The trachealis muscle at the posterior part of the trachea (400X)

This image shows the smooth muscle at the posterior part of the trachea. The contraction and relaxation of the trachealis muscle play a role in adjusting the size of the tracheal lumen (the central opening of the trachea). During swallowing, for example, the trachealis muscle can contract to narrow the trachea temporarily, preventing food or liquids from entering the airway. After swallowing, the muscle relaxes, allowing normal airflow.