okay so this is a continuation of our discussion on chapter 11 the fundamentals of the nervous system we're going to kind of merge together all of the concepts that we've already been talking about especially the physiology of how graded potentials are created and how that gets converted to an action potential and then ultimately leading towards this concept of a chemical synapse okay so the next slide is going to look a little scary this is something I put together on on drawing tablet something similar to what I would have done in a face-to-face setting except I would have done it piece by piece on the board and kind of walked you through the entire process and so you wouldn't have seen the entire big picture image all at once but for the sake of time I am I'm just gonna show you the entire big big big picture and I'm going to kind of dissect it and work with you piece by piece and then show you how this all kind of flows together okay so just kind of focus on the regions that I am discussing and try not to wander away and focus on other regions of the of the slide so just kind of follow the transition with me okay you guys ready all right let's do this here we go so this is the chemical synapse okay and there's so much that goes on here but then some possibly have already been talking about so I just kind of want to explain a few things here right off the bat okay so I have my new Ron right there so you should be able to recognize this soma and those are the dendrites okay and here is the axon hillock that's where the action potential is created and then you see the axon process extending past the axon hillock towards the distal endings these are my terminal branches or leading to the axon axon terminals okay so we've been talking about graded potentials and action potentials it's gonna add a few more details to this first before we move on to our continuation of you know the discussion of what's a chemical synapse okay so we let's kind of recap a few things okay so we already said that the dendrites and the soma these are the receptive regions after neuron whereas the axon process is the conducting region and then you've got your terminal branches and especially your axon terminals those would be the secretory regions and they secrete neurotransmitters okay so let's start on the left with the dendrites okay so when the dendrites respond to some kind of stimulus okay and now this the soma the plasma membrane of the soma can also respond to that stimulus so these are both receptive really for the sake of simplicity I'm going to focus on on a dendrite right here so if I was to zoom in on one cross-sectional area of a dendrite okay I'm saying that based on our discussion so far right this is where whatever the stimulus is right the stimulus could be we said pressure touch vibration stretch in skeletal muscle it could be what else it could be temperature changes pain anything like that it could be it could be a special sense organ so it could be like information related to light energy or auditory information chemicals dissolved in your food chemicals dissolved in in orders that you that you smell any of these could be stimuli right so in response to any of these stimuli the dendrites would convert these stimuli by the process of transduction into a graded potential and a potential is a voltage is a membrane voltage right and there were two different types of great tensions that we talked about just a while ago okay so here on the bottom you're seeing the classical action potential graph okay so here's my dendrite before it received any stimulus it is at resting membrane potential negative 70 millivolts okay in response to this stimulus right it's two different types of stimuli that can be received one could be excitation the other could be an inhibition kind of a signal right so if it was an excitation stimulus that would result in a graded potential that results in depolarization of the plasma membrane of that dendrite correct so again so this is going to result in depolarization you can see all of these orange graphs here or these orange tracings these are just to kind of show you that this is depolarization meaning you're changing that RMP towards a more positive voltage meaning you're moving it towards your threshold towards zero towards that positive 30 basically so you're moving it towards a more positive voltage and of course depending on the strength of the stimuli you could have different degrees of intensity of this graded potential or off this depolarizing voltage right we called this epsp excitatory postsynaptic potential so any depolarizing grady graded potential that moves a voltage of the dendrite or that received them receptor region towards a more positive voltage would result in an epsp I want to be clear there are different types of graded potentials typically I'm focusing on postsynaptic potentials because I'm leading towards a chemical synapse here so typically if this greater potential was generated in this case and in the inner dendrite if it was generated in response to a neurotransmitter okay or chemical then it would be a postsynaptic potential and I'll tell you why in just a little bit so bear with me for right now this is an epsp an excitatory postsynaptic potential so excitation would be a depolarization event where you're making the plasma membrane of the dendrite of the soma less negative moving their RMP to a threshold so we got that correct okay