It really represents a very complex mechanism -- the cough reflex arc.
There are cough receptors from the upper airway leading all the way down
to the terminal bronchioles, not including, however, the terminal
bronchioles and the alveoli. There are cough receptors in the nose and
there are cough receptors in the ear canal. So some of you may have had
patients who began coughing when you began doing otoscopic examinations
-- and that's why, because you began stimulating their cough receptors.
These afferent impulses travel via the vagus nerve to the medullary
cough center, and from there a very complex but integrated mechanism
occurs traveling back through efferent vagus nerves that go to the
larynx, the chest muscles, the diaphragm, abdominal wall, pelvic floor,
and the bronchii themselves. And a very complex and very integrated
motor response that leads ultimately to what we see, finally, as the
cough.
http://www.medscape.org/viewarticle/430253
