How is swallowing triggered

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Acta Radiol. Download references. This review article was born out of conversations at a meeting in Christchurch, New Zealand, in We recognize Dr. Maggie-Lee Huckabee, who had the vision to organize that meeting and initiate those discussions. The views expressed do not necessarily reflect those of the ministry. This article is distributed under the terms of the Creative Commons Attribution Noncommercial License which permits any noncommercial use, distribution, and reproduction in any medium, provided the original author s and source are credited.

You can also search for this author in PubMed Google Scholar. Correspondence to Catriona M. Reprints and Permissions. Steele, C. Dysphagia 25, — Download citation. Received : 08 December Accepted : 14 August Published : 03 September Issue Date : December Anyone you share the following link with will be able to read this content:. Sorry, a shareable link is not currently available for this article.

Provided by the Springer Nature SharedIt content-sharing initiative. Skip to main content. Search SpringerLink Search. Download PDF. Abstract Over the past 20 years, research on the physiology of swallowing has confirmed that the oropharyngeal swallowing process can be modulated, both volitionally and in response to different sensory stimuli.

Table 1 Potential sensory stimuli that modulate or can evoke swallowing Full size table. Anatomy Supporting Sensory Input to Swallowing Sensory Fibers The pharyngeal phase of swallowing is triggered by specific sensory inputs and is then completed by an entire sequence of bilateral muscle activity [ 6 ].

Pathways that Enable Sensory Input to Influence Swallowing Afferent input that may affect the threshold to induce swallowing can include stimuli that increase salivation [ 32 , 33 ]. Central Connections Sensory fibers of the glossopharyngeal and vagus nerves synapse directly in the NTS and do not appear to synapse in the trigeminal sensory nuclei [ 20 ].

Potential Mechanisms to Alter Swallowing Observed Variations Demonstrate the Potential for Sensory Modulation Evidence of the potential for sensory modulation of swallowing can be drawn from variations observed in swallow physiology across different bolus consistencies and subjects [ 69 ].

Effective Mechanisms and Stimuli for Sensory Modulation Swallow elicitation appears to involve the activation of multiple sensory fibers across many receptive fields [ 5 ]. Tactile Stimuli Touch and pressure have been used to stimulate pharyngeal swallowing in human subjects and experimental animals. Thermal Stimuli Experimental studies have shown that stimulating the anterior pillars with a cold probe while simultaneously stimulating the iSLN increases the number of pharyngeal swallows elicited in the anesthetized adult cat [ ].

Chemical Stimuli Saliva is an important sensory stimulus in the normal swallow: methods to enhance its secretion improve pharyngeal swallow elicitation. Esophageal Responses to Different Stimuli Different esophageal reflexes can be induced depending on the site and type of sensory stimulation [ ]. Sensory Input and the Cortex Increased sensory input can modify motor areas of the cerebral cortex, fostering the concept that increased sensory input might be useful in rehabilitating dysphagic patients with cortical strokes [ , ].

Future Directions This review has summarized the current state of knowledge regarding the anatomy that subserves sensory input to swallow initiation and modulation and evidence supporting the potential for modulation of swallowing in response to sensory stimuli. Effective Mechanisms and Stimuli for Sensory Modulation An early animal study by Doty [ 5 ] using iSLN stimulation found that optimum frequencies to evoke swallowing were between 30 and 50 Hz in the anesthetized dog, monkey, and cat.

Pressure and Tactile Stimuli Larger boluses elicit shorter latencies to pharyngeal swallow onset and increased muscle contractile activity [ , ]. Chemical Stimuli Few studies have controlled for or explored the olfactory aspects of stimuli that might affect swallowing [ 35 ]. Summary Boluses of liquids and solids normally initiate pharyngeal swallowing using multiple modalities, including taste, water, touch, pressure, and possibly temperature to excite several types of sensory fibers of different diameters that innervate the receptors in the oropharyngeal mucosa.

References 1. PubMed Article Google Scholar 2. PubMed Article Google Scholar 3. PubMed Article Google Scholar 5. PubMed Article Google Scholar 9. PubMed Article Google Scholar PubMed Google Scholar Article Google Scholar The food bolus is then voluntarily moved further into the oropharynx upper part of the throat. From the oropharynx, the food bolus is further channeled by the back of the tongue and other muscles into the lower part of the pharynx throat.

This step also requires the voluntary elevation of the soft palate in order to prevent food from entering the nose. The muscles that control the oral phase of swallowing are stimulated by nerves located in the brainstem, called cranial nerves. The cranial nerves involved in coordinating this stage include the trigeminal nerve, the facial nerve, and the hypoglossal nerve.

As the food bolus reaches the pharynx, special sensory nerves activate the involuntary phase of swallowing. The swallowing reflex, which is mediated by the swallowing center in the medulla the lower part of the brainstem , causes the food to be further pushed back into the pharynx and the esophagus food pipe by rhythmic and involuntary contractions of several muscles in the back of the mouth, pharynx, and esophagus.

Because the mouth and throat serve as an entryway for both food and air, the mouth provides a route for air to get into the windpipe and into the lungs, and it also provides a route for food to get into the esophagus and into the stomach.

A critical part of the pharyngeal phase is the involuntary closure of the larynx by the epiglottis and vocal cords, and the temporary inhibition of breathing. The closure of the larynx by the epiglottis protects the lungs from injury, as food and other particles that enter into the lungs can lead to severe infections and irritation of the lung tissue.

Lung infections caused by problems with the pharyngeal phase of the swallowing reflex are commonly known as aspiration pneumonia. As food leaves the pharynx, it enters the esophagus, a tube-like muscular structure that leads food into the stomach due to its powerful coordinated muscular contractions.

The passage of food through the esophagus during this phase requires the coordinated action of the vagus nerve , the glossopharyngeal nerve, and nerve fibers from the sympathetic nervous system. The esophagus has two important muscles that open and close reflexively as the food bolus is brought down during swallowing.

These muscles, called sphincters, allow the food bolus to flow in a forward direction while preventing it from going in the wrong direction regurgitation. Both esophageal sphincters, first the upper, and then the lower, open in response to the pressure of the food bolus and close after the food bolus passes. The upper esophageal sphincter prevents food or saliva from being regurgitated back into the mouth, while the lower esophageal sphincter ensures that food remains in the stomach, preventing regurgitation back into the esophagus.

In doing so, the esophageal sphincters serve as a physical barrier to regurgitated food. In general, healthy people can swallow with very little deliberate thought and effort. If the nervous system is disrupted due to a stroke or another disease, then problems with swallowing can occur. Swallowing difficulties are referred to as dysphagia. Dysphagia can lead to problems such as choking, lack of appetite and weight loss, and aspiration pneumonia.

If you have experienced a stroke or another neurological illness, you may undergo a swallowing evaluation to determine whether you have dysphagia. If you have signs of dysphagia, you will need to have speech and swallow therapy so that your swallowing muscles can have the chance to improve as much as possible. Sign up for our Health Tip of the Day newsletter, and receive daily tips that will help you live your healthiest life. Updated March 6, Your Privacy Rights. To change or withdraw your consent choices for VerywellHealth.

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