Tensor tympani muscle

The tensor tympani is a muscle within the middle ear, located in the bony canal above the bony part of the auditory tube, and connects to the malleus bone. Its role is to dampen loud sounds, such as those produced from chewing, shouting, or thunder. Because its reaction time 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.

The tensor tympani is a muscle that is present in the middle ear. It arises from the cartilaginous part of the auditory tube, and the adjacent great wing of the sphenoid. It then passes through its own canal, and ends in the tympanic cavity as a slim tendon that connects to the handle of the malleus. 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 via the superior tympanic branch. It is one of two muscles in the tympanic cavity, the other being the stapedius.

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

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

The tensor tympani acts to damp the noise produced by chewing. When tensed, the muscle pulls the malleus medially, tensing the tympanic membrane and damping vibration in the ear ossicles and thereby reducing the perceived amplitude of sounds. It is not to be confused by the acoustic reflex, but can be activated by the startle reflex.

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, 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."