Transcript for:
Understanding the Autonomic Nervous System

hi everyone dr mike here in this video we're taking a look at the autonomic nervous system and i'm going to try my best to tell you all the things that i think are most important when it comes to looking at the sympathetic and parasympathetic divisions first thing we should begin with is what is the autonomic nervous system well it's a subdivision of the nervous system itself so the nervous system being the collection of neurons in glia that allow for communication to occur if we were to take a look at the nervous system and just have a look at the hierarchy in various divisions you can take the nervous system and you can subdivide it into what we call the central nervous system and what we call the peripheral nervous system remember the central nervous system is going to be things like the brain the brain stem the spinal cord and the cerebellum that's the central nervous system it's central anatomically because it sits right down the middle but it's also central functionally because this is the site of integration this is where we make sense of information so that's the central nervous system peripheral nervous system is everything that shoots out and away and comes back into the central nervous system so all the neurons that come and shoot out and away and all the neurons that go back in to the central nervous system they're termed the peripheral aspects of the nervous system and think about it like this any signal that's going out and away from the central nervous system it's obviously going to be a motor signal so it's sending information to muscles tissues or glands to tell them to do something muscle to contract gland to release some sort of substance any signal going into the central nervous system it must be sensory it's going to tell the central nervous system about what's happening to the environment outside or the environment inside so that means through looking at this the peripheral nervous system can be divided up even further into the sensory aspect and the motor aspect now in actual fact you can break this up even further because think about it what type let's first look at sensory what type of sensory information can we have we can have sensor information that's coming in that we can become consciously aware of information about touch pressure pain temperature for example this type of sensory information we call somatic sensory somatic sensory and it actually goes to a part of the brain actually goes to a part of the brain which sits right here in the parietal lobe called the somatosensory cortex the somatosensory cortex somato means body so you can actually have the somatic division and this is telling us information that we're going to become consciously aware about right now you can also have sensory information that's coming in that you don't become conscious about but it's giving your central nervous system information about the organs of your body so how dilated or constricted are your blood vessels how dilated or constricted are certain hollow tubes so your gastrointestinal tract your reproductive tract your renal system for example it gives information about all those different structures and you do not become consciously aware of that and we call that visceral sensory so then we've got the visceral division here and it's all about unconscious information you don't become consciously aware all right so there's sensory motor what about motor well what type of motor output can you have it can again be about conscious movement which is going to be skeletal muscle basically and you can have unconscious movement now motor isn't just movement motor is muscles tissues glands and again it could be the glance to secrete something for example so let's just take a look motor can be divided into somatic which is again the conscious movement and that's basically just skeletal muscle right and then you can have visceral here you can have the visceral aspect so this is organs and it's unconscious unconscious so when we take a look at the visceral the unconscious aspect somatics conscious skeletal muscle visceral is going to be things like cardiac muscle so your heart smooth muscle hollow inside of your organs and glands as well to secrete hormones or other various substances could be salivation for example it could be your digestive enzymes a whole bunch of stuff so that's unconscious now this is where and you're probably thinking ah finally he's getting to this is where we start looking at the autonomic division because this visceral aspect is autonomic it's unconscious so you could call this autonomic which sounds like automatic which is basically what it's referring to it's the autonomic division of the motor system which is a division of the peripheral nervous system so this autonomic division you can actually break up further right so think about this now i want you to think about this if you've got all this motor output it's coming out it's going to your organs to tell them to do stuff unconsciously what type of things is it going to tell to do the heart to contract and beat it's going to tell the smooth muscle inside all your body that's blood vessels gastrointestinal tract renal system reproductive system whole bunch of areas to either constrict or dilate it's going to tell glands to release substances whether it's salivation or digestion or maybe it's various hormones right how could you divide that even further well you can divide it like this because the whole reason why this system exists is to maintain homeostasis without you being consciously aware of it and how can you maintain homeostasis well you can maintain homeostasis in times of relaxation sitting down having a bite to eat having a chat reading a book you're relaxed so maintaining homeostasis in this relaxed state but you can also maintain homeostasis on the flip side of that a stress state somebody's coming at you with a knife or a dog is barking and jumping at you right times where you're fearing for your life two very different things resting and relaxing and fighting or