Tensor tympani
Encyclopedia
The tensor tympani, the larger of the two muscles of the tympanic cavity
, 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
.
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.
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).
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.
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 )).
Tympanic cavity
The tympanic cavity is a small cavity surrounding the bones of the middle ear.It is formed from the tubotympanic recess, an expansion of the first pharyngeal pouch....
, 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
Mastication
Mastication or chewing is the process by which food is crushed and ground by teeth. It is the first step of digestion and it increases the surface area of foods to allow more efficient break down by enzymes. During the mastication process, the food is positioned between the teeth for grinding by...
.
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
Malleus
The malleus or hammer is a hammer-shaped small bone or ossicle of the middle ear which connects with the incus and is attached to the inner surface of the eardrum...
, near its root.
Function
When tensed, the action of the muscle is to pull the malleus medially, tensing the tympanic membrane, damping vibrationOscillation
Oscillation is the repetitive variation, typically in time, of some measure about a central value or between two or more different states. Familiar examples include a swinging pendulum and AC power. The term vibration is sometimes used more narrowly to mean a mechanical oscillation but sometimes...
in the ear ossicles
Ossicles
The ossicles are the three smallest bones in the human body. They are contained within the middle ear space and serve to transmit sounds from the air to the fluid-filled labyrinth . The absence of the auditory ossicles would constitute a moderate-to-severe hearing loss...
and thereby reducing the amplitude
Amplitude
Amplitude is the magnitude of change in the oscillating variable with each oscillation within an oscillating system. For example, sound waves in air are oscillations in atmospheric pressure and their amplitudes are proportional to the change in pressure during one oscillation...
of sounds. This muscle is contracted primarily to dampen the noise produced by chewing. (Compare to the more general dampening function of the stapedius
Stapedius
The stapedius is the smallest skeletal muscle in the human body. At just over one millimeter in length, its purpose is to stabilize the smallest bone in the body, the stapes....
muscle.)
In many people with hyperacusis
Hyperacusis
Hyperacusis is a health condition characterized by an over-sensitivity to certain frequency ranges of sound...
, 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 divisionMandibular nerve
The mandibular nerve is the largest of the three branches of the trigeminal nerve.-Roots:It is made up of two roots:* a large sensory root proceeding from the inferior angle of the trigeminal ganglion....
of the trigeminal nerve
Trigeminal nerve
The trigeminal nerve contains both sensory and motor fibres. It is responsible for sensation in the face and certain motor functions such as biting, chewing, and swallowing. Sensory information from the face and body is processed by parallel pathways in the central nervous system...
(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
Trigeminal ganglion
The trigeminal ganglion is a sensory ganglion of the trigeminal nerve that occupies a cavity in the dura mater, covering the trigeminal impression near the apex of the petrous part of the temporal bone.-Relations:It is somewhat crescentic in shape, with its convexity...
, 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 )).
See also
- Acoustic reflexAcoustic reflexThe acoustic reflex is an involuntary muscle contraction that occurs in the middle ear of mammals in response to high-intensity sound stimuli....
- Otoacoustic emissionOtoacoustic emissionAn otoacoustic emission is a sound which is generated from within the inner ear. Having been predicted by Thomas Gold in 1948, its existence was first demonstrated experimentally by David Kemp in 1978 and otoacoustic emissions have since been shown to arise by a number of different cellular...
- Equal-loudness contours
- AudiometryAudiometryAudiometry is the testing of hearing ability, involving thresholds and differing frequencies. Typically, audiometric tests determine a subject's hearing levels with the help of an audiometer, but may also measure ability to discriminate between different sound intensities, recognize pitch, or...
- HyperacusisHyperacusisHyperacusis is a health condition characterized by an over-sensitivity to certain frequency ranges of sound...