Upon lying down the parapharyngeal tissues become compressed by the weight of the
mandible and attached tissues. This increases the local tissue pressure which pushes
inwards on the lateral pharyngeal walls. Full loading of the parapharyngeal tissues is
prevented by activation of the pterygoid muscles.
In Stage III/IV and REM sleep, there is less activation of the pterygoid muscles
and more of the weight of the mandible and attached tissues is borne by the parapharyngeal
tissues. This results in a further decrease in the lateral dimension of the pharynx. The
soft palate also sags because of decreased activation of the tensor veli palatini muscles.
Advancing the mandible pulls the base of the tongue forwards.
Advancing the mandible decompresses the parapharyngeal tissues and allows the
lateral pharyngeal walls to spring outwards.
Advancing the mandible puts tension into the soft palate through the palatoglossus
Advancing the mandible lifts the pharynx off the cervical spinal column - an
important action in patients with hypertrophy of the longus capiti/colli muscles such as
wrestlers and bodybuilders.