 Welcome back to the lectures and animal physiology in NPTEL. So, we are in section 5 and lecture 9. So, today will be discussion about the special senses. Senses which are fairly advanced in human being and in other species some of these senses are better than human being yet some others are lesser than human being. So, one the senses which will be talking about which will include hearing which is fairly well developed in human being. There are certain other species like dogs and few others which could sense vibrations at much lower frequencies which we cannot sense. Apart from it will be talking about the vision which is very very well developed in human being as compared to other species. Then we will be talking little bit about the taste and then we will talk about all faction. In case of all faction in human being it is less developed as compared to species like rats or some other species which depends a whole lot on all factions. So, the logic is like this the modality or the sense which is used maximum by species is much more well developed as compared to the modalities which are used less. So, in case of small rodents like you know mice or rats they needed a lot of support from the all faction because they had to smell around and they had to read their food or their target. Whereas, in our situation we depend whole lot because we are kind of you know a straight like an erect. So, we have to look around. So, we are tall. So, we depend a whole lot on our vision and our hearing these are much more well advanced modalities as compared to all faction may be at some point or other well human being was evolving all faction may would have been a better modality. But currently our all factory power is far less as compared to all factory power of rat or a mice. Whereas, our taste buds are much more fine tuned. So, let us start with kind of you know getting an idea what is happening. But basic theme what one has to which I will be drawing anyway has to realize is that these special sense organs are nothing, but various specialized neurons. These neurons of the ability to sense the special modalities like light frequencies or sound waves or a particular molecule binding which is for gustatory or taste buds or volatiles in the form of nose in the nose the volatiles are being identified. And these information are coded all along and reaches to the central nervous system. And within the central nervous system these are being decoded because it is something like this say for example, someone in your child to taught you while you are growing that this is an apple. So, now you see an apple then that wave moves through the brain and in the brain the specific area which has already a stored memory of apple tells you to realize so this is an apple same way you smell something say for example, you smell H 2 S gas which are kind of very awkward smell. So, if someone has you went to the went to your first chemistry practical may be long back in class 6 or 7 when someone taught you know that is an H 2 S gas. So, that all factory memory remains somewhere stored in your brain. So, next time when you go to a new place and you smell that you say that is H 2 S. So, that H 2 S is basically you smell a fresh H 2 S in another lab which is a new lab. Now, that signal went from your nose all the way to the brain through the sensory modalities through the sensory neurons. And there it was decoded by the brain because it already has a stored piece of information it terms of by a may be long term potential or long term depression may be some totally unknown pathway it is already known. And that signal or that stored memory helps you to realize oh this is H 2 S and then you decode that piece of information and same holds true for hearing also. So, you hear from your childhood you hear the sound of your say father and mother. So, that frequency is kind of coded in your brain in the all fact in the in the hearing area it is all coded in the there are cortical zones where the hearing information are being processed. And based on that you make your oh this is my father who is speaking or this is my mother over a phone you never had to process that who is talking unless it is a some totally different voice. So, the modality remains the same here is the sensor in the either in your eyes or in your tongue or in your ear or in your nose. And those sensors senses the signal electrically coded the signal all the way to the brain. And in the brain brain decode the signal based on the memory traces which are already stored it is kind of a matching you know sometime you say you know this is smell is very similar to hydrogen sulfide smell or H 2 S smell. That means this is not really that, but it is kind of close in other word then information or the electrical signal which is stored is very similar to the electrical signal of this x y z molecule which you say it is very similar, but it is not the same. So, with this let us formally draw the different structures and kind of get into it and kind of appreciate the way nature has designed us or evolved us to make us more smart individuals. So, we are into section five nervous system and within nervous system now we are into special senses special senses and we are into lecture nine. So, let us first start with our all faction which is not very well developed so regarding all faction. So, this is the nose of an individual. So, what exactly is happening on the nose? So, these are volatiles they could be several kind of volatiles which are reaching and these volatiles molecules enters. So, let us represent the volatiles in terms of something like this these are different kind of volatile molecules different colors represent different kind of volatiles. So, these volatiles are entering your nose. So, inside the nose what is happening is out here there is a area which is called regio olfactoria. So, it is called regio olfactoria and on top of regio olfactoria is bulbous olfactorius something like this bulbous olfactorius and if you really look at the cross section of this at the cellular details if I say it looks like this. So, there are individual cells like this these are the olfactory cells likewise. So, these