your nervous system is a is composed

of living tissue right that's made of cells the cells in the nervous system fall

into two major categories the first category are going to be neurons neuron neurons are individual cells in the

nervous system that receive integrate and transmit information neurons are going to be what allow communication

within the nervous system to actually take place we're going to focus most of our

attention in this lecture on neurons themselves the other type of cell that we won't

spend very much time talking about but I just want to make sure that we're all familiar with it and aware are going to

be glial cells a glia cell are going to be cells that are found throughout the nervous system and what these do is they

provide various types of support for neurons right so neurons are going to be kind of the stars of our communication

system within the nervous system Glee are going to be more of the support network for the neurons

glia literally means glue what glial cells do is they do things like Supply nourishment to neurons they remove the

waste products that are created by neurons and they also provide insulation around many of the axons of the neurons

these glial cells are going to be smaller than neurons but they outnumber neurons about ten to one so they're

smaller than neurons but there are a lot more of them these glial cells are going to account

for approximately 90 percent of the actual brain volume this is an image that we'll see a couple

of times today as we talk about this topic of communication within the nervous system the primary thing that I

want you to focus on is going to be that this is going to be a network of neurons that are all connected and so what we'll

be talking about and one of the things you'll be responsible for knowing for quizzes and exams will be a bit about

the structure of the neuron and how the neurons are communicating with each other so for example we'll start looking

at some of these structural elements like these are dendrites here that are leading to the Soma the cell body and

then this is an axon that's then leading away from one neuron into another one and there's this sort of insulation

called myelin sheathing along the axon to help the signal the conduct along the length of the Axon so we'll be talking

about all of those different parts as we kind of move through and begin learning more about the structure of neurons

so let's start by talking about the parts of the neuron so they're going to be three parts that

we're going to focus on the first is going to be the dendrite dendrites are parts of the neuron that are specialized

to receive information right so in addition to knowing that dendrites were one of the three parts you'll also be

required to remember that what the dendrites are doing is they're receiving information from other neurons

so they receive information from other cells in some cases thousands of other cells right so if we think about our

brains there's this complex web of neurons right lots a lot of connections going on between these neurons first of

all there are a lot of neurons and also each neuron can be connected with up to a thousand other neurons so there's

tremendous complexity what the dendrites are doing is they're receiving information from other neurons

the second structure of the neuron that we're that you need to be familiar with is going to be the Soma or cell body

this is going to contain the cell nucleus as well as much of the chemical Machinery that's common to most cells

right so Soma is Greek for body the final part of the neuron that we need to be familiar with is the axon the

axon is going to be a long thin fiber that transmits signals away from the Soma to other neurons where the muscles

or glands axons can be quite long in some cases several feet and they may Branch off to communicate with a number

of other cells so as we go through and as we talk about this process one of the thing that's important one of the things

that you'll be required to remember is that when you think about the flow of information through the neuron

information comes in via the dendrites right the dendrites are receiving information the Soma then integrates

that information right it's kind of making sense if you will in a very simplistic way of the signals that are

being received by the dendrites then the axon is going to be responsible for transmitting the signal away from

the Soma toward other receivers other neurons or muscles or glands right so the flow of information goes dendrite

Soma axon right so information comes into the dendrites is processed by the Soma and then is transmitted along the

axon to other neurons so one of the things also that's crucial here is that the as information is

traveling along the axon there's something called myelin sheathing which is an insulating material that encases

some axons right so these are going to be glial cells like we were talking about previously what this myelin

sheathing does is it's a sort of fatty coating that basically is going to speed up transmission along the axon now this

is important for a number of reasons one is that in a perfect world right you want information flowing along the axon

as quickly as possible so for example let's let's let's talk about the idea of of perception so for

example when we're seeing the world around us as we look out at the world what's really happening is that light is

passing through our eyes and stimulating receptors at the back of the eye right from that point what's happened is in a

series of neurons or communicate or basically communicating that information to the back of our brains where it's

actually being processed what we want is for that information to make its way from the back of our eye right so the

place the back of our brain and the occipital lobe as quickly as possible so that we can process information and see

things as close to real time as possible right now one of the kind of weird things to think think about is that what

we're actually seeing is slightly delayed from what is actually going on the world around us now the information

travels very very quickly right but there's still a very tiny delay right as we're processing visual information

