students we are on our last lab topic hooray last topic is muscles muscles of course are one of our four basic tissue types along with epithelial connective and nervous we know muscles create movement and you should remember from many lectures ago that there are actually three kinds of muscle skeletal muscle cardiac muscle and smooth muscle what we're going to do today is look at those three types of muscle we're going to look at them under the microscope and then we'll look at a model of skeletal muscle so that is our plan let's get to it so this right here that you're looking at this is skeletal muscle so this guy right here that my mouse is going over that is a skeletal muscle fiber right there so it's going horizontally on your screen skeletal muscle cells are known as skeletal muscle fibers because they're long and they're skinny so this is a skeletal muscle fiber right here i can actually see a bunch of skeletal muscle fibers on this micrograph right here i mean this is one here there's another one here's a third a fourth a fifth a six and a little piece of one down here and a little piece of one up here so i have like six full ones and a couple chunks of other ones so these are muscle fibers skeletal muscle fibers all right the word skeletal means that these guys usually attached to bone not all of them do go ahead smile really quickly all right when you smile and you pull your lips up in that lateral superior way you're not pulling on bone there but skeletal muscle but most skeletal muscle pulls on bone okay and skeletal muscle is generally considered to be voluntary although there are exceptions um like reflexes are not voluntary your sphincter muscles for pooing pooing pooing pooping there we go and peeing can be involuntary at times your diaphragm which is your on your breathing muscles can be involuntary too anyway let's look at what we got here so this guy right here this guy right here all these guys are skeletal muscle fibers i want you to notice that there is this like pattern to them they have these stripes to them the stripes are called striations and the reason they have these stripes is because there are these proteins in skeletal muscle that are responsible for contraction so naturally they're called contractile proteins and one's called actin and one's called myosin and the arrangement of them in this skeletal muscle fiber gives you these stripes or striations now i also want you to notice just how many nuclei these cells have like this is you know one fiber down here and i see just a bunch of these nuclei like look how many nuclei we're seeing inside these cells skeletal muscle cells are multi-nucleate this is because when you're an embryo you have these tiny embryonic muscle cells or like stem cells they're actually called myoblasts the embryonic ones remember osteoblasts fibroblasts all those blasts here's another one and the embryonic muscle cells the myoblasts together to make adult muscle cells so an adult muscle cell which is what we're seeing here which is what you have each one is made of the fusion of lots of smaller embryonic muscle cells and that's why these muscle cells these adult ones have multiple nuclei all right that is pretty incredible where we've looked at these skeletal muscle cells or fibers we saw their striations which is because of the overlap of actin and myosin and we saw that they are multinucleate excellent okay let's keep on going i have another picture of skeletal muscle cells here skeletal muscle fibers i want you to pause this find all the fibers count them all and then find striations and find nuclei once you've done that unpause and continue onward with me all right we're back and we are on cardiac muscle cells cardiac muscle cells are found in the heart that's the only place they're going to be they're in the wall of the heart you're going to see these guys more in amp2 they're going to be on your first amp 2 lab exam so you kind of get ready for that today as well now cardiac muscle is involuntary so it's unlike skeletal muscle which is mostly voluntary cardiac is involuntary you don't control it at all it has its own rhythm its own strength that you are not consciously controlling now when we look at this guy we are going to notice striations like i can really see them right over here i can see them down here they're not as prominent they're not as beautiful as the striations in skeletal muscle but they are there so what that means is we have that overlap of actin and myosin again i do also see nuclei like here's a nucleus right here a nucleus right here but these guys cardiac muscle cells they are uninucleate so they're like regular good old-fashioned cells they have just one nucleus although occasionally they can have two they're definitely not predominantly multinucleate like our skeletal muscle cells all right what i can also see is something that is unique to skeletal muscle cells the thing that's unique to skeletal muscle cells are these vertical things there's one right there there's one right there with the two next to it there's one right there as well one right here boom boom boom those guys are all intercalated discs intercalated discs intercalated means like kind of stuck in between now the intercalated discs are structures they're special structures that join cardiac muscle cells in two ways ways that are in fact familiar to us do you remember gap junctions gap junctions electrically connect cardiac muscle cells together that way when the electrical signal that stimulates the muscle cell to contract is affecting one cell it also then affects all its neighbors and its neighbors neighbors and its neighbors neighbors and so on and so on and what that does is it allows her