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How do middle-ear muscles protect the inner ear from loud sounds?

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Cross-section diagram of the human ear showing the outer ear, middle ear, and inner ear, with labeled parts including the auricle, auditory canal, tympanic membrane, ossicles, cochlea, semicircular canals, and nerves. — human ear Structure of the human ear.

The middle ear contains two small muscles, the tensor tympani and the stapedius, which help regulate the intensity of sound reaching the inner ear.12

When triggered by high-intensity sounds, these muscles contract reflexively to alter the tension of the ossicular chain:

Tensor tympani: By pulling the handle of the malleus inward, it increases the tension of the tympanic membrane.23
Stapedius: It pulls the footplate of the stapes outward from the oval window, which reduces the intensity of sound vibrations transmitted to the cochlea.23

While this reflex is thought to provide protection similar to an eye blink, it has limitations. Because the contraction is not instantaneous, it cannot protect against sudden, impulsive noises like gunfire or explosions. Furthermore, because these muscles fatigue quickly, they offer limited protection against prolonged exposure to high-level noise in environments such as industrial workplaces or concerts.3