 Welcome back to the lectures in animal physiology in NPTEL. So, we are into the last lecture of section 5, which is the 10th lecture. And in this lecture, we will be talking about autonomic nervous system. What really is autonomic nervous system? To start off with, let us do some situation or aspect, which may help you to appreciate it better. So, think of it, you are walking in a lonely or walking in a dark street in the night or you are sitting in your room studying late hour of the night. All of a sudden, you hear a loud noise or you hear like it is a stormy night and you hear the breakage of the window panes or outside you hear some cracker or something. You all of a sudden get scared and subsequent set of events, which take place like you know try to escape or you feel scared and all of a sudden the blood flow enhances in your body and you lose the sensation of thirst or urination or anything. And all over there is some kind of a panic, we are scared. What is that reaction? What kind of circuits regulates that kind of situation? This falls under something called autonomic nervous system. In day to day life, if you think about. So, how many times we really use conscious thought processes? Well, you are studying, you of course use it. You are crossing the road, so you have to ensure the buses are not coming or the motor vehicles are not coming. So, you are at a safe distance from them, you have to cross the road. Other than that, most of the time we do not even know that we are being controlled by our own system in a autonomous manner, in an automatic manner. Something like you know, we do not decide that we are going to get urination. We do not even command to tell our digest system that you digest our food. We do not tell the heart that you beat. We do not decide the secretion of the hormones. They all happen. They all happen in their own course in a kind of as if within this whole system of ours, there are inbuilt circuit, intrinsic circuits which ensures that all our day to day events takes place without even we giving any command. They are involuntary. I mean we have no command or control on all those kind of things. So, this is exceptionally essential for you people to understand and we will talk about that how the nervous system really deal with this kind of actions. Let us take another situation which will help you to appreciate it much better. We hear this you know like somebody is brain dead. In other word, somebody is lying in the hospital and who is not responding to any signal or anything and yet doctors are unable to declare this person dead. And there is always a kind of debate or controversy over this. Shall we give this person some kind of injection so that this person dies or like you know. There is lot of debate over it and is euthanasia allowed in this kind of situation or not. Though this person is brain dead, he or she is not at all responding to any stimuli, but yet his heart is beating and the defecation is taking place, urination is taking place and all these events are taking place. Then what is that coordination? So, this is the zone of autonomic nervous system. So, now let us get into the way we will talk about it is that. We will talk about the circuits involved in it, the autonomic circuits and we will compare with it with the other circuits which does not follow the autonomic system. Then we will talk about the classification of autonomic nervous system which falls under parasympathetic and sympathetic systems and we will talk about some of the situations and I promised you that the cardiovascular control and all these things and we will talk about the neurotransmitters which are involved in it and how that circuit functions in this section. So, let us start with our section 5 and lecture 10. This is nervous system and within nervous system, today we are dealing with autonomic nervous system. This is what we are going to deal with. Within the autonomic nervous system, the first thing we will do is kind of draw out a classification of all of the nervous system what we have already talked about which I termed as technically somatic nervous system and A N S as autonomic nervous system. So, this is also called A N S. So, whenever I have drawn the circuit of autonomic nervous system, let me. So, this is basically in the somatic, this S stands for somatic, somatic nervous system. So, this falls under conscious thoughts and plans whereas, in this section we talked about I talked to you about persons with brain dead. I give the example of that I talked about other functions. So, let us what all A N S is controlling is this just an example. What A N S is controlling essentially is cardiovascular system, respiratory system, respiratory system, digestive system, urinary system, reproductive system. And here I wish to highlight that during 1960s, if a person would have been suffering from gets an heart attack, most unlikely was that you could really either you know recover this person or the life expectancy used to reduce very sharply. But today almost 50 years down the line, these are not a big deal when after 100 a couple of heart attacks people survive. Because now we have reached to a point where we can intercept the control circuits of the nervous system or in other word we could intercept the autonomic nervous circuits which regulates the cardiovascular movement, the blood flow, the blood pressure and the cardiac excitation and all these things. So, these are slowly under the pharmacological intervention. So, there are series of drugs which could bring down your blood pressure. Essentially what they do is that they target the autonomic nervous