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Muscle Contraction – Cross Bridge Cycle, Animation.

August 19, 2019

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. – The troponin units on the actin myofilaments
are bound by calcium ions. The binding displaces tropomyosin along the
myofilaments, which in turn 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. – The myosin heads release these phosphates
and bind to the actin myofilaments via the newly exposed myosin binding sites. – 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 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. – The myosin heads resume their starting positions
along the actin myofilament, and can now begin a new sequence of actin binding. – The presence of further calcium ions will
trigger a new cycle


  • Reply Ritijhi Patel December 27, 2016 at 6:24 pm

    very nice video

  • Reply Md Ibrahim kholil January 29, 2017 at 3:13 pm

    Thank you , helpful video !

  • Reply Angad Prasad February 27, 2017 at 6:40 am

    very nice study for me.thanks a lot

  • Reply Kyle Wiseman March 23, 2017 at 12:15 pm

    Great job!

  • Reply Siddharth Jain March 31, 2017 at 12:23 am

    at 1:08, it exposes actin binding sites and NOT myosin binding sites

  • Reply ishwarlal laiphrakpam April 13, 2017 at 6:25 pm

    Can you upload visual pathway

  • Reply ishwarlal laiphrakpam April 13, 2017 at 6:26 pm

    And about transport across cell membranes

  • Reply Alila Medical Media April 25, 2017 at 12:33 am

    Thank you for watching! Follow us on Twitter for instant notification of our new videos!

  • Reply Shooby Doo May 13, 2017 at 7:56 am

    I hate this fuckin work.

  • Reply MADHUSMITA SETHI June 4, 2017 at 7:20 am


  • Reply Mandeep Kaur June 8, 2017 at 6:07 pm

    very nice and understandable video… keep doing this good work…??

  • Reply Ayushi Verma June 27, 2017 at 1:20 am

    thank you so much… reading the book i was going mad and this made it so easy for me to understand… ?

  • Reply Puhiza Os June 29, 2017 at 1:06 pm

    thanks a lot

  • Reply jellyandme July 28, 2017 at 1:27 pm

    Thank you for this, helped me tidy up my notes.

  • Reply airotkiv August 3, 2017 at 9:03 am

    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!

  • Reply Brahma Chemitikanti August 29, 2017 at 7:56 pm

    Superb vedio.thank you. ..

  • Reply Xio Arleen October 1, 2017 at 8:38 pm

    When the actin is at rest does it always carry the phosphate and ADP? When the cycle restarts, does new calcium come in or the same calcium stays attached?

  • Reply utkal mohapatra October 5, 2017 at 2:13 am

    Thanks for such good video. This is truly understandable one, than any other video i saw

  • Reply Christina Kalogerias November 6, 2017 at 9:24 am

    short, succinct, to the point, animated. No unnecessary comments that take up time or throw me off. Thank you so very much for this and so many other videos.

  • Reply Tiffany Bartram November 9, 2017 at 3:04 am

    This was nice and slow and very easy to understand. Thank you so much

  • Reply Thulasi G December 3, 2017 at 2:57 am

    Thanks for this video pls upload more videos

  • Reply Taha Bin Rashid December 17, 2017 at 9:47 am

    Give animation about latch bridge mechanism of smooth muscle

  • Reply A Noli December 29, 2017 at 5:55 pm

    First semester at med school, lots of gratitude from Greece!

  • Reply bobby g January 4, 2018 at 9:18 pm

    would've been good if a huge water mark wasn't placed on the video

  • Reply Pravalika sweety January 20, 2018 at 3:15 pm

    very useful video awesome one

  • Reply zhraa ! February 2, 2018 at 4:09 pm

    Thanks ?

  • Reply Noah Gendron February 3, 2018 at 12:26 am

    helpful refresher, thanks guys

  • Reply bigel tapot February 12, 2018 at 10:43 am

    Thanks for this animation. It helps a lot.

