The
cough reflex has both sensory (
afferent) mainly via the
vagus nerve and motor (
efferent) components. Pulmonary irritant receptors (cough receptors) in the epithelium of the respiratory tract are sensitive to both mechanical and chemical stimuli. The
bronchi and
trachea are so sensitive to light touch that slight amounts of foreign matter or other causes of irritation initiate the cough reflex. The
larynx and
carina are especially sensitive, and the
terminal bronchioles and even the
alveoli are sensitive to chemical stimuli such as
sulfur dioxide gas or
chlorine gas. The rapidly moving air usually carries with it any foreign matter that is present in the bronchi or trachea. Stimulation of the cough receptors by dust or other foreign particles produces a cough, which is necessary to remove the foreign material from the respiratory tract before it reaches the
lungs.