Stapedius muscle

Stapedius is one of the two middle ear muscles. it plays a crucial role in protecting the inner ear from acoustic injury by dampening the vibrations of the stapes, one of the auditory ossicles.

Anatomical details

1. Origin

From the posterior wall of the tympanic cavity, specifically within the pyramidal eminence (a small conical projection of the temporal bone).

2. Insertion

Onto the neck of the stapes.

Innervation

Facial nerve (cranial nerve VII) via the nerve to stapedius, which arises in the facial canal before the chorda tympani branch.

Blood supply

From branches of posterior auricular, anterior tympanic, middle meningeal arteries.

Actions

• Primary Action: Pulls the stapes posteriorly, stabilizing it in the oval window of the cochlea.

  • It reduces the amplitude of stapes movement.

  • Decreases transmission of sound energy to the inner ear.

  • Protects cochlear hair cells from potential damage due to loud sounds. The stapedius muscle contracts reflexively in response to loud noises — part of the acoustic (stapedial) reflex.

Clinical Correlation

Paralysis or Lesion of the Nerve to Stapedius (CN VII branch):

• Leads to loss of stapedial reflex → hyperacusis.

• Patients perceive normal sounds as abnormally loud or painful, especially low-pitched tones.

• Commonly occurs in facial nerve palsy (e.g., Bell’s palsy) when the lesion is proximal to the branch to stapedius.