cells what you see so this is where this is the zone where this is all the criss crossing out here these are the nucleus of this individual sensory cells. So, these are the sensory cells and these volatiles what you are seeing out here reaches here all the different volatiles. So, these volatiles bind to these specific neurons specific cellular. So, these are the sensory. So, what you see out here what I have just now drawn are olfactory you can call them olfactory sensors. So, what is happening is that these specific volatiles bind to these cells and once they bind to these cells. So, they generate electrical current out here these electrical current is all the way traveling to the spinal cord depending on. So, these there are either these are either these are these individual cells what you see they bind to a specific kind of volatiles or they may be a combinatorial output. So, say for example it means say for example this one say I name them as A B C say for example one option is that A binds to say only this blue ones B binds to only to the red ones C binds to only to the green ones that is one option how the electrical signal can reach or there may be like you know that all of them bind to all of them, but there is a different kind of coding. But most likelihood is like this that there are individual set of sensors which binds to specific volatiles and based on that a signal is being generated out along this pathway and it reaches to the brain. So, say for example now we have a mixed volatile coming which has few reds say for example 100 molecules of red 20 molecules of blue and say 10 molecules of green. So, total number of signal of the one which is the highest will be bound and that will create the highest amount of signal as compared to the other one which are 10 and 20. So, those signals will be less. So, automatically when the brain will be processing this information. So, brain will tell the one which has highest number of signals that smell is being dominated by those volatiles which are present in higher concentration in a mixture or you may be have a pure red on a all the red molecules are there or may be a pure green or a pure blue or nth. So, there are thousands and thousands of volatiles all across the world and based on that we have all factory memories which are I would not say well developed it is good enough for our survival in human being as compared to rats or mice or other rodents which have to depend a whole lot. So, but this is the basic architecture. So, from here these signals eventually reaches to the brain via spinal cord to brain via spinal cord and in the brain these are process in the cortex and based on that we identify a smell. So, this is the basic architecture of all faction. So, from here we will move on to the next all factory sorry next sensory system which is our tongue. So, think of it let us first of all try to practically understand it you take sugar very clear this is sweet one option you take salt you know this is salty now say for example, you take something which is which is a mixture of little bit salt and little bit sugar and say you know it is kind of a mix how we identify all these things or you take say vinegar you say you know or you go to a Chinese restaurant they use all this kind of different salts which gives a very pungent smell you know it is something or you go to have ice cream you kind say you know these are it is it is hot or something like that it is cold you know it has this kind of in a smell or likewise. So, how the tongue actually does all these things if you look at the so talking about basically it is also called the statory or let us call it as taste receptors what I will do I will draw the map of the of the tongue to give you an idea. So, this is how your tongue looks like I am giving for all the different kind of situation I am just drawing all the four. So, for example, when we say sweet something is sweet so within this there is a map a specific region which gets activated which is the tip of the tongue you can try out this experiment all by yourself it is this region which is mostly affected when we talk about sweet something is sweet. So, you take sugar and you put it on the tip of your tip of your tongue and you will feel that this part is the one which senses the sweetness. Now, there is a next one which is your salty something which is just reverse salt is tested partly by the same region, but slightly more in the map if you look at it is the same region which is testing, but it is much more spread out as compared to the as compared to the sugar and in between there is another zone which is taking care. So, let me write it down this is salt and in between lies certain regions which are say for example, you take yogurt or something like that this is the one which is taking care of your sour kind of feeling yet there is another region which is taking care of your bitterness something which is very very bitter that part lies somewhere in the back of your. So, what essentially this means this essentially means these different areas of salt sugar sour bitter there is specific sensory neurons. So, whenever we eat something those molecules which imparts us taste those taste molecule goes and bind to those specific spots. Once they bind to those spots they generate an electrical signal those electrical signal again follows the same functional architecture they from there move on to the spinal cord from the spinal cord they move on to the brain and within the brain if for that particular taste we already have a stored memory then it is fine it is able to correlate this is sugar you know this is sour this is and based on that they say this is ice cream or this is say mango or this is some other fruit say for example, orange or something, but if it is not there then that new piece of information it stores and if it is there then it can it you are in a position to tell them you know or then you say something like orange, but it is not orange so mind it whenever we talk about orange or say mango you always have to remember the other side for that piece of information there is not only a taste, but there is a visual information too. So, whenever