Understanding the Three Muscle Types: Skeletal, Cardiac, and Smooth

hi everybody Dr Mike here in this video we're taking a look at the three different muscle types of the body

skeletal cardiac and smooth and we're going to compare and contrast each of them

[Music] importantly we need to begin by talking about what muscle tissue is it's one of

the four tissues of the body we've got epithelial we've got nervous we've got connective and we've got muscle tissue

and the job of muscle tissue is to perform mechanical work it allows for us to move whether it's to move our body

consciously whether it's to move the blood into and out of the heart or whether it's to move various substances

through our digestive tract our renal system or our reproductive tract all of this occurs because of muscles and

muscles are excitable tissue this is really important for students to understand excitable tissue there's only

a couple of different excitable tissue types in the body you've got nervous tissue endocrine tissue and muscle

tissue now a tissue being excitable means it has the capacity to do something it can be excited like me it

can do nothing but when it's excited something happens so nervous tissue when nothing's happened it doesn't fire any

signals off but it can be excited to send what we call an action potential a signal for communication the endocrine

system when these cells aren't doing anything nothing's happening but they can be excited to do something which is

to release hormones into the bloodstream and muscle tissue when they're not doing anything they just sit there but they

can be excited to contract and when muscles contract and shorten they can help move things around so if it's

skeletal muscle when this muscle contracts it moves the skeleton and allows for locomotion when cardiac

muscle contracts it decreases the volume of these little cavities inside the heart known as atra and ventricles and

pushes blood around the body and the smooth muscle that lines the inside hollow organs of our digestive tract our

renal tract and our reproductive tract and also our blood vessels when they contract they help push substances

through the body so that's really important for you to understand let's first begin with skeletal muscle

skeletal muscle is muscle that's attached to our skeleton and generally speaking these muscles cross joints for

example I've drawn up the biceps brachii it crosses both the shoulder joint and the elbow joint and when you excite

skeletal muscle to contract it will shorten and if it shortens and it shortens across joints those joints move

so contract biceps brachii I get elbow flexion I can track biceps

brachii I get shoulder flexion and this is the result of skeletal muscle now all skeletal muscle contracts consciously we

must write that down so it is conscious let's say voluntary is a better one it's voluntary

movement voluntary movement now compare that to something like cardiac right do you

consciously tell your heart to contract no thank God we don't because imagine how much mental time and energy it would

take to constantly tell our heart to beat once every second it would be horrible so cardiac muscle is

involuntary and like I said you should be grateful for that smooth muscle this is going to be the muscle that lines the

inside of our hollow organs like I said a digestive tract so our esophagus our stomach our small large intestines all

the way through and our urinary tract so our ureters our bladder our urethra and our reproductive tract and our blood

vessels as well this is all smooth muscle again you don't tell this muscle to contract so it contracts in

voluntarily please I'll just write involuntary like I did

for the other one so only one is voluntary contraction that's skeletal muscle I want you to think about what

these cells look like under a microscope because it tells you a lot about their function so if I were to draw up

skeletal muscle and see what it looks like under a microscope what you'll find for skeletal muscle is number one it's

shaped like a cylinder compare that to cardiac muscle if I were to compare cardiac muscle under a microscope what

you'll find is that it's branched and then if I were to compare that to smooth muscle under a microscope it

has this shape to it like a spindle shape like an eye all right so that's the first thing that's how they look

under the microscope quite different than nuclei we must talk about the nuclear because it's very important

particularly for skeletal muscle now the nuclei we know houses DNA and if we look at skeletal muscle you're actually going

to find that it is multi nucleated multi-nuclear let's write this down let's write down the fact that it

is cylinder shaped let's write down the fact that cardiac

is Branched and write down that smooth muscle is spindle shaped

and then let's write down that skeletal muscle is multi nucleated

has many nuclei if we compare that to cardiac it's uni or by nucleated and it's usually found

right in the center so let's write uni or sometimes by nucleated and then let's compare this to smooth

muscle which is uni nucleated now again and it's sitting right in the center

what's so important about look the nuclei well it's really important for skeletal muscle think why which of

these three muscles or muscle types do you think has the capacity to grow most hypertrophy is the term that we use for

muscle growth or tissue growth really it's skeletal muscle you go to the gym you lift weights the whole reason why

muscle grows or skeletal muscle grows is because you expose it to stress and that stress is a heavy load and that muscle

goes this is difficult I don't want it to be this difficult next time so I'm going to release growth factors and I'm

going to stimulate the synthesis of more proteins to allow for muscle contraction to occur we know that proteins are made

from the DNA in our nuclei DNA gets transcribed into RNA RNA gets translated into amino acids which fold into

proteins and proteins can be used for contraction and growth and that's what happens with skeletal muscle so the more

nuclei the more capacity you have for hypertrophy and growth and that's why skeletal muscle has so many nuclei our

heart has less of a capacity hence why it's uni or binucleated and as smooth Muscle really doesn't have the capacity

for hypertrophy hence why it's only uni-nucleated let's talk a little bit about their appearance as well because

what you're going to find is down the microscope skeletal muscle has these Stripes like these tiger

looking Stripes to it so does cardiac cardiac has these Stripes as well we call these Stripes striations so

let's write this down so this is striated skeletal muscle this is also striated

this is cardiac muscle but smooth muscle now this is where the name comes from right skeletal muscle makes sense it's

attached to the skeleton cardiac muscles easy It lines the ventricles and atria of our heart smooth muscle tells you

nothing about where it is but about what it looks like under the microscope smooth muscle looks smooth it does not

