The Art of Deglutition
1. the first stage of swallowing is voluntary: the anterior part of the tongue is raised and pressed against the hard palate, the movement commencing at the lingual apex and spreading rapidly back. A bolus formed behind the apex, is pushed posteriorly. At the end of this stage, the soft palate descends on to the lingual dorsum, helping to grip the bolus. Lingual movements are effected by the intrinsic muscles, especially the superior longitudinal and transverse. Simultaneously, the hyoid bone is moved up and forwards by the geniohyoid, mylohyoid, digastric and stylohyoid. The postsulcal part of the tongue is drawn up and back by the styloglossi and the palatoglossal arches are approximated by the palatoglossi, pushing the bolus through the oropharyngeeal isthmus into the oropharynx.
2. the second stage of swallowing is involuntary: in swallowing liquids, the intrinsic lingual muscles squirt liquid backwards in the mouth, after which the mylohyoid contraction bulges the lingual base into the oropharynx. in swallowing solids, only the mylohyoid action is needed,except in cleansing the mouth of saliva and debris after a bolus is swallowed. the soft palate is elevated by the levator muscles, tightened by the tensor muscles and firmly approximated to the posterior pharyngeal wall by the palatopharyngeal sphincter. The pharyngeal isthmus closes tightly to prevent food from ascending into the nasopharynx. While the larynx and the pharynx are drawn upwards behind the hyoid bone. Simultaneously, the aryepoglottic folds are approximated and the arytenoid cartilages drawn up and forwards by the aryepiglottic, oblique arytenoid and thyroarytenoid muscles. Partly by gravity, partly by successive contractions of the superior middle constrictors, the bolus slips over the epiglottis. Its passage is facilitated by the palatophayngei, which shorten the pharynx by elevating it, on contraction, they make the posterior pharyngeal wall into an inclined plane directed infero-laterally.
3. the last stage in swallowing is expulsion: through the inferior constrictors, of the now compressed bolus in the esophagus.
During swallowing, elevation and forward movement of the hyoid precede laryngeal elevation.
I am blogging about not only splanchology, but also the physiology involved behind it because my bimonthly exam tomorrow is about the GIT in 4 different subjects, namely Anatomy, Physiology, Histology and Biochemistry. So this is a little integration of what I have absorbed from Gray’s Anatomy 38th edition and Gray’s Anatomy 40th edition by Drake, Vogl and Mitchell. 🙂