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

1	An action potential enters a neuron...
	A)	by diffusion.
	B)	by the T-tubules.
	C)	by the sarcolemma.
	D)	by the sarcoplasmic reticulum.
	E)	by the actin myofilament.
2	What structures do the calcium ions bind to when muscle contraction is initiated?
	A)	the actin myofilament.
	B)	the troponin molecule.
	C)	the tropomyosin molecule.
	D)	the sarcoplasmic reticulum.
	E)	the sarcolemma.
3	Cross bridges form between...
	A)	troponin and tropomyosin.
	B)	calcium and sodium.
	C)	the sarcolemma and the sarcoplasmic reticulum.
	D)	the T-tubules and the sarcolemma.
	E)	the actin filaments and the myosin heads.
4	An action potential introduced at the neuromuscular junction is propagated along the sarcoplasmic reticulum.
	A)	True
	B)	False
5	In response to an action potential entering the neuron, calcium ions diffuse from the sarcolemma into the sarcoplasm.
	A)	True
	B)	False