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042 How Calcium ion release results in Muscle Contraction

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– In this video, I show how the release of Calcium ions from the sarcoplasmic reticulum results in skeletal muscle contraction at the level of the sarcomere. Enjoy

Hello and welcome to another episode of interactive biology tv where we’re making biology fun my name is leslie samuel and in this episode episode 42 i’m going to talk about how the release of calcium ions results in muscle contraction so let’s get right into it so here we’re looking at a muscle and there are a few terms that i want you to know this is called the

Fascicle so this section right here that’s a fascicle and that is basically a bundle of muscle cells and this of course then would be individual muscle cells or as i said in the last episode you can also call it muscle fibers and what i’m going to do now is we’re going to take this muscle cell and we’re going to look at it much larger hair here you can see we have

The muscle cell the muscle fiber and that is made up of these individual myofibrils so this would be a mayo fibro and we looked at the myofibril in the previous episode and we showed how they are made up of sarcomeres and i’m going to call a sarcomere from right here where you see this part here to here that is one sarcomere and as i said in a previous episode

This is the functional unit of contraction and we’re going to look at how calcium ions is responsible for the contraction of the sarcomere and we’re going to look at an animation of how that contraction looks so let’s go to the next slide here we’re looking at the sarcomere and we looked at the parts of the sarcomere and we said that we had a thick filament and

That thick filament was myosin and then we had a thin filament and that thin filament is called acting now when muscle contraction happens it’s because of the sarcomere becoming shorter this is moving in and i’m going to animate that for you this is contraction happening and then the muscle relaxes and it goes back to how it was before contraction happens the

Muscle relaxes and then it goes back to how it was before and to put that in perspective this is me working out in the gym and as i contract the muscles in my arm this is what happens so my bicep muscles contract i pull it up you can see it’s shortening the sarcomere is getting shorter and we looked a little bit at how that happens we said that there are myosin

Heads on the myosin that actually pulls along and pulls the actin so that this entire unit gets shorter as the sarcomeres get shorter and you have many of them along the myofibrils as they get shorter the muscle contracts and that causes my lower arm to move up in that direction so now let’s take that and look at a little more detail so we’re going back to this

Picture where we’re looking at the muscle fiber so that’s this part here again and as we look at the muscle fiber there’s something that i want you to notice here we have the membrane that surrounds the muscle fiber and that membrane we’re going to call that the sarcolemma now you probably know the thing that i’m using this prefix arco a lot that prefix arkell

Refers to the muscle so the sarcolemma the sarcomere anytime you hear circle you can assume that we’re talking about something relating to muscle the interesting thing about the sarcolemma is that you have these little openings where the membrane actually goes deep into the cell and you can see it coming here you can see it going through err where the membrane

Goes deep into the cell that’s called t tubules so they’re basically these little tubes that go deep into the cell and they serve a very important purpose this is how it works last time we looked at the fact that axons come in and make synaptic connections synaptic connections with the muscle cells this is called a neuromuscular junction so when a signal comes

Down and it releases the neurotransmitter in this case the neurotransmitter is acetylcholine it releases that neurotransmitter it binds to the receptors that causes a signal in the muscle cell membrane in the sarcolemma that signal then travels deep into the cell via these t tubules and something very important happens now you can see that it looks like it’s one

Tube that’s going down deep into the cell but that tube i’m going to take that and draw it over here and it’s not by itself so here we have the t tube you’ll and then surrounding the t tubules next to the t tubules we have the sarcoplasmic reticulum so i’m going to draw those hair and it’s just going to look like tubes coming down next to the t tube you it’s not

Shown here but i’m going to show that over here and as i said that is called the sarco plasmic reticulum and the sarcoplasmic reticulum stores calcium ions so we have calcium ions inside the sarcoplasmic reticulum so let me illustrate that here so c a2 + c a2 + and that’s all throughout the sarcoplasmic reticulum it’s being stored there for when it needs to be used

So once again we have a signal that’s coming down the axon causing a signal in a sarcolemma that signal then goes deep into the muscle viateur t tubules on the t tubules we have a receptor that we call the dihydropyridine receptor and under sarcoplasmic reticulum we have a receptor that we call the ryanodine receptor so let me write those over here the red is the

Dye hydro pyridine hopefully i’m spelling this right and here we have in blue the ryanodine receptor alright so we have our signal the signal comes along the sarcolemma that’s signal spreads deep into the muscle cell via the t tubules that’s going to cause a dihydropyridine receptor to interact with the ryanodine receptor that it opens a channel and let calcium

Ions flow out into the cell okay so calcium is flowing out into the cell out of the sarcoplasmic reticulum and when that calcium flows out that then causes muscle contraction i’m not going to go through all the details as to how it causes muscle contraction in this video but i’m going to do that in the next episode that aiko message is the signal comes via the

Axon causes a signal in the sarcolemma that signal travels deep into the muscle cell feel the t tubules because of the relationship between the dihydropyridine receptor and the ryanodine receptor that causes calcium that is stored in the sarcoplasmic reticulum to be released and the calcium release then causes muscle contraction so we can look at it here again and

We can see here this is where calcium is being released and then the calcium is pumped back out calcium is being released calcium is pumped back out now there’s one thing i didn’t mention and that’s the second part with calcium being pumped back out you have the t-tubule you have the sarcoplasmic reticulum and in the membrane of the sarcoplasmic reticulum you also

Have calcium pumps and once the signal is over the calcium pumps pump the calcium right back into the sarcoplasmic reticulum so that’s what’s happening here calcium being released calcium being pumped back in calcium being released calcium being pumped back in that’s all the content for this video if you have any questions of course you can ask them in the comment

Section below and as usual you can visit the website at interactive – biology comm for more biology videos and other resources that’s it for this video and i’ll see you in the next one you

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042 How Calcium ion release results in Muscle Contraction By Interactive Biology