  • Reply B.M.B Ghalib February 13, 2018 at 11:10 am

    just awsome….keep it up guys

  • Reply Faisal Bhat February 28, 2018 at 6:11 am

    Thank you so much, it helped

  • Reply Iza Khan March 18, 2018 at 9:03 am

    Thanks very helpful

  • Reply Parallel Coaching - Personal Trainer Courses March 21, 2018 at 5:21 am

    Great description. It's really clarifying to see the molecules interact like this. Thank you

  • Reply Hang Nguyen March 24, 2018 at 1:30 pm

    its such an awesome video. You made it really simple to understand. Thanks a lot!

  • Reply Kg Mh March 29, 2018 at 3:38 pm

    Best video ?????

  • Reply Anina Nazirah April 19, 2018 at 2:35 pm

    Thanks a lot..this video is helpful

  • Reply Dallin King May 3, 2018 at 4:24 pm

    Great video, but thumbs down for adding the annoying pop-ups that you have to change screen size to escape out of.

  • Reply Unicorn Power May 8, 2018 at 10:52 am

    Its crazy how this all happens in nano seconds

  • Reply Sabiha Aouchiche May 8, 2018 at 11:29 pm

    thank u , this video helped me so much

  • Reply Messia Abraham May 24, 2018 at 10:06 pm

    I do understand that copyright is a problem, however can you please place your organizations name in the corner of the video. It is hard to see the terminology and pay attention to the content of the video with "Allia…" written on top of the animation.

  • Reply Alila Medical Media May 29, 2018 at 11:17 pm

    If this video is helpful to you, please consider supporting our next projects. As a token of our appreciation, we also offer great rewards in return, please check us out here:

  • Reply C Fields July 22, 2018 at 1:53 pm

    What? Could you repeat that in English please?

  • Reply Azam Naseri September 6, 2018 at 7:42 am

    great.thanks alot

  • Reply Nadia Abizaid September 14, 2018 at 4:19 am

    This will definitely make my first physiology exam easier. Thank you so much! Mexico says hi

  • Reply Michigan September 17, 2018 at 12:59 pm

    Damn! 2 minutes and I get it! Thank you

  • Reply Komal Gaikwad Iam proud of you September 26, 2018 at 8:05 am

    bohot hard he

  • Reply Walker J. November 9, 2018 at 12:28 pm

    very helpful, thank you!

  • Reply Peace597 November 30, 2018 at 7:37 pm

    Thank you so much

  • Reply Anjli Jatav December 4, 2018 at 2:08 pm


  • Reply ThatGooberInTheCorner December 14, 2018 at 6:06 pm

    Thicc muscle amirite?

  • Reply Thomas Kelleher December 16, 2018 at 12:31 pm

    Thank you so much for this! Great animation, it certainly made it easier for me to understand.

  • Reply Mio Minato December 31, 2018 at 6:59 am

    Subhan Allah

  • Reply rhea sabella January 6, 2019 at 5:13 am

    Thank you!!

  • Reply ONEY TV January 7, 2019 at 12:11 pm

    Thank you

  • Reply comedian comedian January 23, 2019 at 2:56 pm

    Uoosi main apna channel ka advertising bhi kar raha hai to kya dekhe

  • Reply Shola Shaikh February 23, 2019 at 3:36 am

    Best explanation

  • Reply Alexey Anisimov March 7, 2019 at 11:21 pm

    This video was very helpful in terms of describing the internal energy stored in myosin heads. The ADP and Pi are not instantly released from the head when the hydrolysis had occurred.

  • Reply MangleTangle Lolly March 15, 2019 at 5:03 pm

    This is boring ???????

  • Reply snowy smile2 March 28, 2019 at 3:04 am

    why am I learning this in 11th grade biology ….everyone here is in med school wtf

  • Reply RASHID MEHMOOD June 21, 2019 at 5:18 pm

    Thanks ?

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