inferior pharyngeal constrictor cranial nerve 9

Secreted saliva also facilitates dissolving and lubricating solid boluses and is the major stimulus for the basal swallow rate between periods of ingestion. The tongue also helps reduce softer or dissolvable solids by mashing them against the bony structures bounding the oral cavity and mixing them with liquid elements of the ingested bolus. During this process the cheeks and tongue function to position the solid over the grinding surfaces. This action requires complex variations in the force and velocity of mandibular movement, holding and grinding solids with the teeth. Mastication is necessary for rendering solid ingested boluses into a size, shape, and consistency that is amenable to transport.

Such suction may also serve to drive entry of saliva into the oral cavity from the salivary glands. These actions generate a subatmospheric pressure within the oral cavity that facilitates flow of fluids into the oral cavity. Lowering of the mandible along with depression and retraction of the tongue are accompanied by bracing of the cheeks and mouth floor. During ingestion by sucking, such as with a straw, the lips remain sealed around the delivery vessel and the exit to the back of the oral cavity is closed by the tongue and soft palate. Ingestion of a bolus usually requires active lowering of the mandible, opening of the lips, and depression of the tongue-actions that increase the size of the oral cavity to accommodate the ingested bolus. The oral cavity is bounded by the lips anteriorly the cheeks laterally the teeth, alveolar ridge, hard palate, and soft palate anteriorly the teeth, alveolar ridge, floor of mouth, and tongue inferiorly and the soft palate, uvula, tonsillar pillars, and posterior part of the tongue that form the posterior opening of the oral cavity or the oropharyngeal isthmus. It can be divided into preparatory and transfer phases. The oral phase includes all swallowing activities that occur within the oral cavity. ( Source: Netter medical illustrations with permission from Elsevier. All structures of pharynx have returned to resting position.

Communication with nasopharynx has been re-established. Epiglottis is beginning to turn up again as Hyoid bone and larynx descend. The bolus has largely passed through the upper sphincter into esophagus. The contraction wave has reached vallecula and is pressing out last of bolus from them. Trickle of food enters also laryngeal opening but is prevented from going farther by closure of ventricular folds. Cricopharyngeus muscle is opening to permit entry of bolus into esophagus. Soft palate has been pulled down and approximated to root of tongue by contraction of pharyngopalatine muscles, and by pressure of descending pharyngeal contraction wave. Contraction wave on posterior pharyngeal wall moves downward. Hyoid bone and larynx move upward and forward. Bolus is pushed backward in groove between tongue and palate.

It shows tip of tongue in contact with anterior part of palate. Illustrates the onset of the swallowing reflex.

Inferior pharyngeal constrictor cranial nerve 9