systems and especially they target the receptor for the neurotransmitters which regulates your blood pressure or under unusual situation there is increase in blood pressure and how to bring that down. So, these are and this particular system of autonomic system is of extreme important from pharmacological perspective. Now, what we will do in the next slide we will compare the autonomic nervous the structure of the autonomic nervous system and the structure of the somatic nervous system. So, whenever I drew it so this side on my left this is basically somatic nervous system. So, this is the side view of the of the brain and the spinal cord. So, I have drawn like this this is this is the brain here is the and here imagine this is the target tissue. So, I have always mentioned that you may have two possibilities you may have higher motor neuron which is synapsing on the second series of motor neuron which are lower motor neurons and they are synapsing on the target tissue and this is how the circuit works. This is the basically a very simple way of defecting it. So, these are the higher M n motor neuron these are lower or somatic motor neuron M n you have talked about it. So, now what about the autonomic nervous system again the same drawing the spinal cord in the brain. So, there are two options here what happens is say for example, there are certain specific neurons which are sitting out here. They send out signal and out here you have in the ganglion I should told you that there are ganglions around it. So, in the ganglion there is another set of neurons which take the message to the target. So, this is the target and in other word. So, basically what you have if you compare these two. So, here what you see is from level 1 level 2 and this is the control level C l here essentially what is happening 1 this is the level 1 which is getting of course, the signal from the brain higher even higher centers from the brain. This is level 2 there is another bifurcation which is outside the system. So, possibilities are there say for example, if you look at it if it is a reflect circuit then it will be like this a signal reaching here. So, just with 1 level of processing the signal comes back here the processing is not at 1 level there are 2 level of processing. In other word this essentially the signal will go like this from here it will come back to 1 level of this thing and this is the second level of it and this second neuron which is involved is called ganglionic neuron and the message is coming like this ganglionic neuron. The first neuron which is giving the ganglionic neuron a message is called pre ganglionic neuron pre ganglionic neuron. This particular ganglia is called autonomic ganglia. Ganglia is basically a series of neurons which gathered together at one spot autonomic ganglia. There are within the ventral horn there are spots there are zones which are called autonomic nuclei of spinal cord or autonomic centers autonomic control centers which are mostly regulated by pacemaker cells of the nervous system autonomic nuclei of spinal cord. So, this is the basic geometry of the somatic nervous system and here you have A, N, S autonomic nervous system. So, if you look at it in a simple way if you look at it in a simple way. So, in case of somatic nervous system here is the target tissue a signal reaches a processing signal comes back fine. There is a possibility that this part of the signal may go up to the brain and comes back fine and in the case of A, N, S it is slightly different. I will show you the complete circuit signal reaches hit upon a center from their signal comes to the ganglia from the ganglia another set of neurons bring the signal back to the target. It is slightly more longer root out here. So, now this A, N, S is further subdivided into two parts and come in depth, but before that I will draw the circuit one is called sympathetic and other one is called parasympathetic. These are the two classes of autonomic nervous system from here what I will do I will draw the complete circuit. So, that will kind of help you to appreciate the whole process. So, let us start like here these are the somatic sensors. So, somatic and visceral receptors. So, the receptors present in the digestive system within the viscera of the body. These receptors are sensing some kind of a change and these are transmitted via the sensory the sensory information are sent via sensory neurons. These are the sensory neurons and this is the sensory information sensory information. Sensory information these are all part of the peripheral nervous system. This is the classification here and this is the part of the central nervous system. This dotted line separates the central nervous system and the peripheral nervous. So, this is the schematics to which you have to understand from here the possibility of the sensory information is to either it moves to a reflex circuit like this or it goes directly to the higher centers of the brain via the ascending pathway if you guys remember I taught you the ascending pathway all the way. So, the signal is moving like this from here sensations moving like this moving like this one option to the brain one option. The other option is that it bypasses it does not go to the brain all the signal reaches here which is mostly in the case of the in the case of the reflex circuits from here the signal is being transmitted to something called a pre ganglionic neuron via inter neuron or may be some other neuron. Now, this pre ganglionic neuron now synapse on a ganglionic neuron. This ganglionic motor neuron these are also called motor neurons technically speaking they are