right it's a little old right it's it's just you know fractions of a second right but we're just a tiny bit out of

sync right with the world around us now what happens is with Mile and Shibu is it's helping speed up that signal right

it's helping conduct the signal along the length of the Axon and so it's speeding up this process which is great

that's what we want right we want perceptual information to be processed as quickly as possible when we send a

command to our body for example if you want to reach over and pick up a bottle of water right you want that information

to flow as quickly as possible Right myelin sheathing helps with that there's a condition known as multiple

sclerosis which involves a loss of muscle control and the cause of multiple sclerosis is the degeneration of myelin

sheathing for example if you want to have kind of a better more concrete idea of what myelin sheathing does if you

think about your phone charger right so the cord that you plug into the electrical outlet to charge your phone

it has this coating this rubber coating along it along the length of the of the charging cord and what that does is it

conducts the signal right it conducts the electricity so it can reach your phone but if you scrape away some of

that rubber coating what can happen is you can get shorts where uh the signal the electricity may not make its way all

the way to your phone the same sort of idea applies here with the myelin sheathing that encases our axons when

the myelin sheathing is in place what it allows the signal to do is to move more quickly by kind of jumping across right

these little insulated areas and basically preventing the lost signal that is what happens with multiple

sclerosis or MS another bit of terminology we need to be familiar with are terminal buttons

terminal buttons are small knobs at the end of the axon which secrete chemicals called neurotransmitters

neurotransmitters are chemical Messengers that may activate neighboring neurons

when we're talking about this idea of how information is communicated across neurons it's an electrochemical process

right we call it an electrochemical process because within the neuron we can think of it as being primarily

electrical now this will be even more complicated in a little while as we continue talking about this process

because even the electrical process within the neuron has chemical components to it so we'll come back to

that but we can think about it in the simplistic way for the moment as being an electrical process within the neuron

however there's a little bit of a gap that we'll talk about in a moment between neurons so when one neuron wants

to communicate with another neuron it has to release these chemical Messengers called neurotransmitters that travel

across these little gaps between neurons and so when we talk about the idea of neural transmission being an

electrochemical process we're talking about it being an electrical process within the neuron and then being a

chemical process between the neurons as we'll go into more detail about as we continue today

so a synapse is going to be the junction where information is transmitted from one neuron to another the synapse is

going to be the space between the terminal button of one neuron right the presynaptic neuron and the dendrite of

another neuron the postsynaptic neuron right so the synapse is going to be that Gap we were talking about right a

microscope a microscopic little space between the presynaptic neuron and the postsynaptic neuron right the

presynaptic neuron is the one doing the communication right sending the signal releasing neurotransmitters that float

across the synapse and the postsynaptic neuron is the one that's receiving the information so the neurotransmitter

floats across the synaptic gap and it binds with receptors on the postsynaptic neuron right the dendrite of the

postsynaptic neuron so let's go back and take a look at this image that we saw earlier now that we

have a bit more terminology and we've talked a bit about how these neurons actually function right so let's start

here in in the background here we can see the dendrite for this neuron so information would be coming in through

the dendrites because this neuron it within that information would then be processed by the Soma if the neuron was

then going to fire was going to get emit a signal of its own that signal would then travel along the axon to where it

would then reach the terminal buttons here at the end of the axon little neurotransmitters would be released it

would travel across to bind with receptors on the dendrites of the next neuron right and then the process starts

all over again in the next neuron in this little sort of chain right if you've ever played with

dominoes and set up a series of dominoes and knocked one over and watch each domino fall into the next one that's

sort of similar to What's Happening Here with neural transmission right one neuron is receiving information so

another Domino falls into it if you will causing it to then send the signal of its own causing it to fall over and and

communicate with the next Domino right the next neuron in this case uh also we talked about the idea of

myelin sheathing and here we can see the myelin sheathing which is going to provide insulation so essentially the

signal is going to kind of jump along the length of the axon which helps speed it up and increase the the clarity of

the signal so it isn't being diluted and taking a lot longer to travel along the axon so again what we want with neural

transmission is we want Fidelity right we want to make sure that's trans that the information the signal right is

being sent on to other neurons but we also want speed right we want these TR we want these signals to be transmitted

as quickly as possible right so that so that what we're experiencing so for example when visual information is

