COUGHING, considered physiologically, consists, 1st, in a long inspiration which fills the lungs to a greater extent than usual; 2d, in the closure of the glottis, or narrow opening in the organ of voice (see LAitvxx), at the commencement of the act of expi ration; and 3d, in the sudden forcing open of the glottis by the violence of the expiratory movement. In this way, a blast of air is driven upwards from the lungs through the mouth, which carries with it any sources of irritation that may have been present in the air-passages. C. may occur from irritation in the back of the throat, in the larynx, trachea, or bronchial tubes, and may be excited by acrid vapors, by irritant gases, or by articles of food or drink—such as even a drop of water or a crumb of bread—making their way into the air-passages instead of into the pharynx, or by excessive or morbid secretion from the walls of the air-tubes, or even by the entrance of cold air, when the lining membrane of the air-passages is abnormally irritable.
It is not very easy to explain to the non-professional reader how cough is produced. From the medulla oblongata, or uppermost part of the spinal cord (lying within the cavity of the cranium), there is given off a very important nerve, called, from its distri bution to the lungs and stomach, the pneumogastric nerve (q.v.), which contains both
sensory and motor filaments. The sensory filaments are distributed to the mucous lining of the larynx, trachea, etc. Any of the irritating substances already mentioned may produce an impression upon these sensory filaments which, being conveyed to the medulla oblongata, gives rise, through the motor filaments, to the transmission of motor impulses to the various muscles which are concerned in the net of coughing. Other motor nerves, especially those supplying the intercostal muscles and the diaphragm, co-operate powerfully with the motor filaments of the pneurnogastrie.
The object of C. in the animal economy is unquestionably to guard against the danger of the entrance of mechanical and chemical irritants into the air-passages; and accordingly the mucous membrane, especially of their upper part, is endowed with a most exquisite sensibility, which, when aroused by irritation or by a state of disease, provokes incessant coughing until the irritation be allayed or removed. Cough is an exceedingly common symptom of all diseases of the respiration. See PNEUMONIA,