The oral phase can be considered completed when the bolus tail enters the oropharynx, at which point the posterior dorsum of the tongue remains sealed against the soft palate to prevent retrograde escape of bolus back into the oral cavity. Concurrent with this action, the soft palate elevates, while the cheeks, floor of mouth, and jaw are braced. The force of this tongue action can be volitionally modified. In a rapid sequence, the tongue presses against the hard palate, generating a pressure wave directed posteriorly that propels the bolus into the oropharynx. Especially with large liquid boluses, the posterior aspect of the tongue and soft palate are closed together to prevent premature spill of the bolus into the pharynx. Indeed, in the process of normal combined eating and drinking, solid and liquid bolus material may even enter the pharynx before onset of the oral transfer phase of the majority of swallows.Īt the start of the oral transfer phase the superior perimeter of the tongue is pressed against the hard palate, sealing the bolus from the anterior oral cavity. The bolus is frequently partitioned, with that part not transported remaining within the oral vestibule or on the floor of the mouth. Not all of the oral cavity contents are necessarily transported together in a single swallow. The oropharyngeal isthmus open as the transfer phase begins. Once the bolus has been adequately prepared it is positioned in a recess on the dorsum of the tongue, primarily by action of the tongue, but with assistance for some boluses by action of the muscles that move the lips, cheek, mouth floor, and mandible. 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.
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