hello everyone and welcome back to my playlist of physiology joham Guyton say continue and today we are going to start chapter number six which is about contraction of skeletal muscles very important topic or students early days of the medical school it's a very very important for examination purposes hair simple straightforward chapter about 40 of the body is actually skeletal muscle so uh it's a big percentage your name most of your body is actually made up of muscles as you can see okay and perhaps another 10 percent is smooth in cardiac muscle fifty percent of the body is made up of muscles skeletal muscles and about ten percent are smooth muscles which are in the for example GI tract in the excretory system and other parts of the body and also the cardiac muscle which is present in the heart so 50 is a big number 50 of your body is made up of muscles some of the basic principles of contraction apply to all these types of muscles although each chapter may we are going to focus only on skeletal muscles but the general principles will also apply on cardiac muscle contraction and smooth muscle contraction which we will deal separately in chapter number eight in chapter number nine respectively today is chapter number six okay um physiological anatomy of a skeletal muscle now that's something important because muscles are composed of numerous fibers ranging from 10 to 80 micrometers in diameter each of these these fibers is made up of successively smaller subunits and described in describe in most skeletal muscles each fiber extends the entire length of the muscle except for about two percent of the fibers each fiber is innervated by only one nerve ending suppose we talk about any muscle so say for example there is a bone and this bone is a humerus bone and then there are radio ulna okay so these are the bones that is the bicep muscle okay so bicep muscle is that if you take that bicep muscle for example and try to have a look so here they have shown bicep muscle okay so this is humerus and this is radiolna and that is the bicep muscle so bicep muscle and cross section so internally it is made up of small uh fibers then you won't be able to understand properly the whole bundle is known as muscle fasciculus okay you see there are these small fibers that's a fiber that's a fiber or egg fiber so muscle fiber simple thing so the muscle is composed of muscle fascicles the fasculus is composed of many muscle fibers organ is and these smaller units inside a muscle fiber they are known as myofibril so myofibril is the smaller unit so it goes like this muscle fascicles to muscle fiber to myofibril operating myofability there are different types of proteins acting myosin and what not okay basic terminologies then what is a muscle fiber and then what is a myofibril okay so all these terminologies go in the descending order of thinness fasciculus is the whole bundle fasciculus is composed of fibers and fibers are composed of myofibrils okay or Fair um usually in the center of the muscle is so usually the muscles are innervated by only one nerve ending okay located near the middle of the muscle fiber now the sarcolemma this is another terminology that we have to understand it's nothing but actually the cell membrane or the membrane it's a thin membrane cell membrane though exactly but it's a thin membrane which enclose the skeletal muscle fiber yeah that is known as sarcolemma so sarcolemma is the terminology used to describe the outer covering or the membrane of a skeletal muscle fiber the circular consists of true cell membrane-like structure the plasma membrane and the outer core made up of thin layer of polysaccharide material that contains numerous thin collagen fibrils so cell membrane modifications at each end of the muscle fiber this surface layer of the sarcolemma fuses with a tendon fiber and the tendon then attaches onto the bones so at the top it will be all covered each muscle fiber will be covered with sarcolema or circular Tendencies so that will happen Okay so this paragraph is clear now myofibrils are composed of actin and myosin is composed of different types of proteins okay that is actin the other protein is known as myosin so each muscle fiber contains several hundreds to several thousands of myofability these are muscle fibers muscle fibers and these are myofibrils and they are in account of about you know several hundreds it's a big number two several thousands even ache muscle fiber again okay now each myofibril is composed of about 1500 adjacent myosin protein flements and about 3 000 in a double the number so myosin card double is the number for actin ABI 30 years these filaments can be seen longitudinal view in an electron micrograph and a represented diagrammatically the octane diagram the thick filaments in the diagram are the myosin and the thin plummets are actin now these are both proteins okay so if you look here this is a myofibril this is a myofibril sky portion electron microscope it appears like this but if you have a look here so thick protein hair this is myosin single thin proteins these are basically represent in acting so acting they are thin proteins and myosin are the thick flamen okay so thick filament myosin thin filaments actin okay let's move forward now myosin and actinflamence partially interdigitate and thus cause the myofibrills to have an alternative dark and light bands as Illustrated in the diagram the light bands contain only actin filaments and are called the eye bands because they are isotropic to polarize light the dark bands contain myosin flamens as well as the actin filaments where they overlap the myosin and these are called the a bands note also the small projection from side of the myosin flement which are known as the cross Bridges