A powerpoint from the OLD syllabus, much is still relevant.
This is an amazing gif from tabletop whale – you have to check it out:
Fantastic animated tutorials from McGraw Hill Education – Action Potentials & Muscle Contraction, Myofilament Contraction, sarcomere contraction & breakdown of ATP & cross-bridge movement.
Paul Andersen explains The Muscular System in 5m 59s.
In Crash Course Biology #30 – The Skeletal System: It’s ALIVE!, Hank introduces us to the framework of our bodies, our skeleton and in #31 – Big Guns: The Muscular System, he tells us the story of the complicated chemical dance that allows our skeletal muscles to contract and relax.