Functional Compartments of the Tensor Veli Palatini Muscle

Objective: To evaluate a dual role for the tensor veli palatini muscle in tubal and palatal function. Materials and Methods: The eustachian tube region of guinea pigs and macaques was fixed and processed for analysis by serial section histologic examination, microdissection, or both. The attachment, fiber direction, and regional relations of potentially discrete functional compartments in eustachian tube muscles were noted. Results: The tensor veli palatini muscle in macaques has two anatomic sub-bellies. One appears to be a tubal dilator, the other to make the tube rigid along its longitudinal axis. No other muscle is directly associated with the eustachian tube in macaques. The tensor veli palatini muscle in guinea pigs has one gross belly that may affect palatal tensing and tubal dilation, rigidification, and stabilization. Other muscles of the eustachian tube in guinea pigs are a medial sub-belly of the medial pterygoid muscle, not previously described, and the levator veli palatini muscle. Conclusions: The muscular elements underlying tubal-palatal function in guinea pigs are more distinct and spatially separated than in macaques or humans. These differences may explain the confusion about the role of accessory muscles in tubal function. Muscular compartments of the eustachian tube complex in guinea pigs are easily accessible, which facilitates a more discrete and confident placement of electromyography electrodes. The guinea pig may be a useful model to better understand the interaction of multilevel compartmentalized physiologic sequences that underlie coordination of swallowing, breathing, and middle ear aeration.