1. A contraction cycle
A) cannot begin until Ca2+ has bound to troponin.
B) cannot begin until the myosin-binding sites on actin are exposed
C) cannot begin until Ca2+ has bound to tropomyosin
D) A and B are correct
E) B and C are correct
2. How is excitation of the sarcolemma coupled to the contraction of a muscle fiber?
a) excitation continues into the T-tubules causing Ca2+ active transport channels to open, thus removing Ca2+ from the cytoplasm
B) excitation causes synthesis of more calsequestrin, thus allowing more Ca2+ to be stored in the sarcoplasmic reticulum.
C) excitation continues into the T-tubules causing Ca2+ release channels to open, thus starting a contraction cycle.
D) excitation causes Ca2+ to be released from troponin, thus allowing more crossbridges to from between myosin and actin.
E) Excitation cuases a number of intracellular events, which lower Ca2+ levels, thus stimulating a contraction cycle.
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