Muscle Contraction Explained!
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- Опубліковано 20 кві 2024
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Video Transcript: Skeletal muscles… Without them, you wouldn’t be able to move around. Muscles provide the force that is needed to pull on your bones to allow for all of the body movements that we can do. They do this by contracting. When a muscle contracts, it gets shorter and pulls on bones to create movements of the skeleton. But, how do they contract? What’s really going on? Let’s find out!
Muscle Structure:
First, we should understand some basics of muscle structure. A muscle is made up of bundles of muscle fibers surrounded by connective tissue. Each muscle fiber is actually a single long cylindrical cell that has lots of nuclei and mitochondria. Inside of each muscle fiber, we have many smaller myofibrils. Each myofibril is divided into sections called sarcomeres. These are made largely of two proteins that allow muscles to contract, actin and myosin.
Muscle Contraction
So how does this structure of a muscle allow for the muscle to contract? To find out, let’s zoom in on a sarcomere and see what’s going on. The way that muscles contract is by shortening the sarcomeres that make up each myofibril. You can see that this is accomplished when myosin heads pull on actin filaments. Now, let’s examine how this happens in more detail.
When you decide in your brain that you want to move a muscle, you send nerve impulses that trigger the muscle to contract. When the impulse reaches a muscle fiber, this triggers the release of calcium ions by the sarcoplasmic reticulum (a specialized form of ER found in muscle cells). This calcium attaches or binds to a protein complex called troponin. This causes troponin to change shape and move another protein, tropomyosin, so that it no longer blocks the myosin-binding sites on actin. Now that these myosin-binding sites are open, myosin heads can bind to actin. This attachment of myosin to actin is called a cross-bridge.
But, in order to power muscle contraction, energy is obviously needed. This energy comes in the form of ATP. ATP binds to myosin and breaks the cross-bridge connecting it to actin. Then, ATP is broken down into ADP and phosphate. This breakdown releases energy that “powers up” (add power up sound) the myosin head, causing it to change its position to a “high-energy” configuration and reattach to actin. This position of the myosin head makes it like a spring or loaded catapult. It has potential energy stored up. So, when the ADP and phosphate are released, the myosin head snaps back to its original, low energy configuration, pulling on actin as it does so. So the actin slides and shortens the sarcomere. After this, ATP again attaches to myosin, breaking the cross-bridge and allowing the process to start over. As this cycle continues, the muscle continues to contract.
When you decide to stop contracting your muscle, you stop sending nerve impulses, so calcium stops being released. Without calcium ions, troponin changes shape and causes tropomyosin to cover the myosin-binding sites again. Now, myosin heads can no longer bind to actin, so actin slides back to its original position, the sarcomeres lengthen, and the muscle relaxes.
Because actin filaments are sliding past myosin in this model of muscle contraction, it is often called the sliding filament model of muscle contraction.
That’s probably a lot to take in! I’d recommend trying the muscle contraction game linked in the description to practice what you just learned! And don’t forget, there are many more learning games and experiences to be had on the BioMan Biology website: biomanbio.com.
Credits:
Video by Marc Espejo: www.pexels.com/video/front-fl...
Video by Mary Taylor: www.pexels.com/video/a-man-do...
Video by Леха Квачёв: www.pexels.com/video/a-man-do...
Video by cottonbro studio: www.pexels.com/video/skateboa...
Video by Tima Miroshnichenko: www.pexels.com/video/man-doin...
Image by brgfx on Freepik
Image by brgfx on Freepik
Sound Effect from Pixabay
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Going into my finals next week and I just wanted to thank you, as these videos have helped me a ton.
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Thank you for your great explanation and for making a complex concept understandable.
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please make videos on the circulatory system, your videos are so easy to understand they make me pass.
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