coming into our eyes we're processing that as quickly as possible when we send a command to our arm into our hand to

grab a bottle of water right we want that command to be followed very quickly rather than having a delay or something

of that sort so let's talk more about the electrochemical beginnings of these

neural impulses right so what happens when a neuron is stimulated right what is the nature of the neural impulse that

moves through the neuron right we've already started addressing this but let's go into a little more detail

so Hodgkin and Huxley uh in 1952 were working with Squid axons the reason they were working with Squid axons rather

than human axons is because uh squid axons are much much larger and thicker right than human axons still they're

only about as thick as a human hair but still much easier for people to work with and to try to understand what's

going on because the same ideas about how information is Flowing along the squid axon can then be applied to human

axons as well what a Hodgkin and Huxley discovered is that the neural impulses are actually

rather complex electrochemical reactions what's happening is there are fluids that are inside and outside of the

neuron right containing charged particles called ions right positively charged ions like sodium and potassium

are good examples of positively charged ions and negatively charged ions like chloride they're flowing across the cell

membrane at different rates creating a negative charge inside the cell there's something called a resting potential of

a neuron right so this is what's what's what's going on when there isn't any sort of signal being transmitted to a

particular neuron right when it is at rest right a resting potential is a stable negative charge right when the

cell is inactive great and the resting uh potential of neurons is about negative 70 millivolts right so there's

this very small negative charge that neurons have when nothing is kind of going on right when there isn't any sort

of information being communicated through a particular neuron when it's just kind of resting and not being

stimulated it's resting electrical charges negative 70 millivolts right so a small negative charge

right I've mentioned previously that there won't be a lot of numbers that I'll ask you to remember but this will

be one of them negative 70 millivolts be fair game for quizzes and exams so be sure you remember that that's the

electrical charge that's the resting potential for neurons we also want to talk about something

referred to as the action potential right so this will be really important so as you're going through and studying

make sure that you're very clear on how Action potentials work so a neuron is going to remain quiet

meaning no messages are being sent it's going to stay at its resting potential until it is stimulated right by

connected neurons right or other sorts of signals that we'll talk about later what happens is when this sort of

stimulation occurs right this causes a cell membrane to open briefly when the cell membrane opens this allows

positively charged sodium ions to flow into the cell and what happens as a result of that is

that for a brief flicker of an instant right the neurons charge becomes less negative right and in some cases becomes

positive and what this does is it creates something called an action potential

so an action potential is going to be a very brief shift in a neuron's electrical charge that travels along an

axon right so again we've got this axon right this long kind of fibrous tube and we can think about this action potential

kind of traveling along the axon kind of like a spark like traveling along a trail of gunpowder right or like if

you're setting off fireworks on the fourth of July when you when you like the fuse right you can watch the the

flame right the little kind of flicker of flame travel along the fuse right that's similar to what's happening with

the axon the action potential is traveling along the Axon so here's an idea of of how this neural

impulse or action potential is is working so again when a neuron is at rest when there isn't any sort of

stimulation it's at its resting state which is about negative 70 millivolts right as we've talked about previously

right so up here we see a neuron that isn't receiving any sort of information it's not being stimulated right it's

going to stay at roughly right around negative 70 ml right negative 70 millivolts

however when a neuron is receiving information and it's emitting this action potential the action potential is

going to travel along the axon right as the action potential is going to pass through areas of the axon what it's

going to do is it's going to be registering as this sort of action potential so what we'll see is that it

goes from this resting state of negative 70 millivolts to where it now begins to increase becomes less negative right in

this case actually becomes positive right for a brief flicker of a second and then it becomes negative again and

eventually settles back into its resting state of about negative 70 millivolts right we can think of this brief surge

right of less negative charge or even positive charge that's us tracking the action potential along the length of the

axon right this is going to be like that flicker a flame traveling along the fuse or the flame traveling along the trail

of gunpowder for example okay so let's decompose what the action potential actually looks like right so

we talked earlier about the fact that we start off with a resting potential negative 70 millivolts however now as

the charge begins to increase right as the Action Insurance traveling across right part of the axon what we're seeing

is the charge becomes less negative right that each of our neurons will have this uh threshold of excitation around

negative 55 millivolts right for many and so what happens is once the uh once the polarization right surpasses this

