The tensor tympani is a

muscle Muscle is a soft tissue, one of the four basic types of animal tissue. There are three types of muscle tissue in vertebrates: skeletal muscle, cardiac muscle, and smooth muscle. Muscle tissue gives skeletal muscles the ability to muscle contra ...

within the

middle ear The middle ear is the portion of the ear medial to the eardrum, and distal to the oval window of the cochlea (of the inner ear). The mammalian middle ear contains three ossicles (malleus, incus, and stapes), which transfer the vibrations ...

, located in the bony canal above the bony part of the

auditory tube The Eustachian tube (), also called the auditory tube or pharyngotympanic tube, is a tube that links the nasopharynx to the middle ear, of which it is also a part. In adult humans, the Eustachian tube is approximately long and in diameter. It ...

, and connects to the

malleus The ''malleus'', or hammer, is a hammer-shaped small bone or ossicle of the middle ear. It connects with the incus, and is attached to the inner surface of the eardrum. The word is Latin for 'hammer' or 'mallet'. It transmits the sound vibra ...

bone. Its role is to dampen loud sounds, such as those produced from

chewing Chewing or mastication is the process by which food is crushed and ground by the teeth. It is the first step in the process of digestion, allowing a greater surface area for digestive enzymes to break down the foods. During the mastication proc ...

, shouting, or

thunder Thunder is the sound caused by lightning. Depending upon the distance from and nature of the lightning, it can range from a long, low rumble to a sudden, loud crack. The sudden increase in temperature and hence pressure caused by the lightning pr ...

. Because its

reaction time Mental chronometry is the scientific study of processing speed or reaction time on cognitive tasks to infer the content, duration, and temporal sequencing of mental operations. Reaction time (RT; also referred to as "response time") is measured ...

is not fast enough, the muscle cannot protect against hearing damage caused by sudden loud sounds, like explosions or gunshots, however some individuals have voluntary control over the muscle, and may tense it pre-emptively.

Structure

The tensor tympani is a

that is present in the

. It arises from the cartilaginous part of the

, and the adjacent great wing of the sphenoid. It then passes through its own canal, and ends in the

tympanic cavity The tympanic cavity is a small cavity surrounding the bones of the middle ear. Within it sit the ossicles, three small bones that transmit vibrations used in the detection of sound. Structure On its lateral surface, it abuts the external audit ...

as a slim

tendon A tendon or sinew is a tough band of fibrous connective tissue, dense fibrous connective tissue that connects skeletal muscle, muscle to bone. It sends the mechanical forces of muscle contraction to the skeletal system, while withstanding tensi ...

that connects to the handle of the

. The tendon makes a sharp bend around the ''processus cochleariformis'', part of the wall of its cavity, before it joins with the malleus. The tensor tympani receives blood from the

middle meningeal artery The middle meningeal artery (') is typically the third branch of the maxillary artery#First portion, first portion of the maxillary artery. After branching off the maxillary artery in the infratemporal fossa, it runs through the foramen spinosum t ...

via the superior tympanic branch. It is one of two muscles in the

, the other being the

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 or stirrup bone of the middle ear. Structure The stapedius emerges from ...

Nerve supply

The tensor tympani is supplied by the tensor tympani nerve, a branch of the mandibular branch of the

trigeminal nerve In neuroanatomy, the trigeminal nerve (literal translation, lit. ''triplet'' nerve), also known as the fifth cranial nerve, cranial nerve V, or simply CN V, is a cranial nerve responsible for Sense, sensation in the face and motor functions ...

. As the tensor tympani is supplied by motor fibers of the trigeminal nerve, it does not receive fibers from the trigeminal ganglion, which has sensory fibers only.

Development

The tensor tympani muscle develops from mesodermal tissue in the 1st pharyngeal arch.

