 Welcome back to the lecture series in bioelectricity. So in the previous lecture we talked about hearing and the previous to that we talked about vision. So among the special senses in the beginning we decided we will be talking about vision, hearing, olfaction, taste and some of the skin related proprioceptors and everything. So we have covered the stretch reflex arc where we talked about you know the pressure which is there through muscle spindle. Then we talked about vision where we talked about the rods and the cones. Then we talked about the hair cells in responsible in hearing as well as in equilibrium. So this class we will be discussing about the olfaction or the smell from olfaction all the way to the gustation which is basically the taste. So to start off with have you ever wondered why the mosquitoes kind of home around you in the night or some of the insect get attracted towards human being. What it is? Is it they have a fantastic vision they understand that this is human being so we should get good amount of blood from them we will rush towards them. So if you look for all the vector bone diseases like in mosquito takes and the relevant diseases like malaria and sleeping sickness like using sexy flies and all how they get attracted towards human being. So one possibility could be the warmth of the body the IR radiation they have a sensor they could sense it is a warm body and they move towards it. Of course this is one of the mode by which they identified there are other modes some of the other modes includes they have a extra ordinarily well developed olfactory system which is not that well developed in case of man because we rely a lot on our vision instead of our smelling abilities. Whereas if you see a dog a sniffer dog it can smell lot of things which are human being with it is very limited repertoire of olfactory receptors unable to do whereas in the case of insect they are even much better they could you know they could distinctly smell the smell of your sweat or the body order they could distinctly smell the octinol known on all these kind of compounds which are found in your sweat or they have very extraordinary carbon dioxide receptor. So if you look at these insects they get attracted towards you by the plethora of receptors in their antennae by virtue of which they could detect the smell and not only that they could detect the smell it is very interesting the order plumes say for example there is a kind of order coming out emanating from my body. So it forms a plume all those volatiles which are there which are forming a plume and these insects say for example insect is here it could follow the plume either it will like or dislike it say for example one of the chemicals called deat DWET this is an mosquito repellent. So whenever it the mosquitoes experience is a plume of deat they repel and they run away from that or they fly away from that source of that smell or some kind of mosquito repellent or some kind of ointment what we put on the skin. So this all these things are being processed by a well developed olfactory system. So here what we will do I will just give a overall outline of it and we will discuss about just the same way we have discussed about vision and we have discussed about hearing we will be discussing olfaction and then I will give you some very specific example from the insect world telling how these studies are being conducted and what are their ramification how these studies are helping the economic entomology where especially with the tropical insects or tropical diseases especially the vector bone diseases where it comes so handy and few other references which I wish you people should go through in order to enrich your database of or opening up your window to see how these different electrical signals are being exploited in order to develop different kind of modalities to counter different vector bone pathogen. So let us start the lecture number 21 lecture number 21 so one second so here we will be dealing with olfaction and gestation. Gestation is taste and olfaction is your smell within olfaction we will be dealing with the world of insects and this whole area falls under a domain of chemical ecology or it is also called sensory ecology and in case of human being which as I have mentioned has a fairly low olfactory ability as compared to the insect world and here we will be talking about some of the vector bone diseases. Now coming to the basic architecture again we will go by the basic architecture first if you look at the basic architecture so say for example this is for the olfaction your major is the nose so essentially happens you have these volatiles which there are one second so these are the volatile molecules all over the place different kind of volatile molecules in red as well as orange blue green ok. So these are the volatile molecule which are experienced by our nose and we detect a certain smell so from the nose this there are specific cells olfactory neurons first of all olfactory olfactory cells you can call them the one which receive the signal and then through olfactory neurons they are all neurons though these are the first line it all the way way way goes to the through spinal cord goes to the brain and decodes the message and this is what makes you feel that say it could be acetone alcohol CO2 nononal betaic acid likewise so so many different smell ok the plethora of different smell in the case of human being if you see human being at the time of their birth could detect approximately 10,000 different smells and it has been observed with age this ability to detect smell after 50 years with the onset of the aging the ability to detect the smell takes a down downward downhill as you grow old your detection limits kind of goes on decreasing ok now coming back to the basic architecture how it looks like so at the level of nose if we kind