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PubMed1979

Fatigue and recovery of the human acoustic stapedius reflex in industrial noise.

The fatiguability of the acoustic stapedius muscle reflex in an actual noisy industrial environment was investigated in normal-hearing subjects. In a laboratory situation a small depression was found with a considerable individual variability. The stapedius reflex recovered slowly, approximately as a linear function of time. In a field study on an entire day of exposure in a ship-building yard the reflex depression was on the average 4 dB in response to a stimulation of 2000 Hz 10 min after the end of the workday. This corresponds to less than 8 dB immediately at the end of the exposure.

Acoustic Impedance Tests↗
PubMed1991

Threshold and suprathreshold temporal integration effects in the crossed and uncrossed human acoustic stapedius reflex.

Threshold and suprathreshold temporal integration (TI) effects were studied in the crossed and uncrossed human acoustic stapedius reflex. Changes in reflex threshold were compared at four stimulus durations and for six threshold response criteria; suprathreshold effects were similarly compared at four stimulus durations and at five stimulus sound-pressure levels. Our results showed that reflex thresholds were significantly lower for the uncrossed condition and for longer duration stimuli. Both effects were dependent on threshold response criteria. Threshold TI measurements in both crossed and uncrossed conditions were equivalent at low criterion levels (0%-4%, p greater than 0.05) but were significantly larger in the crossed condition at higher criterion levels (5%-6%, p less than 0.05). Prominent suprathreshold effects also occurred. The main effect was characterized by significantly larger reflex magnitudes in the uncrossed condition. Duration dependent slope differences in magnitude intensity functions (MIFs) were also observed and were characterized by steeper slopes for longer duration stimuli. Saturation effects and/or intensity-dependent slope decelerations in MIFs were predominant in the uncrossed condition and for stimulus durations exceeding 20 ms. These data provide further quantitative evidence for asymmetric threshold and suprathreshold response properties of the crossed and uncrossed human acoustic stapedius reflex and demonstrate the dependence of these effects on stimuli of different durations.

Acoustic Stimulation↗
PubMedDate not supplied

The tensor tympani, stapedius, and tensor veli palatini muscles--an electromyographic study.

Electromyographic recordings of the activity of the tensor veli palatini, tensor tympani, and stapedius muscles were obtained from several adult human subjects. Muscle responses were recorded under four stimulus conditions, ie, contralateral intense wide-band noise, air jet to the eye, swallow, and electrical stimulation of the tongue. The results indicated that the two tensor muscles responded to the same stimuli in similar patterns. The latter muscle differed from the response of the stapedius.

Acoustic Stimulation↗
PubMed1994

Motor unit size of M. stylohyoideus and M. stapedius in the mouse.

To elucidate the relation between the caliber of myelinated nerve fibers (MNFs) and motor unit size (i.e., number of muscle fibers per motor unit), motor unit size was measured for the mouse m. stylohyoideus, innervated predominantly by extra large MNFs, and compared with that of the mouse m. stapedius, innervated predominantly by large MNFs. All muscle fibers and MNFs were counted morphologically, and mean motor unit size was calculated for each muscle. The results showed that the average of 12 mean motor unit sizes for the m. stylohyoideus (35.8 +/- 8.2), innervated predominantly by extra large MNFs, was greater than that for the m. stapedius (6.5 +/- 1.3), innervated predominantly by large MNFs.

Animals↗
PubMedDate not supplied

Decay and recovery of the acoustic stapedius reflex in humans.

The time course of decay and recovery of ipsilateral and contralateral stapedius reflex responses to 2 000 Hz pure tone stimulation was studied in 10 normal-hearing subjects. Reflex responses were found to follow a closely similar time course with respect to both decay and recovery in simultaneous bilateral recordings. The similarity is compatible with the assumption that decay and recovery originate in the afferent auditory system, and not in the muscles. Recovery was 50% complete 250 ms after the end of the stimulus and most subjects had reached their initial amplitude after 1-3 s. The individual correlation between decay and recovery was negative but weak, which is interpreted as showing that these processes have a tendency to balance each other, but are based partly on different mechanisms. The implications of the present results for diagnosis of disorders of the lower auditory system as well as for the evaluation of the protective role of the stapedius reflex against noise damage are pointed out.

Acoustic Stimulation↗
PubMedDate not supplied

Fatigability of the stapedius reflex in industrial noise.

Normal hearing subjects were monaurally exposed to 30 min of tape recorded shipyard noise (97 dB (A)) which is characterized by a variable temporal structure. The stapedius muscle activity was continuously recorded in the opposite ear as a change of the ear's acoustic impedance. The reflex function was, in addition, assessed as stimulus-response curves obtained before and, at various times after, exposure. A slight reflex fatigue was observed, together with a parallel shift of the stimulus-response curve (average 4 dB). The recovery was slow and not complete even 10 min after the end of the exposure. The individual variability was large. For 5 of the subjects the exposure was repeated at a later session and the individual degree of fatigue was found to be largely producible. The present results suggest that the stapedius reflex might play a role in the clinical picture of noise induced hearing loss.

