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Human Body Study

Smooth Muscle

The involuntary muscle of the body’s hollow organs and tubes.

The three muscle types and the tendons that anchor them A four-panel plate: three comparative panels of skeletal, cardiac and smooth muscle drawn so the visual differences carry the classification, plus a fourth panel showing skeletal muscle attaching to bone via a tendon. Each panel links to that subject's article. Skeletal muscle long striated multinucleate fibres, attached to bones Cardiac muscle branched cells joined by intercalated discs, with a central nucleus Smooth muscle spindle-shaped cells with a single central nucleus; no striations Tendon — connection to bone a skeletal muscle's belly tapers into a cord of parallel collagen fibres, anchored into bone muscle tendon bone Three muscle types — one mechanism, three cell forms — plus the tendon, by which a skeletal muscle pulls on bone.

Where it is

Section titled “Where it is”

The walls of the digestive tract, blood vessels, airways, bladder, and uterus, and within the eye.

Structure

Section titled “Structure”

Small, spindle-shaped cells with no stripes — hence “smooth.” It contracts slowly and can sustain tension for long periods with little fatigue.

How it works

Section titled “How it works”

Works automatically, controlled by the autonomic nervous system, hormones, and local conditions, without conscious input.

What it does

Section titled “What it does”
  • Propels contents along tubes (food, urine).
  • Adjusts the diameter of vessels and airways.
  • Drives slow, sustained actions such as changing pupil size.

Key idea

Section titled “Key idea”

Smooth muscle is the quiet workhorse — it runs the body’s internal plumbing continuously and unnoticed.