the they reaches the target which is visceral effectors visceral effectors among the visceral effectors you have blood vessels cardiac muscle smooth muscle which is part of the digestive system and then you have the adipocytes of the fat cells. So, this one is your pre ganglionic neuron and the second one is the ganglionic neuron. This is the circuit of the n s and there are major reflex which it controls is falls under visceral reflex. We have talked about the stress reflex arc this is another form of reflex which is called the visceral reflex essentially this is the one which regulates how the food are getting digested in everything. And these neurons which are the pre ganglionic neurons are under the tone of another set of neurons from the higher center specially from the hypothalamus which will be touching in the endocrine system. It is I will just show you where exactly hypothalamus this is basically the higher centers which are controlling the motor commands they issue the motor commands and set the tone or set the pace for this. So, this is essentially is I had to kind of highlight this this is essentially is the territory of the autonomic nervous system with the command from the higher centers. And even sometime these commands from the hypothalamus comes without even getting any sensory information. So, this is all falls under a n s or autonomic nervous system. Now, we will talk about here couple of things which is worth mentioning is a couple of things which is worth mentioning is that please remember the post ganglionic parasympathetic system. So, this could be sympathetic or parasympathetic and I will come to just for it just gather this information parasympathetic fibers. So, this going back. So, this is essentially is the sympathetic and the parasympathetic control out here these this circuit falls under two categories sympathetic and parasympathetic. So, post ganglionic parasympathetic fibers also releases. So, the neurotransmitter involved is acetylcholine I mentioned it also because of a reason the major neurotransmitter is acetylcholine and it is effect could be inhibitory or effect could be inhibitory or excitatory. This is the first thing you have to realize here sorry second thing is that most post ganglionic sympathetic fibers secretes. So, we talked about parasympathetic that they secretes acetylcholine, but most post synaptic sympathetic fibers secretes neurotransmitter. So, now you might realize that how important are these neurotransmitters they are the ones which offers the functionality to the nervous system nor epinephrine or epinephrine nor epinephrine or epinephrine and the effect could be effect is mostly excitatory. Now one more piece of information which from that circuit we obtain is all pre ganglionic autonomic fibers which includes sympathetic and parasympathetic release. So, this is acetylcholine always remember this if I go back to the circuit out here out here this pre ganglionic fiber this is the one of interest this pre ganglionic fiber out here this is the one whether it is sympathetic or parasympathetic this exclusively releases acetylcholine just remember this it is the change is after this irrespective of this pre ganglionic fiber will always release sympathetic or parasympathetic into the circuit all pre ganglionic autonomic fibers sympathetic or parasympathetic releases acetylcholine and the effect is excitatory this is very very important effect is excitatory I exclusively want whenever you draw the circuit just keep this in mind this is very very important. So, with this we will move on to the sympathetic division what the sympathetic division means. So, sympathetic division sometime is also called fight or flight fight or fight system generally the sympathetic system prepares your body for height and level of somatic activity. So, in other word prepares your body for height and level of somatic activity in other word. So, this is a situation when say for example I give you this example in the beginning that suppose you are sitting in a dark room you are just studying late out of the night all of a sudden you hear the window panes have broken you just get scared all of a sudden your mental alertness is start it goes up like there is something wrong you are feeling like you wanted to go to urinate all of a sudden the urination stop you really do not feel that you just forget even if you are feeling that you are hungry you just forget as if all of a sudden everything all part of your body is kind of you know almost frozen your metabolism goes up you started perspiring you are like you know as if lot of sweating is taking place and your sweat gland as if got completely activated and you are energetically very very high in a really very active state. So, if I put them all together in terms of like you know for you to understand. So, the first thing increase is mental alertness you become very alert at that point then there is a digestion goes down your metabolic rate goes up and then you are going to your heart rate goes up. So, here comes the control system your heart rate goes very very up. So, then your blood pressure goes up these are the control systems of the heart rate and so in other word what is happening the sympathetic system we are talking about sympathetic system which is secreting in other word if I if I again go back to the circuit if this is the pre ganglionic neuron and here you have the ganglionic neuron and the signal is coming like this and with the higher centers setting the tone for it. So, this is the pre ganglionic and this is ganglionic and we are talking about the sympathetic system. So, now when we know that