we talk about the storage of informations in our brain for any specific thing there are multiple ways how we code that information for a mango there is a visual cue. So, you know you see a mango you say this is a mango or you see a lemon you say this is a lemon fine that is a visual way of looking at it, but the same piece when you taste it has sweet or you know sour or bitter whatsoever there is another set of information fine. So, now for mango you have one information which is coming from your tongue, one information coming from your memory, sorry from your from your eyes. So, there are for the same thing when you have to decode all these things comes into your mind and you say this is a mango or something which is not a mango, but very similar to mango you say it is very similar to mango or some other fruit or some other anything for everything we have different special sensory modalities, but based on which we identify this is mango this is x y z this is this this is that likewise there are several ways how we kind of look into like decode the information. So, now after doing the olfactory and the taste receptors now what we will do we will want to the eyes which is much more complex system to look with or the visual system visual system. So, what I will do the first thing I will do I will draw the eye. So, that gives you an idea exactly how it looks like at the structural detail. So, what you see this is structure is the lens the outermost structures it is actually double layer this is called cornea which is devoid of a devoid of blood vessels the cornea this is a blank space with filled with fluid called viterous gel or viterous space. Then on the back side of it is the this thing called this is your retina which is drawing a red and of course here there is a spot from where the signal goes. So, this is your retina and in between there are few other things which are not very important. So, just for your understanding sake so this is called aqueous humor aqueous humor this one is called iris which is holding just in front of the lens slightly on the side and this is the lens. So, I am just putting the lens like this it is a transparent tissue out here. So, what happens is that when the light falls light passes through this passes through this and then falls on the retina like this. Couple of things here for you to understand I told you the cornea is a non vasculated tissue. So, whenever you hear about replacement corneal replacement those are much more successful because there is no vasculature there is hardly any immune reaction cornea from a donate person who donates the cornea is transplanted into another individual. The lens is a transparent tissue this is a transparent tissue means these are cells which are devoid of all the organelles why is it so it is a very interesting cellular process and I will discuss this because these cells which are present out here which are present out here in the lens are follow a same routine as red blood cells. So, in the next section while I will be moving to about the cell types I will talk about how these lens cells are formed because lens cells and red blood cells follow the same pattern. So, at this point just remember that these are transparent cells they do not have anything. So, that the light can pass through it otherwise through a cell a light cannot pass or light will pass because a lot of light will be lost, but here nothing it is lost. So, in case your lens has problem. So, the option is you replace the lens and that is what exactly happens in people who suffer from problems with the blockage in the lens and all those things and then you have the retina which is this red patch what I am putting here. What is the cellular structure of the retina is the most important part to discuss. So, now I will move on to the structure of retina. So, retina is again just like the olfactory receptor or the T's receptors retina consist of two specialized kind of cells which could sense lights of different wavelengths they could sense color they could sense intensity of light. So, there are cells which could sense intensity and those are called the rods different light intensities from very you can see things in the dark you can see things in the very bright. So, these are the rods which are helpful in figuring that out and if there are another set of cells which helps you to sense color those are called cones, cones for cones see for colors just for you guys to kind of you remember it. These cones are not active during the night because if you realize in the night without any kind of. So, if you are in a dark place you look at the trees or look at anything around you it all looks black. So, during the dim light during no light almost hardly any light you are totally dependent on the rods. So, if a system is adapted to live in the dark they have a much well developed rod based system as compared to the cone where cone is not needed because you do not have to distinct about colors. So, just for your understanding sake those fishes or those species in the ocean which lives at a further depth do not have a well developed cone system or they may not have even any cones in their system because they do not need to discriminate color because the water because the light does not penetrate through the water into I mean it hardly penetrates to a certain depth beyond that there is no light. So, and because if you must have you guys who kind of look through discovery channels or anything you must have seen whenever these people go inside the sea they have this huge like lights on their head like you know they should be able to see because there is no lights and light does not reaches there. So, for and there is a huge amount of animal species which survives in those unfathomable depth of the ocean floor and those species entirely depends on the rod based systems they do not depend on the cone because they do not need any kind of any kind of cone support. So, this is the kind of given idea that these sensory receptors have developed or because of our requirements in the evolution which is our condition we have kind of you know developed these sensory receptors have adapted and their