What is the smallest muscle in the human body?

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.

The stapedius dampens the vibrations of the stapes by pulling on the neck of that bone. It prevents excess movement of the stapes, helping to control the amplitude of sound waves from the general external environment to the inner ear.

Paralysis of the stapedius allows wider oscillation of the stapes, resulting in a heightened reaction of the auditory ossicles to sound vibration. This condition, known as hyperacusis, causes normal sounds to be perceived as very loud.

Paralysis of the stapedius muscle may result when the nerve to the stapedius, (a branch of the facial nerve), is damaged, or when the facial nerve itself is damaged before the nerve to stapedius branches. In cases of Bell's palsy, (unilateral paralysis of the facial nerve), the stapedius is paralyzed and hyperacusis may result.