Cough

Cough is an explosive exiration thet provides a normal protective mechanism for clearing the tracheobronchial tree of secretions and foreign material. When excessive or bothersome, it is also one of the most common symptoms for which pateint seeks attention.

Mechanism

Coughing may be initiated either voluntariliy or reflexively. As a defnsive reflex it has both afferent and efferent pathways. The afferent limb includes receptors within the sensory distribution of trigeminal, glossopharyngeal, superior laryngeal and vagus nerves. The efferent limb includes the recurrent laryngeal nerve and spinal nerves. The cough starts with a deep inspiration followed by glottic closure, relaxation of the diaphgram, and muscle contraction against a clossed glottis. The resulting markedly positive intrathoracic pressure causes narrowing of trachea. Once the glottis opens, the large pressure differential between the airways and the atmosphere coupled with tracheal narrowing produces rapid flow rates through the trachea.