Transcript for:
Skeletal Muscle Overview

welcome to the intro to skeletal muscles lecture for anatomy um this powerpoint is going to go over a little bit of everything in terms of the uh cellular structure of skeletal muscles what we're going to start with is the general functions of skeletal muscle and that's going to be to produce skeletal movement meaning movement of the bones to maintain your body's position and posture so your anterior and posterior thoracic region muscles supporting soft tissues in areas where you don't have protection with bones so the abdominal region guarding the body's openings like the mouth anus the vaginal opening maintaining body temperature and storing nutrients and that nutrients we're going to talk about is going to be glucagon a stored version of glucose now properties of all types of muscle tissue remember we have three types skeletal cardiac and smooth but all three of them are similar in these four ways they are contractible so the actin and myosin and all three of those tissues are able to contract they are extensible you can stretch all three of those muscles they are excitable which means they can be influenced with nervous system input and they are elastic meaning once you stretch them they can recoil back to their original length but there are some big differences between these three muscle types as you can tell the skeletal and cardiac muscles have a striated appearance and we'll talk about why that is today um and we're going to talk about the differences between these three muscle types first is skeletal muscle these muscles are very long they are cylindrical they are multi-nucleated meaning they have multiple nuclei within a single muscle cell these guys are the contracting units of your voluntary muscle control and their contractile unit is specifically called a myofibril which we'll talk about today and skeletal muscle is going to be found in all of your limbs and they will all be connected to bone the connective tissue that connects skeletal muscle to bone are called tendons the second type is smooth muscle these guys do not have striated appearances they are spindle shaped which means they have little tips sharp tips at the end of the cells they are uninucleated which means they have a single nucleus and although they don't have a striated appearance they are still made out of actin and myosin the primary place you're going to find these muscle types is going to be in visceral organs which means internal hollow organs you can also find these in blood vessels smooth muscle is involuntary which means you are not in charge of consciously dictating when it contracts or relaxes cardiac muscle like the name states is found in the cardiac region and it's going to only be found in your heart these guys are branched in their appearance they are striated they can be multi-nucleated and they're connected by a specialized junction which you see these dark bands here they're called inter-collated disks they are a type of gap junction and they are there to allow voltage to spread through and pass from one cardiac muscle cell to the next the benefit of this is so that all the cardiac muscle cells contract in unison to generate a nice strong high pressure contraction that's going to push the blood out of the aorta to reach the rest of the body here's a great chart you guys can use um you can delete out the words from the boxes and fill it in yourself but it's basically a review of what we just went over so let's now get into the anatomy of muscles as a whole and then we will kind of trickle down to smaller and smaller contractile units so here's the bone this is a femur and you have a tendon and notice that the tendon connects to the connective tissue all around the muscle that connective tissue that surrounds the entire muscle is called the epineum so the epimesium surrounds the entire muscle and if you can tell the entire muscle is made out of these smaller units and these smaller units are called muscle fascicles it's labeled here these fascicles are surrounded by their own type of connective tissue and that's called the perimysium so epimysium perimysium and that perimysium surrounds a single muscle fascicle and that muscle fascicle is made up of its own units called muscle fibers now if you can next to muscle fiber right muscle cell each muscle fiber is equivalent to a muscle cell so the word fiber is interchangeable with cell that means this whole muscle fascicle is made out of one two three four five six so on and so forth cells so this whole thing is a cell that whole thing is a cell and now if you look at inside the cells they're made up of their own little units right here we'll continue with that in the coming slides but just know that you have a whole muscle covered with the epi museum the muscles made out of muscle fascicles covered with a perimysium and the muscle fascicle is made out of muscle fibers and the muscle fiber is covered by an endo mesium so we'll go through it one more time and then we're going to take it a step further the skeletal muscle is covered by the epimysium and it's made up of muscle fascicles this muscle fascicle is surrounded by the perimysium and it's made up of muscle fibers aka muscle cells the muscle fiber is covered by an endomesium and it's made up of its own units and this is new information now these individual units are called myofibrils now if you look at a myofibril the myofibril is covered by this blue net like structure called the sarcoplasmic reticulum we will talk about its function in just a little bit that sarcoplasmic reticulum covers each myofibril and these myofibrils extend from you see this zigzag line and this zigzag line so these myofibrils are made out of these continuous units of zigzag line to zigzag line this is called a sarcomere there are hundreds of sarcomeres back to back so there's this one there's going to be a neighboring one to another zigzag line there'll be another one to another zigzag line those continuous units are each called sarcomeres and they run lengthwise in the muscle fiber so each myofibril which is here is made up of continuous units called sarcomeres we're going to really focus on this level of the anatomy today and we're going to talk a little bit a little bit about the function so a little bit about the physiology as well now to teach this i want to specifically just stick with skeletal muscles just so that we have some continuity across this anatomy so as we stated skeletal muscles are really long they are multinucleated and the reason they're so