Indeed, it has been demonstrated that pharyngeal stimulation can induce remarkable increases in the excitability of swallowing motor cortex (Sumi, 1969). The central control of swallowing is modified by peripheral feedback from the pharyngeal, laryngeal, and esophageal regions. There is no doubt that the cerebral cortex and subcortex areas and their interaction with brain stem can play an important role in the neural regulation of swallowing reflex. Descending fibers from the frontal cortex have been found histologically to terminate in widespread areas in the reticular formation of the brainstem (Kuypers, 1958). It is well established that the swallowing center receives descending influences from the cerebral cortex and subcortical areas. Nevertheless, extensive evidence supports the existence of a swallowing center within the brain stem (Doty et al., 1967). Although data has shown that only stimulation of the NTS and the adjacent reticular formation could elicit swallowing (Miller, 1972), there has been no evidence to suggest that the swallowing center resides within the NTS. The NTS is not only an afferent portal but has interneurons that perform a more complex level of swallowing control. The swallowing reflex elicited by primary afferents may be modified by lung/chest wall receptors such as vagal and intercostals muscle afferents. Primary afferents from the receptors in the oropharyngeal mucosa travel in the trigeminal (V), glossopharyngeal (IX), and vagus nerves (X), and converge in the solitary tract destined for synaptic contact with second-order neurons in the nucleus tractus solitarius (NTS). It is likely that these receptors can initiate swallowing while responding to water and light touch. However, specific fluid or water receptors and some slowly adapting pressure receptors are known to be distributed unevenly over the pharyngeal and laryngeal regions (Mathew and Sant'Ambrogio, 1988). Receptors responsible for elicitation of swallowing reflex have not been identified histologically. Among these regions, the faucial pillars are the most sensitive region in humans. The receptive regions for reflex swallowing include many locations in oro-pharyngeal space such as the soft palate, uvula, dorsa surface of the tongue, pharyngeal surface of the epiglottis, faucial pillars, glossoepiglottidinal sinus, dorsal pharyngeal wall, and the pharyngoesophgeal junction (Pommerenke, 1928 Storey, 1968 Sinclair, 1971 Mannson and Sandberg, 1974 Miller, 1982).
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