all right so in this video we're just going to talk about an overview of muscular tissue and uh in general you know muscle tissue accounts for nearly half of your body's mass and one thing that's common among all the different types of muscle tissue is that they help to transform chemical energy in the form of ATP into more of like directed mechanical energy which is used to exert Force Through contraction now when we look at muscles we want to basically help to characterize them by their types you know other characteristics and functions of those of those muscle cells will also tell us about what those can do now in terms of just generally talking about terminology here you know myo me and Saro are all prefixes for muscle so we'll find that a lot of the terminology we talk about in this chapter contains these prefixes but they all just refer to muscle and there are three major types of muscle tissue you know we learned about this back in chapter 4 but essentially skeletal cardiac and smooth are the three major types of muscle tissue in the human body skeletal and cardiac orol stried which means they have Stripes smooth muscle tissue is not strided and ultimately this relates to you know uh some of the molecular characteristics inside of these cells we'll talk about later now only skeletal and smooth muscle cells are elongated and therefore also called muscle fibers so a muscle fiber is just technically an elongated muscle cell now skeletal muscle contains skeletal muscle tissue which is packaged into um you know small units called fical we'll talk about and uh these are attached to bones and skin hence the named skeletal muscle now uh because you can because these contain different types of like connected tissues and blood vessels and nerves we consider skeletal muscles an organ and skeletal muscle fibers are some of the longest of all of your muscles because they can be up to feet in length and these cells also have stri which are Stripes now we call skeletal muscle voluntary muscle because it's consciously controlled you know by your will and these also contract rapidly but Tire easily and are typically fairly powerful now some of the key words for skeletal muscle are things like stried and voluntary so when you think of stried voluntary muscle uh that refers to skeletal muscle tissue and when it attaches to Bones that's why it has a name so cardiac muscle tissue is only found in the heart and it makes up the bulk of your heart walls now it's also strided like skeletal muscle is however it's involuntary which means we can't control cardiac muscle tissue consciously rather cardiac muscle will contract at a steady rate doe your due to your heart's own pacemaker electrical potentials and your nervous system can increase the rate but ultimately it's not under conscious control and uh some of the key words for cardiac muscle or cardiac which refers to heart it's also stried but it's involuntary now smooth muscle tissues found in the walls of hollow organs you know things like your gastrointestinal tract your genito urinary tract and your respiratory tract as well as your blood vessels all have smooth muscle within the walls now smooth musle called this because it's not strided yeah in fact you don't find those stripes in spoo muscle because has a different molecular composition and it's also involuntary like cardiac which means it can't be controlled consciously so some skel I'm sorry some smooth muscle can contract on its own without the nervous system uh to stimulate it so just to look at the three types of muscle here we have skeletal cardiac and smooth remember SKS attached to Bones cardiac you find your heart and smooth muscle you find the walls of hollow organs now both skeletal and cardiac are strided which you can see these little Stripes here on the histology slides where smooth does not have those stri there are no Stripes here and ultimately it relates to what types of proteins and arrangement of proteins you find inside of these cells now skeletal muscle cells are not branched where whereas cardiac muscle cells are which gives the cardiac muscle tissue more of a disorganized appearance in skeletal musle muscle cells because they don't Branch are just sort of these long elongated cells which we call fibers and because some skeletal muscle cells can be up to feet in length they have many nuclei all along the length of the cell to basically help regulate little local areas of the cell now cardiac muscle cells are shorter in fact they're so short we can't call them fibers like you would with skeletal and smooth muscle and these cardiac muscle cells are all interconnected by by big aggregations of Gap Junctions and desmosomes which we call the interpolated discs so if you look here these are all these all these darker lines are interpolated discs which are large aggregations of desmosomes to hold these cells together strongly as well as Gap Junctions to allow for the spread of electrical currents from one cell to the next through those little protein tubes which are the Gap Junctions and the reason why this looks sort of disorganized you know due to appearance is that these cells are highly branched and they'll typically branch in like kind of y-shaped patterns which makes this tissue look more disor organized and also it has a you know one to two nuclei per cardiac muscle cell where skeletal muscle cells have many nuclei along your length smooth muscle is pretty easily identifiable again because you don't have striations and you find smooth muscle in the walls of hollow organs it's also under involuntary control like cardiac muscle is and its function is to help with you know uh propulsion of materials and uh regulation of flow and pressure in different areas of your body now uh all muscle tissue shares these four major characteristics so uh all muscle tissue is excitable which means it's responsive and it can receive and respond to stimuli you know stimuli can be electrical or chemical in nature now uh contractility refers to muscle ability to shorten forcibly when stimulated this is basically what muscle tissue does uh all muscle tissue needs to be extensible as well which means it has the ability to be stretched so stretchability makes this tissue more Dynamic and it can actually move when your body moves moves and elasticity refers to this tissue's ability to recoil back to a resting length this is important because when when muscles contract and then they relax you want them to be able to recoil back to their own resting shape now other important functions of muscle include producing movement you know skeletal muscle could do this in terms of like walking otherwise smooth muscle could be involved with digestion or cardiac muscles involved with like pumping blood now other um important functions include maintaining posture and body position like skeletal muscle does that stabilizing joints that's also another function of skeletal muscle and generating heat as they contract uh again skeletal muscle is the type of muscle that contracts during shivering to help uh produce heat to warm your body up now additional functions of muscle could be things like protection formation of valves controlling the size of your pupil to regulate how much light can enter your eye and also cause goosebumps like in your skin