Muscle Contraction - Cross Bridge Cycle, Animation.
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- Опубліковано 30 сер 2016
- (USMLE topics) Molecular basis of the sliding filament theory (skeletal muscle contraction) - the cross bridge cycle.
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Muscle contraction is at the basis of all skeletal movements. Skeletal muscles are composed of muscles fibers which in turn are made of repetitive functional units called sarcomeres. Each sarcomere contains many parallel, overlapping thin (actin) and thick (myosin) filaments. The muscle contracts when these filaments slide past each other, resulting in a shortening of the sarcomere and thus the muscle. This is known as the sliding filament theory. Cross-bridge cycling forms the molecular basis for this sliding movement.
- Muscle contraction is initiated when muscle fibers are stimulated by a nerve impulse and calcium ions are released.
- To trigger muscular contraction, the troponin units on the actin myofilaments are bound by calcium ions. The binding displaces tropomyosin along the myofilaments, which in turn (and) exposes the myosin binding sites.
- At this stage, the head of each myosin unit is bound to an ADP and a phosphate molecule remaining from the previous muscular contraction.
- Now, the myosin heads release these phosphates and bind to the actin myofilaments via the newly exposed myosin binding sites.
- In this way, the actin and myosin myofilaments are cross-linked.
- The two myofilaments glide past one another, propelled by a head-first movement of the myosin units powered by the chemical energy stored in their heads. As the units move, they release the ADP molecules bound to their heads.
- The gliding motion is halted when ATP molecules bind to the myosin heads, thus severing the bonds between myosin and actin.
- The ATP molecules bound to myosin are now decomposed into ADP and phosphate, with the energy released by this reaction stored in the myosin heads, ready to be used in the next cycle of movement.
- Having been unbound from actin, the myosin heads resume their starting positions along the actin myofilament, and can now begin a new sequence of actin binding.
- Thus, the presence of further calcium ions will trigger a new contraction cycle
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This is my 2 hour class in less than 3 minutes 🤯🤯
Thats so true
Sad truth
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Its crazy how this all happens in nano seconds
It's even crazier how firearms get jammed or malfunction every now and then, but for a mechanism as complicated as muscles, it happens millions of times a second with no jamming or malfunction
Qocoshu the body has been refined through natural selection over thousands of years. Modern firearms have not.
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@@yesimfunatparties9337 Well if body developed all these structures, would the primitive men be paralysed maybe?
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I spent 9 hours yesterday trying to grasp this concept. Thank you for summing it up in 2 minutes!!!
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i literally made notes from the narration
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I'm so mad this concept was easily explained in 2 minutes as opposed to my class lectures with over 8 hours of content. SO THANK YOU
This 2 minute video did a better job than what my professor did in a hour
Literally one of my favorite teaching videos. I watched it when I took A&P, again in pathophysiology, and again in graduate level pathophysiology lol! Such a simple refresher that talks about the essential steps in muscle contraction. Thank you.
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A salute to the person who studied all this and introduced us with this concept.
You're making my first semester at med school a bit easier. Best video I've watched on this process so far. Thanks a lot from Germany!
Edit in 2022: since I'm still getting replies to this comment, just fyi, I'm taking my written final exams in April 2023 and I'll be a doctor after a practical year and one more oral exam in April 2024. And I've forgotten all about the cross bridge cycle lmao
Edit in 2024: My final exam is actually in June, I just didn't quite know how it works two years ago lmao
Thanks for watching!
2 years in, hows it going buddy?
@@postmelon645 wow haha this took me aaall the way back! it's actually 3 years now, i just wrote this at the end of the 1st semester that's probably why it says 2. and it's amazing, I'm loving it! I've seen and done so many amazing things already! I've already forgotten everything about muscle contraction though haha
@@postmelon645 idk why but your comment made very happy
@@airotkiv that's great! I'm in my 3rd year of medical school too now. Lol don't worry, even I forgot all about muscle contractions, that why I watched this video today
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Great description. It's really clarifying to see the molecules interact like this. Thank you
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First semester at med school, lots of gratitude from Greece!
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I am not a medical student or professional. Just a patient in pain going to physical therapy who was just told that 7I likely have Actin Myosin Crossbridge. All the info out there is confusing and difficult to understand. This was the easiest to understand for anyone not in a medical profession! Thank you!
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