of you know magnify this further out here something like this it looks like these are the very specialized neurons which could which are the kind of this olfactory receptor cells these are called receptor cells then you have the olfactory gland which is sitting out there in between which is more like structure like this this is the olfactory gland and this could be divided in two parts actually essentially this part is called olfactory epithelium epithelium and out here the second level is called lamina propria here is the olfactory bulb so from here there are series of neurons which takes the message for further coding and out here this is the zone where the different olfactory molecules or the volatiles kind of binds in the yellow and the pink color what I am putting the dots out here so these are the different olfactory molecules so essentially what happens is this these molecules goes and bind on these surfaces once they bind they open up the sodium channels and there is a flux of sodium and this flux of sodium leads to change in the electrical signal and this electrical signal eventually travels all the way and through the synaptic connection is transmitted here and this is the way it goes this is very simple circuit but each one of these cell types has the ability to distinguish or detect one specific kind of order to the maximum ability that does not mean that it cannot detect another order but generally the way it looks like is that each type has the ability really combinatorially they have the ability say for example if I have three kinds of volatiles say A, B and C and D or four kinds so this will be A type this will be B type like there will be C type or a D type so there could be 10,000 different types there will be 20,000 different types and what essentially that means is that A has the maximum ability to bind to if these violet ones are the A molecules if I assume their maximum binding will be of the violets maximum receptor will be of the violet as compared to say the pink one which may be you know B type so this is how these specialized neurons have evolved and this architecture so this is out here what you see actually essentially is the nose so this is if I had to draw a nose it will be almost like this so this is underneath nose that is where the volatiles enters and this is the circuit to follow and these are the ones which are sent to brain and in the brain there are specific cortical areas where the processing starts and then based on that we decode the message so essentially what it translate out to be is this for every order say for example a pungent order or something there is a unique electrical stimulus electrical stimulus codes for say order A for order B likewise and each one of them likewise goes on they have a combinatorial mixing of say order some give a quantity say 5 units of this signal 2 units of this signal 3 units of another signal 4 unit of another signal 7 unit of another signal and then there is a combination of this permutation and combination by which we get a unique order for every individual component we smell so I understand so basically those 10,000 neurons are doing a lot of computation little bit of a signal type a little bit of signal B little bit of signal C and that results in a totally combined into a totally different kind of order so whenever we smell something it smells something like this something like that we are unable to really detect very clearly so this whole combinatorial geometry is very interesting and how this is being dissected out this is very interesting so from here I will take you to the world of insect where these all these things are being detected so some of the modern analytical chemistry tools come fairly handy in deciphering some of these receptors the way it works if for example so this is a simple electrophysiology setup coupled with a gas chromatography setup so if you look at a insect most of the time the insects kind of you know looks like this and you know or if you get a side view of a insight it is something like you know so they are major olfactory sense organ olfactory organs are here they are antennae so now what you can do is say for example so if you could fix an insect like this with its antennas like this say for example some moth you know I am just showing the face of the moth like this and very close to the moth you put an electrode like this we should be able to you know record from the moth now on top of that you have a smell injection setup it is a GC column with its analyzer sitting out here so this is a gas chromatography grass chromatography setup and through this the volatiles which are flowing by are released so you have a control release so you can switch on and off out here so you have a switch and here is the electrode you have and this electrode is connected to certain voltage with the ground electrode very close by ok now you get in your reading panel you are seeing say for example I say from here I am releasing three gases say CO2 alcohol or OH I am just putting OH and acetone and say beta eric acid BA fine these are the four volatiles which I am going to release and the sequence of it will be A, B, C, D fine now my hypothesis is this that this particular moth the antenna of the moth could smell ethanol or OH so now I allow the CO2 eject out and here is the electrode sitting touching on the surface so if this is so so this is say for example the GCP saying that so this is this is scale is showing the upper scale is showing GC, GCMS you could attach it with a mass spec if you have an unknown thing ok so this is the GC scale and here is the electrical signal if it has a CO2 sensor with suppose this is A then there will be an electrical signal you should be able to see in the lower column if it does not have then you would not see anything it will just go like this now if we hypothesize that it has