Gag reflex


The pharyngeal reflex, or gag reflex, or laryngeal spasm, is a reflex contraction of the back of the throat.

It is evoked by touching the roof of the mouth, the back of the tongue, the area around the tonsils, the uvula, and the back of the throat.

It prevents objects in the oral cavity from entering the throat except as part of normal swallowing and helps prevent choking.

It is a reflex in which an environmental stimulus from objects reaching nerves in the back of the throat sends a message via an afferent nerve to the central nervous system.

The CNS receives this message and sends an appropriate response via an efferent motor nerve to effector cells located in the same initial area that can then carry out the appropriate response.

In the pharyngeal reflex: the sensory limb is mediated predominantly by CN IX (glossopharyngeal nerve) and the motor limb by CN X (vagus nerve).

The gag reflex involves a brief elevation of the soft palate and bilateral contraction of pharyngeal muscles elicited by touching the posterior pharyngeal wall.

Similarly, touching the soft palate can lead to a similar gag reflex.

The sensory limb of the soft palate reflex is the CN V, trigeminal nerve response.

The absence of the gag reflex and pharyngeal sensation can be a symptom of a number of severe medical conditions, such as damage to the glossopharyngeal nerve, the vagus nerve, or brain death.

In very sensitive individuals,a simple gag may enlarge to retching and vomiting in some.

Swallowing large objects or placing objects in the back of the mouth may initiate the pharyngeal reflex.

One can learn how to suppress the reflex.

Triggering the reflex can be achieved intentionally to induce vomiting, by those who suffer from bulimia nervosa.

One in three people lacks a gag reflex.

Some individuals have a hypersensitive gag reflex, and it is generally a conditioned response,

Unilateral glossopharyngeal nerve (CN IX) sensory component damage, results in no gag response when touching the pharyngeal wall on the same side of the damaged nerve.

With one-sided vagal nerve (CN X) motor component damage, the soft palate will elevate and pull toward the intact side regardless of the side of the pharynx that is touched.

The sensory component is intact on both sides, and only the motor nerves supplying one side of the soft palatine and pharyngeal muscles is working, therefore the contraction of the muscles in the reflex is asymmetrical.

If both CN IX and X cranial nerves are damaged on one side, stimulation of the normal side elicits only a unilateral response.

There will be deviation of the soft palate to that side, without consensual response.

If both CN IX and X cranial nerves are damaged on one side, touching the damaged side produces no response at all.

It was previously thought that a lack of the gag reflex in stroke patients was a good predictor for difficulty with swallowing or laryngeal aspiration, but its predictive value in determining the risk for swallowing disorders is severely limited.

A study found 37% of healthy people did not have a gag reflex, yet still retained an intact pharyngeal sensation, indicating that the muscles that control the gag reflex remain independent of those that control swallowing.

Reflexive pharyngeal swallow is closely related to the gag reflex, in which food or other foreign substances are forced back out of the pharynx.

The reflexive pharyngeal swallow functions as a protective system for the upper respiratory tract forcing the glottis to close preventing any substances getting into the airways, but also clears the pharynx of any residual substances by a swallow.

Both the digestive system and the respiratory system are connected by the pharynx, and the most preventable cause of damage to these reflexes originates from smoking: the lowest volume at which one of these reflexes is triggered for both the pharyngo-upper esophageal sphincter contractile reflex and reflexive pharyngeal swallowing is increased.

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