now the other greater potential that could be created is an IPS P this is because of a hyperpolarization greater potential and what do I mean by that this is where you're making the plasma membrane voltage more and more negative so I'm moving it away from threshold I'm making it more negative like a negative ad negative 90 or something like that right and the degrees of that ipsp will depend on the strength of the in a bitter e stimulus that's been received by that then by okay now it's quite clear that the goal is to create a greater potential in that dendrite to where you are making that voltage move towards that threshold voltage and in this case I'm going to go with negative 55 millivolts okay so clearly an IPS be all of these tracing shown here in purple they are moving the wrong direction and they are not moving to a threshold they're moving away from threshold if you're moving away from threshold then you cannot generate an action potential with that kind of a graded potential that's why I PSP that's an inhibitory postsynaptic potential because it has no potential to convert to an action potential okay there is my orange tracings here those are depolarizing voltages that's making the voltage more positive moving it towards a threshold voltage moving it towards i- 55 which is which is why this is called an epsp an excitatory signal which if it is strong enough if it keeps going higher and higher right if it reaches that red line that threshold voltage then that epsp will convert to what to an full-blown action potential that all-or-none event that we were talking about just a while ago okay so now let's talk a little bit more about these graded potentials and what channels need to open what ions need to move in and out of this neuron at this site namely the dendrite okay now remember denne right but but I hope you understand that receptive regions also exist on the plasma membrane of the cell body as well but the simplicity I'm just gonna go with dendrite okay so we need to talk about what channels need to open here on the plasma membrane of this dendrite and what ions need to move back and forth to bring about either a depolarization event which translates to an epsp or a hyper-polarization event which obviously translates towards an IPS B okay so that's kind of what I have drawn up here okay so if I was zooming in on a cross-section of the plasma membrane of this region of the dendrite so I have up here here's a dendrite here's the inside of the dendrite this is inside of the neuronal dendritic process nears the outside okay and so okay so well this dendrite was not excited before word received that stimulus remember it was sitting at RMP right resting membrane potential which is your negative 70 millivolts in this state what happened to the plasma membrane well it was polarized if you recall it was mostly negative on the inside and positive on the outside right okay that was polarized but then in response to this stimulus okay let's say let's first start with an epsp in response to this stimulus if it was if it brought about depolarization okay what channel's needed to have opened in order to move that RMP from negative 70 to change it to upset that RMP to where it moves towards your threshold voltage what channel would need to open in this case and that's what you see here on the far right okay so this is if this channel opens this is a this is a sodium channel okay when this channel opens okay actually this is a simultaneous sodium and potassium channel when this channel opens sodium enters the cell and potassium leaves the cell but in this particular case more sodium enters the cell then potassium in the south bottom line is this you are introducing positively charged sodium ions inside of this dendrite remember that the at RMP the inside of that dendrite was at a negative charge right but now you're introducing positively charged sodium ions inside that dendrite so you're sitting at a negative charge if you keep flooding the inside of the dendrite with positively charged sodium ions what's gonna happen to that voltage well it's gonna move from that negative voltage gonna become less negative or in other words more positive and that's why you're seeing these epsps does that make sense to you so introduction I mean opening up these channels is a simultaneous sodium and potassium channel but since more sodium positively charged sodium ions are entering the dendrite that's going to make the interior what more positive and that's why you start to see it creep upwards towards that threshold voltage okay and depending on the strength of this stimulus this excitation signal that would give you different degrees or different intensities of that epsp okay does that make sense so that's on the right here this is a dendrite and this is how you would create an epsp by opening up a channel which allowed so more sodium to come into the cell okay now I want you to think about this okay now why did this channel open okay and then this is where we go back to the types of channels is this a voltage-gated channel or is it a chemical gated channel for a chemical gated channel some kind of chemical like a neurotransmitter like a ligand needs to actually bind to this channel to open it up channels that create an epsp or an IPS P or any greater potential for that matter would be chemical gated channels or ligand gated channels so in response to the stimulus right a neurotransmitter is