Biological Systems MCAT Practice Exam

What structural feature of cardiac muscle allows for the rapid transmission of action potentials between cells?

1. Gap junctions

2. Canaliculi

3. Perforating canals

4. Atrium

The correct answer is: Gap junctions

The rapid transmission of action potentials between cardiac muscle cells is primarily facilitated by gap junctions. These specialized intercellular connections consist of protein channels that create direct pathways for ions and small molecules to flow between adjacent cells. This electrical coupling allows action potentials to spread quickly from one cardiac muscle cell to another, ensuring synchronized contractions of the heart muscle. In cardiac tissue, the effective coordination of contraction is essential for proper heart function, as it optimizes blood pumping. Gap junctions enable the heart's pacemaker activity to dictate the rhythmic contractions, which is crucial for maintaining a regular heartbeat. Other structural features mentioned do not serve this purpose. Canaliculi, for example, are involved in the distribution of calcium ions but do not facilitate direct electrical communication between cells. Perforating canals relate to the structure of bone and are not relevant to cardiac muscle function. The atrium is a chamber of the heart rather than a structural feature influencing action potential transmission.