a sensor for B it has neurons which could sense alcohol so when the alcohol will be eluted out out here this is for B then I should be able to see a sharp heavy signal of electrical signal out here it could be both sides it could be like this also you can write I am just doing the upper side just as a convention nothing else ok. Now say for example now you are eluting out C this is the signal for C so you should be able to see another electrical signal if at all it has a receptor for C or you may not see anything and it will just go like this you know like so this kind of setup of GCMS coupled with electrophysiology is what is used for these kind of insects and of course you can further verify it using certain behavioral assays where you have you know you have these kind of spheres if it is a walking insect and you have the order plume coming from here and you allow the insect to move on it so this is a model of a servosphere so if you ensure that there is definitely for alcohol it has an affinity what you can do you can put the insect moving insect if it is a walking insect of course otherwise if it is a flying insect then you have to have a wing tunnel on a wing tunnel from one side you have to give the order plume and you have to see whether the insect fly towards it or not or it ripple towards it these wing tunnel assays are being done for the mosquitoes ok wing tunnel assay for mosquitoes and other flying insects whereas for the walking insect you use something called servosphere or this is also called locomotion compensator locomotion compensator is a very interesting thing say for example what happened in locomotion compensator say for example this is a walking insect now on top of this you stick certain specific compound a specific material which could reflect the light like this so locomotion compensator is something like this for example so on top of this if this insect walks in suppose the order plume is coming like this and this insect walk towards it or on this side so based on the on top of this is you have to imagine a three dimensional because this is from the surface it is coming the order plume on the top there is a there is a sensor there is a sensor which will tell if the insect moves in this direction it will this is fair will compensate and will come back to its original position if it is moves in this direction it will compensate and will come back to its original position so essentially it will allow the insect to be in the same position facing the plume of of the volatile and if the insect does not really like it it will turn back and it will start moving towards you while you are looking at this is fair so I will request you guys to really look into the servo sphere and locomotion compensator because this is not within the purview of this course I mean it is a behavioral assay if you find really wonderful results in the GCMS column you can really see the servo sphere but this is something very interesting and for this kind of work you should refer to these work of some of these people like you know you should look through the work of Walter Lille in Walter Lille is currently in UC University of California at Davis you should see the work of one individual who is currently a faculty you should see the work of Syed he has worked with Walter Lille currently he is I think University of Nebraska when you should see follow his work he has worked in mosquitoes you should see the work of professors both all of them are professors okay professor Patrick Guirin in University of Neuschertel Switzerland these are the people who there are many other names which I mean I will just try to you know pull up some of these references you should look for their work because they have done significant amount of work in last 20 to 30 years in this area where some of these servo spheres I have been developed and I will give you the original reference which was done by Kramer who actually developed during 1976 the servo sphere model where you can really see the you can do the computation but in the area what I essentially wanted to highlight the reason to you know expose you to these kind of areas is this that the world of electricity by electricity is very wide very very wide from the insect world to the human to the plant it is all well spread out it is essential that you have to keep your mind open to you know appreciate all these things because I mean just 40 lectures or 40 50 lectures is not sufficient really you know kind of open yourself up to the whole world end of the day to realize it is a simple computation whether the modality may change modality may be you know light modality may be sound modality may be modality may be smell or olfaction but end of the day they code an electrical signal through of course rod and cone or for the sound the hair cell for a smell olfactory cells likewise but end of the day they all code certain unique electrical signature and these electrical signatures essentially falls under the whole area of neural code. This is where we say we call an apple and apple because there is an unique neural code for an apple is an unique neural code for a grass is an unique color coding. So, that is what makes our whole world around us so very interesting in the same line touching upon this since I have touched upon the olfaction I have to give given you a very brief exceptionally brief outline about how these are being used how we could utilize these kind of models where it all goes see for example you know for say set C mosquitoes if you know exactly what kind of molecules or volatiles they are getting attracted or say for example you talk about the ticks in the temperate countries this is a huge problem if you know the volatiles which are attracting them or repelling them both ways you know attract or volatiles which you know let me put a different color code for it or the volatiles which you know ripples them so you can develop if you if you know then it is a attractant then you can develop a trap where you can trap them because they will be coming close to it and if you know it is a repellent then you could develop an insect repellent. This is a whole area of amazing research where entomologists along the electrophysiologist are utilizing or exploiting the electrical properties exhibited by these different insects to devise methodologies against vector bound pathogens. So from here I will just take you to the world of taste or gustation which is again in the case of human being starts declining after the age of 50 but I will just give you a very briefly kind of if you look at your tongue and this again gustation is a very interesting topic in the case of insects because if you look at it I mean you see a lot of insects along you know cow dung or you know all this kind of you know places or along this dust bin and everything you know trash why is it so it means they could taste certain material which we cannot of course you know but for x y z reasons. So gustation is again very highly evolved in several lower animals in the case of human if you look at the tongue the structure of the tongue which is involved in it is something like this. So if this is the structure of the tongue then you will observe that there are different areas which have different role like the tip of the tongue if this is the tongue is involved in sweet smell whereas there is a area which is now I am putting in a kind of you know hatched area which is kind of involved in sour then similarly there are there is another area which is kind of overlapping which ensures your sorry I just made a mistake actually this is this is the sweet and this is this is this is essentially is the salt and this is the sour area. And then you have certain areas like you know which ensures for bitterness so if you really look at all these things so from here what essentially this tells you this list can go on and on there you know into this. So what is essentially says underneath these structures there are specific cell types these cells carry the message based on that there are sodium channels which are opening and they are generating a specific kind of you know electrical signal these are carried all the way to the brain and that is where we decode the message. So for individual type for the sweetness for the sour for the salt for the bitterness there are specific kind of cell types, gustatory cell types which are present they ensure that we kind of you know there is always a combination suppose we have something which is slightly sweet and sour. So basically when we talk about the less sweet and sour chicken or sweet and sour vegetable what does that mean when technically that means that you are tasting something which has a sweet component as well as sour component. So the electrical impulses are generating from here electrical impulses are generating from here and the brain is pretty much processing these two together and telling you know it has a sweeter sour list or something as a sweet and bitter or sour and bitter or salt and bitter. So basically there is a computation which is taking place out here as well as out here you know and you may be something which has multiple taste. So end of the day what is the most important key point is they are activating the sodium channels and those sodium channels are leading to electrical signals. So for sweetness anything which is sweet there is an unique electrical signature and obviously for the saltness there is another set of electrical signature for sour and this is just I am randomly drawing. So do not think that you know something for bitterness there may be something like this. They are all unique electrical signature which are being transmitted at a different phase with a different frequency with a different kind of you know density and these signals are being deciphered by the brain and based on that we understand what we are smell what we are tasting. So if you look at this whole if I had to summarize this whole special senses what we have talked about the vision hearing alfaction taste you will see all of them have one common feature they all code if I had to summary the summary of the special senses summary of special senses vision hearing taste smell they are all different coding one common feature they all code for they are all translated into electrical signal they are all involved in sodium channel potassium channel chloride channel likewise these all are sent to the brain for further decoding. This is the overall if I had to give one small layman summary this is how it looks like in the case of vision you have rod slash cones taking care of colors you have the hair cells you have taste neurons you have olfactory neurons and then you have touch neurons like so on and so forth where all of them follows this they all have electrical component all this ionic component ionic electricity which is eventually sent to the brain and this whole area of coding is the final frontier where mankind is heading is neural code what is our neural code in other word a question could be asked could we hear a image in other word you are seeing something and this is connected instead of in the brain to the visual cortex we see or olfactory cortex OC and for hearing auditory cortex AC say for example a visual connection goes all the way to auditory cortex what will happen or a hearing goes to visual cortex what will happen at taste all or gustatory receptor goes to say auditory cortex what will happen these are the questions of the future where we are heading where many of our answers lies about who we are in solving those wonderful questions so I am closing on here in the next class we will be talking about the learning and memory and all the higher functions of the brain thank you.