NEURO-MUSCULAR JUNCTION MECHANISM

all right hi everyone so today we will be discussing the concept regarding the neuromuscular Junction right so first of all what is the exactly neuromuscular Junction it is the junction between the neuron or the nerve ending and the muscle right so here you find this as your neuron and this is your muscle skeletal muscle right any any of the motion you take for suppose this is your biceps muscle right any any of the skeletal muscle right so this is your nerve ending or also called as the axon terminal right the junction between the axon terminal as well as the muscle this particular Junction is called as your neuromuscular Junction so now I am going to enlarge this part and explain how exactly this neuromuscular junction box and one important thing is that knowing the complete details about the neuromuscular Junction is so important because there are some drugs that act in this mechanism and block the receptors so when the receptors are blocked then there will be no neuromuscular transmission leading to several types of muscle weaknesses so to understand the drug action in pharmacology you need to know about the neuromuscular Junction in and detail okay so first of all right so this is your never-ending I mean lodging it and showing you so this is your not burning right and as I told you in turn regarding the skeletal muscle this is your skeletal muscle right so the junction between the new law as well as the skeletal muscle more appropriately speaking in the junction between the nerve ending of a neuron as well as the skeletal muscle so this Junction is called as the neuromuscular objection so first of all the main key role or the main neurotransmitter that is playing a key role in this entire mechanism of neuromuscular Junction is acetylcholine so first of all we need to know how a city of colon is synthesized right no this is the membrane of the axonal nerve ending what we can also call this as pre synaptic membrane on the surface of on the membrane of the presynaptic membrane around the presynaptic nerve ending we find small transporters right so these transporters are named as : transporters because they transfer the colon which is present in the extracellular fluid into the nerve ending : so this is the colon that is present in the extracellular space of the extracellular fluid so this colon is transported with the help of this transporter protein called s : transporter into the presynaptic membrane or the presynaptic nerve running so this is your colon no and one important thing is that you also know on every nerve ending on every neuron nerve ending that is innovating the skeletal muscles or smooth muscles or whatever it may be on every nerve ending there are sodium channels as well as calcium channels so this is your sodium channel right and at the same time okay this becomes your channel so the blue ones are the sodium channels and a black ones are the calcium channels on every external learning you find these channels so let's come back so as I told you the main keyword who is training this neuromuscular Junction is acetylcholine so first of all we need to know how acetylcholine is actually synthesized right as you know you take different types of dietary component a daily different types of food or vegetables whatever you take so as a result of the digestion there are some molecules that are released into the bloodstream of the extracellular fluid so one not that molecule is : so you can also say the source of : is your food itself so CO line through the full it when it is absorbed when the food is absorbed it enters into the bloodstream and through the bloodstream you - interesting to the neuromuscular Junction so now the colon which is present in the X plus LS space so let me write your extracellular space or extracellular fluid whatever it may be so : in the extracellular space with the help of : transporter it enters into the presynaptic nerve ending so this after entering after entering of the colon the police and optic nerve ending we need to combine the colon with one more thing that is acetyl co a so from where this acetyl COAS come in the pre synoptic nerve ending itself there are abundant amount of mitochondria right so mitochondria through several chemical reactions and several cycles finally it produces an end product coalesced acetyl coenzyme a so mitochondria produces acetyl coenzyme a thank know this : as well as acetyl coenzyme a both of them are transformed or converted into combined and converted into acetyl co a both of them are converted into acetyl coline not coeds etc : right so once again : which is present in the extracellular fluid is transported inside the pre synaptic membrane with the help of : transporter next this otaku is obtained from mitochondria through several chemical reactions finally the end product of mitochondria which is released this acetyl coenzyme you know this : as well as acetyl coenzyme a in the presence of an enzyme can't see a T C stands for : a stands for receipt and P stands for transfers : acetyl transferase so in the presence of this enzyme : acetyl transferase : and a step wave both of them are transferred are transformed into or converted into s8 M : so this is how acetylcholine is formed now this acetyl choline must enter into the vesicles because vesicles have to fuse here and release the content right so a stern : now it has to enter into the basicness so as you know here in the nerve ending there are different types of play circles in abundant and not many vessels are present and this vesicles contain these red molecules which I'm drawing here these are the acetyl coline molecules so actually how does this end so this is one which I am watching it and the surface of the membrane on the surface of this vesicle is called as basically a membrane right when this is your pre synaptic and this becomes your vesicular membrane on the presynaptic membrane what are the transporter proteins present and what are the structures that are present on the presynaptic membrane are sodium channels calcium channels and colon transporters and on the surface of the vesicular membrane what are the structures does represent our colon is a tank : transporters here there are : transporters transporting : from extracellular fluid into presynaptic membrane so here there are acetylcholine transporters or acetylcholine and the port to be called us right so this gets transferred inside the help of this acetylcholine and he portal instead calling transported a strain : which is present at the presynaptic membrane finally this is how the basical is containing acetylcholine molecules this is how the vesicle has got this visitor