released on the outside here on the outside of these dendrites and then the neurotransmitter then binds to one of these types of channels okay so therefore it has actually has to bind to these channels and that's why this is called a chemical or a ligand gated channel and upon binding of that neurotransmitter then these channels would open up so let me kind of recap right quick with the with the epsp so in the case of an epsp a depolarization signal was created because a ligand bound to that channel right there opening it up there was more sodium that entered the dendrite making the interior of the dendrite much more positive and that's why you move that voltage towards a more positive number moving it towards that threshold voltage and that would be an epsp okay so if it was a different type of stimulus like an inhibition type of a stimulus right that would result in the release of a different type of neurotransmitter a different chemical right so depending on what type of chemical binds to these channels you could either bring about an epsp or an IPS v so in the case of an IPS we how do you bring about hyper-polarization that would be if a different neurotransmitter bound to either these potassium channels or these chloride channels okay so again think about this we have a dendrite sitting at our MP so the interior is negative okay now what happens if a ligand binds afar if neurotransmitter or a chemical binds to this channel this potassium channel and potassium which is positively charged these ions leave the cell does that make sense the leaves the dendrite lots of positively charged ions makes the interior more negative and that's why you see this hyper-polarization voltage where the RMP becomes even more negative now alternatively you can also bring about an IPS B by opening up these chloride channels which allows entry of CL - which is a negatively charged ion so again introducing more negatively charged ions to the inside of the dendrite obviously makes the voltage even more negative okay so again I want to reiterate the case of graded potentials to bring about depolarization which is an epsp or hyperpolarization which is an IPS P these channels need to bind some specific chemical or a neurotransmitter okay again if it was a neurotransmitter that brought about an excitation kind of signal that's going to depolarize the the dendrite bringing about an epsp or if it was an inhibition stimulus then it would bring about hyper polarization or an IPS v but obviously the channels are different in the case of an epsp it's this one channel here on the right and in the case of ipsp it could be these two varieties so either potassium leaving or chloride entering into the template okay so that's how you create a graded potential and the different channels that are involved in this process now I do want you to remember these are all chemical gated channels in the case of greater protections okay now let's assume okay let's just assume we have created an epsp so here is my greater potential traveling down this dendrite now remember this has to go all the way to the axon hillock right so if this epsp when it arrives at the axon hillock if it was at least at threshold voltage what happens then you would convert this epsp this great potential into what into an action potential correct so you would fire off an action potential at the axon hillock and that's going to then propagate down the axon process all the way down to those terminal endings those axon terminals okay so now what I want to do next is to kind of zoom in on a cross-section of the axon process right there okay so now let's talk about what channels need to open and close with respect to the creation of this action potential so again this part here from RMP to the threshold all of this is basically your greater potential and this has to be your EPS we cannot be your ipsp okay but then once you hit threshold what what causes this further rise which is truly what we call the depolarization phase of the action potential and then what causes this downward return back to the resting membrane potential that would be your repolarization phase so let's examine what these channels look like so if you take a cross-section of the action the axon process okay to bring about depolarization and you already know this we talked about it in in the skeletal muscle physiology and we also talked about it just awhile ago in one of our previous slides as well so for depolarization so here we go this is the cross-section of the axon process the inside and the outside okay so when sodium enters the axon process from the outside when it enters the axon process introduction of positively charged ions makes this voltage even more positive moving it towards the zero and ultimately hitting that positive 30 millivolts at this point when you have hit threshold and you're opening up all of these sodium channels that that's gonna result in the depolarization phase and bringing about the the firing off of the action potential now I do want to point out something here real quick now this sodium channel is this lighting gated channel did a neurotransmitter have to bind to these channels would did a chemical need to bind to these channels in order to open these sodium channels the answer is no because the fact that you hit threshold threshold voltage that's a voltage right reaching threshold would open up those sodium channels and where are these sodium channels this