Function

The tensor tympani acts to damp the noise produced by chewing. When tensed, the muscle pulls the malleus medially, tensing the

tympanic membrane In the anatomy of humans and various other tetrapods, the eardrum, also called the tympanic membrane or myringa, is a thin, cone-shaped membrane that separates the external ear from the middle ear. Its function is to transmit changes in pressur ...

and damping

vibration Vibration () is a mechanical phenomenon whereby oscillations occur about an equilibrium point. Vibration may be deterministic if the oscillations can be characterised precisely (e.g. the periodic motion of a pendulum), or random if the os ...

in the ear

ossicles The ossicles (also called auditory ossicles) are three irregular bones in the middle ear of humans and other mammals, and are among the smallest bones in the human body. Although the term "ossicle" literally means "tiny bone" (from Latin ''ossi ...

and thereby reducing the perceived

amplitude The amplitude of a periodic variable is a measure of its change in a single period (such as time or spatial period). The amplitude of a non-periodic signal is its magnitude compared with a reference value. There are various definitions of am ...

of sounds. It is not to be confused by the

acoustic reflex The acoustic reflex (also known as the stapedius reflex, stapedial reflex, auditory reflex, middle-ear-muscle reflex (MEM reflex, MEMR), attenuation reflex, cochleostapedial reflex or intra-aural reflex) is an involuntary muscle contraction that ...

, but can be activated by the startle reflex.

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). Some individuals can voluntarily produce this rumbling sound by contracting the muscle. According to the National Institute of Health, "voluntary control of the tensor tympani muscle is an extremely rare event". The rumbling sound can also be heard when the neck or jaw muscles are highly tensed as when yawning deeply. This phenomenon has been known since (at least) 1884. In a 2013 case of a 27-year old man who was complaining of

tinnitus Tinnitus is a condition when a person hears a ringing sound or a different variety of sound when no corresponding external sound is present and other people cannot hear it. Nearly everyone experiences faint "normal tinnitus" in a completely ...

, otolaryngologists discovered that he was voluntarily contracting the tensor tympani muscles in both ears at the same time. In a 2017 study of five volunteers, otorhinolaryngologists found "a low frequency conductive

hearing loss Hearing loss is a partial or total inability to hear. Hearing loss may be present at birth or acquired at any time afterwards. Hearing loss may occur in one or both ears. In children, hearing problems can affect the ability to acquire spo ...

Involuntary control (tympanic reflex)

The tympanic reflex helps prevent damage to the inner ear by muffling the transmission of low frequency vibrations from the tympanic membrane to the oval window. The reflex has a response time of 40 milliseconds, not fast enough to protect the ear from sudden loud noises such as an explosion or gunshot. LDV_AR_measurement_USAARL

Thus, the reflex most likely developed to protect early humans from loud thunder claps which do not happen in a split second. The reflex works by contracting the muscles of the middle ear, the tensor tympani and the stapedial muscle. However, the stapedial muscle is innervated by the facial nerve while the tensor tympani is innervated by the trigeminal nerve. The tensor tympani pulls the manubrium of the malleus inwards and tightens it while the stapedial muscle pulls the stapes inward. This tightening damps the sound vibration that is allowed to penetrate the cochlea. Withdrawal from drugs such as

benzodiazepine Benzodiazepines (BZD, BDZ, BZs), colloquially known as "benzos", are a class of central nervous system (CNS) depressant, depressant drugs whose core chemical structure is the fusion of a benzene ring and a diazepine ring. They are prescribed t ...

s had been known to cause tonic tensor tympani syndrome (TTTS) during withdrawal. The tympanic reflex will also activate when loud vibrations are generated by the person themselves. The tensor tympani can often be observed vibrating while shouting at an increased volume, damping the sound somewhat.

Clinical significance

In many people with

hyperacusis Hyperacusis is an increased Hearing, sensitivity to sound and a low tolerance for environmental noise. Definitions of hyperacusis can vary significantly; it often revolves around damage to or dysfunction of the Stapes, ''stapes'' bone, stapedius ...

, 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). The mechanisms behind dysfunction of the tympanic tensor muscle and their consequences are hypothesized. However, in a published study, researchers studied the case of an acoustic shock whose mechanisms suggest dysfunction of the tympanic tensor muscle. This study appears to be the first to provide experimental support suggesting that middle ear muscles (MEM) may behave abnormally after an acoustic shock. It is suggested that abnormal contractions (e.g. tonic contractions) of the tympanic tensor muscle may trigger neurogenic inflammation. Indeed, fibers with substances P and CGRP were found in close proximity.Yamazaki M, Sato I. Distribution of substance P and the calcitonin gene-related peptide in the human tensor tympani muscle. European Archives of Oto-Rhino-Laryngology. 2014;271(5):905-911. doi:10.1007/s00405-013-2469-1.

Additional images

File:Gray907.png, External and middle ear, opened from the front. Right side. File:Gray911.png, View of the inner wall of the tympanum (enlarged)

References

External links

McGill

{{Authority control Muscles of the head and neck Ear