flighting running away right and these are the two divisions of the autonomic and we call them the sympathetic division and the para sympathetic division and the way we look at that is the sympathetic division is the fight or flight and the parasympathetic is the rest or digest division now you can take a step back and go what type of organs are going to fit and activities are going to fit underneath each of these that's what i want to take a look at now so let's now take a look at the sympathetic parasympathetic nervous system in more detail i want you to think about if the sympathetic nervous system if this gets activated in times of fight or flight in actual fact it's known as the four refs fight flight fright and making love now when this gets activated its job is to keep you alive in that moment to maintain homeostasis in that particular moment so what organs will you activate and what would be their function so an easy experiment to do here is we've all been scared before all right so if you've ever nearly walked across the street haven't looked to the side and nearly got hit by a bus firstly what did you feel like was the first thing you felt your heart rate right so here one of the things that happens is in regards to your heart that's going to be one of the organs that's affected here what happens well heart rate increases why would your heart rate increase during this moment well if your heart beats faster it's going to pump more blood around your body why is that important well your blood beca your blood contains oxygen and nutrients which if you want to fight or run away you need to deliver that to your muscles so heart rate increases to deliver more oxygenated and nutrient-rich blood to your muscles that's the first thing the other thing is you can feel like your heart's about to pump out of your chest right so the contractile force the contractile force increases as well for the exact same reason the harder the heart pumps the more blood that gets ejected more oxygen and nutrients gets delivered to the important tissues of your body so that's the heart what else happens what happens to your breathing your breathing rate increases so the respiratory system is affected and in what way well breathing rate increases what we call respiratory rate increases why same reason is here more oxygen in more oxygen into the cardiovascular system gets delivered to the system the other thing that actually happens which you wouldn't be aware of is your airways dilate they open up and so we call that bronchodilation bronchodilation your airways relax and open up again to let more air in that contains more oxygen to be delivered to the tissues of your body so that's a respiratory system what about when you look in the mirror what do you look like you look really pale right so something's happening to your blood flow so you could say cardiovascular cardiovascular so what's happening there well it's really interesting because the blood vessels in your peripheral vascular system so your peripheral blood vessels they constrict why well they constrict because there's no point to living delivering all this blood to your skin when your muscles need that blood so they redirect or shunt that blood to deeper areas of your body for two reasons one to deliver all that oxygen and nutrients to the muscles so you can fight or flight but two if you get cut or damaged you're less likely to bleed out very smart so cardiovascular system so peripheral the peripheral blood vessels will constrict will constrict but other various blood vessels like those of the muscles blood vessels of the muscles they dilate for example and so more blood gets redirected to other important areas of the body and finally and there's other system effects but last one i want to really talk about is that of your pupils what happens to your pupils they dilate they get bigger why would your pupils dilate and get bigger it's so that you can see more around you if your pupils are constricted it's because you're focusing in on one point but if your pupils are dilated you can see more now the image may not be better but you can see more in your peripheral and you can see attackers coming at you so your pupils dilate so you could say your eyes pupil dilation pupil dilation brilliant these are some of the effects make sense they're all there to keep you alive in that moment what about the parasympathetic nervous system what do you think is happening here so this is resting and digesting relaxing it's actually the flip side of this so you can basically take all the same organs and then flip it upside down so what happens when you're relaxing let's first take the heart well when you're relaxing your heart rate drops and the contractile force drops so heart rate decreases and the contractile force decreases now the whole reason why is because there's no point wasting your heart capacity its ability to pump harder and faster that requires energy right but you're in time of resting and relaxation so during this time your heart doesn't need to beat as hard or as fast it's conserving its energy so it relaxes both heart rate and contraction what about your respiratory system so if we look at the respiratory system your respiratory rate decreases for the exact same reason as we spoke about there what about your airways they actually constrict you actually get broncho constriction bronco so your airways bronco because you got your bronc eye the big airways and the bronchioles the smaller ones that have the smooth muscle in it it's those we're talking about so you could say bronchiola dilation or bronchiola constriction but let's just say broncho so we've got broncho constriction and you might be thinking wait why would i want to constrict my airways but it's just because you don't need such a great capacity when it comes to resting and relaxation for breathing so you get bronchoconstriction now i want you to keep this in the back your mind keep this in the back your mind that when you stimulate sympathetic nervous system your airways open up but when you stimulate the parasympathetic