threshold right this threshold of excitation right it's going to fire right it's going to continue

transmitting this information on along and so what's happening is once it gets past that right it's going to fire right

it doesn't matter if it goes well past that or just barely surpasses it all that matters is that it surpasses this

threshold right in this case right the uh the neuron is the action potential is going far beyond that right here's our

peak of the action potential it begins to repolarize it then starts to come back down becoming more negative it's

then going to go past the threshold of excitation and it will then briefly become even more negative right the

negative 70 millivolts right so for a brief period of time this is referred to as hyperpolarization when it becomes

actually more negative than it normally is eventually it will kind of settle back into its normal resting state of

negative 70 millivolts right so a couple of crucial pieces of information I just want to make sure

everyone's clear about one we've got the resting potential negative 70 millivolts as the action potentials begin in the

form what's happening is it's going to become less negative and at some point if it's if it exceeds right this

threshold of excitation the neuron will emit the signal right after some period it will then begin to come back down and

eventually stabilize back to negative 70 millivolts again so after the firing of an action

potential the membrane that allows sodium into the cell closes it then takes a bit of time before the

neuron can fire again right this is referred to as the absolute refractory period so it's going to be the minimum

length of time after an action potential is emitted during which another action potential cannot begin right so

essentially the neuron has to have a brief period of time when it's kind of recovering right from the activity of

creating the action potential one of the important things to remember is that neurons are going to operate on

something called the all or none law neurons either fire or they do not fire right you can't partially fire a neuron

right you also can't really really hard fire a neuron right just like we'll use the analogy of a gun for example right

you can't kinda half shoot a gun right either you pull the trigger hard enough right to trip the firing mechanism and

you cause the gun to fire or you don't right the same thing happens for neurons right for a neuron they're either going

to surpass right that threshold of excitation which would be as the amount of pressure

you'd have to exert on the trigger of a gun to trip the firing mechanism or you don't

right if you surpass that threshold of excitation the neuron is going to fire right it doesn't matter how far you go

past that right kind of like if you're trying to fire a gun if you really slam the trigger of the gun the gun doesn't

care right once you've gone once you've pulled exerted enough pressure on the trigger to trip the firing mechanism the

gun's going to fire but the bullet isn't going to come out of the barrel any faster if you really slam the trigger or

if you just barely squeeze it enough to trip the firing mechanism same thing happens for neurons it's an

all or none sort of principle right the neuron either fires and emits an action potential or it doesn't right you can't

have a really strong action potential the action potential is what it is right it's released or it's not

right now what's important to keep in mind with regard to this is that neurons can communicate stimulus intensity right

so for example if you put your hand on something that's just kind of sort of warm right neurons are going to be

firing their neurons in the tips of our fingers that are sensitive to temperature

so those neurons are going to start being stimulated right they'll start sending signals but each action

potential is going to be an all or none sort of sort of deal right either the actual is going to be released or it

will not be released right as the intensity of the stimulus increases right so it's the thing that we're

touching gets hotter and hotter and hotter right the way that our neurons are communicating the intensity of the

stimulus is by the rate of their firing right so it isn't that the action potentials are getting larger and

stronger they're becoming more rapid right and that's how we get the idea that's how we detect stimulus

intensities by the rapidity right of the firing right now again as we were talking about a moment ago there's a

refractory period right for each neuron so it takes a little bit of time right for the neuron to kind of recover right

in the same way that if you were firing a gun right guns can't fire uh campfire consistently right so they can't fire in

a seamless fashion right even a machine gun right an automatic machine gun right there are brief pauses right as the

bullets are firing right so it isn't like a a perfectly steady stream of bullets traveling out of the barrel of

the gun rather it takes a moment right for the next bullet to be put into the chamber right same sort of idea applies

to the way in which our neurons work right there are these brief refractory periods but our our neurons recover very

very quickly right so there can be pretty rapid firing it's this isn't perfectly continuous right each neuron

needs a fraction of a moment to kind of recover right in that moment is referred to as the absolute refractory period

we've mentioned the idea of synapse but let's talk a little bit more about Synapse in the synaptic cleft right so

the synaptic cleft is going to be that microscopic gap between the terminal button of one neuron right the

presynaptic neuron right and the cell membrane of the dendrite of the other neuron that's receiving the signal right

