Orofaringiyal Yutmanın Nörofizyoloji ve Nörolojisi

Abstract

The neurophysiology and neurology of the human deglutition has been reviewed in this paper. Swallowing is subdivided into three phases: oral, pharyngeal and esophageal phases. The oral and pharyngeal phases are highly interrelated and the term of oropharyngeal phase is rather preferred. However, the oral phase is often accepted as voluntary while the pharyngeal phase is considered a reflex response. Oral phase is primarily related with the oral preparation of the food and triggering of the pharyngeal phase. Sensory inputs from posterior oral cavity and pharyngeal mucosa are necessary for triggering and modulation of the bolus during swallowing. The sensory inputs are transmitted to the medullary nucleus tractus solitarius (NTS) and to the cerebral cortex. Once swallowing is initiated, a cascade of sequential muscle activation occurs from the perioral muscles to downward. During the transportation of the food, the all airwayis protected and closed by several laryngeal muscles and the larynx is pulled up. The sequential activity of swallowing muscles can be demonstrated by some EMG methods. Submental/suprahyoid muscles are useful to demonstrate the onset and duration of the oropharyngeal phase of swallowing. Cricopharyngeal muscle of the upper esophageal sphincter is tonically active in rest and the tonic activity ceases during a swallow. Similarly a movement sensor could be applied for the duration of the pharyngeal phase of swallowing. The neural network is located in medullary-brainstem. These reticular network are known for the swallowing central pattern generator (CPG). The premotor neurons of CPG ar e located fundamentally in and aroun d NTS and nucleus ambiguus (NA). There are anatomical connections mediated by nerve fibers between NTS an d NA and the reticular fibers crossing the midline and connecting the two medullary regions. Descending excitatory and inhibitory drives from cortex and subcortex influence the oropharyngeal swallowing and trigger and modulate medullary CPG. The recent advancements in functional brain imaging (ie .. fMRI, PET. .)now offer the opportunity of examination of the cortical representation of swallowing in human. The cortical involvement in swallowing is multifocal and bilaterally represented especially in the fallowing areas: sensory-motor cortex, prefrontal cortex, anterior cingulate and insular cortex and opercular and parieto-temporal regions. Although human voluntary swallowing is represented bilat erally, there is also interhemispheric asymmetry independent from hande dness. İnsular cortex is faunded to be lateraliz ed to the right hemisphere in right handed subjects for voluntary saliva swallowing. The extend of cortical and subcortical representation explain why so many cortical/subcortical neurological conditions produce dysphagia. There is a critical role for the intact hemisphere re-organisation in recovery ofdysphagia in stroke. The proper and increased sensory inputs may facilitate the cortical plasticity after the dysphagia due to stroke. EMG methods described previously and summarized in this review are very useful for the diagnosis of neurogenic dysphagia objectively and quickly. They are important to understand the physiological mechanisms for deglutition and its disorders.