Acoustic Impedance Tests↗
PubMedDate not supplied

A histochemical characterization of muscle fiber types in the middle ear muscles of the cat. 1. The stapedius muscle.

The muscle fiber content of the stapedius muscle of the cat was determined histochemically using a combination of oxidative enzymes and glycolytic markers. The major fiber type present was determined to be the fast oxidative glycolytic type (FOG; 77%). Two other types of fiber were found that could not be placed into any of the classical muscle fiber categories. One of these fibers had little staining for actomyosin ATPase (1', 13%) while the other stained densely for this enzyme (2', 10%). These fibers could also be separated using fiber diameter as a criterion. The mean diameters of these different fibers were 22.8 Mm+/-6.3 (FOG fiber type), 14.8 micrometers+/-3.7 (1' fiber) and 14.9 micrometers+/-5.5 (2' fiber). Since the predominant fiber type (FOG) is adapted for fast contraction and fatigue resistance, the stapedius muscle of the cat is probably capable of fast repetitive contractions, a conclusion that fits well with much of the physiological data. Due to the fact that the 2' fibers were always paired with the 1' fibers, it is conceivable that these pairs may represent some specialized sensory structures (i.e. unencapsulated muscle spindles).

Actomyosin↗
PubMedDate not supplied

Fatigability of the stapedius reflex in industrial noise. A field study.

The depression of the stapedius reflex after a whole workday in industrial noise was studied in 11 normal-hearing employees at a shipbuilding yard. The reflex activity was assessed with simultaneous bilateral recordings of impedance change induced by stimulation with 2 000 and 500 Hz tones. One ear was exposed for approximately 7 hours in the plant, the other one was protected. The dose was measured individually at 89--103 dB(A) equivalent level. Utilization of bilateral recordings together with a unilateral exposure enabled an analysis based on the whole stimulus response curves. The results show that the reflex is depressed on the average 4 dB at 2 000 Hz 10 min after end of workday. By extrapolation the stapedius reflex was estimated to be depressed less than 10 dB at the end of the exposure. Since the stimulus-response curves are shifted in parallel, the contraction during the high-level components of the noise were largely unaffected. No evidence was found for creation of transtympanic pressure differences during noise exposure. It was concluded that the reflex fulfils one necessary condition for influencing the individual pattern of noise damage to the ear, fatigue resistance in the presence of long-term exposure to hazardous noise.

Acoustic Impedance Tests↗
PubMedDate not supplied

Results of stapes operations with preservation of the stapedius muscle tendon.

The material consisted of 195 operated otosclerotic ears. In 101 ears the stapedial tendon was left intact and in 94 ears it was divided. The follow-up period was approximately 8.0 years. The stapedius reflex was tested in 85 ears with intact tendon and in 25 with divided tendon. It was elicited in 50 of the former but in none of the latter. Both bone and air conduction thresholds were postoperatively poorer in ears with preserved tendon than in the ears with divided tendon. Revision surgery was performed in 19 ears, 13 of which had an intact stapedial tendon. The reason for reoperating was usually the fixation of the stapedial crus at the oval window margin. The crus may have shifted because of the pull exerted by the stapedial muscle. In spite of the better circulation to the stapes and the long process of the incus, and of possible protection against loud noises, we cannot, in the light of our experiences, recommend preservation of the stapedius muscle tendon.

Adolescent↗
PubMed1980

High frequency audiometry and stapedius muscle reflex thresholds in juvenile diabetics.

Sixty-one juvenile, insulin-treated diabetics below 50 years of age with a duration of diabetes mellitus longer than 10 years underwent impedance audiometry with determination of stapedius reflex thresholds at 500 Hz, 1, 2, and 4 kHz, conventional pure tone and speech audiometry, and high-frequency audiometry up to 20 kHz. The results were compared with a normative material of non diabetic subjects selected after exactly the same criteria. No significant differences in hearing or stapedius reflex thresholds were found. Among half of the subjects there was a diabetic retinopathy. A comparison between those with and those without retinopathy did not reveal any significant difference in audiological findings. Even subjects with severe diabetic complications and almost life-long diabetes had normal hearing. Recent investigations on plasma-lipoids have discussed the possibility that insulin might prevent a premature ageing of hearing which has been reported by other authors. It is concluded that no statistical data exist that confirm a correlation between hearing impairment and diabetes.

Acoustic Impedance Tests↗
PubMed1999

[Hearing status after stapedectomy with preservation or cutting of stapedius tendon].

