
No really, I’m not trying to make any metaphors this time. This is a post about muscle cells and the Sliding Filament Theory of muscle contraction. Boring eh? For the last week I have been studying my ass off for this anatomy exam and I’m sorry but all I can think about are muscle tissues and bones (and a LOT of other stuff). So, really, I have been learning maaaany new things every day, only nothing I would really like to write any posts about… until now.
Yesterday my professor embarrassed me… in front of me! And well, in front of him, too. I have been studying for hours on a daily basis and the one topic I decide to ask him about yesterday, turns out to be a shit-show.
During review yesterday, my table had this model of a tube with many other tubes coming out of it and several layers wrapped around these tubes. My table members kept shouting out different names for the different parts but really, they were all different! I ask them to go slowwwwerrr because I am very confused and this lady, who is reallyhyper and talksreallyfast, starts explaining but someone else cuts in, “No, no this is epimysium!” and I’m like okay screw this I am asking him, our professor, what the hell we are looking at.
I scoop up the model and take it to his desk.
“Dr. Egert”, I politely ask, “I just have a few questions. Everyone in my group thinks everything on this model is something different and I, myself, don’t even have a clue. What the hell am I looking at?!”
Pointing, he replies, “Okay, so what do we call this?”
Blank. “Endosteum?” I guess.
He gives me an expression as if to say ‘are you serious’? “No” he replies bluntly, “that’s bone tissue. This is a muscle cell. They are completely different. This is endomysium.“
“Oh, yeah, that’s what I meant.”
He looks at me questionably.
“Okay, so if that is the endomysium, what is this?”
Blank again.
“Uhhh… I don’t know.” God why is he doing this?! I told him I didn’t have a clue!
“Okay what are all muscles wrapped in?” I think he is getting frusterated.
My brain is searching for any answer but really I just want to turn away.
“I have no idea”, I reply, “like I said, I really don’t have a clue and I don’t know what I am even looking at.”
It doesn’t matter, he wants to know what muscle tissues are wrapped in, not what model we’re looking at. He turns and starts drawing on the board… ‘this goes in here, and this and this’, but I can’t concentrate because I feel like such a fool for not knowing this stuff 2 days before the test, but I’m really trying to hear what he is saying, I really am, but I would really like to go consult the book now instead of looking like a parakeet.
“…see and this is where the muscle fibers wrapped in endomysium are.”
“Okay, thanks, I need to study this a lot more, I just wasn’t sure what model this was, but I think I understand, okay, thanks!”
I need to get away quickly so I start backing away but I can tell he has something else to say.
He is still holding that expression when he says, “Yeah, you don’t want to confuse the parts of the bone with parts of the muscle. Bone stuff tends to end in -osteum, not the muscles.”
Great. My face is hot and I would like to bury my head now. When I go back to the table everyone wants answers and I tell them I don’t know, I’m not even familiar with the terms so I can’t repeat what he said. Now I’ve done it.
Seriously, the ONLY thing that I didn’t study over the weekend.
I was so worked up on this that I came home and jumped right into my book and outlined the text on muscle cells and the Sliding Filament Theory. I made flashcards with all of the -mysium terms and watched endless youtube videos. I will not look like a fool ever again on the Sliding Filament Theory.
Yesterday I was pissed at my professor for making me feel like a complete idiot. This morning I am actually kind of thankful because now I know this topic and it will probably save me a few extra points on the test. I guess sometimes you gotta feel like an idiot to become the expert.
Now for muscle cells and the Sliding Filament Theory.
(If you’re interested this is great, but this is kind of for my own review)
Muscles are wrapped in a dense connective tissue call epimysium. Within the muscle are fascicles wrapped in a fibrous connective tissue called perimysium. Within these fascicles are muscle fibers, or muscle cells, bound by sarcolemma and surrounded by endomysium. These muscle fibers are filled with sarcoplasm, a sarcoplamic reticulum, which stores calcium, many nuclei, and myofibrils. Myofibrils contain sarcomeres, the basic unit of muscle contraction, made of thin filaments called actin and thick filaments called myosin.
With the power of ATP, myosin goes into a “cocked” position, like pulling back a lever. When ATP is released, myosin “springs”, or the lever is released, causing what is called a “powerstroke”.
In detail:
1. Calcium is released from the sarcoplasmic reticulum
2. Calcium binds to traponin, which changes the traponin’s shape, and pulls tropomyosin (which keeps myosin from binding actin) out of the way so the myosin can grab the actin.
3. When the myosin grabs the actin, this causes the “powerstroke” as it pulls the actin closer together. This is the contraction.
4. If calcium is still present, the muscle will keep contracting. Otherwise, if the muscle is at rest, ATP needs to re-cock myosin and have it detach from actin.
And THAT, ladies and gentleman, is what we call the Sliding Filament Theory.