The stapedius is the smallest skeletal muscle

Skeletal muscle

Skeletal muscle is a form of striated muscle tissue existing under control of the somatic nervous system- i.e. it is voluntarily controlled. It is one of three major muscle types, the others being cardiac and smooth muscle...

 in the human

Human

Humans are the only living species in the Homo genus...

 body. At just over one millimeter in length, its purpose is to stabilize the smallest bone in the body, the stapes.

The stapedius emerges from a pinpoint foramen in the apex of the pyramidal eminence (a hollow, cone-shaped prominence in the posterior wall of the tympanic cavity), and inserts into the neck of the stapes.

Function

It reflexively dampens the vibrations of the stapes by pulling on the neck of that bone. It prevents excess movement by the stapes, helping to control the amplitude of sound waves

Sound

Sound is a mechanical wave that is an oscillation of pressure transmitted through a solid, liquid, or gas, composed of frequencies within the range of hearing and of a level sufficiently strong to be heard, or the sensation stimulated in organs of hearing by such vibrations.-Propagation of...

 from the general external environment to the inner ear

Ear

The ear is the organ that detects sound. It not only receives sound, but also aids in balance and body position. The ear is part of the auditory system....

. The stapedius muscle dampens the ability of the stapes vibration and protects the inner ear from high noise levels, primarily the volume of your own voice. Compare also the role of the tensor tympani

Tensor tympani

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...

 muscle, which primarily dampens those sounds associated with chewing.

Innervation

The stapedius is innervated by the nerve to stapedius, a branch of cranial nerve VII, the facial nerve

Facial nerve

The facial nerve is the seventh of twelve paired cranial nerves. It emerges from the brainstem between the pons and the medulla, and controls the muscles of facial expression, and functions in the conveyance of taste sensations from the anterior two-thirds of the tongue and oral cavity...

. This is the first branch of the facial nerve after it exits the facial canal

Facial canal

The facial canal is a Z-shaped canal running through the temporal bone from the internal acoustic meatus to the stylomastoid foramen. In humans it is approximately 3 centimeters long, which makes it the longest human osseous canal of a nerve...

; the second branch is the chorda tympani

Chorda tympani

The chorda tympani is a nerve that branches from the facial nerve inside the facial canal, just before the facial nerve exits the skull via the Stylomastoid foramen...

 which carries special sense (taste) and parasympathetic fibres of cranial nerve VII. It provides taste sensation to the anterior 2/3 of the tongue

Tongue

The tongue is a muscular hydrostat on the floors of the mouths of most vertebrates which manipulates food for mastication. It is the primary organ of taste , as much of the upper surface of the tongue is covered in papillae and taste buds. It is sensitive and kept moist by saliva, and is richly...

 by joining with the lingual nerve

Lingual nerve

The lingual nerve is a branch of the mandibular nerve , itself a branch of the trigeminal nerve, which supplies sensory innervation to the tongue...

 - a branch of the Mandibular nerve

Mandibular 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....

 (V3) - in the infratemporal fossa

Infratemporal fossa

The infratemporal fossa is an irregularly shaped cavity, situated below and medial to the zygomatic arch.* anteriorly, by the infratemporal surface of the maxilla and the ridge which descends from its zygomatic process...

.

Pathology

Paralysis

Paralysis

Paralysis is loss of muscle function for one or more muscles. Paralysis can be accompanied by a loss of feeling in the affected area if there is sensory damage as well as motor. A study conducted by the Christopher & Dana Reeve Foundation, suggests that about 1 in 50 people have been diagnosed...

 of the stapedius, such as in Bell's palsy

Bell's palsy

Bell's palsy is a form of facial paralysis resulting from a dysfunction of the cranial nerve VII that results in the inability to control facial muscles on the affected side. Several conditions can cause facial paralysis, e.g., brain tumor, stroke, and Lyme disease. However, if no specific cause...

, allows wider oscillation

Oscillation

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...

 of the stapes, resulting in heightened reaction of the auditory ossicles to sound vibration. This condition, known as hyperacusis

Hyperacusis

Hyperacusis is a health condition characterized by an over-sensitivity to certain frequency ranges of sound...

, causes normal sounds to be perceived as very loud.