have those striations so let's write this down let's write striations and then let's put a

cross through it no striations what are these striations these striations are the protein

microfilaments that allow for contraction to occur so if I were to take either cardiac sorry cardiac or

skeletal and have a look at it in a bit more detail it's going to look a little bit like this

you're going to have two major types of proteins you're going to have what's called myosin

and this myosin has these little Golf Club looking heads to them like this these little arms and golf club looking

heads and they need to bind to the second protein and that second protein is

called actin so let's draw up some actin so here's some actin now we're going to have these things

called Z discs over here and what was actually what we've actually just drawn up here is what we

call a sarcomere so this actual thing here called a sarcomere is actually the smallest contractile

unit of muscle what happens is the mice and heads bind to the actin they walk along it and they shorten the whole

thing that's contraction if you shorten a contraction shorten and contract this you're going to shorten and contract the

muscle tissue so you've got the myosin which is the blue I'll write that down for you we've got the myosin

and you've got the actin now I was saying to you about the striations what are the striations well

can you see here that you've got Parts where both proteins overlap so you've got an area here no overlap

here overlap no overlap overlap no overlap when you look at that under a microscope you get stripes the areas of

overlap look darker and they're the striations which tells you that in both skeletal muscle and cardiac muscle actin

and myosin are arranged in this fashion for contraction to occur but when we look at

smooth muscle it's not arranged in this fashion in and the reason why is this because they're arranged in series and

parallel right so basically take this sarcomere and go boom boom boom boom and then go boom boom boom boom and add them

in series and parallel so they're all in the same direction so that when they contract the whole thing shortens which

means when skeletal muscle contracts the whole thing shortens when cardiac muscle contracts

the whole thing shortens but the difference here was smooth muscle is that they're not

arranged in series and parallel they're arranged in what seems to be this mishmash different shape and if it's

arranged in this mishmash shape you don't get these pattern striations and why would we want our smooth muscle to

be arranged in a weird way because we don't just want contraction of our smooth muscle to go like that we want

contraction of our smooth muscle to go in many directions why well because smooth muscle is not

just straight like skeletal muscle where we want it to shorten like this and bend the joint or cardiac muscle where we

wanted to shorten and contract over ventricle we have smooth muscle lining a tube and so if we've got a tube like

this what you want is you want to narrow the diameter of that tube similar to what

happens here but you also want to shorten the length of the tube and this is how things move through if you were

to get a tennis ball put it into a stocking and you were to squeeze that tennis ball through the stockings what

you're doing is you're narrowing the diameter but you're also shortening the tube and that's peristalsis that's how

things move through tubes and it can only happen if the uni uh sorry if the smooth muscle cells have their

contractile proteins arranged in what looks like a mishmash sort of random way so hopefully that makes sense to you so

we've got voluntary fiskeletal involuntary for cardiac involuntary for smooth we've got multi-nucleated for

skeletal we've got uni or binucleated for cardiac and we've got uni nucleated for smooth we've got uh cylinder shaped

for skeletal branched for cardiac and we've got spindle shaped for our smooth muscle all right what's the next thing

we need to look at we need to have a look at how are they connected to one another so

what you'll find here for the skeletal is that they're simply just sitting on top of each other like parallel right so

you're going to have there's one there there's one there

there's one there right when we look at cardiac it's going to be attached like this

because it's branched it wants to be attached to other ones like this so you've got all these branches

attached to each other now why is this the case this is important because

little for a second because because it's rained arranged in parallel it's like that on purpose take them you're going

to have the it arranged for the biceps for example these big long cylindrical cells like this right

like that I know my lines aren't very straight but it's like that so that when it contracts

it shortens like that that's easy but the branching because it moves around these ventricles and Atria they're

actually connected through little gaps called Gap Junctions you've got these

intercalated discs that hold each cell together intercalated discs they hold each one together and then you've got

these Gap Junctions let's write this down you've got intercalated discs enter

collated discs right which hold things together and then you've got Gap Junctions

which allow for communication talk to each other now why do we want them to talk to each

other here's the thing you probably are aware that when a heart contracts you don't just contract one part of the

heart muscle you contract all of the heart muscle but the stimulus for contraction begins in one spot the

sinoatrial node it begins at around about up here

an electrical signal gets sent in this fashion around the tissue now the electrical

signal needs to spread through the muscle now it spreads through these Gap Junctions so if you start an action

potential or you know sodium jumping into this cell it gets the spread to this one and spreads to this one so when

that contracts that contracts and then that contracts and it contracts in what we call a sensation it means that if you

stimulate one muscle cell to contract all the rest will contract that's not the same here you need a different motor

neuron innervating each of these muscle cells if I have a motor neuron coming down it needs to innovate that one it

needs to innervate that one it needs to innovate that one to tell it to contract not the case here you only need to

innovate this first one and it spreads the signal to the rest and they all act as one when all muscle

cells act as one we call that a sin session spelled that wrong see I shouldn't

shouldn't talk at the same time sin I've probably spelled it wrong again but anyway the term is sensation I promise

you that it's just that my spelling is pretty poor and then when we've got smooth muscle

they're going to be connected as well like this so I've got a spindle I'm going to have

another spindle I'm gonna have another spindle we're gonna have another spindle

I'm gonna have another spindle like that and again it's so they contract in multiple directions to help move things

through all right so these are the similarities and differences between skeletal cardiac

and smooth muscle and I hope that it helps hi everyone Dr Mike here if you enjoyed this video please hit like And

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