<P> At the end of the oral preparatory phase, the food bolus has been formed and is ready to be propelled posteriorly into the pharynx . In order for anterior to posterior transit of the bolus to occur, orbicularis oris contracts and adducts the lips to form a tight seal of the oral cavity . Next, the superior longitudinal muscle elevates the apex of the tongue to make contact with the hard palate and the bolus is propelled to the posterior portion of the oral cavity . Once the bolus reaches the palatoglossal arch of the oropharynx, the pharyngeal phase, which is reflex and involuntary, then begins . Receptors initiating this reflex are proprioceptive (afferent limb of reflex is IX and efferent limb is the pharyngeal plexus - IX and X). They are scattered over the base of the tongue, the palatoglossal and palatopharyngeal arches, the tonsillar fossa, uvula and posterior pharyngeal wall . Stimuli from the receptors of this phase then provoke the pharyngeal phase . In fact, it has been shown that the swallowing reflex can be initiated entirely by peripheral stimulation of the internal branch of the superior laryngeal nerve . This phase is voluntary and involves important cranial nerves: V (trigeminal), VII (facial) and XII (hypoglossal). </P> <P> For the pharyngeal phase to work properly all other egress from the pharynx must be occluded--this includes the nasopharynx and the larynx . When the pharyngeal phase begins, other activities such as chewing, breathing, coughing and vomiting are concomitantly inhibited . </P> <P> 5) Closure of the nasopharynx </P> <P> The soft palate is tensed by tensor palatini (Vc), and then elevated by levator palatini (pharyngeal plexus--IX, X) to close the nasopharynx . There is also the simultaneous approximation of the walls of the pharynx to the posterior free border of the soft palate, which is carried out by the palatopharyngeus (pharyngeal plexus--IX, X) and the upper part of the superior constrictor (pharyngeal plexus--IX, X). </P>

When does the pharyngeal phase of the swallow begin