they can actually constrict keep that in the back your mind all right cardiovascular the blood vessels again it's the opposite right cardio vascular effects and we're talking about blood vessels predominantly here so peripheral blood vessels those in the periphery they actually can dilate you get dilation of the peripheral blood vessels and then when you get those of the muscles it's going to be constriction constriction constriction again blood vessels and then pupils if we look at the eyes they're going to constrict and again because when your pupil is constricted you get to focus in you might be reading a book you're relaxing and your pupils constrict so what we've highlighted here are some of the major functions and effects of both the sympathetic and parasympathetic nervous system and we needed to go through them because of the next part what we now need to look at is the anatomy of these systems the neurotransmitters that they use and how they speak to the organs glands or target structures in order to tell them to do these things so let's now take a look so what i've drawn up here is the brain brain stem and spinal cord and we're going to take a look at the neurons associated with each of these remember this is motor output this is a subdivision of the peripheral nervous system and that subdivision is the motor system and obviously its subdivision is that of the autonomics so a couple of things here is this when we look at both the sympathetic and parasympathetic divisions they are both two neuron chains that means two neurons will come out of the brain brain stem or spinal cord and one will come straight out speak to a second neuron which will come out and speak to the target organ or gland let's have a look at that firstly sympathetic nervous system the sympathetic nervous system actually has another name and that other name and we're going to write it up in red that other name is the thoraco lumbar system the thoracolumbar so there's two words there thoraco meaning thoracic lumbar meaning the lumbar region so the thoracic and lumbar region of the spinal cord if we take a look at that thoracic lumbar thoracic and lumbar the neurons for the sympathetic nervous system come out of the thoracic and lumbar regions so let's take a look at that we're going to have a neuron come out like that and let's just do one here as well have a neuron come out like that and so what we can see is they're very short neurons and they're going to talk to their second neuron and the second neuron is really long really long all right that's the first thing let's now take a look at the parasympathetic when we look at the parasympathetic it's not called the thoracolumba it's called the cranio sacral cranio sacral and that's because there's got cranial for cranium or cranial like cranial nerves and sacral referring to the sacral aspect so craniosacral cranial or cranial it's right cranial and then sacral now these neurons that come out the first one is usually quite long and the second one is quite short same goes here first one is quite long and the second one is quite short all right let's name these right it's a two neuron chain for both i said that one two and that's the parasympathetic nervous system one two and that's the sympathetic nervous system these neurons have have names the first of which the first one that comes out is called the pre-ganglionic neuron the very first one is called the preganglionic neuron and the reason why it's called that is because that anytime you've got a collection of cell bodies there's a cell body there's a cell body there's a cell body there's a cell body any time you've got a collection of cell bodies that sits outside the nervous system it's called a ganglion a ganglion is a collection of cell bodies outside the nerve the nervous system right hence why this is called the preganglionic neuron because its cell body is in the central nervous system so it's not called a ganglion this one is so that's why this second one is called the postganglionic neuron because you can see this neuron shoots out after the ganglion postganglionic neuron postganglionic neuron so now we've labelled those all right let's first start with the actually let's start with the pre-ganglionic neuron of every single one in order for it to speak to the next one it must release a chemical that can speak to the postganglionic neuron that chemical is going to be a neurotransmitter because we're talking about the nervous system what is the neurotransmitter here that we need to talk about well this releases a neurotransmitter that crosses the synapse this releases a neurotransmitter that crosses the synapse so does that and so does that all right what is this neurotransmitter in actual fact it's the exact same neurotransmitter for all four and that neurotransmitter is acetyl choline which we sometimes just write as capital a capital c lowercase h acetylcholine so this is acetylcholine acetylcholine acetylcholine in order for it to have its function it must bind to acetylcholine-specific receptors and there's two major types there's nicotinic and muscarinic nicotinic and muscarinic nicotinic and muscarinic what's the one here the receptor here that it needs to bind to for all of them in actual fact so here's the receptor that it must bind to that's called a nicotinic receptor so let's write it here nicotinic let's just write it as n so this is going to be nicotinic nicotinic nicotinic perfect now it's bound stimulated action potential has been sent down this postganglionic neuron for each and now it's going to go towards its target organ it's a factor so let's have a look let's draw up some of the ones we spoke about right so what did we say we said the eyes in pupil that was one so we've got the i and the pupil so that was one another one we spoke about we didn't draw up but we spoke about was salivation right salivation and release of digestive enzymes so let's put this up here salivation let's see if i can draw this i'm not the best drawer as you're aware and let's have that tongue that comes out that is a tongue and