SUSUMU NISHINAGA / SCIENCE PHOTO LIBRARY SUSUMU NISHINAGA / SCIENCE PHOTO LIBRARY
Smooth muscle. Coloured scanning electron micrograph of smooth muscle from the trachea (windpipe). Smooth muscle is not under voluntary control, unlike skeletal (striated) muscle. Smooth muscle comprises bundles of muscle fibres (brown). These contain the contractile proteins actin and myosin, which slide over each other to contract the muscle.
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