to contract as a single big unit i mean think about it your heart has millions of muscle cells right they can't do their own thing they have to work together electrically connecting them allows for this togetherness now we also in those intercalated discs fine desmosomes if you recall from a while ago desmosomes are used to strongly i use the word mechanically here strongly physically attach cells together we don't want cells to separate or come apart okay fantastic here is another slide with cardiac muscle cells i want you to find some striations intercalated discs and some nuclei if you haven't done so already pause it find them and then rejoin me okay we got two down guys we're gonna look at the microscopic version of one more and then we're gonna do some we're gonna do a model all right this is cardiac muscle ah why did i say cardiac muscle what is this you guys can read you can tell i you we know you just did cardiac muscle this is smooth muscle one day i'm gonna make a mistake free video here this is smooth muscle smooth muscle cells are generally found in the walls of hollow organs so i'm talking blood vessels you know arteries and veins i'm talking food passageways esophagus stomach intestines i'm talking respiratory passageways trachea bronchi um i'm talking urine passageways ureters your urinary bladder your urethra reproductive passageways uterine tubes uterus vagina um vas deferenses i've spaced out in the guys reproductive organs there um epidemic so anytime you anytime you basically have a tube that stuff's going through it's probably got smooth muscle in the wall smooth muscle is involuntary and it's cold smooth because it lacks striations so there are no striations here no striations there are nuclei but no striations now here's the deal though the smooth muscle still has those contractile proteins actin myosin but it does not have striations um we're actually looking at cells that are in transverse section that's why they look like just little round guys here and then longitudinal sections why they look like long skinnier fibers okay cool done here we got smooth muscle oriented transversely here longitudinally here this is actually from the small intestine sweet so last thing actually second to last thing for today is to look at a model of a skeletal muscle fiber remember skeletal muscle fiber same thing as skeletal muscle cell what i'm looking at here is the outside of it this is the plasma membrane of the skeletal muscle cell the plasma membrane is called the sarcolemma sarco means flesh or meat lemma means covering so it's like the meat covering we can also see the connective tissue wrapping around the muscle cell this is called the endomysium the endomysium is loose connective tissue so it's mostly like or connective tissue and its main job is to attach muscle cells to their neighbors all right if we flip this guy around we can still see the sarcolemma we can still see the endomysium and we can see a special part of the sarcolemma right here this is called the motor end plate the motor end plate now this is the end of a neuron right here these three guys boom boom boom are telodendria here's my axon this is an axon terminal here the axon terminal has been removed right here so you can see the motor endplate the axon terminal releases a neurotransmitter called acetylcholine the acetylcholine binds to the motor end plate binds to receptors there causes the muscle fiber to have an action potential that action potential then eventually results in muscle contraction now before we keep going i want you to notice how folded the membrane is on the sarcolemma right here on the motor end plate looks like a sea shell to me and the folding here what that is going to do is going to maximize the surface area and what that does is it gives us more receptors more receptors for what well more receptors for acetylcholine all right good stuff let's keep on going okay what we got here is the same skeletal muscle fiber model another different view i still got my endomesia up my sarcolemma my endomysium i see a nucleus now would i just find one now i'd find a lot more than just one i see one here but i'll have more than one because skeletal muscle cells are multinucleated i also see the axon terminal right here and then a motor end plate right there awesome i also see these cylinders made of proteins these vertical cylinders made a protein here these are called myofibrils little muscle strings is what the word means they are bundles of proteins including the two contractile ones that we met which are called actin and myosin and we can even see the striations look if we look kind of like how they're striped horizontally we can see the striations all right excellent here in the top view we can see a nucleus we can see all these myofibrils and of course the sarco lemma okay this is the last thing to look at guys it is another microscopic view of skeletal muscle but there's something else first of all check it out i got one two three four five six and a chunk of skeletal muscle fibers i see their beautiful striations here lovely but also see these black strings here these are telodendria these are telodendria which means this guy right here is an axon terminal this guy is an axon terminal axon terminal axon terminal now the synapse remember when an axon when an axon terminal meets another cell that junction is called a synapse this synapse between the axon terminal and the adjacent motor end plate which we know is like under it that synapse has a special name that synapse is called a neuromuscular junction and guys i am excited because this was a short video 16 minutes long this is good we are done with lab number 23 so i'll see you next time bye bye