View the animation below, then complete the quiz to test your knowledge of the concept.

1	Muscle contractions are initiated by binding of
	A)	potassium ions to troponin.
	B)	potassium ions to tropomyosin.
	C)	calcium ions to troponin.
	D)	calcium ions to tropomyosin.
	E)	calcium ions to both troponin and tropomyosin.
2	During muscle contractions, cross-bridges form between
	A)	myosin heads and tropomyosin filaments.
	B)	myosin heads and actin filaments.
	C)	myosin heads and ATP molecules.
	D)	actin heads and troponin filaments.
	E)	actin heads and tropomyosin filaments.
3	Which of the following is the site of ATP binding and hydrolysis?
	A)	troponin
	B)	tropomysin
	C)	actin
	D)	myosin
	E)	Both A and B
4	The binding of ATP allows the muscle filaments to slide past one another.
	A)	True
	B)	False
5	After cross-bridges form, phosphate is released and then ADP follows.
	A)	True
	B)	False