According to the textbook:

• Option B is Correct: A neural signal reaching the neuromuscular junction releases a neurotransmitter (Acetylcholine) which generates an action potential in the sarcolemma .
• Option A is Incorrect: Muscle contraction is initiated by a signal sent by the CNS via a motor neuron, not a sensory neuron .
• Option C is Incorrect/Imprecise: While increased Ca++ leads to binding with troponin, the text specifies it binds with a subunit of troponin on actin filaments, and the result is the removal of masking . Option B is the direct verbatim process described.
• Option D is Incorrect: The binding of calcium to troponin removes the masking of active sites for myosin, it does not activate masking .