another terminology and cross Bridges also the Light bands and the dark bands is Concepts measure foreign so here if you see uh you see there are areas which are appearing a little darker so basically there is diagram this diagram of a myofibril is this is light color area all this is light brown then there is a dark brown area so light brown area here light bend that is known as eye band that dark area is known as a band is made up only of the actin proteins okay it is only made up of the actin protein it is made up of um it is made up of this and this we mean myosin protein like in her myosin protein actin protein so you see here that's a myosin protein all this area is basically the dark band this is all known as uh the dark band or you can simply call it the a Bend okay it is made up of only act influence it is made up of actin as well as myosinflammation terminology Concepts what we are talking about okay now Z discs your hair it is um basically a protein as well or is protein acting attached so the actin on one end is a tangent of the Z so that's the Z disc is z disc or dusray Beach so sarcomere is the basic contractile functional unit of the muscle fiber and the sarcomere lies between uh one Z disc and the other Z disc okay is from this disk these filaments extend in both the directions to interdigitate now this is all what I've already told you the portion of the myofibril that lies between two successive Z disc is known as a sarcomere it is the basic functional unit of the muscle okay now the length of the sarcomere is about two micrometers at this length the ectane elements completely overlap the myosin flowment and the tips of the actin filaments are just beginning to overlap one another as discussed later in this chapter the muscle capable of generating its greatest force of contraction at this particular lens so that's the sarcomere is roughly around uh two millimeters two micrometers is so that is the optimal length of a sarcomere for muscle contraction right let's move ahead cross Bridges cross Bridges basically you thank you myosinflammatory myosin flamen maybe 30 years this head is actually known as the cross Bridge or a cross Bridge muscle contractions but for now just understand okay not tight inflamentous molecules keep up the myosin and act influence in place so this is a sarcomere because here we see a z membrane here we see another Z membrane Z or Z membrane it's all the sarcomere or is all that thick protein is the myosin foreign this is all that I have already told you okay now sarcoplasm is the intracellular fluid between myofability myofiber your muscle fiber outer layers of muscle cells so sarcoplasm is this is nothing but the cytoplasm of muscle fibers many myofibrils are suspended side by side in each muscle fiber the space between the myofibrils is filled with the liquid intracellular fluid and this is known as sarcoplasm it contains large quantities of potassium Magnesium phosphate plus multiple protein enzymes also present are tremendous number of mitochondria because muscle contract or contract ATP energy mitochondria so the muscle fibers have very high number of mitochondria these mitochondria Supply Contracting myofibril is a large amount of energy which is required okay ATP so sarcoplasm another addition to your vocabulary another word is the sarcoplasmic reticulum structures extract structure hotel that is called endoplasmic reticulum muscles is the word for muscle okay so sarcoplasmic reticulum also in sarcoplasm surrounding the myofibril each muscle fiber again there there are sarcoplasmic reticulums because they are the storage sites for calcium calcium contractions you also need calcium so calcium from the sarcoplasmic reticulum now the rapidly Contracting types of muscles have especially extensive bow muscles foreign so an action potential travels along a motor nerve to its ending on the muscle fiber basically Arrangement there is a muscle fiber so say for example this is [Applause] foreign the nerve secretes a small amount of neurotransmitter called acetylcholine this acetylcholine acts on the local area of the muscle and opens up the acetylcholine garate cation channels or bojokation channels here were basically sodium channels the opening of the acetylcholine Gary channels allow large quantities of sodium to diffuse to the anterior of the muscle fibers this action causes local depolarization depolarization initiation of action potential depolarization all the same thing sodium under enter or now the action potential travels along the muscle fiber membrane in the same way that the action potential travel along the nerve fiber the action potential depolarizes the muscle membrane and much of the action potential electricity flows through the center of the muscle here it causes sarcoplasmic reticulum to release large quantities of calcium and those calcium actually are stored within the sarcoplasmic reticulum they are now released and once they are released they initiate the attractive forces between actin and myosin or contraction and after a fraction of second the calcium ions are pumped back into the sarcoplasmic reticulum the energy sarcoplasmic reticulum calcium or muscle contractions simplest form of explanation Machinery channels initiation of action potential depolarization so depolarization of the membrane action potential videos foreign foreign alone it is not sufficient for contraction contractions so that's the general General phenomena at the very first Herring we have to understand this terminology which is called sliding flamen theory yes sliding flamen mechanism basically is so if I draw a diagram something like this so say for example this is a myosin Flamin or is they are present on the sides and above and below the myosin so