Paratubal musculature Traditionally four muscles are commonly cited as being associated with the eustachian tube: tensor veli palatini, levator veli palatini, salpingopharyngeus, and tensor tympani. Each has at one time or another been directly or indirectly implicated in tubal function .Usually the eustachian tube is closed; it opens during such actions as swallowing, yawning, or sneezing, thereby permitting the equalization of middle ear and atmospheric pressures. Although the mechanism of tubal dilation remains controversial, most anatomic and physiologic evidence supports active dilation induced either solely by the tensor veli palatini muscle or with assistance from the levator veli palatini (Swarts and Rood, 2005). Closure of the tube has been attributed to passive reapproximation of tubal walls by extrinsic forces exerted by the surrounding deformed tissues, by the recoil of elastic fibers within the tubal wall and cartilage, or by both mechanisms. More recent experimental and clinical data suggest that, at least for certain abnormal populations, the closely applied internal pterygoid muscle may assist tubal closure by an increase in its mass within the pterygoid fossa; this increase applies medial pressure to the tensor veli palatini muscle and consequently to the lateral membranous wall of the eustachian tube . The tensor veli palatini is composed of two fairly distinct bundles of muscle fibers divided by a layer of fibroelastic tissue. The bundles lie mediolateral to the tube. This muscle is composed predominantly (60%) of the white (fast) fiber type. (Swarts and Rood, 2005)
The more lateral bundle (the tensor veli palatini proper) is of an inverted triangular design, taking its origin from the scaphoid fossa and from the greater wing of the sphenoid bone superior to the eustachian tube cartilage. The force this muscle exerts on this origin creates the lateral osseous ridge of the sulcus tubarius . The muscle descends anteriorly, laterally, and inferiorly to converge in a tendon that rounds the hamular process of the medial pterygoid lamina about an interposed bursa. This fiber group then inserts into the posterior border of the horizontal process of the palatine bone and into the palatine aponeurosis of the anterior portion of the velum. The more posterosuperior muscle fibers, lacking an osseous origin, extend instead into the semicanal of 7 the tensor tympani muscle. Here they receive a second muscle slip, which originates from the tubal cartilages and sphenoid bone. These muscle fibers converge to a tendon that rounds the cochleariform process and inserts into the manubrium of the malleus. This arrangement imposes a bipennate form to the tensor tympani muscle.( Franz B et al,2002)
The tensor tympani does not appear to be involved in the function of the eustachian tube. The medial bundle of the tensor veli palatini muscle lies immediately adjacent to the lateral membranous wall of the eustachian tube and is called the dilator tube muscle. ( Ghadiali SN,2002)
It has its superior origin in the posterior one half of the fibrous lateral membranous wall of the cartilaginous eustachian tube . The fibers descend sharply to enter and blend with the fibers of the lateral bundle of the tensor veli palatini muscle. This inner bundle is primarily responsible for active dilation of the tube. The levator veli palatini muscle arises from the inferior aspect of the petrous apex of the temporal bone. The fibers pass inferomedially, paralleling and lying beneath the tubal cartilage and luminal floor . In most instances the interaction of the levator veli palatini with the posterior one half of the cartilaginous eustachian tube lumen is precluded by an extension of the medial arm of the cartilage. Near the nasopharyngeal end of the eustachian tube, when the cartilage is at its maximum height, the levator veli palatini lies lateral to its medial arm . The fibers of this muscle insert by fanning out and blending with the dorsal surface of the soft palate.(Ramet M et al,2001)
Most investigators deny a tubal origin for this muscle and believe that it is related to the tube only by loose connective tissue. This muscle is composed of equal numbers of red (slow) and white (fast) fiber types .
The levator is not the primary dilator of the tube but probably contributes by elevating the medial arm of the cartilage at the nasopharyngeal end of the eustachian tube ,The salpingopharyngeal muscle arises from the medial and inferior borders of the tubal cartilage via slips of muscular and tendinous fibers. (Swarts and Rood, 2005)
Figure 8: muscles of Eustachian tube