molecules so while you remember fussy about this : transporter and as well as this anti port I mean acetylcholine antiport because there are some drugs right there are some pharmacological drugs that bind this : transporter and there are some other form of Gavi contracts that bind this acetylcholine antiport right so the drugs that are binding this : transporter are mainly one blood wait it is Hemme Collini 'm right chemical inin is a track that binds to this : transporter and does not let the : to enter I said when : does not enter inside instead : can't fuse with any other thing except other than : right and that then : it car cannot fuse to any other thing you can fuse only with : so when : is not there finally acetate : formation is stopped or ceased in the same way as I told you this is a staple and antiport right then binds to this acetylcholine antiport and does not allow a sitter Ecoline to enter into vesicle es so that drug is the single all right so there are mainly two pharmacological drugs which you need to remember here regarding the transporter proteins chemical in him is the track Amica lynnium is the pharmacological drug that mainly binds to the colon transporter and does not let colon to enter inside at the same way on the situated on the vesicular membrane there is acetylcholine at the port binding to this ester call in and report there is way similar so when we were small pharmacological it binds to this it does not allow a stair colon to enter a cell when a still coolin cannot enter inside the empty basically cannot fuse even though it fuses it releases its empty substances I mean nil there is no a straight colon in that type no finally we learned about the synthesis of s 10 colon and transport of his type colon into the vesicle now we will learn about the fusion of acetylcholine I mean fusion of acetylcholine containing vesicle to the presynaptic membrane so finally what has to happen is that this is the vesicular membrane right blue color bond surrounding the vesicle and this is the presynaptic membrane so finally this vesicular membrane of presynaptic membrane both of them must fuse together and release acetylcholine into the neuromuscular Junction or we also call this as synaptic cleft right now how does this exactly happened you need to know one thing that on the surface of the vesicular membrane there is a protein like this binding protein so this binding protein is called as syntex see not cobraman right and there is one more protein located on the presynaptic membrane that is syntaxin so let me write it here this protein present on the vesicular membrane this is called as synapse toe driven right and the protein that is located on the presynaptic membrane it is syntax in syntax in right now as I told you these are blue color ones or sodium channels and these are calcium channels you know from electrophysiology that whenever a cell is electrically stimulated automatically the sodium channels open and sodium enters inside so when the neverending Northam in the neuron right this is your right this is your cell body is your action and this is the nerve ending so this part of the nerve ending you have drawn it here right now when you stimulate this neuronal now I mean when you stimulate this cell body electrical electrically when you stimulate this cell body automatically the electric current from the cell body passes down into the axon and from the axon it passes into the axon terminal these two are called as the axon terminals and finally enters into this nerve ending or the presynaptic learning so now this electrical impulses is coming from the axon into that already so by the time when the electrical impulses reach immediately the sodium channels get sensitized or they get altered and immediately the sodium channels open and there is sodium influx right so this is how the sodium is coming in so once again when you irritate or when you electrically stimulate this cell body the electric currents from the cell body pass down to the axon and from there it passes to the axon terminal and finally enters into the presynaptic nerve would see this is that when the current enters into the presynaptic nerve ending the sodium channels get sensitized or altered or get irritated and immediately open its pores when the pores are open as you know extracellular fluid contains a rich amount of sodium so sodium passively diffuses into the presynaptic nerve ending right and you know from electrophysiology one more thing that whenever after stimulating a cell when sodium enters inside the cell gets depolarized right so the same thing is happening here whenever the sodium from the extracellular fluid enters in the presynaptic membrane the same time presynaptic nerve ending gets depolarized the movement of when this marbling gets depolarized immediately the calcium channels opens that is the reason why we call these calcium channels as depolarization sends it to calcium channels because they are opening as a result from the sodium depolarization main are the sodium enters it gets the entire nerve running gets to be polarized that depolarization current makes this calcium channels to open that is the reason why we call these calcium channels as depolarize depolarization sensitive calcium channels can be some channels don't open simply they open only when there is a depolarization here depolarization is brought up in the nerve running by the sodium influx right now the calcium ions have opened I mean calcium channels are open and there is influx of calcium as calcium channels are large so there will be more and more calcium influx right so the calcium is entering and one important thing I forgot is that as I told this protein that is present on the presynaptic membrane is shrimp eccentric syntax in so this is your st. accent right syntaxin has to speak like structures like this so here there is one stiff leg structure and here the second one right there are two drums or stick like this sticks these two sticks when out they're closed like this the syntax and I mean the active site of the syntax and molecule is closed when these two sticks open the app two sites are open right now these streets are closed so that the active site is not open and this synaptic Riven cannot fuse with the same text now as a calcium channel a calcium channels got open and when calcium enters inside this calcium here one calcium ion binds and on the other stick the other calcium iron bands right so here there are two commands one came along the right stick and next condition on the left stick you know collisions are ions are positively charged so here when there is one positive charge so let me explain this so this