The authors analysed the influence of preservation or cutting of stapedius tendon during stapedotomy on postoperative hearing improvement. The material analysed was 110 operated ears, which were divided into two egual groups considering preservation or cutting of stapedius tendon. All operations were performed by the same surgeon using stapedotomy with tarflen prothesis. In all cases before and after operation there was performed tonal audiometry within a range from 0.5 to 4.0 kHz, speech audiometry with indication of speech reception threshold using mono-syllable test. The comparison of operation results did not show significant statistical differences between the studied groups of operated ears.

Adult↗
PubMed1990

[Origin of the human stapedius muscle].

More than 100 human embryos and fetuses, beginning from 6 mm (25-26 days) up to newborns have been investigated by means of histological serial sections, as well as by means of macro- micropreparation of the tympanic cavity. The m. stapedius is not independent, but takes origin from muscle fasciculi of the musculi digastrii posterior belly. The latter approaches the eminence of the future mastoid process, gives a part of muscle fasciculi into the tympanic cavity; they get through the stilomastoid cleft and run to the hammer neck, forming the m. stapedius. That is why both muscles are innervated from the facial nerve.

Anthropometry↗
PubMed1987

[Latency of the acoustic evoked stapedius reflex and its clinical significance].

We measured the mean latency of the stapedius reflex by normal listeners. We observed a prolongation of the latency by patients with operative and histological confirmed neurinoma of the VIII. nerve. Even if the measured stapedius reflex latency considerably varies, this method represents, any way, an important support to BERA to discover tumours of the cerebello-pontine angle.

Adolescent↗
PubMed1987

[Innervation of the stapedius muscle. A study using horseradish peroxidase in the guinea pig].

The numbers and locations of motoneurons to the stapedius muscle were determined by retrograde axonal transport of horseradish peroxidase (HRP) in the guinea pig. With the aid of a drill the bulla was opened and the stapedius muscle exposed. HRP solution (0.2-0.3 microliter) was injected into the muscle. Following a survival time of 1-2 days the animals were perfused with a fixative and the brains were removed. Frozen sections were reacted fro the demonstration of HRP using tetramethylbenzidine as chromagen. All labelled neurons were observed not within the traditionally recognised facial nucleus but ventral and medial to the latter. All parent cells (up to 64) lay ipsilateral to the injection. These neurons were remarkably smaller in shape than the neurons in the facial nucleus.

Afferent Pathways↗
PubMedDate not supplied

Stapedius reflex decay in normal hearing subjects.

The fatigue of the stapedius reflex was studied in 100 normal ears. Stimulus frequencies 500 and 1000 Hz were used,and the decrement of the stapedius reflex at 5, 10, and 15 dB above the reflex threshold was estimated. No decrement at all (less than 10% decay 10 sec after the onset of a stimulus 10 dB above the reflex threshold) was present in a majority of the ears. Between 27 and 58% of the ears showed reflex decay depending on variations of different factors such as stimulus frequency, intensity of the stimulus, and the method to register the reflex. Reflex decay was more often seen at 1000 Hz than at 500 Hz stimulus frequency. Reflex decay was also more often seen 5 dB above the reflex threshold than at higher intensity levels. The reflex decay thus observed in normal ears was generally small and did only very occasionally reach values which can be regarded as pathological.

Acoustic Impedance Tests↗
PubMed1980

[Binaural summation of the ipsilateral and contralateral acoustic stapedius reflex (author's transl)].

The binaural summation of the simultaneous contra- and ipsilateral acoustic stapedius reflexes was examined in 20 normal-hearing patients. In these patients, the effect of summation was most pronounced with subthreshold intensities. A contralateral reflex was increased by ipsilateral intensities 8 db below threshold. A reflex could also be elicited by binaural intensities which were contra- and ipsilaterally 4 db below threshold. As a result of our studies, we recommend a revision of the definition of a positive Metz-recruitment. Because of possible binaural summation effects, the absolute value of the contralateral stapedius reflex threshold should not exceed 105 db HL in spite of possible sensorineural hearing loss.

Acoustic Impedance Tests↗
PubMed1983

[New stapedius reflex patterns].

Basing on the stapedius reflex patterns, published by Jerger, the author reports about stapedius reflex patterns of patients who had recovered from facial palsy. The reflex patterns of these patients did not correspond to those which could be expected; they did not reflect the damaged and the undamaged branch of the acousticofacial reflex band, but showed patterns indicating a lesion of the brainstem. On the basis of these findings the question arises whether the lesion in Bell's palsy is really peripheral or central.

Facial Paralysis↗
PubMed1983

Identification of the motoneurons innervating the stapedius muscle in Gallus gallus: a horseradish peroxidase study.

The location of the stapedial motoneurons in Gallus gallus was investigated by means of the retrograde transport of HRP, injected into the stapedius muscle. The labeled neurons are located in both the ventral and dorsal divisions of the VII nerve nucleus, in a lateral and ventral position respectively, facing the superior olivary nucleus. The neurons are distributed in two size classes. The functional implications of these findings are discussed, in relation both to the absence of the acoustic stapedial reflex in birds and to the functional properties of the stapedius muscle.

Animals↗