Stapedial

Stapedial is an anatomical term relating to the stapes, one of the auditory ossicles in the middle ear. In common usage, stapedial refers to structures and processes associated with the stapes, particularly the stapedius muscle (the stapedius) and the stapedius reflex.

Anatomy: The stapes, the smallest bone in the human body, forms a movable contact with the incus at the incudostapedial joint. The stapedius muscle originates from the pyramidal region of the temporal bone and inserts on the neck of the stapes. Innervation is by the stapedius branch of the facial nerve (cranial nerve VII). The auditory system uses the stapedius reflex to dampen vibrations in response to loud sounds, reducing energy transmitted to the inner ear.

Physiology: The acoustic reflex involves contraction of the stapedius (and tensor tympani) in response to high-intensity sounds, with a typical onset latency of tens of milliseconds. The contraction increases impedance at the oval window, decreasing stapes mobility.

Embryology: The stapedial artery is an embryonic vessel that traverses the stapes during development and supplies portions of the face and brain through the second aortic arch. In normal development it regresses and is replaced by the permanent arterial system; remnants can be seen as anomalies in the middle ear.

Clinical notes: Otosclerosis can immobilize the stapes, causing conductive hearing loss. Facial nerve palsy can impair stapedius function, sometimes resulting in hyperacusis on the affected side. In rare cases, persistence of the stapedial artery or other stapedial anomalies may be seen in imaging or during otologic surgery.