How does cardiac muscle differ from both voluntary and smooth muscle?

Cardiac muscle is striated like skeletal muscle but acts involuntarily like smooth muscle, and it is specialized for nonstop rhythmic pumping of the heart.

Why it is unique

• Sinoatrial node makes its own impulses (pacemaker).
• Gap junctions spread ions quickly, so chambers contract together.
• Long refractory period prevents tetanus and keeps beats separate.
• Calcium-induced calcium release coordinates force and timing.