usage and their non usage has dependent on absolutely on what kind of physical modalities we had to detect. So, with this small background I will come to the circuit of the retina. So, I have already shown you the position of the retina. So, now I will draw the circuit. So, the circuit looks something like this. So, imagine the I showed you the side view of the retina imagine that I draw the eye like this once again and the light is falling like this. So, here you have the retina and now I am doing drawing the cross section of the retina out here. So, it is something like this they are the the furthest layer is called so, these are the typical morphology of the rod cells then you have these are the cones. So, I am just for simplicity sake I am only drawing four different cell cells here so that I will explain it what does that mean. This is one layer which is the called the rod and cone layer and beyond that layer there is something called red pigment epithelium cell PGE layer pigment epithelial cells cell layer and top of this you have another another set of cells which are called horizontal cells which are spread out like this. These are all different kind of neuronal cells and they are forming synapses with this is the horizontal cell layer and then you have another something called a bipolar cell layer you have something like cells like this. So, this is the bipolar cell layer then you have something called this is the very interesting cell these are called amacrine cells. I will talk about what are the functions of these amacrine cells these are currently under intensive study and then you have these. So, these are the ganglion cells so let us start naming them. So, these red ones are the horizontal cells horizontal cells then you have the here the bipolar cells then you have the blue ones as amacrine cells amacrine cells and then you have the ganglion cells. So, if you look at the structure of the retina this is a five cell layer structure if you look at the absolutely the furthest layer. So, that is the back which is retinal pigment epithelial cell which is out here shaded for you. So, this is that layer which is and this is the cell layer which supports the rods and the cones then you have the rods and the cone flares layer 2 out here layer 3 you have the horizontal layer, layer 4 you have the bipolar layer, layer 6 layer 5 1 2 3 4 layer 5 amacrine layer and layer 6 which is the ganglion layer it is a very beautifully arranged. So, if you take a cross section of the retina it is very beautifully arranged and the light is falling now this is light is falling from this side. So, light is falling like this once again here with me. So, light is falling like this. So, light passes through these and because none of these cells in between none of these cells in between have any kind of sensory receptors out here. So, the light reaches all the way out here and from here the signal transaction starts. So, what essentially happens is this now if we look at the structure of the rods and cones in further details while I was drawing I told you that I will come back. So, there is some very intricate details which needs our specific attention. So, these this is a classic rod what I am drawing now. So, this is how the rod cells are rod or then I will follow the cone which is more like there is a membrane a structure out there. So, this is called the outer membrane of the rods and cones both for them this is the outer membrane and here you have lot of mitochondria and here you have the nucleus same for both of them nucleus you have lot of mitochondrias and this is the synaptic zone. This is where it is synapsing with the next layer which is if you look at the picture. So, it is synapsing in the horizontal and the bipolar cells at this layer and. So, mind it they are always synapsing on multiple cell types it is not only synapsing on one cell type. So, coming back. So, these are the synaptic zone and this is the zone if you look at it in further detail if I if I blow this up or blow this up. So, this zone is something like membrane disk it is something like this and this dimension is around 20 nanometer from here to here around 20 nanometer and this is called membrane disk and there are great number of membrane disk out here which you can see I am just for simplicity sake I have just drawn few of them membrane disk with visual pigments. So, this is basically essentially the architecture of the rods and the cones. So, what is exactly happening is this in this zone if I further blow this up there are receptors which are setting like this. So, the receptors are setting like this all the red spots are the receptors on that membrane and same is for the color for the cones. Now, what is happening when the light is falling here is a light photon H nu light is falling. So, whenever the light is falling these it binds to these receptors the photons likewise and when the photon binds that leads to electrical signal this is how it works. So, this so here there is something which you people have to realize this is something there is something called a dark current what does that mean you understand this concept then you will be able to realize. So, under normal conditions when light is not falling say for example, it is normal suppose I am in a dark place and light is not falling on me these neurons are sending signals to the next layer. So, without any any ligand no light is falling as soon as the light starts falling they stop sending the signal. So, in other word what is happening is this if I draw it say for example, this is a matrix I am drawing and let me put it like this three situation one situation two situation three and these are the sensor elements these are the sensor elements and I have a reputation here 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4. So, this is the same panel which is. So, now in the dark so all of them are under this situation all of them are active active. So, this circle means they are all active there is no light you put it no light and imagine these are the different rods and cones which are sitting there or it is just for simplicity say things these are all rods which are sitting there no