Which of the following structures is commonly seen at the boundary between adjacent cardiac muscle cells?

Which of the following structures is commonly seen at the boundary between adjacent cardiac muscle cells?

• A. Endomysium
• B. Sarcolemma
• C. Nucleus
• D. Intercalated Disc

Answer: (D)

Intercalated discs are specialized junctions that connect cardiac muscle cells end-to-end. They contain desmosomes that grip adjacent cells together, providing mechanical strength, and gap junctions that allow ions to pass directly between cells, enabling the rapid spread of electrical impulses. This combination is what lets heart muscle cells work in a synchronized, coordinated manner. The other options don’t sit at the boundary between cells: the endomysium is connective tissue surrounding each muscle fiber, the sarcolemma is the muscle cell membrane, and a nucleus is an internal organelle. So the boundary structure you’d observe is the intercalated disc.

Intercalated discs are specialized junctions that connect cardiac muscle cells end-to-end. They contain desmosomes that grip adjacent cells together, providing mechanical strength, and gap junctions that allow ions to pass directly between cells, enabling the rapid spread of electrical impulses. This combination is what lets heart muscle cells work in a synchronized, coordinated manner. The other options don’t sit at the boundary between cells: the endomysium is connective tissue surrounding each muscle fiber, the sarcolemma is the muscle cell membrane, and a nucleus is an internal organelle. So the boundary structure you’d observe is the intercalated disc.