Cardiac Muscle Structure and Function: How It Pumps Blood
Cardiac muscle (myocardium) is uniquely structured for continuous, rhythmic pumping.
Key Structural Features
- Intercalated discs: Junctions between cardiomyocytes containing desmosomes (mechanical coupling) and gap junctions (electrical coupling) for synchronized contraction.
- Branching cells: Form a 3D network for efficient force transmission.
- Striations (sarcomeres): Organized actin/myosin filaments for contraction.
- T-tubules: Deep invaginations rapidly spread action potentials to cell interior.
- Abundant mitochondria: Provide ATP for continuous aerobic respiration.
- Specialized ion channels: Voltage-gated Ca2+, Na+, K+ channels regulate excitation-contraction coupling.
Functional Integration
Coordinated atrial then ventricular contraction (via conduction system) ensures efficient blood ejection. Structural specialization allows the heart to beat ~100,000 times/day without fatigue.
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