The Muscular System
The three muscle types and what each one does, how a muscle actually contracts, the difference between a strain and a sprain, and why crush injury and prolonged immobility turn skeletal muscle into a systemic emergency.
8 min read · Updated September 10, 2026
Three Types of Muscle
Every muscle in the body falls into one of three types, and the differences are worth knowing because they explain why some things are under your control and some are not.
| Type | Control | Appearance | Where |
|---|---|---|---|
| Skeletal | Voluntary | Striated | Attached to bone, moves the skeleton |
| Smooth | Involuntary | Non-striated | Blood vessels, airways, gut, bladder, uterus |
| Cardiac | Involuntary | Striated | Heart only |
Type
- Control
- Voluntary
- Appearance
- Striated
- Where
- Attached to bone, moves the skeleton
- Control
- Involuntary
- Appearance
- Non-striated
- Where
- Blood vessels, airways, gut, bladder, uterus
- Control
- Involuntary
- Appearance
- Striated
- Where
- Heart only
Skeletal muscle is what you think of as muscle. It makes up most of the body's mass, it works on conscious command, and it fatigues.
Smooth muscle lines the hollow structures. It squeezes blood vessels to raise blood pressure, narrows or widens the bronchioles, and pushes food along the digestive tract. You have no conscious control over any of it.
Cardiac muscle is unique. It is striated like skeletal muscle but involuntary like smooth muscle, and it has a property neither of the others has: automaticity, the ability to generate its own electrical impulse without any signal from a nerve. That is why a heart continues beating in a patient whose brain is no longer sending it anything.
Quick check
Which property belongs to cardiac muscle alone, and what does it mean?
Frequently asked questions
What are the three types of muscle?
Skeletal muscle is voluntary and striated and moves the bones. Smooth muscle is involuntary and lines the blood vessels, the airways and the digestive tract. Cardiac muscle is involuntary, striated, and found only in the heart, where it can generate its own impulse.
What is the difference between a strain and a sprain?
A strain is an overstretched or torn muscle or tendon, and a tendon attaches muscle to bone. A sprain is an overstretched or torn ligament, and a ligament attaches bone to bone. Strain is muscle, sprain is joint.
Why is a crush injury dangerous after the weight is lifted off?
Muscle that has been compressed for hours breaks down and fills with potassium, myoglobin and acid that cannot reach the circulation while the pressure is still on. Releasing the weight opens that dam, and the potassium load can stop the heart. The patient often looks fine right up until the moment of release.
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