COUGH AND SNEEZE REFLEX

By 

Tanlaka Lucas Mengnjo

Scientific Journal Club

Faculty of Health Sciences(FHS)

University of Bamenda (UBa),Cameroon 
tanlakalucas@gmail.com

Cough reflex

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 (the point where the trachea divides into the primary bronchi), are especially sensitive and the terminal bronchioles and even the alveoli are sensitive to corrosive chemical stimuli such as sulfur dioxide gas or chlorine gas.

Afferent nerve impulses pass from the respiratory passages mainly through the vagus nerves to the

medulla of the brain. There, an automatic sequence of events is triggered by the neuronal circuits of the medulla causing the following effects:

First, up to 2.5 liters of air are rapidly inspired.

Second, the epiglottis closes and the vocal cords shut tightly to entrap the air within the lungs. 

Third, the abdominal muscles contract forcefully, pushing against the diaphragm while other expiratory muscles, such as the internal intercostals, also contract forcefully. Consequently, the pressure in the lungs rises rapidly to as much as 100 mm Hg or more. 

Fourth, the vocal cords and the epiglottis suddenly open widely so that air

under this high pressure in the lungs explodes outward.

Indeed, sometimes, this air is expelled at velocities ranging from 75 to 100 miles per hour. Importantly, the strong compression of the lungs collapses the bronchi and trachea by causing their noncartilaginous parts to invaginate inward so that the exploding air actually passes through bronchial and tracheal slits. The rapidly moving air usually carries with it any foreign matter that

is present in the bronchi or trachea. The pathway is shown below:

Sneeze Reflex

The sneeze reflex is very much like the cough reflex except for the fact that it applies to the nasal passageways instead of the lower respiratory passages. The initiating stimulus of the sneeze reflex is irritation in the nasal passageways; the afferent impulses pass in the fifth cranial nerve to the medulla where the reflex is triggered. Series of reactions similar to those of the cough reflex take place. However, 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. This is shown in the figure below                                                                                                            

References :TETBOOK OF MEDICAL PHYSIOLOGY ,Eleventh edition by Guyton & Hall,Page 840,Colour ATLAS OF HUMAN PHYSIOLOGY  5th Edition completely revised and expanded,page 133