that's the postsynaptic neuron chemical signals are going to cross the synaptic cleft and they're going to

activate the electrical signal right in the next neuron right that's going to be again this electrochemical process right

so we have the electrical process playing out within one neuron when that signal reaches the end of the neuron the

terminal button at the end of the axon on the presynaptic neuron it's going to release these chemical Messengers right

neurotransmitters that will crack that will travel across the synapse right and bind with receptors on the postsynaptic

neuron again presynaptic neuron the the neuron before the synapse are it's going to

release neurotransmitters these neurotransmitters are chemicals that transmit information from one neuron to

another there are a number of neurotransmitters and we'll talk about some of them a bit later

synaptic vesicles are going to be small sacs that within the presynaptic neuron that will hold neurotransmitters and

when these synaptic vesicles are activated they release the neurotransmitters into the synapse the

neurotransmitters and Float across the synapse and bind with receptors on the dendrites of the postsynaptic neuron

right so the postsynaptic neuron is really important because it has receptor sites right that are going to recognize

and respond to certain types of neurotransmitters okay so here's an image of the synapse

that we were just talking about so here's our original image we talked about earlier but now let's kind of zoom

in on this little location right here where we can see the axon of the presynaptic neuron right the terminal

button here coming very very close to being in contact with the dendrite of the postsynaptic neuron down here

the this is going to be the axon again of the sending the presynaptic neuron we have the neural impulse right the

exponential traveling along the axon these are synaptic vesicles which contain neurotransmitters of a certain

type when The Accidental reaches the terminal button it's going to trigger the release of these synaptic vesicles

which then float down to the end of the terminal button they release their neurotransmitters right these little

molecules right into the synapse right the gap between the presynaptic and postsynaptic neuron

these neurotransmitters and flowed across the synaptic cleft and they some of them will bind with receptors on the

dendrites of the postsynaptic neuron one of the important things to remember about this process is that the

transmitter is going to fit into certain receptor sites right so we're going to talk about this sort of lock and key

sort of mechanism right so we can think about the neurotransmitters as being the keys and the receptors being the logs

right so certain neurotransmitters are going to fit into certain receptor sites if a transmitter neurotransmitter

doesn't fit into a particular receptor site it's usually then going to kind of float back into the synaptic cleft

without doing anything right because it hasn't gone into the right block right similar if you go home to your apartment

tonight and maybe you're really busy for some reason and you accidentally go to your neighbor's apartment and you put

your key into your neighbor's lock hopefully what will happen is that your lock will not your key will not unlock

your neighbor's door right if so you've got a problem at your apartment complex but hopefully your key is going to be

unique to your the lock on your door right same sort of idea here where what we're looking for is for the

neurotransmitter to only bind with certain types of receptors right and so when these

neurotransmitters float across and binds then this is going to send information right to the postsynaptic neuron right

so here within the presynaptic neuron we have an electrical process this then shifts to a chemical process between the

two neurons and as these neurotransmitters are are bonding with receptor sites on the pre on the

dendrites of the postsynaptic neuron this is then potentially starting right the electrical process all over again in

the postsynaptic neuron so let's uh talk a little bit more about this process we went through this

briefly but we'll kind of go through it in a more organized fashion so to begin with in the presynaptic neuron we have

the synthesis and storage of the neurotransmitter molecules uh in synaptic vesicles which we can see here

these little sacs that contain neurotransmitters when The

Accidental travels down along to the terminal button it then signals the release of the neurotransmitters through

the synaptic vesicles so the synaptic vesicles flow down they release the neurotransmitters into the synaptic

cleft next up we see The Binding of the neurotransmitters to the receptor sites

on the postsynaptic membrane of the of the postsynaptic neuron like the dendrite of the postsynaptic neuron

after a brief flicker of time goes by right these neurotransmitters are inactivated by enzymes or they're

removed they Drift Away uh from the receptor sites then we see this reuptake and reabsorption process where the

neurotransmitters are then essentially kind of sponged or vacuumed up by the presynaptic neuron so that they can then

be repackaged in synaptic vesicles to either be reused again or at least kind of recycled for parts in some ways

so one of the important things just to keep in mind is that once neurotransmitters have been released

into the synaptic cleft or synaptic gap right and they stimulate and they bind with receptors on the postsynaptic