this is Central margin these are the actin filaments orange or vertical lines and these vertical lines are the Z membranes okay contractions so the theory is okay at the time of muscle contractions it will be something like this if you see again there is a myosin here but now if you see the diagram you should be able to appreciate a difference which is a very primary difference between the two sets of diagram although my diagram is not very good but again is diagram number one or is diagram foreign so here is the horse standing here as well and here is a horse standing here as well so if you now imagine this it looks like a sarcomere type of thing so that Raja is that thing in the center here uh is actually mimicking in our particular case myosinflammit you see so that is myosin in the center these are representing actinflamence the idea is they are trying to torture this guy or your goodest Direction but the idea is that the man is so powerful okay just like on a myosin flement actin filaments are actually sliding so that is also an example of sliding flaming Theory I hope this concept is very much clearer now so that's the first heading that we had to understand the concept of sliding filament theory flemen's slide okay now there is a figures shows the relaxed state of a sarcomere and a contracted state of the sarcomere so let's have a look at figure 6.5 and at the figure 6.5 you if you have a look here so this is the relaxed State and this is the contracted state in the contracted State what's actually happening is you have to actually look at this area is a big overlap so they are basically sliding actin proteins are actually sliding inward on the myosin protein okay in the relaxed State the end obviously the sliding filament mechanism is what I have already told you now next paragraph says but what causes the actin flamage to slide inward among the myosin flummates now this whole process comes you know in a form of a very high energy dependent mechanism basically we need a lot of ATP for muscle contraction and yes in the next few sections we describe these molecular process of contraction in detail so is okay now let's talk about uh something about myosinflammation has a molecular weight of about 480 kilo Dalton you have 480 000 shows the organization of many molecules to form a myosin fluid as well as their interaction abomycin molecule is composed of six polypeptide chains there are two heavy chains protein chains each with a molecular weight of 200 kilodals and four light chainsaw heavy or light chains diagram so if you look at this diagram these are the heavy chains the tail of the myosin flemen the tail is formed by you know intertwining of two heavy chains these are the heavy chains heavy chains economy the two heavy chains wrap spirally around each other to form the detail and then we have also discussed how the head is produced and the head is also what we call the cross Bridge okay now the myosin Flamin is made up of 200 or more individual myosin flaminations roughly around 200 miles okay so 200 even more individual molecules make up the myosin filament the central portion of one of these filament is shown there obviously diagram this is all something that we have covered cross bridges that angle is important for the movement of actin and myosin flowments okay actually Mars in the movement now the total length of each myosin flamen is uniform it's almost about 1.6 micron meters node however that there are no cross Bridges held at the center of the myosin filament for the distance that's a simple philosophy in the body now to complete the picture the myosin flamen is Twisted so that each successive pair important point is this twisting is a twisting of phenomena here myosin uh protein it ensures that the cross Bridges extend in all the directions around the filament proteins okay so I'm going going very steady and very slow with this chapter so that you understand all the terminologies now the next concept adenosine triphosphatase activity of the myosin heads composed of heavy chain and light chains is [Applause] simple words okay so that's the whole bottom line which is written here another feature of the myosin head that it is essential for muscle contraction its function has atpa is enzyme as explained later this property allows the head to cleave the ADB and use the high energy phosphate from the ATP you just start a fundament that's the whole bottom line of the story okay head can combine with or cleave the ATP into ADB and phosphate and this activity is known as atpa's activity so head ke pass now let's talk about something else foreign actin protein molecule represented by two light colored strata each strand of the double F actin Helix is composed of this is well too much details so don't worry about the sizes nanometers and all these things each employment is about one micrometer again this is not required up tropomyosin molecules so this is all representing the protein actin actin flamen is so we have this you know uh intertwined yeah intermingled protein filaments USA these are the core and they are made up of affecting protein there are also these dark shade one called the tropomyosin so actinotropomycin apas may I say uh these are the troponin proteins so troponin proteins proteins also contains another protein which is called tropomyosin so is 70 kilo Dalton a length of about 40 nanometer don't remember the size this is not important for you um contraction occurs only when appropriate signal causes a confirmation change in topromycin that uncovers the active sites on the actin molecule that initiate so it's tropomycin or actin or troponin complex hidden sites start hoga okay um attach intermittently along the sides of the tropomyosin are additional proteins