there's salivation that's happening what else we talk about we spoke about the heart right we also spoke spoke about the airways we spoke about all these and we spoke about blood vessels so they're all and there's obviously others but there's some of our target structures now what are we going to do firstly we should talk about which one let's talk about the parasympathetic the rest and digest and the reason why i want to talk about that one first is it's easier because the neurotransmitter it releases here right at the end so the postganglionic neuron releases acetylcholine again acetylcholine acetylcholine so you get asked the question in an exam the parasympathetic nervous system the only neurotransmitter it deals with is acetylcholine at both the pre-ganglionic and postganglion neuron what receptors nicotinic here at the postganglionic neuron but at the target structure it's muscarinic muscarinic so you're going to have a muscarinic receptor at the pupil here and at the heart muscarinic receptor at the salivary glands i know that's not on the tongue but it's muscarinic so i'll write it here and then we'll just use muscarinic and then we'll just use m like that so muscarinic muscarinic it's going to be here on the airways muscarinic and on the blood vessels muscarinic beautiful now think about what happens the acetylcholine binds to the muscarinic receptor and has its effects so at the pupils the pupils will die no they'll constrict right it's it's parasympathetic we're resting and digesting so the pupils constrict when acetylcholine binds to muscarinic receptors at our salivary glands we salivate so we can digest food better at our heart acetylcholine binds to muscarinic receptors to slow it down at our airways it binds to it to constrict to constrict at the blood vessels well it depends which blood vessel if it's periphery dilate muscular constrict all right so we've done that important point here is you might be thinking cranial i've heard of cranial nerves before remember there's 12 pairs of cranial nerves those 12 pairs 0.02 touch and feel very good velvet are heaven all right there's four cranial nerves that are also known as parasympathetic nerves do you know what those four cranial nerves are they're cranial nerves three so that's ooo olfactory optic oculomotor so that's oculomotor nerve seven oh oh to touch and feel f facial nerve facial nine 002 touch and feel very good glossopharyngeal and then last one is cranial nerve ten which is vagus the vagus nerve so we've got oculomotor facial glossopharyngeal and vagus they're all cranial nerves that are also parasympathetic in their effect what do they do so number three is actually responsible here that's the the cranial nerve that comes out to tell your pupils to constrict is going to be the oculomotor nerve seven for facial salivation nine glossopharyngeal also salivation but different types of salivation because we're different at sublingual sub-maxillary parotid so it's just they have different effects right different targets and then the vagus nerve actually does pretty much all the others right does the heart does the airways does aspects of the blood vessels right perfect perfect perfect all right next is sympathetic so what is the neurotransmitter that's been released here so we've got acetylcholine at the preganglionic postganglionic is not acetylcholine but i want you to think it's an easy one to remember why is it easy to remember when you have a sympathetic effect some people say i just had an adrenaline rush so the neurotransmitter is noradrenaline also known as nor epinephrine nor adrenaline also known as nor epinephrine so let's just write it as nor add nor add nor add it will bind to adrenergic receptors so it's adrenaline it binds to adrenergic receptors receptors that will either allow for noradrenaline to bind to or adrenaline what's the difference between noradrenaline and adrenaline they're pretty much the same but here's the major difference noradrenaline that's the neurotransmitter adrenaline that's a hormone that's the major difference all right they're going to bind to adrenergic receptors and there's more than just the two kinds that we have for acetylcholine nicotinic and muscarinic there's alpha and beta and i want to talk to you about those and what they do but very quickly think about this no adrenaline binds to these structures pupils dilate salivation stops heart rate increases airways dilate blood vessels depending on where they are will either constrict or dilate last point here is this there is a pre-ganglionic neuron that comes out all the way out all the way and i'm going to put it here and it's just a preganglionic neuron no postganglionic neuron and it speaks to and this is not going to be a surprise that's the kidney and the kidney has a hat that sits on top do you know what that hat's called the adrenal gland now it's called add meaning on renal kidney the on kidney gland but that's the prefix of adrenaline why because this preganglionic neuron now what neurotransmitter do preganglionic neurons release they all release acetylcholine and so adrenergic sorry the adrenal gland will have acetylcholine specific receptors nicotinic right and it's going to bind and it's going to stimulate the adrenal gland to release something what is that something going to be it's going to be adrenaline it releases adrenaline now where does it release this adrenaline to the bloodstream remember i said it was a hormone it's a hormone hormones get released into the bloodstream and if it's in the bloodstream it goes everywhere so that means that the adrenaline that's released from stimulating the sympathetic nervous system goes into the bloodstream and literally will go to all of these structures to tell them to do their thing which means what does this mean for the sympathetic nervous system you can't have a localized sympathetic effect you don't just have your pupils dilate you don't just have your heart rate increase you don't just have your airways dilate in a fight or flight response you have all of them happen and that's because the