is along the axon process so therefore this is an example of a voltage-gated sodium channel and likewise for the downward return back to RMP this is the repolarization phase in this case see these are potassium channels potassium leaving the cell would result in repolarization this is also a voltage-gated channel right because once you hit that positive 30 that depolarizing voltage is what caused the opening of these potassium channels okay so just to recap your sodium channels would bring about depolarization and your potassium channels bring about repolarization and both of these channels are located along the plasma membrane of the axon process and these channels are all voltage-gated channels there is the channels that you see there bring about an epsp or an IPS P in the case of a greater potential those are located along the dendrites and on the soma and these are all chemical gated channel so there's a clear difference between the channels that are used to create the graded potentials versus the ones that create the action potential okay so let's continue on with this story so when that action potential is is fired or basically triggered and it conducts down the axon process it's going to make its way down to those axon terminals right and then if you think back to the skeletal muscle physiology ok this was exactly where we had you poised at that time it is an action potential traveling down the traveling down to the axon terminal will then make contact with what with the sarcolemma of the skeletal muscle fiber and then if you remember there were several events that occurred at that neuromuscular Junction so that was a neuromuscular Junction meaning it was a junction between what neuro which is a neuron and you run like this okay and the muscle namely the skeletal muscle so a junction between a neuron and an effector in this case the in factor here is your skeletal muscle cells so when you talk about a junction between a neuron and any effector that's called a synapse okay so I don't have it drawn here I don't have the skeletal muscle cell drawn here but what I'm showing you here is a synapse between this neuron and a second neuron right this is the same scenario it's still a synapse it's still a communication a junction between here is the the origin of that action potential and here's the target cell the this case the effector is another neuron and because we're focusing on this because we're talking about the nervous system neuron to neuron communication okay but this is essentially an example of our office and apps and if you remember from what you talked what we discussed with the neuromuscular Junction the same events occur here whether it's neuron to neuron as well and if you recall and I have a slide where we can kind of review this here in just a little bit if you recall what happens here okay there were calcium channels here on the axon terminal these are voltage-gated calcium channels because they opened up in response to this voltage namely the action potential right and then there were little vesicles here on the inside of this axon terminal that were loaded with what chemicals neurotransmitters in the case of the nmj the neurotransmitter that was released into this space here called the synaptic cleft what was that neurotransmitter if you recall it was ACH acetylcholine right and then what happened to that ACH the ACH then bound specific channels here chemical gated channels on what on the cosmic membrane of the of the skeletal muscle it's the same thing that's happening here as well so everything that we talked about here on the dendrites these chemical channels here's the chemical imagine if this was ACH right there that bound to that that channel caused it to open up and there was simultaneous entry of sodium and exit of potassium the same thing is happening here on these dendrites as well so the story repeats itself right so if this if this neurotransmitter that's released into this synaptic cleft was one that depolarized these dendrites over here then it would what it would create an epsp that epsp would then travel towards the axon hillock and if that epsp was at least at threshold voltage what would happen to that epsp you would convert it into an action potential which would then travel along the axon process down to its own axon terminals where you may have what another neuron you may have a little muscle you may have cardiac muscle smooth muscle you may have a gland you may have any different effector but the story is still the same and so what I'm explaining here is a synapse and what am i calling it a chemical synapse because this is a synapse between one cell and a second cell so it's a synapse between two cells so it's a junction between the two cells and what happens in this Junction here in that synaptic cleft is what's secreted neurotransmitters are secreted and a neurotransmitter is a chemical and that's why this is a chemical synapse okay so what I explained here is a chemical synapse as well again in response to certain chemicals where ligand gated channels open either creating an epsp or an IPS v but the propagation I mean creation of a an action potential is dictated by voltage-gated channels and then when you get to the distal endings here of your axon terminals again it's the same thing where you have neurotransmitters released and then again you've got your ligand gated channels on your dendritic ends similar to what we explained over