Tensor tympani muscle

File:Tensor tympani-muscle.jpg

Insertion of the tensor tympani muscle onto the malleus. . AA’ ( two fibrous collagenic layers); B épidermis; C mucous membrane; D head of malleus; E uncus; F stapes; G tensor tympani; H lateral process of malleus; I Manubrium of malleus; J stapes muscle.

The tensor tympani, the larger of the two muscles of the tympanic cavity (the other being the stapedius), is contained in the bony canal above the osseous portion of the auditory tube. Its role is to dampen sounds, such as those produced from chewing.

Origin and insertion

It arises from the cartilaginous portion of the auditory tube and the adjoining part of the great wing of the sphenoid, as well as from the osseous canal in which it is contained.

Passing backward through the canal, it ends in a slender tendon which enters the tympanic cavity, makes a sharp bend around the extremity of the septum, known as the processus cochleariformis, and is inserted into the handle (manubrium) of the malleus, near its root.

Function

When tensed, the action of the muscle is to pull the malleus medially, tensing the tympanic membrane, damping vibration in the ear ossicles and thereby reducing the amplitude of sounds. This muscle is contracted primarily to dampen the noise produced by chewing. (Compare to the more general dampening function of the stapedius muscle.)

In many people with hyperacusis, an increased activity develops in the tensor tympani muscle in the middle ear as part of the startle response to some sounds. This lowered reflex threshold for tensor tympani contraction is activated by the perception/anticipation of loud sound, and is called tonic tensor tympani syndrome (TTTS). In some people with hyperacusis, the tensor tympani muscle can contract just by thinking about a loud sound. Following exposure to intolerable sounds, this contraction of the tensor tympani muscle tightens the ear drum, which can lead to the symptoms of ear pain/a fluttering sensation/a sensation of fullness in the ear (in the absence of any middle or inner ear pathology).

Innervation

Innervation of the tensor tympani is from the tensor tympani nerve, a branch of the mandibular division of the trigeminal nerve (cranial nerve V, specifically V3). As the tensor tympani is innervated by motor fibres of the trigeminal nerve, it does not receive fibres from the trigeminal ganglion, which has sensory fibres only.

Voluntary control

Contracting muscles produce vibration and sound. Slow twitch fibers produce 10 to 30 contractions per second (equivalent to 10 to 30 Hz sound frequency). Fast twitch fibers produce 30 to 70 contractions per second (equivalent to 30 to 70 Hz sound frequency). The vibration can be witnessed and felt by highly tensing one's muscles, as when making a firm fist. The sound can be heard by pressing a highly tensed muscle against the ear, again a firm fist is a good example. The sound is usually described as a rumbling sound. Some individuals can voluntarily produce this rumbling sound by contracting the tensor tympani muscle of the middle ear. The rumbling sound can also be heard when the neck or jaw muscles are highly tensed as when yawning deeply. This phenomenon is known since (at least) 1884 (cf : Tillaux Paul Jules, Traité d’Anatomie topographique avec applications à la chirurgie, Paris Asselin et Houzeau publishers (4°ed. 1884, p. 125 )).

Additional images

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  Base of skull. Inferior surface.

• Gray907.png

  External and middle ear, opened from the front. Right side.

• Gray911.png

  View of the inner wall of the tympanum (enlarged.)

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  Auditory tube, laid open by a cut in its long axis.

This article was originally based on an entry from a public domain edition of Gray's Anatomy. As such, some of the information contained within it may be outdated.

See also

• Acoustic reflex
• Otoacoustic emission
• Equal-loudness contours
• Audiometry
• Hyperacusis

External links

• Template:MuscleLoyola
• McGill
• MadSci Network [1]