Final answer:
Intercalated discs are structures that connect cardiac muscle cells and play a crucial role in cardiac muscle contraction. They contain gap junctions for the transmission of electric signals and desmosomes to ensure cell stability during contraction.
Step-by-step explanation:
Intercalated discs are structures that connect cardiac muscle cells. They are part of the sarcolemma and contain two important structures for cardiac muscle contraction: gap junctions and desmosomes. Gap junctions allow the depolarizing current to flow between adjacent cardiac muscle cells, facilitating the quick transmission of action potentials and the coordinated contraction of the entire heart. Desmosomes anchor the ends of cardiac muscle fibers together, preventing the cells from pulling apart during contraction.