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The pharyngeal reflex or gag reflex is a
reflex In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, physiological mechanisms, ...

reflex
muscular contraction of the back of the throat, evoked by touching the roof of the
mouth In animal anatomy Anatomy (Greek ''anatomē'', 'dissection') is the branch of biology concerned with the study of the structure of organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμός, ''organismos'') is ...

mouth
, the back of the
tongue The tongue is a muscular MUSCULAR (DS-200B), located in the United Kingdom The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain,Usage is mixed. The Guardian' and Telegraph' use Brita ...

tongue
, the area around the
tonsils The tonsils are a set of lymphoid organs facing into the aerodigestive tract, which is known as Waldeyer's tonsillar ring and consists of the adenoid tonsil, two tubal tonsils, two palatine tonsil Palatine tonsils, commonly called the tonsils ...

tonsils
, the
uvula The palatine uvula, usually referred to as simply the uvula, is a conic projection from the back edge of the middle of the soft palate The soft palate (also known as the velum, palatal velum, or muscular palate) is, in mammal Mammals (from ...
, and the back of the
throat In vertebrate anatomy, the throat is the front part of the neck, internally positioned in front of the vertebra, vertebrae. It contains the Human pharynx, pharynx and larynx. An important section of it is the epiglottis, separating the esophagus f ...

throat
. It, along with other aerodigestive reflexes such as reflexive pharyngeal swallowing, prevents objects in the
oral cavity In animal anatomy, the mouth, also known as the oral cavity, buccal cavity, or in Latin cavum oris, is the opening through which many animals take in food and issue vocal sounds. It is also the cavity lying at the upper end of the alimentary cana ...
from entering the throat except as part of normal
swallowing Swallowing, sometimes called deglutition in scientific contexts, is the process in the human or animal body that allows for a substance to pass from the mouth In animal anatomy Anatomy (Greek ''anatomē'', 'dissection') is the branch of ...
and helps prevent
choking Choking, or foreign body airway obstruction (FBAO) is the fourth leading cause of unintentional injury death. It occurs when breathing is impeded by a constricted or obstructed throat or windpipe, resulting in oxygen deprivation. Although oxygen ...
, and is a form of coughing. The pharyngeal reflex is different from the laryngeal spasm, which is a reflex muscular contraction of the vocal cords.


Reflex arc

In a
reflex arc A reflex arc is a neural pathway A neural pathway is the connection formed by axon An axon (from Greek ἄξων ''áxōn'', axis), or nerve fiber (or nerve fibre: see spelling differences Despite the various English dialects D ...

reflex arc
, a series of physiological steps occur very rapidly to produce a reflex. Generally a
sensory receptor Sensory neurons, also known as afferent neurons, are neuron A neuron or nerve cell is an membrane potential#Cell excitability, electrically excitable cell (biology), cell that communicates with other cells via specialized connections called sy ...
receives an environmental stimulus, in this case from objects reaching nerves in the back of the throat, and sends a message via an
afferent nerve A sensory nerve, also called an afferent nerve, is a nerve A nerve is an enclosed, cable-like bundle of nerve fibers called axon An axon (from Greek ἄξων ''áxōn'', axis), or nerve fiber (or nerve fibre: see American and British English ...
to the
central nervous system The central nervous system (CNS) is the part of the nervous system In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecu ...

central nervous system
(CNS). The CNS receives this message and sends an appropriate response via an
efferent nerve Efferent nerve fibers refer to axon An axon (from Greek ἄξων ''áxōn'', axis), or nerve fiber (or nerve fibre: see American and British English spelling differences#-re, -er, spelling differences), is a long, slender projection of a ne ...
(also known as a
motor neuron A motor neuron (or motoneuron or efferent neuron) is a neuron A neuron or nerve cell is an electrically excitable cell Cell most often refers to: * Cell (biology), the functional basic unit of life Cell may also refer to: Closed spaces * ...
) to effector cells located in the same initial area that can then carry out the appropriate response. In the case of the pharyngeal reflex: *the sensory limb is mediated predominantly by CN IX (glossopharyngeal nerve) *the motor limb by CN X (vagus nerve). The gag reflex involves a brisk and brief elevation of the soft palate and bilateral contraction of pharyngeal muscles evoked by touching the posterior pharyngeal wall. Touching the soft palate can lead to a similar reflex response. However, in that case, the sensory limb of the reflex is the CN V (trigeminal nerve). In very sensitive individuals, much more of the brain stem may be involved; a simple gag may enlarge to retching and vomiting in some.