which are known as troponin these protein molecules are actually complexes of three Loosely bound protein subunits Each of which plays a specific role in controlling the muscle contraction one of the subunit troponin eye has a strong affinity for actin the other which is called troponin T has a strong Affinity with tropomyosin and a third which is called troponin C has a strong Affinity with calcium now that's very important protein molecules they are made up of three subunits these are the triple triple units you see here though it binds with actin jotropenin T here it binds with tropomyosin or the t-cira portion C it binds with calcium now this complex is believed to attach tropomized into the acting this obviously there is high calcium concentration or a high calcium concentration what was the cycle the cycle was this there was acetylcholine by the nerve ending increase sodium entry into the cell which was depolarization increased sodium sarcoplasmic reticulum say increase calcium calcium complexing and bind with calcium is they become uncovered and then they go and bind with the heads of myosin protein or ferries are a contractions protein is very important in muscle contraction very very important now interaction of one myosinflamma and two ectane and calcium ion causes contractions a pure actin filament without the presence of troponine tropomycin complex binds instantly and strongly with the heads of the myosin molecule then if troponin tropomycin complex is added to the x-inflamence The Binding between the actin and Marcin does not take place therefore it is believed now listen to this carefully therefore it is believed that the active sites on the normal actin filament are inhibited or physically covered by a troponin tropomycin complex or Jesse calcium is dropping in tropomyeline complexes these are all the actin filaments foreign in the presence of large amounts of calcium the inhibitory effect of troponine tropomyosin complex on the actin climate is inhibited which means a calcium complex available then they will bind with myosin heads so this diagram is this up here this is the actin protein this here is the myosin protein or the active normalizing because your interactions there is high concentration of calcium so calcium will inhibit and move the troponin tropomycin complex interactions so this should now be making sense to you okay now interaction of the activated actin Flamin and myosin cross Bridges the walk along Theory the walk along theory yes if you remember sliding flaming Theory sliding inflammatories contract or your contractions as soon as the actin filament is activated by calcium ions the heads of the Cross Bridges form from the myosin flamen become attracted to the active sites and the contraction process starts that's it simple stuff that simply basically is each of the Cross bridge is believed to operate independently of the other half now ATP is the energy source for this contraction this contraction is not free of cost it requires a lot of energy in the form of ATP there are muscle contracts work is performed muscle contractions then we need ATP and atps are actually cleaved into ATP okay now large amounts of ADB are cleaved to form ADP during the contraction process and the more work performed by the muscle the more ADB is cleaved this phenomena is called the fan effects now the following sequence of events is believed to be the means whereby effects occurs before contraction begins the head of the Cross Bridges bind with the ATP State they had the atpa's activity so ATP um now this has a high energy okay now when the troponin tropomycin complex binds with calcium active sites on the actin flammator uncovered the bond between the head of the Cross Bridges and the active side of actin filament causes confirmation change in a power stroke happens so in inward moment of acting started your terminologies what is head of myself what is acting I'm just using them in the sentences now once the head of the Cross Bridges tells the release of ADP and phosphate 9 were they were previously attached to the head is allowed um after the head has detached from the actin the new molecule of ATP is cleaved interactions when the cocked heads with its stored energy derived from the cleaved ATP binds with the new active siteonectum it becomes uncooked again so this process goes and goes and goes on ATP uh by the head of myosin active size expose that sort of thing okay that's the process again and again proceeds until the action performance pulled Z membrane against the end of the mycenae process suppose again this is the myosin here and suppose this is the actin filament here yes okay now the amount of acting and massive employment overlap determines the tension developed by the Contracting muscle now that's too much of something to understand leaking MapQuest Graphics so if you look at this graph here we have on x-axis the length of sarcomere and on the y-axis we have the tension developed in the muscle fiber obviously simple cheese the more the contractions there will be decrease in the size of sarcomere sarcomere is tensions for example sample Point number D Point number deeper length of the sarcomere substance there's a very long you know length of the sarcomere as compared to any of the other points so this is the situation you see length of the sarcomere is one two three or four Beach Mass so very high length of the sarcomere so each diagrams contractile capacities point B and point C are the points both these points if you look here these are the points something like this BNC you see medium-sized sarcomere or medium-sized sarcomere this is the uh tension yeah and if you look at Point a so point a sarcomere length the shortest subscribers as compared to all these