big and they have so many nuclei is because they're formed from a fusion of cells we call myoblast cells so if we see on the next picture during development the myoblast cells fuse together until they make a larger muscle fiber and with that fusion you're fusing all their nuclei as well so the muscle fiber has hundreds of nuclei in it i want you to notice that there is a yellow cell that's not fusing at any point it simply stays sitting on top of the muscle fiber that is called a satellite cell and satellite cells are really cool because they're helper cells and they help bring nutrients to the muscle fiber they help repair the muscle fiber if it gets damaged so the reason these cells are so large is because it is made up of a fusion of myoblast cells that term is here again and the satellite cells don't fuse they're actually there to be helper cells now within that cell again we said that you have the muscle fiber it's made out of units called myofibrils and those myofibrils are made out of this continuous units that run from zigzag line to zigzag line called a sarcomere the zigzag lines are actually called z lines so kind of easy to remember for you they're called z lines and they run from sarcomere to sarcomere so this one unit from z line to z line is called a sarcomere in that sarcomere is the functional unit of skeletal muscle so we're going to look at how that sarcomere actually works to make your muscle shorten and generate force now here all the terms that i'm going to use for the next slide i'm not going to read off of this slide i'm just going to move to the next slide and i'm going to teach it to you on this illustration so z line is here z line is here sometimes they can be called a z disk but on your exam i'm going to call it a z line so from z line to z line is one sarcomere now the middle of that sarcomere is called the m line and then we have the z line and the sarcomere is made out of two major proteins in this illustration the green protein is going to be called actin and that's written on the left side as well but we'll write it on the right side here too it's actin so this is actin this is actin this is actin and this is actin the purple thicker protein is called myosin so we've got actin and myosin these are the names of the two proteins we call them myofilaments of any type of muscle now the length of the myosin from here all the way to here is called the a band then you have the distance between the two actins and i'm gonna kind of overlap this writing from here to here so this space between the two actin filaments that's called the h zone and lastly if i may i'm going to draw a few more myosins here this is the neighboring sarcomere the distance from one myosin to the next one that is called the i band so the i band here is just showing from the tip of the myosin to the z line but in fact it is the tip of one myosin to the tip of the other myosin which is the i band so we've got actin in green the h zone is the region between the actins we have myosin in purple the length of that myosin is called the a band the distance between two myosin tips is called the i band and the zigzag lines are called the z lines the middle of a sarcomere is called the m line be sure you're able to both label an illustration that looks somewhat like this and you're able to do descriptions of what each of these regions represents now in the picture previously you see the myosins just kind of floating in there it looks like it's just not being held on by anything but it actually is being held on by this slinky looking protein on both sides and that slinky looking protein is called titan that's what we're looking at on this slide you see it in yellow here titan is a spring-like protein that connects the end of myosin to the z lines and it has three main functions that i'd like you to know it prevents the muscle from over stretching it of course holds that thick myosin filament in place and it allows for the muscle to recoil back to its original state after stretching so titan's very very important in terms of the elasticity of skeletal muscle so now we're going to get into the anatomy of the muscle cell at a microscopic level so we talked about the actin and myosin and just so you know the thin filament is the actin because it's visibly thinner the thick filament is what we call the myosin because it is thicker in its size so what we're going to do right now is we're going to look at what the entire muscle cell is and then what the individual myofibrils look like and then what all of these units and structures are that are part of this muscle cell the first thing i want to talk about is the membrane that surrounds every single muscle cell if you have taken cell biology or basic bio or remember anything from a previous science class you know that cells have a membrane called a cell membrane and it's made out of a phospholipid bilayer however for muscle cells we don't call it a cell membrane we call it a sarcolemma and the inside jelly solution is not called the cytoplasm we call it a sarcoplasm so the sarcolemma is the cell membrane the sarcoplasm is the cytoplasm the sarcolemma has a very specialized function that's a little bit different than what a normal cell membrane does the sarcolemma is able to transmit voltage quickly in all directions of that cell and that's important because for skeletal muscles to be able to contract a neuron has to send a voltage signal to the sarcolemma and that voltage signal needs to literally shoot everywhere on the outside of that muscle cell so if you notice that voltage will shoot all around the perimeter of the skeletal muscle cell but what about the inside what about all of these contractile units in the middle does the voltage get to them also well yes it does using a structure called a t tubule the sarcolemma actually has these pores in them that are like a freeway system that run down to the core of the actual skeletal muscle cell these t-tubules i believe there's a photo let's just look at this picture so the sarcolemma is here the voltage can travel down the t-tubule deeper and deeper and deeper into the core of the skeletal muscle this transmits any voltage out here from the perimeter to the inside deep into the middle of the skeletal muscle because how is it going to help you if you just contract the outer region of the muscle and you don't contract any of the middle of it that would create a pretty weak force i would say so the t tubules are there to transmit action potentials also known as voltages deep into the core of the cell