Muscles, Part 2 - Organismal Level: Crash Course A&P #22

Hank calls in a friend to do his push ups for him today to explain how skeletal muscles work together to create and reverse movements. Hank and Claire also demonstrate the role size plays in motor units, the three phase cycle of muscle twitches, and how the strength and frequency of an impulse affects the strength and duration of a contraction. This episode also explains twitch summation, tetanus, and isotonic vs. isometric movements. Pssst... we made flashcards to help you review the content in this episode! Find them on the free Crash Course App! Download it here for Apple Devices: https://apple.co/3d4eyZo Download it here for Android Devices: https://bit.ly/2SrDulJ Table of Contents Skeletal Muscles Work Together to Create and Reverse Movements 1:14 Motor Units 3:52 Three Phases of Muscle Twitches 4:41 Strength and Frequency of Impulses 5:29 Strength and Duration of a Contraction 5:29 Twitch Summation vs Tetanus 6:19 Isotonic vs Isometric Movements 8:50 *** Crash Course Psychology Poster: http://www.dftba.com/crashcourse?utm_medium=product_shelf *** Crash Course is now on Patreon! You can support us directly by signing up at http://www.patreon.com/crashcourse Thanks to the following Patrons for their generous monthly contributions that help keep Crash Course free for everyone forever: Mark Brouwer, Jan Schmid, Steve Marshall, Anna-Ester Volozh, Sandra Aft, Brad Wardell, Christian Ludvigsen, Robert Kunz, Jason, A Saslow, Jacob Ash, Jeffrey Thompson, Jessica Simmons, James Craver, Simun Niclasen, SR Foxley, Roger C. Rocha, Nevin, Spoljaric, Eric Knight, Elliot Beter, Jessica Wode ***SUBBABLE MESSAGES*** TO: Ariela FROM: Gavi I love you so much, stay awesome as always! -- TO: Josiah P. FROM: Amy P. I love you! ***SUPPORTER THANK YOU!*** Thank you so much to all of our awesome supporters for their contributions to help make Crash Course possible and freely available for everyone forever: Vanessa Benavent, Les Brown, John Hadfield, Damian Shaw, Burt G. Clothier & Tad A. Saine, Ashley Williamson, Carrie Williamson, Melissa A, Lopin Forsythe, Trevor Sacks -- Want to find Crash Course elsewhere on the internet? Facebook - http://www.facebook.com/YouTubeCrashCourse Twitter - http://www.twitter.com/TheCrashCourse Tumblr - http://thecrashcourse.tumblr.com Support Crash Course on Patreon: http://patreon.com/crashcourse CC Kids: http://www.youtube.com/crashcoursekids