Suppression and activation

Swallowing unusually large objects or placing objects in the back of the mouth may cause the pharyngeal reflex. Some people, for instance
sword swallower
sword swallower
s, have learned how to suppress it. In contrast, triggering the reflex is sometimes done intentionally to induce vomiting, by those who suffer from
bulimia nervosa Bulimia nervosa, also known as simply bulimia, is an eating disorder An eating disorder is a mental disorder defined by abnormal eating behaviors that negatively affect a person's health, physical or mental health, mental health. Only one eat ...
. According to one study, one in three people lacks a gag reflex. However, on the other end of the spectrum are people with a hypersensitive gag reflex. This hypersensitivity can lead to issues in various situations, from swallowing a pill or large bites of food to visiting the dentist. Hypersensitivity is generally a conditioned response, usually occurring following a previous experience. There are a variety of ways to desensitize one's hypersensitivity, from relaxation to numbing the mouth and throat to training one's soft palate to get used to being touched. Anti-nausea medicines,
sedative A sedative or tranquilliser is a substance that induces sedation by reducing irritability or Psychomotor agitation, excitement. They are Central nervous system, CNS depressants and interact with brain activity causing its deceleration. Various ki ...
s,
local Local may refer to: Geography and transportation * Local (train), a train serving local traffic demand * Local, Missouri, a community in the United States * Local government, a form of public administration, usually the lowest tier of administrati ...
and
general anaesthetic General anaesthetics (or anesthetics, see spelling differences) are often defined as compounds that induce a loss of consciousness in humans or loss of righting reflex in animals. Clinical definitions are also extended to include an induced coma t ...
s, herbal remedies, behavioural therapies,
acupressure Acupressure (Chinese - Tui na), is an alternative medicine technique often used in conjunction with acupuncture Acupuncture is a form of alternative medicine and a key component of traditional Chinese medicine Traditional Chinese medi ...
,
acupuncture Acupuncture is a form of alternative medicine Alternative medicine is any practice that aims to achieve the healing effects of medicine Medicine is the Art (skill), art, science, and Praxis (process) , practice of caring for a patient a ...
, laser, and prosthetic devices can be used to manage exaggerated gag reflex during dental treatment. Studies showed with very low‐certainty evidence that acupuncture and laser at the P6 point (located in the wrist) reduced gagging without sedation. However, there was no difference when practiced with sedation. Therefore, more research needs to be carried out regarding these interventions.


Absence

In certain cases, 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 glossopharyngeal nerve (), known as the ninth cranial nerve Cranial nerves are the nerve A nerve is an enclosed, cable-like bundle of nerve fibers called axon An axon (from Greek ἄξων ''áxōn'', axis), or nerve fiber (or nerv ...
, the
vagus nerve The vagus nerve, historically cited as the pneumogastric nerve, is the tenth cranial nerve Cranial nerves are the nerve A nerve is an enclosed, cable-like bundle of nerve fibers called axon An axon (from Greek ἄξων ''áxōn'', axi ...
, or
brain death Brain death is the complete loss of brain function A brain is an organ that serves as the center of the nervous system In Biology, biology, the nervous system is a Complex system, highly complex part of an animal that coordinates its B ...
. In unilateral (one-sided) glossopharyngeal nerve (CN IX- sensory component) damage, there will be 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. This is because the sensory component is intact on both sides, but 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 are damaged on one side (not uncommon), stimulation of the normal side elicits only a unilateral response, with deviation of the soft palate to that side; no consensual response is seen. Touching the damaged side produces no response at all. At one point, it was thought that a lack of the gag reflex in stroke patients was a good predictor for dysphagia (difficulty with swallowing) or laryngeal aspiration (food or drink entering the
larynx The larynx (), commonly called the voice box, is an organ Organ may refer to: Biology * Organ (anatomy) An organ is a group of Tissue (biology), tissues with similar functions. Plant life and animal life rely on many organs that co-exist ...

larynx
), and was therefore commonly checked for. However, in one study, 37% of healthy people did not have a gag reflex, yet all subjects except for one still retained an intact pharyngeal sensation. These results suggest that the muscles that control the gag reflex remain independent of those that control normal swallowing. Since this reflex is commonly not found in healthy people, its predictive value in determining the risk for swallowing disorders is severely limited. Pharyngeal sensation, on the other hand, as seen by this study, is rarely absent, and could prove better at predicting future problems with swallowing.


Reflexive pharyngeal swallow

Closely related to the gag reflex, in which food or other foreign substances are forced back out of the
pharynx The pharynx (plural: pharynges) is the part of the throat behind the human mouth, mouth and nasal cavity, and above the esophagus and trachea – the tubes going down to the stomach and the lungs. It is found in vertebrates and invertebrates, thou ...

pharynx
, swallowing generally pushes food through the digestive system into the stomach. This reflex in particular functions as a protective system for the upper respiratory tract as it not only forces the glottis to close, thereby preventing any substances getting into the airways, but also clears the pharynx of any residual substances by a swallow. This particular reflex is simply one of several aerodigestive reflexes, including also the pharyngoglottal closure reflex (in which no swallowing occurs yet the
glottis The glottis is the opening between the vocal folds In humans, vocal cords, also known as vocal chords, vocal folds or voice reeds, are folds of tissue in the throat that are key in creating sounds through vocalization. The size of vocal cor ...
still closes) and the pharyngo-upper esophageal sphincter contractile reflex, which occurs mainly during gastroesophageal reflux episodes. All either forcibly close the glottis or allow the pharynx to remove particles into the digestive tract that may have been forced back up by both this tract and the upper respiratory tract. These reflexes can also protect the airways from any food or liquids that may spill over from the hypopharynx. The hypopharynx is the bottom part of pharynx, and can be considered the first area where the digestive tract splits from the airways. However, if the maximum capacity of fluids that the hypopharynx can safely hold is exceeded, then this excess fluid spills into the
larynx The larynx (), commonly called the voice box, is an organ Organ may refer to: Biology * Organ (anatomy) An organ is a group of Tissue (biology), tissues with similar functions. Plant life and animal life rely on many organs that co-exist ...

larynx
and from there into the lungs. Therefore, these reflexes prevent levels reaching this maximum volume. Since both the digestive system and the respiratory system are connected by the pharynx, there are many problems and diseases that occur when the body is unable to regulate passage of food and air into the appropriate tracts. Perhaps the most preventable cause of damage to these reflexes originates from smoking. One study has shown that, when compared to non-smokers, the threshold volumes (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.


See also

*
Retching Retching (also known as dry heaving) is the reverse movement ( retroperistalsis) of the stomach and esophagus without vomiting. It can be caused by bad smells or choking, or by withdrawal from some medications after vomiting stops. Retching can also ...
, also known as dry heaving


References

{{Authority control Human throat Reflexes Vomiting