The Sneezing Reflex: - The initiating stimulus is irritation in the nasal mucosa, the afferent impulses pass in the trigeminal nerve to the medulla. - Amoderate amount of air is inspired. - The uvula closes the posterior nasal opening. - Pressure is built up in the lungs and pharynx behind the uvula. - Then suddenly the uvula is depressed so that large amounts of air pass rapidly through the nose, thus helping to clear the nasal passages of foreign matter. المحاضرة الخامسة

The Cough Reflex: - The cough reflex is the means by which the passage ways of the, lungs are maintained free of foreign matter. The following effects take place: 1. A moderate amount of air is inspired. 2. The epiglottis closes, and the vocal cords shut tightly to intrap theair with in the lung. 3. The abdominal muscles contract very forcefully, pushing the diaphragm up into the chest while other expiratory muscles also contract, thus the pressure in the lungs increases very much.

4. The vocal cords and epiglottis suddenly open widely so that the air under pressure in the lungs explodes out ward. The rapidly moving air usually carries with it any foreign matter that is present in the bronchi and trachea. Volume of Respired Air

1- The Tidal air: Tidal volume is the volume of air breathed in an out in a single quite respiration. It's about 500 ml. 2- The inspiratory reserve volume: It is the volume of air taken by the deepest inspiration more than the tidal air. It is about 3000 C.C. This amount if added to the tidal volume is called inspriatory capacity. 3- The expiratory reserve volume: It is the volume of air given off by the deepest expriation more than the tidal air. It is about 1200ml. This amount if added to the tidal volume is called the expiratory capacity.

4- The Residual Air Volume: Equals the volume of air the remains in the lungs after a maximal expiration. It's amounts is about 1200ml. It's volume cannot be measured by the spirometer. The lung is composed of 4 Capacities as follows: