Development of Nervous System | Neuroanatomy

0:00 right so today we are starting our series of lectures on neuro Anatomy this is a subject some doctors regard it as a terrorist subject because this there are many doctors were horrified by the neurosciences but actually if you really fall in love with the neurosciences you will find it these are not ads difficult to handle as usually they are considered art of understanding the neural net males start learning step by step and first concentrate on the basic concepts right in our today's lecture first of all we'll start with the development of central nervous system and development of central nervous system we'll start right from the

0:46 beginning that how zygote starts developing and how in the end when zygote is converting into a embryo and fetus there is central of a system developed or peripheral nervous system developed let's start with it from the very early part let's suppose here is uterus now what really happens here it is flow peon tube ovary right in the mid cycle you know when Griffin follicle is fully mature there is a Ledge surge right and

1:33 from the Griffin follicle this release of over right and this ohm is taken up by the fallopian tube in the improv ample impure region and from here this own start moving towards a uterus if by chance or somehow sperm happens to be there not one many of them right and if funds form fuses with this right we say that ovum is fertilized once the ovum is fertilized now let's pose this is the next stage now this ovum is fertilized it means it has genetic material from ovum as well

2:18 as from the sperm now if I draw this over mouth side this ovum is basically having zouna panda sudha a special layer around it now the first stage is that as soon as it is fertilized ovum is fertilized ovum completes its second meiotic division this point is very important attention please when ovum is released from here is the right ooh boom has cell membrane and it is having zona pellucida and their corner radiator cells around it right when ohm is coming here at that very time if it has completed its first meiotic to be on but

3:04 it is it has not yet completed its second meiotic devian right what I really want to say that over miz ad the metaphase of the second meiotic division whom is stuck at the metaphase of second meiotic division if ovum does not receive sperm if ovum does not receive spam then what really happens if this is not receiving the sperm whom is never going to complete it second meiotic metaphase it will die without completing that write down this point that when ovum is released it is already completed its

3:50 first meiotic division right and it has started its second meiotic division if this particular ovum never fuses with a sperm that is if this particular ovum never gets fertilized if it never gets fertilized it is never going to complete its second meiotic division rather it will undergo death process who ovum cannot live without sperm longer but if the real scenario is different let's pose when ovum came into fallopian tube there were many sperm also approaching that area you know that sperm will try

4:38 to fuse with the ovum and sperm there trying to fuse with the ovum there's not one sperm there are many many sperm will not go into detail of fertilization process but as soon as the first ovum first bomb which touches the ovum something strange happens as soon as sperm touches the ovum ovum becomes certainly active and immediately completed second meiotic division that's the point to understand the point which I'm highlighting as soon as spawn built at the ovum over male women rash will complete its second meiotic division release one more polar body and now it

5:25 become definite evolve now it become definitive over and when genetic material of ovum is already within the ovum and now sperm genetic material is pushed into that right this may become female pronucleus and male pronucleus let me repeat it as I told you the room as immediately as soon as sperm touches ovum Oh has completed its yes second meiotic division and release one more polar body and now it has been converted into definitive ovum definitive ovum has a nucleus with 23 nucleus with how many chromosomes 23 chromosomes maternal chromosomes meanwhile from the sperm genetic

6:14 material from the paternal side has arrived that will also consist of haploid number that is 23 chromosome now this particular ovum which is fertilized has 23 chromosome from maternal side and 23 from paternal side now when we talk about this thing that there are 23 from maternal and 23 from paternal these are called female pronucleus and male pronucleus then these two nuclei have fused together and that is the moment when they will mix up their genetic material now today it is not applied you can say it is 2n cell it is diploid cell from the three chromosome from maternal side 23 chromosomes from paternal side total how many chromosomes 46 once it

7:00 has achieved at 46 diploid number now this particular cell will plan to divide now it does not have any intention to die I told you if one does not receive the sperm it is going to die but because it has received a sperm now it is not going to die now it will plan to multiply right as time will pass by let's see what really happens here right that zona pellucida remains there zona pellucida is there and this ovum divides into two cells of course with mitotic Devere it is two cell stage right let's follow at this line this is a fertilized

