Final answer:
Gap junctions are part of intercalated discs in cardiac muscle, enabling quick action potential transmission and synchronized contraction.
Step-by-step explanation:
The gap junctions in cardiac muscle are part of specialized cell junctions called intercalated discs. These discs are critical for the synchronized contraction of the heart muscle. Gap junctions allow for the quick transmission of action potentials between cells, while the remainder of the intercalated disc is composed of desmosomes, which help anchor cardiac muscle fibers together, preventing them from pulling apart during contraction.