The Anatomy of the Stapedius Muscle

Table of Contents
View All
Table of Contents

The stapedius muscle is a muscle within the ear that stabilizes the stapes bone of the inner ear. It’s the smallest skeletal muscle in the body and plays an important role in hearing. This article will discuss the stapedius muscle's anatomy, location, associated conditions, and treatment.

Person with noise sensitivity troubled by hyper-acute hearing in bed at night

MICROGEN IMAGES/ SCIENCE PHOTO LIBRARY / Getty Images

Anatomy 

Shaped like a sickle, the stapedius muscle is often described as the smallest skeletal muscle in the human body. However, some sources suggest its average size may be larger than the often-cited 1 millimeter length.

A 2018 paper describing dissections and inspections of the inner ear and stapedius muscle published in the Indian Journal of Otolaryngology Head Neck Surgery puts the measurement at between 9 and 11 millimeters. ​​The tendon, which is attached to the handle end of the sickle-shaped muscle, measures about 2 millimeters in length.

Location 

The stapedius muscle is located inside the ear cavity, specifically inside the tympanic cavity, in the middle portion of the ear. In a healthy hearing canal, the tympanic cavity is filled with air. 

The muscle extends from the back portion of the stapes bone, with the thinnest part of the muscle connecting to the neck of the stapes. It emerges from a small opening of the pyramidal eminence, which is a hollow part of the tympanic cavity wall. The stapedial tendon attaches to the bottom portion of the stapedius muscle.

Two arteries supply blood to this small muscle:

The facial nerve, also called the seventh crainial nerve, supplies nerves to the stapedius muscle. 

Anatomical Variations 

In rare cases, a person can be born without a stapedius muscle or tendon. This may cause issues with hearing, such as hearing loss.

Function 

The small stapedius muscle plays a crucial role in your ability to hear. Its main function is to stabilize the stapes bone, the smallest bone in your body. The middle ear’s job is to facilitate the movement of sound waves from the outer ear to the inner ear.

This chain of events is set in motion as you hear sounds. Sound waves stimulate inner ear receptors that send signals to your brain. Your brain stem then sends an alert to your middle ear, telling your stapedius muscle to contract. 

As sound waves pass through the middle ear’s three ossicles, the stapes bone hits the oval window, the part of the ear that delineates the middle and inner ear. When the stapes bone activates the oval window, fluid inside the inner ear begins to move, which starts the sound processing process.

By stabilizing the stapes, the stapedius dampens sound vibrations that eventually make their way to the inner ear. Think of the stapedius muscle as a sort of volume control mechanism. Without it, loud sounds could easily damage your inner ear.

This reflex to protect your hearing is part of the acoustic middle ear reflex, an involuntary reflex. Healthcare providers can test your acoustic middle ear reflex using certain tools, and the results can provide valuable information about your hearing health.

It’s not a fail-proof mechanism, though. You’re probably aware that you can experience hearing loss when hearing sudden loud sounds. The stapedius muscle and acoustic middle ear reflex have their limitations. Loud noises can still cause inner ear damage.

Associated Conditions 

Issues with the stapedius muscle can cause problems with hearing. 

For example, paralysis of the muscle prevents sound dampening. People with stapedius muscle paralysis have what’s known as hyperacusis, which makes things sound much louder than they are. It’s also known as sound sensitivity.

If you have hyperacusis, you may be less tolerant of certain sounds than others, like running water, vehicle noises, or paper shuffling.

This kind of paralysis can happen because of facial nerve damage. Bell’s palsy is an example of a condition that can cause hyperacusis. Other conditions that can cause this kind of sound sensitivity include:

  • Head trauma
  • Damage to the ear because of exposure to loud sounds
  • Ototoxicity (ear damage due to medications or toxins)
  • Viral infections other than Bell’s palsy
  • Lyme disease (a bacterial infection spread by tick bite)
  • Temporomandibular joint (TMJ) syndrome (a condition affecting the joint and muscles that control chewing)

Additionally, some conditions are associated with hearing hypersensitivity but aren’t necessarily the cause of it. These include:

You can also experience idiopathic middle ear contractions. Idiopathic means there’s no known medical cause. For example, some people may occasionally hear sounds like fluttering or clicking inside their ears. Some experts believe some of these sounds result from the stapedius muscle contracting when it shouldn’t.

Obstructions in the ear that impact sound transmission and stapedius muscle contraction can affect your acoustic reflex. Other things that can affect the acoustic reflex include:

  • Perforations in the tympanic membrane (ear drum)
  • Abnormal pressure in the middle ear

Rehabilitation 

While there’s no cure for hyperacusis, treating the underlying issue may help. For instance, if you’re taking medications that are causing ear damage, stopping the drug may prevent further damage.

Sound therapy may also help improve sound tolerance. In this therapy, you wear a noise-generating device that produces barely audible white noise. It retrains the brain to accept sounds you hear throughout the day.

Summary

The stapedius muscle is a small muscle located inside the middle ear. It helps stabilize the stapes bone and is involved in regulating sound and protecting your inner ear from damage due to loud sounds. 

8 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Prasad KC, Azeem Mohiyuddin SM, Anjali PK, et al. Microsurgical anatomy of stapedius muscle: anatomy revisited, redefined with potential impact in surgeriesIndian J Otolaryngol Head Neck Surg. 2019;71(1):14-18. doi:10.1007/s12070-018-1510-5

  2. Behera SK. Congenital absence of stapedius muscle and tendon: rare finding in two cases. Indian Journal of Otology. 2017;23(1): 43-45. doi:10.4103/0971-7749.199511

  3. Johns Hopkins Medicine. How the ear works.

  4. NYU Langone Health. Diagnosing facial nerve paralysis.

  5. National Institute on Deafness and Other Communication Disorders. Noise-induced hearing loss.

  6. American Academy of Otolaryngology–Head and Neck Surgery Foundation. Hyperacusis.

  7. ENT & Audiology News. Middle ear muscle disorders: Presentation, diagnosis and management.

  8. Open Access Guide to Audiology and Hearing Aids for Otolaryngologists. Acoustic (stapedius) reflexes