preganglionic neuron that speaks to the adrenal gland tells it to release adrenaline that goes into the bloodstream and goes everywhere final thing i want to tell you about are the different receptors associated with adrenaline and noradrenaline and what they do how can we distinguish about telling because i said tells heart rate to increase but tells airways to relax and open up so how does this work let's take a look so here is your cheat sheet for understanding adrenergic receptors the different types and how they work do this for me so with your adrenergic receptors you can have alpha and you can have beta so do alpha beta like that now do alpha beta like that as well now write a1 b1 now write a2 b2 now draw a box around them like this and under here right stimulate under here right inhibit all right we're getting there now where do you find alpha 1 receptors remember we're talking specifically sympathetic nervous system here right right i mean you know now the organs that it affects so a1 is found on all sympathetic organs found on all relevant sympathetic organs all smooth muscle glands and tissue of the sympathetic nervous system they all contain alpha one beta one is located at the heart and juxtaglomerular cells glomerular cells now if you haven't done the renal system yet just write kidneys b2 is found on sorry b2 is found on all the relevant smooth muscle glands and tissue of the sympathetic nervous system and a2 is found on the pre-synaptic terminals of sympathetic neurons pre-synaptic terminals now what does all this mean all right if i so alpha 1 and beta1 if you throw adrenaline or noradrenaline at these receptors they stimulate the structure to do their function so for example any smooth muscle glands or tissue that has alpha 1 receptors if i throw adrenaline or noradrenal adrenaline at them if it's smooth muscle it's going to tell them to constrict if it's a gland it's going to tell it to release its substance compare it here to beta2 which if i were to throw adrenaline or noradrenaline at beta2 receptors it will tell the smooth muscle glands and tissues to not do their function so if i throw adrenaline noradrenaline at beta2 and it's located on a smooth muscle it will tell that smooth muscle to relax it will tell it to dilate it will tell the gland to not release its hormone or chemical or substance hopefully that makes sense here at beta 1 it stimulates so beta 1 is found at the heart it's stimulating the heart increase heart rate increase contractile force the juxtaglomerular cells are important for blood pressure right the renin release so if beta 1 is located at these cells if you throw adrenaline and noradrenaline at the beta 1 cells in the kidneys here it stimulates it to release renin and then you get the renin angiotensin aldosterone system i'll just write that the renin angiotensin aldosterone system i've done a whole video on it so please feel free to watch it it's how your kidneys maintain long-term blood pressure and then finally if i throw adrenaline noradrenaline at alpha 2 receptors and they're located at the presynaptic terminals its job is to inhibit the postsynaptic neuron the post synaptic or the postganglionic sympathetic neuron to send its signal remember it's a two neuron chain right one two and let's just say you've got a particular tissue here here's some cells right and they've got they're going to have a sympathetic effect if you stimulate them but alpha 2 pre-synaptic terminals so here if you throw adrenaline at it it stops it from sending the signal to the next neuron so inhibitory hopefully that makes sense so now you can think about this let's look at specific examples so the heart's easy this is the one that's responsible for increasing heart rate and increasing contractile force this one's easy stimulates blood pressure why do you want your blood pressure to go up because it pushes more blood around the body to distribute oxygen nutrients so forth so beta1 is really important blood pressure heart right alpha one stimulate what's it going to stimulate well it's going to stimulate peripheral blood vessels to constrict so this is a peripheral blood vessel and it stimulates it to constrict for example so that's really important it's going to now think about this right let's go over here to inhibit what muscle do we want to inhibit our airways remember you want your airways to open up so beta2 receptors are found on your airways so it's going to tell your bronchioles to dilate so you can get more air in that's how that works it just as muscles relax they open up really really important and then the alpha 2 receptors are just going to be found at neurons where we want to inhibit that particular effect obviously you can take any sympathetic organ and now fit it and reverse engineer instead of memorizing what receptors sit you can reverse engineer it and say okay i know this structure does this it's likely to have which particular receptor so we can now take a look very quickly and talk about beta blockers we know that's a drug or medication beta blockers beta blockers and you can have specific and non-specific beta blockers think about it if you have a non-specific beta blocker it's going to block both beta1 and beta2 what's going to be the effects well it's going to slow your heart rate down but it may also result in what bronchoconstriction so maybe an asthmatic doesn't necessarily want a non-specific beta blocker so a specific beta blocker they're usually targeted at inhibiting the heart slowing the heart rate down reducing blood pressure reducing the contractile force so beta blockers can and have been used for people with hypotension elevated blood pressure for example that's just an example so hopefully you enjoyed this this is a summary and overview of the autonomic nervous system hi everyone dr mike here if you enjoyed this video please hit like and subscribe we've got hundreds of others just like this if you want to contact us please do so on social media we are on instagram twitter and tick tock at dr mike tadovich at d-r-m-i-k-e-t-o-d-o-r-o-v-i-c speak to you soon