Final answer:
Cardiac muscle cells are joined at specialized structures called intercalated discs, which are critical for the synchronized contraction of the heart. These discs consist of desmosomes that anchor cells and gap junctions that facilitate the transmission of electrical impulses between cells.
Step-by-step explanation:
Cardiac muscle cells form Y-shaped branches and join to adjacent muscle cells at junctions known as intercalated discs. These critical structures support the synchronized contraction of the heart muscle and are composed of desmosomes and gap junctions. Desmosomes work to anchor the ends of cardiac muscle fibers together so that cells do not pull apart during the stress of contraction, while gap junctions create channels that allow ions to pass between cells, enabling quick transmission of action potentials and coordinated contractions.
Furthermore, cardiac muscle fibers form a functional unit known as a syncytium, allowing them to synchronize their contractions. Unlike skeletal muscle fibers, cardiac muscle cells, or cardiomyocytes, are single cells typically with a single centrally located nucleus and can contract on their own intrinsic rhythms without external stimulation.