points okay so that's a graphs usually after undergrad examples but anyways the figure shows the effect of sarcomere length and the amount of myconnecting fluent overlap uh to the right or the different Bloom boring at Point d e on the diagram acting from has pulled all the way out to the end of the mass inflament and no actin myosin overlap is there so Point D parameters okay at this point the tension developed by the activated muscle is zero there is zero tension zero tension they had a very low tension very low tension and very high sarcomere length then as the sarcomere shortens and the actin filaments begin to overlap the length of the sarcomere decreases but there is increase in tension that's the whole bottom Point bottom lines then another very I would say boring Herring is effect of muscle and the force of contraction in the whole but that's like something so I'm actually skipping this graph for now otherwise so I'm just leaving it okay now relation of velocity of contraction to load a skeletal muscle contracts rapidly when it contracts against no load to a state of full contraction in about 0.1 seconds so it contracts very very rapidly when loads are applied exercise the velocity of contraction decreases progressively as the load increases when the load has been increased to an equal the maximum force that the muscle can exert the velocity becomes zero yeah okay Suppose there will be no contraction in the muscle muscle this decreasing velocity of contraction with load occurs because a load on a Contracting muscle is reverse force that opposes the contractile Force what is the concept of the load and the work and the force basically yeah foreign work is equal to load multiplied by the distance of movement against the load so that D is the distance of movement uh against the load so L into D is actually work the energy required to perform yes so if this is for example your arm and forearm or your Hopkins that is the distance okay distance of the movement against lower to EA contraction because your distance here that is d now the energy required to perform the work is actually derived from the chemical reactions in the muscle cells during contraction as described in the following sections three sources of energy for muscle contraction most of the energy required for muscle contraction is used to trigger uh the walk along mechanism just sliding filamenturity or some energy but small amounts of energies are also required for pumping of the calcium ions many steps calcium is sodium actually action potential generated so atbs are also required for something other than the sliding filament theory okay so sliding filament mechanism foreign and that happens in a fraction of seconds okay which allow the muscles to continuously uh contractors exercise the first source of the energy to reconstitute EDP is a molecule which is known as possible creatinine phosphocreatinine it carries a very high energy phosphate is this high energy phosphate Bond of phosphocreatine has a slightly higher amount of free energy than each of the ATP bond is irrelevant therefore phosphor creating an instantly cleaved and it releases its energy or your foreign foreign the importance of this glycolysis mechanism is twofold first the glycolytic reactions can occur even in the absence of oxygen glycolysis and therefore the muscle continues to contract and now the capacity is enhanced to one minute you see I guess if muscle can indigenous so only one to two seconds five to eight second capacity contraction key glycolysis now second advantage of glycolysis glycolysis can occur even in the absence of oxygen up second Advantage the rate of ATP formation of glycolysis is about 2.5 times as rapid as ADP formation in the response to Cellular food scrubs such as oxidative phosphorylation so oxidative phosphorylation Okay the third and the final source of energy is oxidative phosphorylated phosphorylation food particles in the Krebs cycle and the oxidative phosphorylation is the third source of energy more than 95 percent of all energy used by the muscle for sustained long-term contraction is dry from oxidative so that's basically the main supply of energy main supply of ATP formation TK and eight allows you to contract your muscles for two to four hours wow beautiful beautiful only from the stored carbohydrates and you can even contract the muscles for longer time okay oxidative phosphorylation okay now efficiency of muscle contraction they call muscle contractions foreign the reason for this low efficiency is that about half of the energy the food stuff is lost during the formation of ADB and even then only 40 to 45 percent of the energy ADB itself can be converted back to work okay also very low efficiency engine low efficiency engine in your body okay one example is muscles remember this maximum efficiency can be realized only when the muscle contracts with a moderate velocity if muscles contract slowly or without him that's not a very high yield staff the concept that I have given you is important that the efficiency of muscle contraction is only about 25 to 30 not more than that okay foreign right now the last bit of this chapter irrelevant yeah unnecessary stuff important definitions some characteristics of whole muscle contraction many features of muscle contraction can be demonstrated by eliciting muscle twitches experiments this may actually foreign what do we actually mean is that in these types of contraction the muscles do not shorten yeah whereas in isotonic contractions muscles shorten at a constant tension now muscle contraction is said to be isometric when the muscle does not shorten during contraction an isotonic when it's shortened but the tension Remains the Same I've been diagnosed with some in the isometric