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Mnemonic

Cardiac Muscle Versus Skeletal Muscle

A memory aid for the differences between cardiac and skeletal muscle.

Physiology Histology Cardiology Cardiovascular Muscle Tissue Cardiac Physiology and Pharmacology
Expansion

Cardiac muscle is a functional syncytium with a long refractory period and cannot tetanise

Expansion

Feature Cardiac Skeletal
Control Involuntary Voluntary
Nuclei One or two, central Many, peripheral
Cell junctions Intercalated discs with gap junctions None
Electrical behaviour Functional syncytium, all-or-none Individual motor units, graded recruitment
Action potential 250 ms, with a plateau 2 to 5 ms
Refractory period Long, most of contraction Short
Tetany Impossible Possible
Calcium source Extracellular trigger plus sarcoplasmic reticulum Sarcoplasmic reticulum alone
Force graded by Preload and contractility Motor unit recruitment and frequency

The long refractory period is the single most important difference: it makes tetany impossible, which guarantees that the heart relaxes and refills between beats.

Since force cannot be graded by recruitment, the heart instead varies force through the Frank-Starling mechanism and through changes in contractility.