this allows the entire skeletal muscle cell to contract all at one time to create a nice strong force now we've covered the sarcolemma we've covered the t tubules the next location where that voltage travels is also right and left to these thick blue regions called cisternae they're also termed terminal cisternae when the voltage shoots from the t-tubules to the terminal cisternae remember that it also goes down we're doing this all the same time that voltage charge that hits the terminal cisternae gets the terminal cisternae really excited and when i say really excited it means that it allows these doors these open channels in the terminal cisternae to open and allow the calcium that's stored in here which is a lot of calcium by the way these terminal cisternae store a ton of calcium it gets the calcium that's stored in here to be released out of the terminal cisternae and go into the actual sarcomere that's underneath do you notice that there's actin and myosin under here that is underneath all of this blue net-like structure so the terminal cisternae are able to store calcium and it's going to release calcium into the actual sarcomere when the voltage travels down the t tubules and across to the terminal cisternae the sarcoplasmic reticulum is similar it is also excited by voltage and it also releases calcium into the skeletal muscle sarcomere when excited i want you to know just thus far that the voltage travels through the sarcolemma down the t tubules across to the cisternae to allow calcium channels to open and calcium gets sprinkled onto the sarcomere calcium is required for a muscle to contract so this whole process is imperative it is very important so we went over this the only new piece of information here is that two cisternae plus a t tubule make something called a triad a triad is just really the series of locations that a voltage travels to in order to release calcium so the calcium gets released but let's look at the sarcomere underneath so again this is the second time you're seeing this picture you have actin and myosin but what's new on this picture are these little nubs sticking out of myosin those nubs are called myosin heads these myosin heads attach onto the actin on both sides and they pull the actin filaments along with the z lines toward this m line remember the middle of it this line here is called the m line so these myosin heads they grab grab and pull towards the middle and they keep pooling until these actin filaments are basically touching each other this whole thing is called the sliding filament theory the sliding filament theory states that the myosin heads grab onto actin and the actin slides in between the myosins towards the m lines what i want you to know about this is the changes that take place the z lines move closer together the eye bands get shorter so look at here the eye band was from here to whatever the next myosin was and now it's shortened to here the h zone disappears so here was the h zone initially and now look no more h zone but if you notice the length of myosin stays the same myosin does not squish myosin does not stretch all were really moving are the actin filaments and we're sliding them in towards the m line now innervation of the skeletal muscles you learned about the voltage traveling through the sarcolemma down the t tubules to the cisternae but what voltage are we talking about well without getting into too much of the physiology make sure that you know these three points the neuron comes and sits its little terminal boutons that's what it's called a terminal bouton that word is right here sits the terminal bouton on top of the sarcolemma that thing where you have the junction of the terminal bouton on the sarcolemma is called the neuromuscular junction makes sense because it's the neuron and the muscle and it's the junction between them let's take a closer look the zoomed in region here what exactly is happening to get a voltage signal to pass from the neuron to the muscle well the neuron releases these little vesicles that are full of chemical called ach make sure you know that chemical it is acetylcholine so the nerve impulse reaches the end of the terminal bouton and it causes exocytosis of ach onto the sarcolemma the ach will stimulate this sarcolemma and cause creation of voltage that's going to shoot across the sarcolemma down the t tubules across to the cisternae in order to release all those little calcium nuggets down onto the sarcomere those calcium nuggets again are required for muscle contraction now to finish off this lecture we're not going to go into more physiology we're going to talk about different types of skeletal muscle types but before i teach you about the types i want to give you a little bit of terminology we name skeletal muscle fiber types based on two things one how they make their atp they either use oxygen to make it which is called oxidative or they don't use oxygen to make it which is called glycolytic the second way is naming how fast they contract initially some muscles contract really fast some muscles pick up slowly and take a little bit of time to contract now with that being said i want to go over two terms that you should already know but maybe you don't in terms of the oxidative fibers when i said use oxygen to make atp that means you're making atp aerobically glycolytic means you're not using oxygen that means you're making atp anaerobically so what are the three muscle types slow oxidative picks up slowly but is able to use oxygen to make more atp in the long run fast glycolytic picks up really fast and doesn't use oxygen to make new atp which means you're not really going to make that much new atp you're going to get tired kind of quickly fast oxidative is like the best of both worlds your muscle can contract really fast and it can use oxygen to keep making more atp in terms of chicken meat slow oxidative fibers are more red these guys are considered dark meat in the chicken white meat is going to be the fast glycolytic fibers that's for chickens what do humans have this one we have fast oxidative although with some intense olympic training you can convert some of this into that or into that but it will require a lot of intense physiologically based training the last three slides be sure you read them on your own these guys are the descriptions more in depth of the slow oxidative the fast glycolytic and the fast oxidative i will let you know these last three slides are a matching section on your next exam let me know if you have any questions after going over this video