Cough reflex

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The cough reflex has both sensory (afferent) and motor (efferent) pathways. The internal laryngeal nerve, a branch of the superior laryngeal nerve (CN X), carries the sensory information away from the area above the glottis in the larynx to the CNS via cranial nerve X (vagus). Stimulation of this area by dust or other foreign particles produces a cough, which is necessary to remove the foreign material from the respiratory tract before it reaches the lungs. [1] The mechanism of a cough is as follows:

Diaphragm (innervated by phrenic nerve) and external intercostal muscles (innervated by segmental intercostal nerves) contract, increasing the volume of the lungs and making the pressure of air within the lungs lower than atmospheric pressure.
Air rushes into the lungs in order to equalise the pressure.
The glottis closes (muscles innervated by recurrent laryngeal nerve) to prevent air escaping whilst the diaphragm relaxes and expiratory muscles contract.
This reduces the volume of the lungs, therefore increasing pressure.
The pressure of air within the lungs is now greater than atmospheric pressure and so air is trying to escape.
Glottis opens, releasing air at over 100 mph.

Therefore, respiratory muscle weakness, tracheostomy, or vocal cord pathology (including paralysis or anesthesia) may prevent effective clearing of the airways.

The reflex is impaired in the person whose abdominals and respiratory muscles are weak. This problem can be caused by disease condition that lead to muscle weakness or paralysis, by prolonged inactivity, or as outcome of surgery involving these muscles. Bed rest interferes with the expansion of chest and limits the amount of air that can be taken into lungs in preparation for coughing making the cough weak and ineffective. This reflex may also be impaired by damage to the internal branch of the superior laryngeal nerve which relays the afferent branch of the reflex arc. This nerve is most commonly damaged by swallowing a foreign object, such as a chicken bone, resulting in it being lodged in the piriform recess (in the laryngopharynx) or by surgical removal of said object.