is one stick and this is the other stick right here there is one calcium here there is another condition and both are kept near to each other I mean the positive just positive Church come together immediately they get repelled right the movement when they get repelled the movement when these both speaks get repelled like this this basically containing the signal cobraman comes and fuses with that st. axon right so I will show you the fusion here so when they get fused they look like this right so this is how the fusion takes place so sodium ions are important to enter here because when there is no influx of sodium then there is no depolarization means there is no depolarization there is no calcium ions opening the channels of calcium ions will not open unless there is depolarization in the presynaptic nerve running so depolarize descends to calcium channels get opened calcium enters inside you know calcium is positive charge it binds to two of this pixel is two sticks were closed so when calcium binds to the right hand the left when they come near to each other I mean they are already near to each other so both of the calcium ends bind here and make and positive positive just come here they get repelled and make the active site open so now the active site is free for C not the brimming molecule so that C not really easily comes and fuses with the syntax now what happens there is furthermore fusion in this so as a result of this fusion it finally the vesicular membrane and the presynaptic membrane finally fuses together and finally there is a release of acetylcholine into the synaptic cleft right so this is how acetylcholine is synthesized and instead colon is transported into the vesicle and acetyl and the vesicle containing instead colon is fused and finally released so this is the important thing which you need to run and next once a certain following is the released into the synaptic cleft how does it act so this we consider the post synaptic membrane this becomes your presynaptic membrane obviously this is your post synaptic membrane so on the surface of your on the surface of your post synaptic membrane you find ion channels right so here on the surface of your post synaptic membrane you find ion channels so these are the ion channels located on the surface of here one but there are quite many ions and some thousand right so this ion channel is made up of five proteins alpha 1 alpha 2 beta gamma delta so these all five proteins together right when you take this as your ion channel so this is one protein this is one this is one in this way in this way all the five proteins alpha 1 alpha 2 beta gamma delta all of them fuse together circularly they fuse together to form this ion channel first suppose this is your alpha 1 this is your alpha 2 this is Beta Gamma Delta so all these five proteins together they're fuse right together they're fuse and finally they form they form the circular ion channel like this so when this ion channel gets open the ions enter inside when this I am channel gets closed I mean when the pore gets closed so there is no influx or a flux of the ions right this ion channel has a site this is called as ligand binding site every receptor is when I will explain the receptors I will be explaining what is ligand binding site right so on every receptor receptor in the sense it needs to receive some ligand molecules right for suppose this is your ligand molecule and this is your receptor so this portion of the receptor is called ligand binding site ligand binding site is the part that is present on the receptor to which the ligand comes in binds here so this is your ligand binding site present on the ion channel now the ligand binds what is the ligand here it is acetylcholine this ligand comes and binds in the moment when ligand comes and binds here it makes the ion channel to open its for right when the core is opened and the pole is open you know extra is rich in sodium so obviously lots and lots of sodium and test anxiety you know when sodium enters inside what happens there is depolarization when the skeletal muscle got as what depolarized it means that there is contraction that is taking place in the skeletal muscle right now so this is the entire concept of neuromuscular Junction and there are mainly two diseases that are mainly acting on this neuromuscular Junction so we call those diseases or disorders as neuromuscular Junction disorders or neuromuscular Junction impaired disorders right there are several many other disorders but most quietly I mean more commonly occurring disorders are those two types one is mice Tinian gravis and the other one is eaten Lambert syndrome so very briefly what happens in mice Tina gravis is that you know these are the ligand binding sites right so due to some of these mice thickness is actually an autoimmune disorder it means that our own antibodies are against ourselves itself right so one antibodies harm over body tissues how does they have so our own antibodies they come and bind to this part like this this is the ligand binding site so when the ligand binding site is equipped or binded with our own auto human antibody then there is no chance of ligand getting attached here in the ligand that's not attached then the poor does not open I mean the poor does not open sodium cannot come in then the sodium cannot come in there is no depolarization and the muscle is said to be paralyzed so that what happens in my stenographers and the other syndrome causes lambert-eaton syndrome in that syndrome these calcium channels are blocked right this calcium channels are completely blocked when the calcium channels are whatever calcium cannot entering and cannot bind with these two sticks so that the active sites will never be open and there will be no fusion of the vesicle with the protein I mean the sign up to syntax and protein when there is no fusion then there is no release of a staff : so this is how the muscle transmission or they separate transmission is stopped right so this is the complete concept of neuromuscular Junction and the important thing is you need to remember how they stood : is synthesized and what are the drugs that are acting on the colon receptor so I : transporter and acetylcholine antiport and how does it exactly gets fused and you also need to know some chemical correlates regarding my senior gravis as well as lambert-eaton syndrome so that's all for today right and in the further videos will be discussing regarding the receptors thank

Channel: Medico tutorial's

Views: 28,848

Rating: 4.867435 out of 5

Keywords: neuron, muscle, acetylcholine

Id: 9d3mCzUaTSA

Length: 26min 58sec (1618 seconds)

Published: Mon Nov 14 2016