Tensor tympani muscle
Tensor tympani is a tiny, but long paired muscle of the middle ear. Together with the stapedius, it belongs to the group of intratympanic muscles. Tensor tympani occupies a bony canal found superior to the osseous part of the auditory tube (pharyngotympanic tube; Eustachian tube).
Its attachment to malleus, one of the three auditory ossicles, allows tightening of the tympanic membrane, reducing its vibration amplitude and thus reducing the sound transmission into the inner ear. Thereby, it plays an important role in the tympanic reflex - an evolutionary adaptation to protect the inner ear from excessively loud noises, which also aids speech coordination.
This article will discuss the anatomy and function of the tensor tympani muscle.
Cartilaginous part of auditory tube
|Insertion||Handle of malleus near the root|
Pulls the handle of the malleus medially
|Innervation||Nerve to medial pterygoid, branch of mandibular division of trigeminal nerve (CNV3)|
|Blood supply||Superior tympanic branch of the middle meningeal artery|
Origin and insertion
Tensor tympani is contained in a bony canal within the petrous part of temporal bone, known as the semicanal for tensor tympani. This bony canal is one of the origin points of the muscle, along with the cartilaginous portion of the auditory tube and the adjacent greater wing of sphenoid bone. Tensor tympani travels posteriorly within the bony canal and exits into the tympanic cavity just above the opening of the auditory tube.
As it emerges from the bony canal, tensor tympani narrows into a long tendon that bends laterally as it passes over a pulley-like projection of the bony canal called the processus cochleariformis. It then inserts into the upper part of the medial aspect of the handle of malleus, near its base.
Tensor tympani travels in its canal together with the superior tympanic artery that supplies it. The bony canal for tensor tympani runs alongside the bony part of the auditory tube, separated from it by a thin bony septum.
Tensor tympani is vascularized by the superior tympanic branch of the middle meningeal artery.
Tensor tympani acts to pull the handle of malleus medially. In turn, the handle of malleus pulls on the tympanic membrane and tenses it. The increased tension reduces the amplitude of the tympanic membrane oscillations and thereby reduces sound transmission to the vestibular window. This lowers the perceived amplitude of sounds.
Tensor tympani acts as part of the tympanic reflex. The reflex is believed to be an evolutionary adaptation to naturally occurring loud noises such as thunder. It takes about 40 ms to occur, which explains why the contraction of tensor tympani, along with other parts of the tympanic reflex, does not protect the inner ear from man-made loud noises such as gunshots.
The tensor tympani, along with stapedius, also coordinates speech with hearing. Without its actions, loud sounds of a person’s own voice could hinder the ability to hear other sounds, or even damage the cochlea.