light all of them are active they are sending certain signals. Now, light starts falling now plus light another photons are started binding. So, light falls differentially a different. So, now the one which has blue on which the lights are falling. So, here there is no light falling here is there is no light falling no light falling no light falling now these are the ones where the light starts falling the photons are binding to these ones. So, as soon as the photons starts binding to this the signal which was it was sending. So, these are the signal which are being sent in stage 2 and this one these neurons are no more. So, now in this situation two you see a pattern so this is active this is active this is active this one so this one is active this one is active this one is active active active active active active active. So, this creates a map now about the structure which you are trying to see and the current which are being sent when during no light situation is called dark current it is just work reverse. So, remember this is very important. So, if I go back into this picture now whenever the light falls the they bind the and the signal ceases to move when the light is not falling the signal is there on the process. So, it is just the reverse of it this is how and that is why it is called the dark current and this is the way you have to kind of appreciate it. So, this is a situation 2. So, there could be a situation 3 where the light is falling at other. So, it makes a different kind of map say for example, now light is only falling to these 6 signals are going and all the rest are no more active. So, you create a different kind of map like this. So, the map which is getting formed is something like this or something which will have to exclude this one somewhere other now think of it. So, this is a new map which form before this the map was something different the map was like this look at the 2 structures they are different. So, this is exactly what I am trying to tell you it is just like you have say for example, those of you have gone to see this cricket matches or something in a flood light panel. So, on a flood light panel I can make an M or I can make a D I can make an A I can make an Q I can make an Z by switching on switching off certain light. So, you can see a pattern out there likewise I can switch off certain light I can switch on certain light on a panel that is exactly is the retina is all about and if this concept is clear to you people. So, now if you look at the structure out here this whole complex circuit. So, if you look at this complex circuit this complex circuit is nothing but a panel and as long as this you understand it as a panel this will make more sense to you people than kind of you know grasping through all the nitty gritty details of cellular geometry which would make sense you have to understand that always think of the analogy of a flood light in any place. So, there is a panel of flood light you can switch on and switch off light and make a pattern on that you can make A you can make Z you can make Q you can make 8 you can make 9 you can make 1 you can switch off all the lights and still you have the 1 not like keep a central line like that you can you can make an I you know like this. So, just exactly is the retina is all about it creates a pattern and that pattern goes all the way to your brain and same way it creates a color coding using your the cone receptors. So, the cones helps in the color but in the dark there is no color. So, this is basically what I expect you people to appreciate and understand this very very fundamental concept the way we store visual information as long as that is clear to you people rest is all k-quad then you can grab anything any book or anything you can figure it out exactly what is happening end of the day it is a coding of ionic electrical phenomena which is stored in the brain and again the same thing happens these ganglion cell through spinal cord see reaches the brain that is it through spinal cord to the brain and from the brain they got decoded and you know that this is 1 this is 8 this is 7 this is 6 this is m this is q this is f this is m likewise. So, this is what I wanted to cover on about the eyes now I will go on to the third modality which is your hearing modality this is almost follow the same thing but they have a slightly different geometry and that is what I am going to discuss now. So, those of you so we have 2 years and if you look at the way the way it is it is basically the sound waves which are moving out here through the canal it moves all the way inside. So, the way it works is this these are the sound waves which are coming and there you have a air conduction zone out here it is a bony matrix out here it is very bony. And then out here it hits upon 3 specific bones the sound hits upon 3 specific bones and the first one is called Malleus second one is called Incus third one is called Stapes this is the third bone which I am drawing now called Stapes and sometime this is also called Auditory Metis M E A T U S. So, now from here starts the journey of the sound waves as it is moving through out inside the yet after it crosses this it goes inside the cochlea. So, this is the zone which is very important for us the structure is a very kind of if you look in the picture it looks a very complex structure, but we will come to that and actually this is not exactly a sorry it is actually more like this do not get worried about this structure I will just try to tell you something which is before I draw this structure in depth. So, whenever you hear a sound you hear a piano you know this is a piano those who have some sense about sound of musical instrument or you hear a drum you say that is a drum beat or you listen to saxophone you say that is a saxophone or you listen somebody is kind of have filled the glasses with different amount of water and you know does that tinkering sound you could figure that out somebody is kind of creating those sound or you create a like whistle you know the sound. So, this whistle trail and all these things you understand all this. So, what exactly that does that mean? So, if you look from