dendrite right after a brief period of time basically they don't simply continue stimulating the the

postsynaptic dendrites permanently rather after a brief period of time their release from those receptor sites

and either they are they are they either drift away they're broken down or they're reabsorbed into the presynaptic

neuron right and this reabsorption is called the reuptake procedure this is when the neurotransmitter from the

synapses absorbed back into the axon terminal from which it was released so if it's still in in good shape it can

simply be re-released or it may be recycled kind of broken down and used for the creations and the synthesis of

other neurotransmitters of the same type so what's happening on the postsynaptic neuron right when these

neurotransmitters bind with the receptor sites so it creates something called a postsynaptic potential right this refers

to the voltage change of the receptor site on the postsynaptic cell membrane right the dendrite right we talked about

dendrites receiving information right this is how they're receiving that information the neurotransmitters float

across the synapse bind with receptor sites right causing this postsynaptic potential right this is going to be due

to that brief binding that a neurotransmitter to the receptor site these postsynaptic potentials are not

all or none right so unlike an action potential right the postsynaptic potential can vary in degree right what

these things are doing is they're changing the probability right of the postsynaptic neuron actually firing

right emitting an action potential there are two types of messages that are sent from one neuron to the next

one type of message is going to be an excitatory postsynaptic potential right so this is going to be a positive

voltage shift that increases the likelihood of firing an action potential right going back to our gun analogy from

earlier right this would be like kind of exerting a little more pressure on the trigger of the gun right so an

excitatory postsynaptic potential is like squeezing a little bit more on the trigger

the other type of message can be an inhibitory postsynaptic potential this is going to be a negative voltage shift

that decreases the likelihood of firing an action potential right so going back to our gun analogy an excitatory

postsynaptic potential is squeezing on the trigger right exerting more force on it making it more likely to fire

an inhibitory signal would be kind of like some way putting their finger behind the trigger and pushing against

that Force right and so what you can probably guess is that if there's a if there are a lot of excitatory messages

right if the pressure squeezing the trigger right is stronger than the inhibitory signals that are pushing

against right the the cell will fire right the neuron will emit an action potential if the post if the if the

postsynaptic potentials that are excited to worry far outweigh those that are inhibitory right or at least if the

excitatory messages are strong enough right they can reach that threshold of excitation we talked about previously

so one neuron may receive signals from thousands of other neurons and in turn right a neuron can pass on messages to

thousands of other neurons right so as we were talking about previously there are tremendous numbers right of neurons

in our in our brain and our spinal cord what we then have is not only are there tremendous numbers but also each of

these neurons can potentially be receiving information from up to thousands of other neurons and also

sending information to thousands of other neurons which is part of what makes our our nervous system so complex

is first of all the large number of neurons and then the tremendous complexity of the of the connections

between those neurons so what this does it requires that neurons integrate the signals that it

receives but so we're deciding whether to send an action potential and I say deciding in in the simplest uh possible

terms right it isn't like each neuron has like a little homunculus in it that's really making decisions right I

don't mean to suggest that at all rather what's happening is going back again to our simple idea of the the gun analogy

it's sort of like the the trigger the gun doesn't decide to fire right either there is enough pressure exerted on it

that it trips the firing mechanism and the gun fires or that doesn't happen right the same thing happens here with

our neurons right the postsynaptic potential simply add up right and the firing of an action potential is based

upon the weighted balance of the inhibitory postsynaptic potentials right and the excitatory ones right as we were

talking about if there are a lot of excitatory postsynaptic potentials relative to the inhibitory ones right

and if that threshold right if the amount of postsynaptic potential kind of raises to it comes up to a certain level

where it actually creates right surpasses that threshold of excitation the action potential is triggered right

in the same way that a a gun fires if the pressure on the trigger is strong enough to trip the firing mechanism same

sort of idea let's briefly talk about neurotransmitters so neurotransmitters

play a vital role in everything from muscle movements to our moods and our Mental Health

these neurotransmitters are going to work at specific synapses in this kind of lock and key mechanism that we were

talking about earlier one of the other things that we want to be familiar with in terms of terminology

will be the idea of Agonist and antagonist and Agonist is a chemical that mimics neurotransmitter action so

for example the drug morphine is going to mimic endorphins which are neurotransmitters right the reason why

