Video · Muscles, part 1 – Muscle Cells: Crash Course A&P #21 TwitterShare on Facebook4K 2 177 975 views Crash Course - June 8, 2015 Science Crash Course More Videos What is Plate Tectonics: Crash Course Geology #10 Science · 2 days ago What is Plate Tectonics: Crash Course Geology #10 Science · 2 days ago How Water Shapes the Land: Crash Course Geology #9 Science · 1 week ago How Water Shapes the Land: Crash Course Geology #9 Science · 1 week ago Myths About Diamonds: Crash Course Geology #8 Science · 2 weeks ago How Do Gems Form?: Crash Course Geology #7 Science · 3 weeks ago How Do Gems Form?: Crash Course Geology #7 Science · 3 weeks ago A Message From Hank Green Science · May 28, 2026