Glossary

Acoustic reflex☆

also: stapedial reflex, middle-ear muscle reflex, AMER

The involuntary contraction of the stapedius muscle in response to a moderate-to-loud sound, measured clinically as a transient reduction in middle-ear admittance.

See also: Stapedius muscle, Admittance, Acoustic reflex arc

Acoustic reflex arc☆

also: reflex pathway

The neural circuit underpinning the reflex: cochlea, eighth nerve, cochlear nucleus, superior olivary complex, facial nerve nucleus, facial nerve, and stapedius muscle.

See also: Afferent limb, Efferent limb, Crossed (contralateral) pathway

Acoustic reflex threshold (ART)☆

also: reflex threshold

The lowest stimulus level that produces a criterion admittance change (commonly 0.02 mmho). Normal tonal ARTs lie roughly 70–100 dB HL.

See also: Acoustic reflex, Metz test

Admittance☆

also: acoustic admittance, immittance

A measure of how readily acoustic energy flows into the middle ear. Stapedius contraction reduces admittance; the recorded dip is the acoustic reflex.

See also: Acoustic reflex, Tympanometry

Afferent limb☆

also: afferent pathway, sensory limb

The incoming part of the reflex arc — cochlea and eighth nerve carrying the signal to the brainstem. A lesion here produces a stimulus-ear pattern.

See also: Acoustic reflex arc, Efferent limb

Crossed (contralateral) pathway☆

also: contralateral pathway, uncrossed pathway

Reflex pathways that cross the brainstem midline drive the contralateral reflex; uncrossed pathways drive the ipsilateral reflex. The distinction localises brainstem lesions.

See also: Acoustic reflex arc, Diagonal pattern

Diagonal pattern☆

also: crossed-pathway pattern

Crossed (contralateral) reflexes abnormal with uncrossed (ipsilateral) reflexes preserved. The signature of an intra-axial brainstem lesion.

See also: Crossed (contralateral) pathway, Probe-ear pattern

Efferent limb☆

also: efferent pathway, motor limb

The outgoing part of the reflex arc — facial nerve carrying the motor command to the stapedius. A lesion here produces a probe-ear pattern.

See also: Acoustic reflex arc, Afferent limb, Stapedius muscle

Metz test☆

also: Metz recruitment

A reflex threshold appearing within 60 dB of the pure-tone threshold (reduced sensation level) indicates loudness recruitment and supports a cochlear site of lesion.

See also: Acoustic reflex threshold (ART), Recruitment

Ossicular chain☆

also: ossicles

The malleus, incus and stapes, which transmit sound from the eardrum to the cochlea. Stapedius contraction stiffens this chain.

See also: Stapedius muscle, Admittance

Probe-ear pattern☆

also: vertical pattern

Reflexes absent for both conditions recorded with the probe in one ear. Points to a lesion of that probe ear — conductive or efferent (facial nerve).

See also: Stimulus-ear pattern, Diagonal pattern

Recruitment☆

also: loudness recruitment

An abnormally rapid growth of loudness with increasing intensity, typical of cochlear hearing loss. It underlies the reduced sensation level of the reflex in cochlear ears.

See also: Metz test, Acoustic reflex threshold (ART)

Reflex decay☆

also: acoustic reflex decay, decay test

Weakening of the reflex during a sustained 10-second tone. A drop to 50% or less of the initial amplitude at 500 or 1000 Hz is a positive (abnormal) result suggesting a retrocochlear lesion.

See also: Acoustic reflex threshold (ART), Retrocochlear

Retrocochlear☆

also: retro-cochlear

Relating to a site of lesion central to the cochlea — typically the eighth nerve or brainstem. Reflex decay and the stimulus-ear pattern are retrocochlear signs.

See also: Reflex decay, Stimulus-ear pattern

Sensation level (SL)☆

also: dB SL

The level of a sound expressed in dB above an individual's threshold for that sound. Reflex decay is tested at 10 dB SL re: the reflex threshold.

See also: Acoustic reflex threshold (ART), Metz test

Stapedius muscle☆

also: stapedius

The smallest skeletal muscle in the body, attaching to the neck of the stapes. Its contraction stiffens the ossicular chain. Innervated by the stapedial branch of the facial nerve.

See also: Acoustic reflex, Efferent limb, Ossicular chain

Stimulus-ear pattern☆

also: horizontal pattern

Reflexes abnormal whenever one ear is the stimulus, regardless of probe position. Points to an afferent-limb (cochlear or eighth-nerve) lesion.

See also: Probe-ear pattern, Afferent limb

Tympanometry☆

also: tympanogram

Measurement of middle-ear admittance as ear-canal pressure is varied. The companion immittance test to the acoustic reflex; type Ad is hypermobile, type As shallow, type B flat.

See also: Admittance, Acoustic reflex

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