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[Physiology](https://durgical.com/en/physiology/) · [Nerve and muscle](https://durgical.com/en/physiology/#s-nerve_muscle)

# Skeletal, cardiac and smooth muscle compared

- Table to know
- 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)](https://durgical.com/en/anatomy/biceps-brachii-long-head/) · [Stomach](https://durgical.com/en/anatomy/stomach/)

## Key points

- Ca²⁺ switch: troponin C in skeletal and cardiac muscle; calmodulin → myosin light-chain kinase in smooth muscle.
- Ca²⁺ source: skeletal = SR only (mechanical DHPR–RyR1 link); cardiac = entry through L-type channels triggers SR release; smooth = extracellular entry plus SR (IP₃).
- Cardiac muscle cannot be tetanized: its long plateau makes the refractory period last almost as long as the contraction.
- Gap junctions (intercalated discs, single-unit smooth muscle) let cardiac and visceral smooth muscle act as a syncytium; skeletal fibers are each driven by their own nerve ending.

## 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

**Rest** −90 mV **Threshold** −60 mV **Peak** +30 mV **Duration** ≈ 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

**Rest** −90 mV **Threshold** −70 mV **Peak** +25 mV **Duration** ≈ 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

| Feature | Skeletal | Cardiac | Smooth |
| --- | --- | --- | --- |
| Appearance | Striated, long multinucleated fibers | Striated, branched cells with 1–2 nuclei, intercalated discs | Not striated, spindle cells, one nucleus, dense bodies |
| Control | Voluntary, somatic motor neuron | Involuntary, own pacemaker; autonomic modulation | Involuntary, autonomic, hormones, stretch, local factors |
| Electrical coupling | None between fibers | Gap junctions | Gap junctions in single-unit; few in multi-unit |
| Action potential | Short spike (≈ 1–5 ms) | Long plateau (≈ 200–300 ms) | Slow waves, spikes or none (graded) |
| Ca²⁺ source | SR only | Extracellular trigger + SR | Extracellular + SR |
| Ca²⁺ sensor | Troponin C | Troponin C | Calmodulin → MLCK |
| Tetanus possible? | Yes | No (long refractory period) | Sustained tone; latch state |
| Repair | Satellite cells, limited | Very 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.

## Memory aid

Skeletal sprints, cardiac keeps a plateau, smooth holds the latch.

## 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.

[Add to my cards (4)](https://durgical.app/estudiar/?add=/en/physiology/skeletal-cardiac-and-smooth-muscle-compared/)

## See it in 3D

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

- [Biceps (long head)](https://durgical.com/en/anatomy/biceps-brachii-long-head/)
- [Stomach](https://durgical.com/en/anatomy/stomach/)

## Related topics

- [Sliding filaments and the cross-bridge cycle](https://durgical.com/en/physiology/sliding-filaments-and-the-cross-bridge-cycle/)
- [Skeletal muscle excitation–contraction coupling](https://durgical.com/en/physiology/skeletal-muscle-excitation-contraction-coupling/)
- [Smooth muscle contraction](https://durgical.com/en/physiology/smooth-muscle-contraction/)
- [The ventricular action potential](https://durgical.com/en/physiology/the-ventricular-action-potential/)

## Related conditions

- [Hyperkalaemia](https://durgical.com/en/conditions/hyperkalaemia/)

[← All of physiology](https://durgical.com/en/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](https://openstax.org/books/anatomy-and-physiology-2e/pages/10-7-cardiac-muscle-tissue) (OpenStax (Rice University), 2022); [10.8 Smooth Muscle](https://openstax.org/books/anatomy-and-physiology-2e/pages/10-8-smooth-muscle) (OpenStax (Rice University), 2022); [10.2 Skeletal Muscle](https://openstax.org/books/anatomy-and-physiology-2e/pages/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.

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License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/physiology/skeletal-cardiac-and-smooth-muscle-compared/