7:47 ovum right or you can say this is zygote now this is zài goat right now the first stages that next stages that zona pellucida will remain intact but this material will divide into zygote will divide into how many cells two cell stage then zygote will go to the next stage what is that yes please for cell stage right when it is passing through this rapid the V n right we call that zygote is converted into blastula this was I good this was as I go out and now this is converted to blast law we

8:40 convert it into blastula when you have blastula further itself will divide and then these cells will make a mass of about 8 to 12 or around that collection of cells right now this collection of cells is still packed within zona pellucida it means as the cells are dividing they are getting larger or smaller entities smaller entities those are right these are called blastomeres and these individual cells are called blastomeres and original zygote first pass through two cell stage for substrate blast to last stage and then

9:26 from the blasts flood stage when it reaches at this about 12 cells tailored around that we call it yes place we call it Mahalo Mahalo we call it Narula so what was their attention there was I got right then zygote convert into blastula blastula convert into morula blastula convert into marula then in next stage what really happens that zona pellucida is still there and attention please these cells some cells make a mess the center some cells make a mass in the center right and the other cells which

10:15 are arranged on the periphery and these cells start differentiating the group of cells in the center and group of the cells in the periphery they are going to develop in a different fashion now the cells which are present in the center thus a group of cells which are present in the center it is called inner cell mass it is called inner cell mass and the cells which are rounded they are called outer cell mass cells which are within they are called inner cell mass and cells which are swarming outside they are called outer cell mass you know baby will grow out of inner cell mass and outer cell mass will

11:03 convert for the supporting tissue for the baby outer cell mass will made you can say coverings on the baby and it will make placenta is that clear so this is very ugly differentiation stage that there's inner cell mass this outer cell mass inner cell mass will eventually convert into different layers which will make the embryo and fetus and outer cell mass will be eventually converting into sporting coverings like a neurotic membranes are there or there are you can say chorionic membranes or more importantly placental tissues this is that layer now after the marula next stage occur and in the next stage what

11:49 really happens right this is inner cell mass inner cell mass and of course that is outer cell mass inner cell mass will eventually convert into definitive embryo now next stage what really happens that blastocyst start zona pellucida sorry zona pellucida start dissolving zona pellucida start dissolving and when zona pellucida is going under dissolving process what really happens when zona

12:36 pellucida is undergoing dissolution process lot of fluid is accumulating within and when a lot of fluid is accumulating within outer cell mass remain like this and within the Saffir of outer cell mass inner cell mass is attached at a particular point this is inner cell mass now this is inner cell mass and blue ring the other outer cell mass and blast now and what is this this is accumulation of fluid this is fluid filled cavity this is a fluid filled cavity when this type of shape is achieved we call it yes please

13:21 blasto cyst we call it blaster cyst and in this blastocyst inner cell mass is now called embryo blast in the cell mass is now called embryo blast and outer cell mass is now called prefer blast prefer blast you see let's go blast means cells which are rapidly proliferating embryo blasts mean the mass of cells which are rapidly proliferating and going to make embryo embryo blasts mean mass of cells which are rapidly proliferating and going to make embryo and prefer blasts mean rapidly proliferating cells which have a

14:06 perfect value trophic value mean growth value that if trophoblast is there trophoblast is responsible to provide the material for the growth of the embryo for example glass will eventually convert into what definitive Pleasant time at advanced age and other membranes around the baby now again out of this embryo blast and trophoblast further development will be seen one thing which will happen there from the trophoblast some finger-like processes will come out we call them will I write these are villi this village specially grow at embryonic pool especially grow at embryonic polls that

14:54 pole of the outer cell mass wherever embryonic mass is attacked so this will especially grow support out from the embryonic pool right and these will I something strange happen now you know these villi are made of the cells but cells which are on the outer side right cells which are outside these cells lose their membranes and all these cells fuse with each other and when all these cells will fuse with each other these cells will make a continuous layer of cytoplasm in which lot of nuclei are embedded again let me tell you what really happens at this point let's suppose this is one point villi this is