here okay so that's a chemical synapse kind of putting together key concepts here like greater potentials where is it occurring what are your channels that are responsible for this are these chemical gated channels or voltage-gated channels how does that tie in with an action potential and again what type of channels are those and then how did what happens at the distal ends of this neuron okay before I leave this light I want to explain just one more thing here okay so in the case of a synapse now what I'm showing you here is one neuron synapses with a second neuron so this is my synaptic cleft right down here in the middle right this is where the synapse the chemical synapse is occurring so therefore this first neuron before the synapse point is called the presynaptic neuron the second neuron after the synapse point is called the postsynaptic neuron okay and that's why these are graded potentials shown here in pink right six same as these guys right here these are graded potentials occurring in this neuron what is this neuron called a postsynaptic neuron that's why this potential is called an excitatory post-synaptic potential because it is a potential it's a voltage change occurring post synapse on this postsynaptic neuron okay now of course if this wasn't an epsp was an IPS feed still the same thing it's still a postsynaptic potential but it's an inhibition type of potential okay now that we have the big picture we've already introduced the concept of a synapse we talked about a chemical synapse let's kind of go back to some of the slides make sure that we've covered most of these concepts and kind of use it as a rationale to kind of hammer and some of these concepts again okay so a chemical synapse well a synapse in general is is a junction between two cells okay where some kind of activity is occurring and you can so in in our previous slide we talked about two neurons synapse in with with each other so the neuron that is prior to the synapse point is for the presynaptic neuron and the new the second neuron post synapse is called the postsynaptic neuron okay so let's talk about a few different synapse options okay so here you go here is the first neuron this is my presynaptic neuron okay so sorry that would be the axon process and the axon terminals of one neuron and here is the second year on with the cell body and here are my dendrites okay so there are different synapses that are possible ACK so somatic means here's an axon of the the first neuron the piece and happy near on making a synapse point directly on the soma of this postsynaptic neuron that's why it's an acts of somatic synapse what I've been classically explaining is some thing that looked like this the accident Riddick synapse so this is where the axon process of the presynaptic neuron makes contact or synapses with the dendritic processes of the postsynaptic neuron okay now XOXO no synapses are also possible so this is axon to axon between the pre and the post synaptic neurons okay but the most common varieties are accident Reddick and the axis somatic synapses okay so we explain why these are called chemical synapses because in these in these synapse regions chemicals such as neurotransmitters are released and binding of those neurotransmitters to specific receptors on the postsynaptic neuron would result in a graded potential which we call an epsp or an IPS P okay so every chemical synapse will consist of two main parts kind of separated by a synaptic cleft the the first part should be the axon terminal of the presynaptic neuron synapsing with some kind of a receptor region normally this is the dendrite or the soma could also be the axon but normally it's the dendrite of the soma of the postsynaptic neuron okay and of course the two main components are separated by a fluid-filled synaptic cleft it's into this and haptic cleft that chemicals or neurotransmitters are released okay so you all have seen this in relation to the neuromuscular Junction so again the nmj is an example of a chemical synapse okay except there we were talking about a neuron synapse in with the skeletal muscle whereas right now we're focusing on the same thing same same physiology except we're talking about neuron to neuron synapses K so we would have focused on just neuron to neuron so here's my presynaptic neuron that's the axon process ending in an axon terminal right here and on the bottom this is my postsynaptic neuron over here okay so if you recall the details that happened the axon I'm sorry I'm sorry the action potential travels down the Saxon process and it reaches the axon terminal where it opens up these voltage-gated calcium channels and why they voltage-gated because they're triggered by the appearance of that action potential when these calcium channels open up calcium floods the interior of this axon terminal and inside this axon terminal you have basically loaded with these green dots which are my neurotransmitters okay now in the case of the nmj those neurotransmitters were ACH acetylcholine but in the case of a neuron to neuron or neuron to cardiac muscle neuron to whatever the other factors are there actually could be about typically this about two or three different neurotransmitters that could be released but in general the most studied neurotransmitters we know about about 50 different neurotransmitters okay so when that calcium comes flooding into the axon terminal then it causes exocytosis of those vesicles