Differences Between Skeletal and Cardiac Muscle Physiology

Muscle Physiology

Differences Between Skeletal and Cardiac Muscle

The physiology of skeletal and cardiac muscle differs in several important ways, particularly in their mechanisms of excitation and contraction. Understanding these differences is essential for comprehending how the heart functions independently from voluntary muscles.

• Self-Excitability in Cardiac Muscle: Some cardiac muscle cells are self-excitable, meaning they can initiate their own depolarization without external nervous system stimulation. This is in contrast to skeletal muscle fibers, which require nervous system input to contract.

• Types of Cardiac Myocytes:

  • Contractile Cells: Responsible for the actual contraction of the heart, generating force to pump blood.

  • Pacemaker Cells: Noncontractile cells that spontaneously depolarize, initiating the depolarization of the entire heart. These cells set the rhythm of the heartbeat and do not require nervous system stimulation.

• Initiation of Depolarization: Pacemaker cells trigger the electrical activity that spreads throughout the heart, leading to coordinated contraction.

Example: The sinoatrial (SA) node in the heart contains pacemaker cells that establish the heart's rhythm, while skeletal muscle relies on motor neurons for activation.

Microscopic Anatomy of Cardiac Muscle

Structural Features of Cardiac Muscle Cells

Cardiac muscle cells possess unique structural features that facilitate their function and connectivity. These features are critical for the synchronized contraction of the heart.

• Intercalated Discs: Specialized junctions between cardiac muscle cells that contain gap junctions and desmosomes.

• Gap Junctions: Electrically connect myocytes, allowing ions and electrical impulses to pass rapidly between cells, ensuring coordinated contraction.

• Desmosomes: Mechanically connect myocytes, preventing them from pulling apart during contraction.

• Nucleus: Each cardiac muscle cell typically contains one or two centrally located nuclei.

Example: The presence of intercalated discs distinguishes cardiac muscle from skeletal muscle, which lacks these specialized junctions.