Detailed Instructions: Given scientific fact as input, generate the question from this fact such that it can be answered from the input.
Q: Cardiac muscle kind of muscle cells undergo twitch-type contractions with long refractory periods followed by brief relaxation periods, allowing the heart to fill with blood for the next cycle.
A:
What kind of muscle cells undergo twitch-type contractions with long refractory periods followed by brief relaxation periods, allowing the heart to fill with blood for the next cycle?