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Muscle Contraction - Medical Animation
 
This animation may only be used in support of a single legal proceeding and for no other purpose. Read our License Agreement for details. To license this animation for other purposes, click here.

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Muscle Contraction - Medical Animation
MEDICAL ANIMATION TRANSCRIPT:
Skeletal muscles are voluntary, controlled consciously by the nervous system, and are made up of fascicles, which are bundles of muscle fibers surrounded by connective tissue, blood vessels, and nerves. Motor nerve axons supply one or more skeletal muscle fibers, constituting a motor unit. Inside a muscle fiber, thread-like structures called myofibrils are organized into contractile units, or sarcomeres, reflecting the striations characteristic of skeletal muscle. Each sarcomere is made up of thick and thin myofilaments, strands of proteins called myosin and actin. Myosin forms thick filaments. Actin forms thin filaments. The protruding heads of myosin filaments form cross bridges that bind to actin filaments and ATP, an energy transport molecule. Thin filaments contain a sequence of actin molecules with myosin-binding sites. At rest, actin molecules bind tropomyosin and troponin, two contractile proteins that inhibit contraction. Skeletal muscle contraction begins at the muscle fibers' plasma membrane, or sarcolemma, with invaginations called transverse or T-tubules that surround each myofibril, and open to the extracellular space. T-tubules connect to a membranous network called the sarcoplasmic reticulum that store calcium and transfer ions via voltage-gated channels into the myofibril sarcoplasm to regulate muscle contraction. In the first step of muscle contraction, called excitation, a motor nerve fires an impulse, or action potential, across the neuromuscular junction, depolarizing the sarcolemma, and generating an action potential that spreads through the sarcolemma into the T-tubules, and excites the muscle fiber. The second step is coupling, wherein the action potential depolarizes the T-tubules. Channels in the sarcoplasmic reticulum release calcium into the sarcoplasm. Along the myofilaments, troponin binds calcium and separates from tropomyosin. In the third step, called contraction, tropomyosin shifts away from actin to expose the myosin-binding sites, enabling myosin to bind to actin, resulting in the activation of ATP and the cross bridges. Released energy causes the myosin heads to rotate and pull the thin filaments inward, sliding past the thick filaments and shortening the sarcomere. The fourth step of muscle contraction is relaxation, in which calcium ions return to the sarcoplasmic reticulum and break the myosin-actin bonds. The cross bridges disengage, and the sarcomere lengthens, resulting in relaxation of the muscle and the end of the contraction. ♪ [music] ♪

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What attorneys say about MLA and The Doe Report:
"For us, the defining feature of effective demonstrative evidence is whether, by itself, the piece will tell the story of the case. Medical legal Art provides our firm with illustrations and animations that are clear and persuasive. Their exhibits tell the story in a way that allows the jury to understand a very complex subject, very quickly."

James D. Horwitz
Koskoff, Koskoff & Bieder, P.C.
Bridgeport, CT

"Your firm is great to work with and, most importantly for me, you get the job done on time and with the utmost professionalism. You should be proud of all those you employ, from KJ to Ben B. I've been especially pleased over the years with the work of Brian and Alice, both of whom seem to tolerate my idiosycratic compulsion to edit, but I've not found a bad apple in the bunch (and, as you know, I've used your firm a bunch!). I look forward to our continued professional relationship."

Kenneth J. Allen
Kenneth Allen & Associates
Valparaiso, IN

"It is with great enthusiasm that I recommend Medical Legal Art. We have used their services for three years and always found their professionalism, quality of work, and timely attention to detail to exceed our expectations. We recently settled two complicated catastrophic injury cases. One medical malpractice case involving a spinal abscess settled for 3.75 million and the other involving injuries related to a motor vehicle accident settled for 6.9 million. We consider the artwork provided by MLA to have been invaluable in helping us to successfully conclude these cases.

I highly recommend MLA to anyone seeking high quality, detailed medical legal artwork."

E. Marcus Davis, Esq.
Davis Zipperman, Krischenbaum & Lotito
Atlanta, GA
www.emarcusdavis.com

"A few words about The Doe Report: recently in a brachial plexus injury case, we used an image from The Doe Report to demonstrate the injury. We downloaded the PDF file image, and were amazed at the quality. The hard copies that you sent were even more clear. As well, we could not have been happier when you customized the image and reversed the injury from the left shoulder to the right shoulder, which is where our client's injury was.

The speed and cost-effectiveness of the product made it the perfect tool for our purposes. We will use The Doe Report again in future cases."

Andrew Needle
Needle Gallagher & Ellenberg, P.A.
Miami, FL













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