this only secret acetylcholine with a irrespective of sympathetic and this one the ganglionic has option to secret nor epinephrine or epinephrine. So, now and this is the target tissue say in our situation let us imagine the target tissue is cardiac heart or cardiovascular or blood vessels. So, essentially what is happening when this sympathetic circuit is activated out here this is all like activated sorry this this is confusing this is this is all all activated when this circuit is activated. So, automatically the secretion of this epinephrine and nor epinephrine by this neuron release leads to the increase in the blood pressure and cardiac output or heart rate. Now, if you have a drug which could target this somewhere or other you could block the secretion of epinephrine or nor epinephrine essentially you can control that control your heart rate as well as your metabolic rate as well as your blood pressure. So, blood pressure goes up urinary function is compromised it goes down your activate energy reserves of your body body and activate the sweat gland. If in your day to day life you try to correlate this situation you will find exactly that is what happens when you get scared or you are concentrating heavily on something this is exactly how the sympathetic system comes into play heart rate increases you respire really fast energy reserves of body starts getting activated likewise. Now, simultaneously so we I told you that this is called fight or flight situation. The next thing is let us talk about the parasympathetic system let us again redraw the circuit sympathetic system. So, if you redraw the circuit. So, these are the higher centers of the brain which are controlling here is the circuit. So, this is secreting acetylcholine A C H and this is the pre ganglionic neuron and this is the ganglionic neuron which also secretes in the case of parasympathetic only P S I am just showing it as P S also secreting acetylcholine. So, in the case of. So, this is one comparison you have to realize in the case of sympathetic system it was the epinephrine or nor epinephrine if you go back couple of slides back. So, this was nor epinephrine or epinephrine and in this situation at both the level it is acetylcholine acetylcholine. Whereas, in the other situation at this level of course pre ganglionic it was acetylcholine, but at this level it was epinephrine or nor epinephrine. So, what essentially is that this is also called arrest and repose as against if you remember as against fight or which was sympathetic sympathetic and here we are talking about the parasympathetic system which is P S what all happens first of all it stimulates visceral activity. In other word your digestion increases promotes secretion along the secretion along the G I track or gastrointestinal track this conserves energy then it enhances digestion brings down heart rate brings down blood pressure just opposite of what happens in the sympathetic system and it increases the salivary gland secretion and increases stomach contraction and metabolic rate goes down. Metabolic energy expenditure metabolic energy expense goes down and blood flow to the digestive track increases that you can figure out in the digestion in terms of blood flow increases out here and blood flow increases and it stimulates urination and defecation. Now what is essential here to understand is this. So, how it modulates its signal. So, this is the preganglionic neuron and this is the postganglionic this is the ganglionic neuron and this is the target tissue and in both the situation. So, it is secreting acetylcholine here also it is secreting let us put it red it will be easy for me to explain acetylcholine here also it is secreting acetylcholine. But, essentially there is something very interesting about this acetylcholine what happens is this acetylcholine which is secreted here and I told you this is all the time the preganglionic one is excited. But, for this acetylcholine which is secreted on the target tissue there are two receptors for acetylcholine. So, here is the situation you have to this is something new which I have not discussed before this. So, for one neurotransmitter there may be multiple receptors that does not mean that if I have acetylcholine out here the receptor will be always same there could be varied kind of receptor and based on the receptor type and based on the binding kinetics the output result will be different. So, in the case of acetylcholine there are two major receptors one of them is called nicotinic receptor the other one is called muscarinic receptor. So, the nicotinic receptor got its name because on the on the. So, just for your understanding I have just introduced this thing once again. So, the receptors are likewise. So, if I blow up this image it will be something like. So, let us redraw this for understanding for better understanding sake. So, here is the target tissue here is the target and here you have the ganglionic system and this is the parasympathetic system out here. So, this is the ganglionic one ganglionic neuron and this is the pre ganglionic neuron P g and at this level it is secreting acetylcholine showing by green here also it is secreting acetylcholine. But the difference lies here there are two kind of receptor like this these are the receptor on the surface inter disperse with another kind of receptor. So, now the I call that as. So, this one I call that as nicotinic as nicotinic receptor and this one is muscarinic receptor. How they got this name muscarinic and nicotinic receptor because nicotin which is found in several sources nicotin binds to these nicotinic acid these receptors