reduction in muscle tone throughout the body hypo tonality may occur in the pharyngeal dilator muscles and they may relax into close proximity creating an obstructive apneic event an occurrence that is facilitated by the mucus film that coats the epithelia of the respiratory passages mucus is a viscous secretion that serves as a diffusion barrier against noxious substances throughout the hollow organs of the body in the pharynx it also serves as a lubricant to minimize airway sheer stresses for example coughs can generate air blasts with velocities over one hundred miles per hour resulting in possible sheer stresses the energetics of sticky thin films such as mucus promote adhesion of opposing tissues so that during sleep the hypo tonality of the pharyngeal dilator muscles promotes a series of obstructive apneic events which are broken when the sympathetic nervous system reacting to the imbalance of oxygen and carbon dioxide in the blood stream launches an adrenergic response mucus is in copious supply in the respiratory tract and the body has an organized set of clearing and scavenging reflexes the cough and the sneeze are examples of reflexes whose source is propulsive movement of the diaphragm there is difference in their neural control however coughs are usually under autonomous neural control but can be instigated by volition the initiation of the sneeze on the other hand is not subject to volition the clearing of the accumulation of mucus in the pharynx can be autonomic but generally is under volition even though most clearing activity does not intrude into consciousness the way that sneezes and coughs do the process of clearing mucus from the pharynx during wakefulness is not needed to prevent the occurrence of a mucus mediated adhesion of pharyngeal tissue because there is sufficient tone in.