and allows for release or secretion of those chemicals those neurotransmitters into this space what is that space called the synaptic cleft right and because you have chemicals being secreted or diffusing into that synaptic cleft this is why this is called a chemical synapse right and then what happened to these chemicals well these neurotransmitters then bind the on this in this case it's specific receptors on the axial lemma of the postsynaptic neuron so if this was a ligand that brought about depolarization it looks something like this okay so this is where sodium would come into the cell into the neuron prostatic neuron and potassium would leave the postsynaptic neuron but why did this channel open it's because of this neurotransmitter this chemical that bound to this channel opening it up okay now as a result of more sodium coming into the cell it brought about depolarization which is an epsp okay now what if this chemical what neurotransmitter was something different and it bound to say those chloride channels which caused more chloride to come into the cell then it would bring about an inhibition signal which is basically hyperpolarizing the plasma membrane therefore bringing about an IPS field so this is where the the variation occurs it really depends on what type of neurotransmitter binds to these channels okay and depending on what type of neurotransmitter it could result in either excitation epsp or inhibition which is an IPS B okay the majority of synapses between neurons within the nervous system especially in adults are chemical synapses but we do have some instances in some regions where electrical synapses are found so this would be still a synapse between a neuron and a neuron but instead of the release of a chemical in the synaptic clip it's slightly different this is more like gap junctions electrically coupling one neuron to another neuron this is found in certain regions that are responsible for rapid eye movements quick movements in certain regions where memory and emotions are controlled like the hippocampus of the brain okay you predominantly saw electrical synapses in embryonic development but shortly after birth most of those electrical synapses are converted into chemical synapses and that's why we're focusing mostly on chemical synapse is here with the nervous system okay so the rest of this is an explanation of postsynaptic potentials epsps I P SPS which I think we've talked about quite a bit so I just want to point out a few things just to revisit these to make sure you understand this so again if resting membrane potential is right here at minus 70 this is occurring say on the dendrite of the soma these are receptive regions binding of some specific chemicals going to open up specific channels which can bring about depolarization and depolarization is moving the membrane potential towards a more positive number right positive meaning moving upwards like that and this would be an example of an excitation or sigh theory postsynaptic potential epsp okay and we already talked about the channels involved in this this is simultaneous sodium and potassium sodium entering potassium leaving before we discussed that okay now in the case of inhibitory synapses it should look something like this so if you had a dendrite at resting membrane potential binding of a specific chemical to either a chloride channel or a potassium channel would bring about hyper polarization of the membrane potential meaning you're moving that voltage towards a more negative number away from threshold right this is called an IPS B because it's an inhibition potential which has no chance of reaching threshold because it was moving in the opposite in the wrong direction okay okay I'm going to move on to integration events and I touched upon this in the discussion the first half of the discussion of this chapter but I want to go into a few more details related to temporal and spatial integration of these neural events so you've got to understand that a single epsp cannot bring about an action potential okay it's a summation of multiple epsps that work together to have a cumulative effect where you would bring about an action potential now ipsps can also sum it and then we also talked about how epsp is an IPS base can kind of work against each other but but kind of whoever whichever signal is stronger is gonna win out okay so let's give you some examples of of these integration events okay so what you see here is okay so we've got an a neuron okay and here is a dendrite that's receiving a signal and epsp shown him as e1 okay an excitatory synapse so this dendrite is at resting membrane potential in response to e1 this epsp okay what happens it depolarizes the plasma membrane but because it did not reach threshold it fizzles out right and now if it goes all the way down to our mpa you hit it again with another epsp you can keep doing this over and over again and never reach threshold so the goal is for these EPS please to come closer together so they can summit so before this first EPS be completely dies down if you hit it with another stimulus then it would have a cumulative effect yes I'm going to explain that here next in this case no summation occur okay because they were to further too far apart here is a case of temporal summation so in this case you have one dendrite that's receiving multiple excitation stimuli right okay so I have my first signal there is some depolarization that