and muscarinic it is from one of these mushrooms one of the poisonous mushrooms it is the muscarinic that particular compound binds to them and based on that they got their name muscarinic and nicotinic acid receptors. So, the secretion of this acetylcholine binds to either to the muscarinic or nicotinic acid receptor and based on that they are rest of the actions rest of the activities takes place. Similarly, which I have mention is I just kind of flipped out from my mind while talking about the sympathetic system yes. In the sympathetic system out here this epinephrine or epinephrine I talked about the receptor for sympathetic system includes alpha receptor and beta receptors and within beta you have beta 1, beta 2 and few more are there and alpha 1 and alpha 2 and few more are there. These are the receptors for the epinephrine nor epinephrine which are secreted as a part of the sympathetic system. Whereas, in the case of and one more thing I will add apart from epinephrine nor epinephrine sometimes sometimes some of the sympathetic system works with acetylcholine as well as nitric oxide NO and acetylcholine sometimes, but those are very rare even when they act with these those kind of receptors. So, coming back where we were the nicotinic and muscarinic receptors. So, muscarinic effect of muscarinic is fairly long lasting as compared to the nicotinic receptor they are short term effect and muscarinic effect could be either excitatory as well as inhibitory depending on the context inhibitory. This is a completely context dependent situation apart from it always there is one thing which people have to appreciate that most of these organs are innervated it is a dual innervation. In other word say for example, this is your heart again coming back. So, this is under both sympathetic and parasympathetic control sympathetic and parasympathetic. So, you have a balance between the parasympathetic system and the sympathetic system. So, which ensures the proper functioning of the of the heart all the time. So, this is something all over our body all the organs are most of them have the dual innervation of sympathetic and parasympathetic which dictates how the signals are being transmitted. So, with this I will close in with the autonomic nervous system to summarize the autonomic nervous system autonomic nervous system is the one which ensures the autonomous functioning of our system which are not in our voluntary control in voluntary your heartbeat moment of the bolus moment of the food across the digestive system you do not say that now digest or secrete this acid that acid or that compound to ensure the food gets digested. The urinary system reproductive system and other secretory systems they are purely under the autonomic control which does not need your conscious thinking or does not need a decision making. This is all completely controlled by a certain group of pacemakers which are sitting at a very specific area of the brain called hypothalamus. I told you that I will show you where hypothalamus is situated. Hypothalamus if this is the site view of the brain is somewhere out here is a hypothalamus and underneath there is something called pituitary and will come to all these things. So, out here somewhere hypothalamus is situated hypothalamus. So, this is a master neuro endocrine gland this master neuro endocrine gland essentially regulates the tone or offers the tone to the autonomic nervous system and from hypothalamus it controls the autonomic centers along the ventral horn of the central nervous system. So, whenever a signal comes a sensory input comes and if it is an autonomic sensory input it needs an autonomic control. Then the sensory input enters into the ventral horn, but instead of going to other centers it hits upon the autonomic center and from there there is a pre ganglionic neuron which comes out and reaches the ganglion. From the ganglion it transmit the signal to another set of sympathetic ganglia sympathetic neurons or sparas empathic neuron which carries the message to the target. So, there is a breakage of information and this is all done to ensure that this is separated out from the somatic nervous system. And if you go back and see the first slide where I started one slide back if you look at it. So, these are the centers which are regulating which is in the hypothalamus which is regulating which is setting the tone out here and then on from here the signal reaches here. So, this is all the ganglionic zone from here it is the motor. So, this circuit the nature of this circuit and the kind of neurotransmitter involved decides whether it is a sympathetic or parasympathetic. And parasympathetic is the one where at both the level at this level at this level the secretion of neurotransmitter at this level at both time it is acetylcholine which regulates it. In the case of sympathetic at this level it is of course acetylcholine, but at the second level out here it is not epinephrine or epinephrine apart from nitrous oxide and other things. Sympathetic is the one which is also called fight or flight and parasympathetic is the one which is called rest or repose it is kind of bring down much of your. So, sympathetic on one hand make your system very excited parasympathetic on the other hand brings it down. And it is the interplay of balancing act between the sympathetic and parasympathetic system which ensures our normal functioning of the body. So, with this and with the control what I highlighted about the sympathetic and parasympathetic control of the art I am closing on the nervous system. So, next we will start with the new section. Thanks for your attention.