morpheme is such a powerful drug is it's similar enough that it can basically trick our bodies into thinking that it's

that it's going to function like endorphins so basically it can bind with the same sorts of receptors right that

endorphins combined with and essentially trick our bodies into thinking that endorphins are binding with these

receptor sites there are also antagonists which are going to be chemicals that

oppose the action of a neurotransmitter so for example there's a chemical called atropine that blocks acetylcholine

receptors right so it prevents acetylcholine from doing its job and binding with receptor sites right so

antagonists work in a couple of ways one of them is by simply kind of blocking these receptors right uh going back to

the idea of the the Locking key sort of mechanism we could think about the idea of your neighbor if your neighbor really

disliked you for some reason maybe they sneak over to your apartment door while you're gone one day and they put like

gum or something uh in the in the lock right that would essentially kind of function kind of like an antagonist

because even though the gum won't actually cause the lock to unlock right it can it can prevent your key from

actually getting into the lock right kind of like atropine does for acetylcholine blocking The receptors

there are 15 to 20 neurotransmitters are known with others being discovered uh the complexity of the way in which these

things function in some cases make it difficult to know if certain uh chemicals really are functioning as

neurotransmitters or not and this is something we'll come back to and talk a little bit about later

so here are some common neurotransmitters and some of their basic functions we mentioned

acetylcholine a few moments ago this is released by motor neurons that control our skeletal muscles it's involved in

things like the regulation of attention arousal and memory uh some a keto some acetylcholine receptors are stimulated

by nicotine which is part of why when people smoke cigarettes for example that have a lot of nicotine in them it can

actually be very arousing right it actually increases arousal levels another neurotransmitter that would be

fair game for me to ask you about is dopamine dopamine contributes to control a voluntary movement and pleasurable

emotions decreased levels of dopamine are associated with Parkinson's disease overactivity that dopamine synapses is

associated with schizophrenia and things like drugs like cocaine and amphetamines Elevate activity at dopamine synapses so

notice here that we've got this idea that people who experience schizophrenia which is a psychological disorder that

we'll talk about later in the semester schizophrenia is characterized by an array of symptoms some of the symptoms

that are often associated with schizophrenia involve things like having hallucinations having sensory

experiences that aren't real seeing things hearing things feeling things that aren't really there or experiencing

delusions false beliefs about things like believing that the police are are are surveilling you when they really

aren't now notice this comes about through associated with increased activity and

dopamine in certain synapses cocaine and amphetamines also increase activity at dopamine synapses one of the

things that can happen with really acute levels of cocaine intoxication for example is that it can simulate some of

the symptoms of schizophrenia right you can get this kind of cocaine-induced brief psychosis right where individuals

may start having symptoms that are similar to schizophrenia because of the increased

level of dopamine activity right caused by things like cocaine or amphetamine use

another neurotransmitter that would be fair game would be norepinephrine it contributes to the modulation of mood

and arousal cocaine and amphetamines also increase activity at norepinephrine and synapses as well

serotonin is another neurotransmitter it's involved in the regulation of sleep and wakefulness it's also involved in

eating and aggression activities as well abnormal levels of Serotonin May contribute to depression and

obsessive-compulsive disorder many of the medications that are used to try to treat depression for example work to

increase the levels of Serotonin for example we'll talk later about the idea of something called selective serotonin

reuptake Inhibitors these ssris are a type of drug that work to basically prevent the reabsorption of Serotonin

and keep more serotonin and synapses so they're available so it's available to bind with receptors on the postsynaptic

neurons right Prozac and other similar antidepressant drugs affect these sorts

of Serotonin circuits uh Gaba is another draw another neurotransmitter it's going to uh it's

going to be a very widely distributed inhibitory transmitter uh drugs like Valium and other anti-anxiety drugs uh

tend to work at Gaba synapses and the last neurotransmitter we'll talk about are endorphins these are going to

resemble opiate drugs both in their structure and their effects they're going to contribute to pain relief as

well as some pleasurable emotions if you are for example if you're a runner and if you've ever run for a long enough

period of time that you kind of you've gone through being really fatigued and tired and you kind of get your second

when you kind of break through that runner's wall right you kind of get a runner's high if so that's probably due

to the release of endorphins which are going to be neurotransmitters they're going to function function like opiates

causing pain reduction and this kind of euphoric feelings