Acoustic reflex

A reflexive response of the middle ear muscles to loud sounds

Acoustic reflex

The acoustic reflex, also known as the stapedial reflex, is an involuntary muscle contraction that occurs in the middle ear in response to high-intensity sound stimuli. This reflex involves the contraction of the stapedius muscle and, to a lesser extent, the tensor tympani muscle, which serve to protect the inner ear from potential damage caused by loud noises.

Anatomy and Physiology

The acoustic reflex is primarily mediated by the stapedius muscle, which is the smallest skeletal muscle in the human body. This muscle is attached to the stapes, one of the three ossicles in the middle ear. When the stapedius muscle contracts, it pulls the stapes away from the oval window, thereby reducing the transmission of sound vibrations to the cochlea.

The reflex arc begins with the detection of loud sounds by the cochlea, which sends signals via the auditory nerve to the cochlear nucleus in the brainstem. From there, the signal is relayed to the superior olivary complex, which then sends efferent signals to the facial nerve nucleus. The facial nerve innervates the stapedius muscle, causing it to contract.

Function

The primary function of the acoustic reflex is to protect the inner ear from acoustic trauma by reducing the transmission of sound energy. This reflex is particularly effective for low-frequency sounds and helps in the attenuation of one's own voice during speaking, known as the "occlusion effect."

Clinical Significance

The acoustic reflex is used clinically to assess the integrity of the auditory pathway and the function of the middle ear. It is measured using a test called tympanometry, which evaluates the reflex threshold and the reflex decay. Abnormalities in the acoustic reflex can indicate various pathologies, such as otosclerosis, facial nerve paralysis, or sensorineural hearing loss.

Measurement

The measurement of the acoustic reflex involves presenting a loud sound to the ear and recording the change in compliance of the middle ear system. This is typically done using a probe that is inserted into the ear canal, which measures the impedance of the middle ear.

Related pages

• Middle ear
• Cochlea
• Ossicles
• Hearing loss

Gallery

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  Diagram of the middle ear anatomy

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  Measurement of the acoustic reflex

Acoustic_reflex

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  Diagram of the middle ear anatomy

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  Laser Doppler Vibrometry measurement of acoustic reflex