Cough motor mechanisms.

Cough is a defensive airway mechanisms which involves the sequential activation of several laryngeal and respiratory muscles in the generation of the typical four-phase motor pattern. Activation of such muscles can be considered to represent the "primary" cough motor mechanism, and its functional significance, although complex, appears to be fairly well established. Nonetheless, the outflows of cough are numerous, and may additionally involve the reflex or mechanical activation of other respiratory and non-respiratory motor systems. These additional, or "secondary", outflows of cough can mainly be regarded as being involved in either enhancing the defensive function of cough, or opposing the possible noxious effects exerted by the mechanical stresses of coughing. In addition, both the primary and secondary cough motor mechanisms are known to play multiple functional roles, thus considerably complicating the cough panorama. Finally, some of the secondary cough motor responses, such as the changes in the pattern of breathing, seem to be devoid of any favourable action and their functional meaning, if any, is not fully understood. Although it is well known that all patterns of cough can be produced voluntarily, the extent to which also volitional cough is accompanied by an array of motor responses similar to that of reflex cough remains to be elucidated.