occurs but before it completely comes back to RMP you hit it with a second excitation stimulus and what happens it picks back up from a partially kind of repolarized state but what happens it then builds on so it builds and builds and become stronger to where it reaches threshold and then at this point you see summation where you have great reach threshold and you can convert this into an action potential this is a case of temporal summation because we're talking about one specific location but it's receiving multiple excitation signals it's some adding in a specific location over time and that's why this is called temporal summation okay okay so now let's look at spatial summation so in this case you've got two different dendrites so two different locations right each receiving its own excitation stimuli so again each of these can sum it together all of these epsps ultimately when it reaches the axon hillock if it is at least at threshold if it's some eights then it would convert to an action potential so this is a case of spatial summation because here we're talking about two different spaces or two different locations where these excitation signals are adding one on top of the other or somatic okay okay now here is the concept of where epsps and ipsps are going to have to work together and see who winds up right so just as much as a specific dendrite producing epsps it can also receive ipsps so here's a dendrite receiving an excitation signal and let's say the soma directly is receiving an inhibition signal so an inhibition signal by itself is gonna bring about hyper-polarization but then if you have an excitation and an inhibition kind of summoning together you have a muted response so just this really depends on okay looking at this graph it tells me that this excitation signal that voltage was stronger than the inhibition signal right now if this keeps building to where there's more epsps versus an IPS bee or a synapse then that's going to reach threshold and then ultimately convert so this is a concept of spatial summation and temporal summation of just epsps and then EPS bees in combination with ipsps bottom line is this regardless of what type of synapses are occurring they all have to sum it to where the ultimate goal is to reach threshold because if you do not reach threshold you cannot convert it into an action potential okay synaptic potentiation is where you repeatedly use a specific synapse point to where the postsynaptic neuron or the postsynaptic cell is extremely receptive to stimuli being or to neurotransmitters being released by the presynaptic cell so it has a greater probability of being excited towards threshold in order to convert it to an action potential this is often seen in complex learning processes and memory related skills associated with the CNS okay and the last concept I'm going to talk about is neural integration so in neural integration this is again where the concept where we're not talking about just one neuron synapse in with another neuron it's not as simplified as that within the brain and the spinal cord and within the nervous system it's multiple hundreds of neurons maybe even thousands of neurons all forming synapses all transferring information so really what's important is how do you integrate all of this information so that's where we talk about neuronal pools ok and how they have to work together function together to bring about neural integration so let's start with a simple neuron pool let's discuss this the discharge zone and the facilitated zone so here is a presynaptic axon process and here's all of the terminal branches leading towards the axon terminals ok so the neurons these are all postsynaptic neurons the neurons that are closest towards this presynaptic neuron these are considered to be in the discharge zone meaning they have the highest probability of reaching threshold and firing off an action potential whereas the neurons that are further away are in the facilitated zone meaning they're gonna need more epsps to summit before you can reach threshold and fire off action potentials in these four synaptic neurons within the facilitated zone let's quickly talk about patterns and neural processing so you can think about this as how neuronal pools work together to accomplish one common goal or one calm function you can think about this as either cereal processing which is the most simplified neuronal pool versus parallel processing circuits so let's start with cereal processing and the the simplest example that comes to mind for cereal processing is a reflex arc which consists of several different components and we kind of started with this concept on I guess the very first slide of this of this chapter but you can think about it in relation to a reflex arc as well so let's go ahead and kind of get started here so this is where you have cereal processing it's it's kind of like a handshake signal it's like a relay race right so you you have a signal that needs to be passed on from the first part to the second to the third to the fourth and so on and so forth so it has to be serially communicated so in response to stimulus the stimulus is picked up by a receptor the receptor files of an action potential which travels down this blue neuron called a sensory neuron so that's the second part then the secondary the the sensory neuron kind of culminates here within the using the cross section of the spinal cord which is part of the