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Human Body Study

Muscular System

The body’s motors. Muscle tissue does one thing — it contracts — and from that single ability comes all movement, internal and external.

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.

Three kinds of muscle

Section titled “Three kinds of muscle”
  • Skeletal muscle — attached to bones, under voluntary control; moves the body and maintains posture. Around 600 of them.
  • Cardiac muscle — found only in the heart; contracts rhythmically and tirelessly, on its own.
  • Smooth muscle — lines hollow organs such as the gut, blood vessels, and bladder; works automatically, without conscious control.

Connection to the skeleton

Section titled “Connection to the skeleton”
  • Tendons — tough cords of dense connective tissue that anchor skeletal muscle to bone, transmitting the pull of a contraction to the lever it moves.

What it does

Section titled “What it does”
  • Movement — of the whole body, and of substances within it (food through the gut, blood through vessels).
  • Posture and stability — constant small contractions hold the body upright.
  • Heat — contraction produces warmth; shivering is muscle used as a heater.

Key idea

Section titled “Key idea”

Muscle only pulls, never pushes. Movement in both directions requires muscles arranged in opposing pairs — one to bend a joint, another to straighten it.