system the muscle contracts against a force without decreasing the muscle lens shown in the bottom panel so for example if you look at this diagram so in that scenario the muscle is actually not Contracting the muscle is not Contracting means the length of the muscle is not changing and when the length of the muscle is not changing such type of contraction actually contractions okay the length is not being able to change so isometric is always when there is too much lower isometric contraction occurs when the load is greater than the force of the muscle muscle so that is what we call isometric contraction the fibers act in and myosin they are still interacting with each other they are trying to pull it up but the force is not enough the weight is too much okay so yeah isometric contraction so that's an easy thing for you to remember okay isotonic May the weight is the load is not heavy or it's not more than the force therefore the muscle can actually contract the muscle contract but the tension throughout the muscle fasciculus Remains the Same so this is isotonic contraction the contraction is happening and this is isometric contraction right characteristics of isometric which is recorded from different muscle this is one thing that I would uh for example skip for now points capacity to handle different load is different obviously is we have some muscles which are very very small muscles for example is a muscle which is present in the air and it's a very very small muscle such as gastroctimus it's a big muscle such as bicep it's a big muscle quadratus femoris big muscle so contractile ability in this term is not tired so massage against yourself so this is all what is written in this heading now this is also very important heading fast versus slow muscle fibers as we'll be discussed more fully in upcoming chapters just made Sports physiology muscle fibers skeletal muscle fibers they are either fast type fibers or slow type fibers muscles that rapidly react including the entire tibialis are composed mainly of the fast fibers as the name indicates these muscles will contract rapidly contraction support such as soleus muscle you know it is important for maintaining the erect posture so such muscles are known as slow type muscles up slow type fibers type 1 fibers slow muscle score type one fibers they're also called red muscles so the slow fibers are a smaller characteristic solo fibers are also inner by smaller nerves slow fibers have more extensive blood supply so that's an important Point okay so they have more blood supply more capillaries more oxygen slow fibers have greatly increased number of mitochondria oxidative slow fibers contain large amount of myoglobin easily they appear red okay myoglobin complex with oxygen and therefore they are called red muscles so all these are characteristics of slow fibers which are also called type 1 which are also called red muscles and then there are fast fibers now fast fibers are also called type 2 fibers they're also called White muscle fibers in characteristics fast fibers are large for great strength of contraction they are large they were small these are large fast fibers have extensive sarcoplasmic reticulum mitochondria large amount of glycolytic enzymes are there fast fibers have less extensive of blood supply okay phosphibos have fewer mitochondria and therefore they are white muscles one of the favorite questions tell me the differences between slow muscle fibers and fast muscle fibers very very important okay right now um some uh some more Concepts they are not extremely uh useless important has such as motor units will simply skip those but I think motor unit is not one of them all the muscle fibers innervated by a single nerve fiber that's the concepts each motor neuron that leaves the spinal cord inner weight multiple spindle muscle fibers um with the number of fibers Innovative depending on the type of the muscle all muscle fibers innovated by a single nerve are actually called motor unit any group of muscle fibers being supplied by a single nerve is all collectively known as a motor unit in general small muscles that that react rapidly fast muscles and whose control must be exact have more nerve fibers for fever muscles your postural muscles so that's the simple principle okay so um in general small muscles that react rapidly and whose control must be exact have more nerve fibers and for fewer muscles example as few as two to three muscles fibers per motor unit in some laryngeal muscles so larynx may obviously we are producing voices it's a very fine movement so multiple motor units there are multiple motor units okay an average figure for all the muscles of the body is questionable well this is not relevant here the muscle fiber in each motor unit are not all bonds together that is also not important now muscle contraction of different force force summations submission it means adding together of the individual touches of contractions to increasing the intensity of the muscle summation occurs in two ways by increasing the number of motor units Contracting simultaneously which is called multiple this is not high yield this is the thing which I'm saying I'm leaving 10 tetonization and all these things because that's all um I mean believe me it's very important to understand medicine these are one of those okay and Physiology is a big big book of Guyton so that is something that you should actually leave okay even when muscles are at rest a certain amount of tautness tightness is usually there in the muscle up on the biceps even at the resting stage have some sort of interaction is okay so that's a simple thing to understand no big deal muscle fatigue for a long strong contractions of muscle lead to well-known state of muscle