MEDICAL PHYSIOLOGY

Detailed explanation-1: -Pharyngeal sensation is achieved chiefly via CN IX. The upper esophagus is innervated by CN X, while the splanchnic plexus and CN X innervate the lower esophagus. The splanchnic plexus keeps the lower esophageal sphincter contracted, while the parasympathetic input via CN X relaxes the lower esophageal sphincter (LES).

Detailed explanation-2: -During the pharyngeal stage, the soft palate elevates and contacts the lateral and posterior walls of the pharynx, closing the nasopharynx at about the same time that the bolus head comes into the pharynx (Fig. 5). Soft palate elevation prevents bolus regurgitation into the nasal cavity.

Detailed explanation-3: -During the pharyngeal phase, the tongue seals the oropharynx. The soft palate and proximal pharyngeal wall seal off the nasopharynx. The vocal cords and arytenoids close off the laryngeal opening and the epiglottis swings down to cover the laryngeal vestibule. These actions seal the airway from the pharyngeal cavity.