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Physiology · Nerve and muscle

Skeletal, cardiac and smooth muscle compared !

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  • Exam priority: medium

The body has three muscle types: skeletal for movement, cardiac for the heartbeat and smooth for organs and vessels. They switch on in different ways.

Updated 2026-11-01

Also called: Types of muscle tissue

See it in 3D: Biceps (long head) · Stomach

What it is

All three muscle types contract by actin–myosin cross-bridge cycling triggered by Ca²⁺, but they differ in structure, where the Ca²⁺ comes from, how it switches on contraction and how they are controlled. These differences explain why drugs and electrolyte problems affect each type differently.

Action potential

Action potential: Skeletal muscle 0123456−100−80−60−40−200+20+40Time (ms)Membrane potential (mV)Rest −90 mVThreshold −60 mVARPRRPRestStimulusDepol.Repol.

Rest −90 mVThreshold −60 mVPeak +30 mVDuration ≈ 2–4 ms

Tap a phase (the pills above or its band) or a refractory period (ARP, RRP) at the base of the plot.

  • Mainly Na⁺
  • Mainly K⁺
  • Rest
  • Threshold
  • ARP: absolute refractory period
  • RRP: relative refractory period
Skeletal spike: a few milliseconds.

Action potential

Action potential: Ventricular myocyte 0100200300400−100−80−60−40−200+20+40Time (ms)Membrane potential (mV)Rest −90 mVThreshold −70 mVARPRRPPhase 4Phase 0Phase 1Phase 2Phase 3

Rest −90 mVThreshold −70 mVPeak +25 mVDuration ≈ 280 ms

Tap a phase (the pills above or its band) or a refractory period (ARP, RRP) at the base of the plot.

  • Mainly Na⁺
  • Mainly K⁺
  • Mainly Ca²⁺
  • Rest
  • Threshold
  • ARP: absolute refractory period
  • RRP: relative refractory period
Ventricular action potential: switch cell type to compare the plateau.

Three muscle types side by side

FeatureSkeletalCardiacSmooth
AppearanceStriated, long multinucleated fibersStriated, branched cells with 1–2 nuclei, intercalated discsNot striated, spindle cells, one nucleus, dense bodies
ControlVoluntary, somatic motor neuronInvoluntary, own pacemaker; autonomic modulationInvoluntary, autonomic, hormones, stretch, local factors
Electrical couplingNone between fibersGap junctionsGap junctions in single-unit; few in multi-unit
Action potentialShort spike (≈ 1–5 ms)Long plateau (≈ 200–300 ms)Slow waves, spikes or none (graded)
Ca²⁺ sourceSR onlyExtracellular trigger + SRExtracellular + SR
Ca²⁺ sensorTroponin CTroponin CCalmodulin → MLCK
Tetanus possible?YesNo (long refractory period)Sustained tone; latch state
RepairSatellite cells, limitedVery limited (scar)Good: cells divide

Clinical notes

  • Ca²⁺ channel blockers relax vascular smooth muscle and slow the heart but spare skeletal muscle, because skeletal muscle does not depend on Ca²⁺ entry.
  • Hyperkalemia is most dangerous for the heart (arrhythmia), while it also causes skeletal weakness by depolarizing the resting membrane.

Test yourself

Think of the answer, then tap the question to see it.

Why can skeletal muscle reach tetanus but the ventricle cannot?

A skeletal action potential lasts a few ms, so new spikes arrive while the fiber is still contracting and Ca²⁺ summates. The ventricular plateau keeps the cell refractory until contraction is nearly over.

Smooth muscle has no troponin. How does Ca²⁺ turn on its cross-bridges?

Ca²⁺ binds calmodulin, the complex activates myosin light-chain kinase, and phosphorylated myosin light chains allow myosin to bind actin. Regulation is on the thick filament.

Why does a drug that blocks L-type Ca²⁺ channels weaken heart contraction but not grip strength?

Cardiac contraction needs Ca²⁺ entry through L-type channels to trigger SR release. Skeletal DHPR opens RyR1 mechanically, so blocking Ca²⁺ flow through it barely affects force.

Which muscle type regenerates best after injury and why?

Smooth muscle: its cells can divide and new cells come from pericytes. Skeletal muscle relies on a limited pool of satellite cells, and cardiomyocytes barely divide, so the heart heals by scarring.

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See it in 3D

The structures of Durgical's 3D anatomy where it happens.

← All of physiology

Educational physiology content; not a diagnostic or treatment guide and no substitute for a health professional's advice. Values are approximate references. No doses are given.

Sources: 10.7 Cardiac Muscle Tissue (OpenStax (Rice University), 2022); 10.8 Smooth Muscle (OpenStax (Rice University), 2022); 10.2 Skeletal Muscle (OpenStax (Rice University), 2022); Hall JE. Guyton and Hall Textbook of Medical Physiology, 13th ed. (ch. 8). Reference book used to check facts; its text and figures are not reproduced (Elsevier, 2016).

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Representative model, for educational purposes only.