the electronics perspective. So, that means you have a sensor which should be able to sense the different sound frequencies that is very very important for different sound frequencies or different wavelength of sound there are only two ways you can figure out the sound either you know the frequency or you know the wavelength based on that you should be able to figure out what kind of sound is that. So, if you look now if you look at the keyboards any keyboard you play on a keyboard. So, you do it like that sorry gamma or like in a door a if you if you are in the western music you say door a llama likewise. So, every time you kind of you know bang on to a specific key it creates a unique signal and based on that you compose a song. So, you know this frequency this frequency this frequency this frequency. So, based on that you create a specific kind of node specific kind of line as long as this concept is clear then a year is a very simple thing. Now, I will come back to the cochlear structure which I told you that this is a complex structure, but do not worry with keep this background in mind. So, the structure of cochlear something like this do not worry about this part what I am drawing in the top that is involved all the balancing act and this tube is more like now with respect to steps which was the last bone it was here and here you have the incus and here you have the malleus and this one is called oval window smaller finer tip. So, this one is oval window and this one is called round window now enters through this likewise from here the sound is entering sound waves are entering here. So, now all along this pathway what you see there are specific cells which are sitting like this now when I am drawing this I will draw your attention to a keyboard imagine these what I am drawing now as the keys of the keyboards. So, for example, I am putting that k 1 k 2 k 3 k 4 k 5 k 6 k 7 likewise all throughout their line like this. So, whenever a sound wave enters here these keyboards based on the frequency of the nature of the sound frequency or wavelength they get activated and these specific component of the keyboards of the year are called hair cells H A I R they are nothing to do with your hair they are very similar to that hair cells similar in terms of the structure. They are called hair cells these hair cells are the ones which are a very specialized kind of neuron just like the rods and the cones which code for a specific sound frequencies and wavelengths. Now, how the hair cell structures look like something like this. So, if you draw a hair cell structure it is like this this is how the hair cell structures look like. So, they have ciliated structures like this. So, whenever there is a sound wave hits upon either they bent they all. So, these are these are underneath these are connected by different cytoskeletal protein. So, whenever a sound wave hits a specific chord and if this particular hair cells which I have drawn is coded for a specific frequency. So, this frequency matches with this frequency out here. So, they all bent in one direction they all bent in something like this. If this bends in one direction it will pull along with it it is kind of a spring it will pull all of them together on the other direction and as soon as they pulls they are something called mechanical sensitive ion channels out here. Mechanos because there is a mechanical motion here sensitive ion channels and as soon as this mechanical sensitive ion channels gets activated this leads to the flow of sodium ions inside it. As soon as the sodium ions goes beyond the threshold it is generated an action potential and this underneath is connected with another set of neurons which takes the information to the auditory cortex in the brain through the spinal cord through spinal cord it takes to the brain. So, now if you go back the previous diagram. So, from here underneath there are these circuits which are sitting which will eventually take all the information from here to the to the brain likewise. So, whatsoever coding is taking place at different points are getting are sent to the brain for further processing this is all about how it works. So, now in context of it you replace this whole thing you replace this whole structure imagine you have this key board sitting here with different keys. These are the green color and the keys are connected to your brain likewise that is exactly. So, you hit upon a specific key specific signal hit upon another key another specific signal moves. So, this is how the here is coding all the different pieces of information and we here. So, based on this coding there is memory storage in the cortical region of the brain which helps helps us to decode that this is the voice of your mother this is the voice of your friend or this is the voice of a bird or this is a vibration from some x y z sources. So, now to summarize what all in the special senses we covered we talked about the olfactory senses where is smell the volatiles we talked about the taste buds where we taste a specific things a specialized cells specialized neuronal cells which senses it then we talked about the rods and the phones which carries the information to the brain which is specialized neurons in terms of visual information and then we talked about the hair cells which carries information of vibrational information to the brain and thereby we here. So, and what I expect you have to a simplistic outlook to look at it that every information every modality every special sense modality which is reaching to your brain is being stored for that specific individual piece of information in several ways it could have a visual component it could have a hearing component it could have a taste component and x y z and based on that we developed that concrete memory about that x y z individual or x y z object it is a very wonderful combinatorial information storage mechanism which mankind is trying to understand and what we started in the beginning that is what we call as the neural neural code and from here we will talk the one of the tail pieces will be sympathetic and parasympathetic system. So, I will close in here thanks a lot for your attention.