fatigue muscles studies in athletes have shown that muscle fatigue increases in almost a direct proportion to the rate of depletion of the muscle glycogen there is therefore fatigue results mainly from the inability of the contractile in the metabolic processes of muscle fiber to continue supplying the same work output both muscle use however experiments have also shown the transmission of nerve signal through the neuromuscular Junction can diminish at least a small amount after intense prolonged muscle activity intense prolonged muscle activity and your muscles are fatigue okay in Interruption of the blood flow on a Contracting muscle leads to almost complete muscle fatigue within one to two minutes of course but well okay your pathology condition is right now um a couple of important headings where we have to talk about remodeling no yeah but the important point is one point which is known as origin or if there is a point which is known as insertion origin or insertion is here we have the fulcrum of the liver and then here you actually see the liver and the bicep is then causing the movement of this machine so that's a simple machine just make fulcrum there is a joint there and there's a liver so muscles actually act in the form of liver okay so that's it says then there is a concept of antagonistic muscles this is an important terminology antagonistic muscles antagonistic muscles in most of the compartments of your body if there is a flexor compartment there will be an extensor compartment on the opposite side so for example there is biceps and then there will be triceps so you tricep over the backside that is the extensor compartment bicep and tricep muscles are antagonistic to each other is one of the muscle now this depends upon a higher centers one of the muscle has more depolarization and therefore is so virtually all body movements are caused by simultaneous contraction of agonists and antagonist muscles on the opposite sides the process is known as co-activation of The Agonist and antagon is so you may read it you may simply leave it you should have the concept of antagonistic muscles they are the opposite muscles one of them wins the race and it depends a higher centers okay your muscles are actually beautifully designed okay they can actually remodel themselves they can remodel themselves according to the needs for example uh those muscles which are which are not completely used they undergo the process of atrophy and then if the muscles are used too much they increase their mass and this is called muscle hypertrophy the increase in the total mass of the muscle is known as muscle hypertrophy bodybuilders pay attention muscles biceps when the total mass decreases this is called muscle atrophy virtually all the muscles hypertrophy result from an increase in the number of acting in myosin filaments causing enlargement of the individual muscle fibers this condition is called fiber hypertrophy foreign is the concept actually number of cells birthday but that's not very very usual common name actually hypertrophy hyperplasia neurot okay hypertrophy you're not hyperplasia hyperplasia cake example here uterus scale muscle during pregnancy then if there is muscle denervation it causes a trophy either for example damage okay when the muscle is no longer receiving the nerve Supply it no longer receives the contractile signals therefore a trophy begins almost immediately after two months denervative changes also begin to appear in the muscle fibers so that is all the effect of muscle denervation okay it can be because of so many things accidents so many things in the final stages of denervation atrophy most of the muscle fibers are destroyed and they are actually replaced by the fibrous tissue or muscles actually contract because of the fibrous tissue these are called contracture a very very serious problem okay so muscle contraction capacity that's the very Advanced stage of muscle damage image by denervation okay now the very few things recovery of muscle contraction in polio malaris development of macromotor units when some but not all nerve fibers through muscle are destroyed as in poliomyelitis the remaining nerve fibers Branch off to form new exons that then innervate many of the paralyzed muscle fibers so that's an important thing is that sort of thing okay several hours after death all the muscles of the body go into a state of complete contraction this is called rigor mortis okay sorry muscles contractors the muscles contract had become rigid even with the action death contractions this rigidity results from loss of all the ADB actually and ATP is required actually for separation of the Cross Bridges from actin filaments um is very hard in those countries where the temperature is very very high uh such as South Asian region India Pakistan Sri Lanka Bangladesh usually temperatures rather than so many hours it appears a little earlier okay now um one of the very commonly reported muscle dystrophy is the chain muscular dystrophy this happens only in males because this is an excellent recessive trait therefore only in males okay only male disease uh Duchene muscular dystrophy dystrophin protein foreign but anyways this is a common problem pathology is now symptoms of the chain muscular dystrophy have include muscle weakness and uh that begins early in the childhood rapidly progresses so the patient is usually in wheelchair by the age of 12 and often respiratory failure by the age of 30 Death a mild form of the disease is called backers muscular dystrophy is also caused by mutation of a gene that codes for dystrophin but has a later onset and a longer survival pathology pathology so congratulations we are done with the chapter of contraction of skeletal muscles take care of yourself