Invited reviewNeurophysiology of swallowing
Introduction
Swallowing is a complex sensorimotor behaviour involving the coordinated contraction and inhibition of the musculature located around the mouth and at the tongue, larynx, pharynx and esophagus bilaterally. During a swallow, different levels of the central nervous system from the cerebral cortex to the medulla oblongata are involved and many of the striated muscles innervated by the cranial nerves (CN) are excited and/or inhibited sequentially for the execution of the passage of bolus from the mouth to the stomach (Miller, 1982, Jean, 1984, Jean, 1986, Jean, 2001, Donner et al., 1985, Broussard and Altschuler, 2000a).
Swallowing has received less attention than other fundamental motor activities such as locomotion, mastication, or respiration. This is probably due to the complexity of the motor pattern along with the greater number of muscles and CN involved, which renders neurophysiological studies difficult in experimental animals and humans. Although recent advances in the evaluation of dysphagia allow for the diagnosis, prognosis, and treatment of swallowing problems, such information in human subjects does not bring much knowledge to the basic understanding of the complex physiology of deglutition (Schindler and Kelly, 2002).
Swallowing and its disorders have been intensively investigated by videofluoroscopic, manometric and endoscopic methods. These studies are especially useful for clinical problems, however, it is necessary to develop new techniques, in order to understand the central neural mechanisms controlling swallowing. This review is limited to the neurophysiology of oropharyngeal swallowing. The esophageal phase of swallowing is beyond the scope of this review.
Section snippets
Peripheral events in swallowing
It has become convenient to state that, swallowing is subdivided into 3 phases: oral, pharyngeal, and esophageal. This conventional division of the human swallowing is usually ascribed to Magendie (1825) (Miller, 1982). The swallow has, however, also been described in two stages i.e. the buccopharyngeal (or oropharyngeal) and esophageal stages (Thexton and Crompton, 1998, Jean, 2001).
The 3 phases of swallowing are probably related to their innervation pattern: the oral phase is often accepted
EMG in swallowing muscles
The sequential and orderly activity of swallowing muscles can be demonstrated by EMG methods. Considerable number of studies have been performed for swallowing muscles in experimental animals and to some extent in man.
Doty and Bosma (1956) described the pattern of EMG activity in the oral and pharyngeal muscles in dog during swallowing elicited reflexively by electrical and mechanical stimuli. The pattern of EMG activity reported in that study and others subsequently, suggests the concept of a
Brain stem and swallowing
We owe almost all our knowledge to experimental deglutition studies except some information that was generated by clinical studies. Therefore, most of the information related to the brain stem and swallowing has been obtained from non-human mammals.
The precise pattern of muscle contraction and inhibition sequentially as mentioned above is dependent on brain stem neural structures that conceptually consist of 3 levels (Broussard and Altschuler, 2000b):
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An afferent and/or descending input level
Cerebral cortex and voluntary swallowing
Although the act of swallowing is thought to be mediated principally by brain stem mechanisms (Jean, 2001) converging evidence from electrophysiological, neuroimaging, and clinical studies indicates that the cerebral cortex also plays a fundamental role in the regulation of swallowing (Martin and Sessle, 1993, Miller, 1999).
In animal models, particularly the non-human primate, studies employing cortical stimulation (Jean and Car, 1979, Huang et al., 1989, Martin et al., 1997, Martin et al., 1999
Conclusions
Swallowing is subdivided into 3 phases: oral, pharyngeal and, esophageal phases. The oral cavity, pharynx, and larynx are anatomically separated but functionally integrated for the complex and sequential motor responses that include chewing, swallowing and speech. From the point of swallowing, the oral and pharyngeal phases are highly interrelated and the term oropharyngeal swallowing is often used. Despite this, the oral phase is often accepted as voluntary, while the pharyngeal phase is
Acknowledgements
This work has been supported in part by the Turkish Academy of Sciences.
We are also grateful for the cooperation of our co-workers, especially Murat Pehlivan, MD, Nur Yüceyar, MD, Nefati Kıylıoglu, MD, Sultan Tarlaci, MD, Yaprak Secil, MD. We thank Nilüfer Ertekin-Taner MD, PhD, who reviewed the English text.
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Analysis of electrophysiological and mechanical dimensions of swallowing by non-invasive biosignals
2023, Biomedical Signal Processing and ControlCitation Excerpt :The same muscles also achieved the highest AUC among the group of the sEMG related features, for almost all swallowing tasks, contrarily to the AUC achieved by the few features selected for the right infrahyoid (see Fig. 4). These observations agree with Ertekin and Aydogdu [43], who claimed that the best way to pick up EMG activity is superficially for suprahyoid, i.e., sEMG, while for infrahyoid the use of needle EMG is required. As expected, the selection of a feature in one specific axis does not mean that it will also be selected for the other axes because they have different spectral content within healthy and dysphagic individuals.