15:40 another willis this is another willis still one more Vella's what it's really happening that in the center core look here this villas was made of cells right and outside there were some cells which are on the sides these cells fuse with each other these cells fuse with each other and this fingertip has internal structure in which cell membranes are well defined but outer cells membrane the fuse with each other and an internal structure nuclei within the cell but in outer structure nuclei are just floating into cytoplasm it means cells which are outside the fuse with each other and

16:25 when these cells fuse with each other they make a network that is called syncytium that is called since ischium now look this inner cellular tissues trophoblast as well as the syncytium tissues also prefer blasts because both of them are derived from the outer cell mass right inner is trophoblast as well as outer is also prefer blast because inner is trophoblast and inner trophoblast has basically made of well-defined cells as it is made of well-defined cells so we should call these points where the cells are very clear-cut with the membranes these structures are called Saito trophoblast and outside where some

17:13 special material is present we call it some CCO roof Oblast right let's recap what really happen up to our attention please let's recap what really happened here come here now that originally there was just you can say ovum right and it was having zona pellucida and there were some cells around it and these cells were making some mass like this right so this is corona radiata right this is how new lead the new you can say ovum which

17:59 has jumped out of Griffin follicle and it has been taken up by fallopian tube right this new cell is approached by sperm as soon as sperm will touch the ovum right ovum will immediately complete its second meiotic division it will complete its second meiotic division and releasing one polar body it will convert into definite native over then within the definitive ovum there will be female pronucleus and from the sperm there will be arrival of male pronucleus male and feel female pronucleus both have 1n chromosome so one end from mother 1 and from the father it will be

18:44 to n the VN so haploid gametes will fuse together to establish the diploid e that is 46 chromosomes and now this cell with 46 chromosome is called yes this is called zygote once they good has been formed right it will go into blastula stage in which cells will start rapidly multiplying and with every division initially cell size is getting smaller right and as onopen sudha initially is kept intact so this stage is called blastula until this cell mass right blastomeres mass will reach somewhere 8 to 12 or 12 to 16 you can say around that cell mass and this cell mass is

19:31 called marula and then within marula if we renew as mobile of further grows we'll come to know the cells in the centre are put together clump together and seldom the periphery are differentiating in slightly different fashion the central mass of the cells is called inner cell mass and outer cells are called outer cell mass right after that what really happens zona pellucida start dissolving fluo start going in and out ourselves make the site ro trophoblast and inner cell max makes embryo blasts right and what really happens because it's some fluid filled cavity as well so this type of rapidly growing tissue in which there is cavity fluid filled

20:17 cavity we call it blastocyst and the blastocyst outer cell mass cells rapidly proliferate some cells keep their membranes intact right and cellular detail intact these cells are called these cells are called cytro trophoblast outside that cytro trophoblast the cells dissolved the membrane they are cytoplasm fuses with each other and it is within the sea of the cytoplasm the nuclei are floating and this tissue is called some C short of a blast now how many days have passed after fertilization how many days have passed after all yes please yes any dog how

21:06 many days have passed about one week right he's right about one week so actually what has happened that on the mid cycle this was released let's pause it this lady as a cycle of 28 days it means on 14th day of cycle this was released right and if she has received form around that time it means around 20 first day of the cycle this product of conception have gone through zygote state blastula stage morula stage and then blastocyst stage by the time it reaches uterus it is in which stage blastocyst stage by the time

21:51 it means by the time development from here has gone up to the extreme end of this world right it has spent about a week it's all happening during the first week and it may be fifth day or sixty or so and now it blastocyst had reached the uterine cavity as soon as blastocyst reaches uterine cavity right let's suppose I draw it here it is inner cell mass it is inner cell mass and here was your site or tofu blast and inside there is embryo blast and what's here these are the villi these are the villi and this villi are covered by displays cincy show yes