central nervous system and here the spinal cord makes sense of the information the sensory information coming in through that sensory neuron ok and then it determines what the output needs to be or what the motor output information needs to be and oftentimes you've got shorter Association neurons like inter neuron that helps to transfer the information from a sensor in your on to the red neuron here called a motor neuron which carries motor output out of the spinal cord towards some kind of an effector like skeletal muscle or whatever are the targets whatever are the effectors to bring about what a response this is an example of different neurons all working together as a neuronal pool are all responding to this one stimulus to bring about this one end goal which is bringing about an appropriate response but to do so it had to do it in a in a serial manner meaning the sensory neuron to the inter neuron to the modern era right so it has to be in that consecutive order so that's an example of a serial processing circuit so we're gonna discuss next our examples of parallel processing so this is where the input or the stimulus right it travels along several different pathways all at the same time this is definitely an example of where this is used for higher level functions in in this in the CNS like processing complex thinking skills problem-solving reasoning critical thinking complex math problems things like that okay so let's give some examples of parallel circuits diverging converging reverberating and parallel after discharge so let's start with diverging so at the top you have one neuron that's receiving an input and notice how it is sending that input down multiple parallel pathways so where one input is directing multiple neurons on the on the other end of things to bring about all of these different outputs so basically one neuron can activate like multiple neurons postsynaptic neurons which can then activate multiple targets like this could be different skeletal muscle cells that are activated by these by these neurons at the at the end of this circuit so this is called a diverging circuit where an input leads to multiple output so it diversifies it diverges okay a converging circuit is right the opposite of a diverging circuit so this is where multiple inputs all come together and they kind of come towards a meeting point in the center to bring about one output okay and this is an example of where multiple stimuli multiple sensory stimuli can bring about the same memory like for example thinking about like Thanksgiving when you are growing up so maybe the smell of pie cooking company or pecan pie whatever the smell of it the taste of it the presence of your family all of these sensory inputs may all converge on one output which is bringing about a recollection of a memory of you growing up and say and attending Thanksgiving dinner or lunch or whatever in your in your grandma's house so that's an example of a converging circuit okay a reverberating circuit looks something like this so you have an but that kind of bounces off of each other to bring about one output this is an oscillating circuit this is often used for rhythmic activity like just normal breathing sleep-wake cycles repetitive activity like like walking okay and the last circuit is a parallel after discharge circuit this is where okay so you have one input culminating in one output but then in between you have several different paths so there's several different parallel paths that are taken okay so this is often used in again complex mental processes such as mathematical calculations where you may have different parts to the problem so one neuron or pool is working on one aspect of the problem but you're kind of storing it away in your in your memory for for a brief few seconds while you're working on a different part of the problem and then all of these different solutions need to come together ultimately to arrive at that final answer and so that would be an example of a parallel after discharge circuit okay so I think that kind of wraps up our discussion of chattel M which is fundamentals of the nervous system now I did not cover neurotransmitters that is included in your PowerPoint slides but I think that's fairly straightforward information it's mostly a classification of the different types of neurotransmitters based on structure and function so I think that's something that you could maybe make sense of yourself most of the physiology though that's the complicated part of how the nervous system works I hope you've gotten a better appreciation and understanding of the differences between action potentials and great greater potentials the different types of channels where is it occurring and just being able to piece it all together to understand how information flows from neuron to neuron and then from neuron to effector cells and the whole concept of our chemical synapse there's a lot that goes on in how the nervous system functions so it's it's a truly fascinating audiences and I hope you can appreciate the complexity that's involved in the nervous system and what all it takes to just do simple things like pick up your cell phone and or complex processes that your brain handles like complex thinking skills and problem-solving and things like that but that is a conclusion of our discussion of the of chapter 11 fundamentals of the nervous system I hope you all have a wonderful rest of your day thank you