Final answer:
Intercalated discs are part of the cardiac muscle sarcolemma and contain gap junctions and desmosomes. Gap junctions facilitate the transmission of action potentials between cardiac muscle cells, while desmosomes keep the cells anchored together during contraction.
Step-by-step explanation:
Intercalated discs are part of the cardiac muscle sarcolemma and contain two important structures: gap junctions and desmosomes. Gap junctions allow the depolarizing current to flow from one cardiac muscle cell to the next, facilitating the quick transmission of action potentials and the coordinated contraction of the entire heart. Desmosomes anchor the ends of cardiac muscle fibers together, ensuring that the cells do not pull apart during contraction.