22:40 please since II show proof Oblast right now this finger tips like Saito trophoblasts ensign sito trophoblast they release enzymes destructive enzymes and these destructive enzymes releasing cells or villi when they touch the maternal endometrium wherever they touch the maternal endometrium they will dissolve the maternal and a Mariam and this is the beginning of implantation it is the beginning of implantation that now blastocyst will get implemented within the endometrium now when blastocyst reaches here when blastocyst reaches here and it is implanting right within the maternal endometrium maternal and metrium at this very time ideally

23:27 speaking is in which phase and the museum is now mainly acted upon by estrogen or mainly acted upon by progesterone right it is progesterone so it means it is an ardent proliferative stage you know estrogen drives the endometrium to proliferative state right but proliferative stages up to 14th day after that what really happens the second half of the cycle the heavy amount of progesterone which is being released by the corpus luteum the remnant of the graafian follicle so progesterone which is coming over from here right project strong that has converted this into which phase of endometrium highly vascular and circulatory endometrium which is very

24:15 very feasible very very you can say good preparation of endometrium for the arrival of blastocyst because by the action of progesterone and the museum has become highly Secretariat's glands have grown well if they're vascularity has grown well it has become soft and it has become highly vascular and now when blastocyst well starts you can say digesting the way Jews most commonly it binds with the implants on the posterior or superior wall of the uterus most commonly superior upper part unusual bindings are also there and as time within 1/2 days it will digest away enough endometrium and it will go within

25:01 the endometrium right and once it is within the endometrium it's about 10 3 or so 9th or 10th day and we say implantation has been done and as you know that corpus luteum can supply progesterone once corpus loot look this was Griffin follicle it released ovum after that is converted into corpus luteum once it is converted into corpus luteum carcass luteum is a natural lifespan of about 10 to 12 days so it means for few days it will keep on giving the supply of progesterone after that usually corpus luteum degenerates and supply of progesterone is automatically lost and if you know when

25:48 supply of progesterone is lost if slab progesterone level goes down rapidly what really happens that endometrium is lost and you can say and the mutual lining along with some bleeding is passed out right and this is called menstrual bleeding right now we have to be careful this time this lady is pregnant right and this time as blastocyst is planted within the endometrium right should this lady lose the endometrium out no so it means menstrual cycle should not start it means this lady will miss the periods right how the request that there should be no period are forwarded by the products of baby itself the cytro

26:36 trophoblast will release a product which is called HCG human chorionic Veneto truffle human chorionic gonadotropin HCG as many function one of the important function is that it has receptors on the purpose leo tiem it will attack the corpus luteum and give the good news that deer corpus luteum the ovum which you had released luckily has met with the sperm the product for conception which have been planted and they are giving message to corpus luteum through the HCG to the corpus luteum that please don't degenerate carbon copper solution luteum receives the HCG this is a signal that there should not be any bleeding

27:22 they should not be the loss of endometrium as this particular endometrium is very precious endometrium because it is carrying the product of conception so what really happens that corpus luteum start growing rapidly right it's so happy and it grows rapidly and it convert into carpus gravy dumb and thus corpus gravid am now releases very large amount of progesterone and of course this region also along with that and this is responsible for many many months to keep the endometrium intact and in the secretory phase so that product of conception dwell up in the uterus properly and normally until

28:07 baby's trophoblastic tissue develops up to such stage that trophoblastic tissues capable of releasing its own is regina progesterone then it start reducing this level of HCG and then maternal maternal purpose gravida will start degenerating because now baby i had got semi-independent as far as student progesterone is concerned is it right now what happens next is the first week in the next week second week we are starting the inner cell mass will convert into two layers

28:55 right so we have seen at the end of the first week and embryo blast is well to allow right and beginning of the second week and now you know blastocyst has implanted over there lots of systems already implanted in the functional layer of endometrium which is that this layer is already in circulatory phase it is under the effect of high progesterone fine now one thing which we were talking about