The Neuro-muscular Junction -
The Muscle Cell Contraction -

How Stuff Works (Senior School Edition)
Contracting a Muscle -
Excitation to Contraction to Relaxation -

Shockwave File - explaining the nerve-muscle synapse junction

Shockwave File - Excellent representation of the muscular contraction:

Slide Share - Muscle Function and Contraction
Link -

Worksheet - complements video - All Systems Go! Again!

Video - Nature Reinvented