Passavant ridges is due to contraction of?

Some of the upper fibers of the palatopharyngeus pass circularly deep to mucous membrane of the pharynx and form a sphicter internal to the superior constrictor.these fibres constitute passvant's muscle which on contraction raises a ridge called the passavant's ridge on the posterior wall of the nasopharynx.when the soft palate is elevated it comes in contact with this ridge the two together closing the pharyngeal isthmus between the nasopharynx and the oropharynx. Ref BDC volume 3;6 th edition pg 225