SUSUMU NISHINAGA / SCIENCE PHOTO LIBRARY SUSUMU NISHINAGA / SCIENCE PHOTO LIBRARY
Trachea muscle. Coloured scanning electron micrograph (SEM) of smooth muscle from the trachea. The trachea (wind pipe) runs from the larynx (voice box) to the lungs. The muscle fibres (round, orange) are surrounded by connective tissue (yellow). Connective tissue supports other tissues and organs. The trachea is held open by incomplete rings of cartilage. Smooth muscle, known as the trachealis muscle, at the back of the trachea completes the rings. The trachealis muscle relaxes with inhalation and contracts with exhalation.
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