SEARCH · PubMed Health

Results for “Stapedius”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 19 recordsLinked to original sources

PubMed1991

Ultrastructural changes of stapedius muscle and stapedius branch nerve endings in otosclerotic patients.

We studied in the electron microscope 12 stapedius muscles and stapedius branches of the facial nerve excised from otosclerotic patients who underwent stapedectomy for hearing restoration. Almost all of the stapedius, muscles demonstrated morphological alterations, such as accumulation of lipids and osmiophilic material, dilatation of the sarcoplasmic reticulum, sarcoplasmic invaginations of the nuclei and accumulation of fibroblasts and satellite cells on the surface of the muscle fibers. The stapedius branch of the facial nerve demonstrated a marked loss of myelinated fibers. Most of the unmyelinated or demyelinated fibers were surrounded by thick processes of the Schwann cell. The axons showed a paucity of neurofilaments and the nerve endings showed a rough dilatation of the cisternae of the smooth endoplasmic reticulum as well as accumulation of osmiophilic material. The morphological alterations of the stapedius muscle and the stapedius branch of the facial nerve in otosclerosis suggest that in addition to the lesions of the bone at various areas of predilaction, a substantial pathological alteration of the muscle and nerve fibers also occurs in the middle ear adjacent or distal to otosclerotic foci, a fact that enlarges the concept of the pathological spectrum of the disease.

Facial Nerve↗

PubMedDate not supplied

The diagnostic value of stapedius reflex and stapedius reflex exhaustion in myasthenia gravis.

Authors studies impedance, stapedius reflex thresholds and stapedius muscle exhaustion on 31 ears of 16 MG patients. Investigations were carried out using GSI 33 computer-assisted middle ear analyzator. Stapedius reflex threshold values were increased in 93% of patients. Stapedius exhaustion was observed in 71% of patients. After the administration of the reversible cholinesterase inhibitor Mestinon (60 mg pyridostigmin bromide), reflex threshold decreased and exhaustion occurred in only 50% of cases. Authors review the literature in context with the audiometric diagnostics of MG and also recommend the use of these methods in more complicated ocular and bulbar cases of MG.

Acoustic Impedance Tests↗

PubMed1986

Stapedius reflex after stapedectomy with preservation of the stapedius tendon.

Stapedectomy with preservation of the stapedius tendon was carried out on 25 patients. Impedance measurements confirm that the stapedius muscle does function thereafter. The results of stapedius reflex tests are shown by an x-y plotter on an Amplaid 702 for permanent records. The compliance of the drum is also increased by about 50 per cent. The characteristics of the reflex are reported and discussed as well as its clinical value. There is better speech discrimination and no pseudorecruitment.

Adult↗

PubMed2002

Measuring the electrical stapedius reflex with stapedius muscle electromyogram recordings.

Previous studies have demonstrated a correlation between cochlear implant recipients' comfort levels (C level, upper limit of dynamic range of stimulation) and the contralateral electrical stapedius reflex (ESR) threshold, detected by acoustic impedance change. However, the utility of the approach is limited because many recipients have no detectable impedance change. The goals of this study were to investigate the utility of the stapedial electromyogram (EMG) for estimating onset and strength of the ESR. Ketamine-anesthetized guinea pigs were implanted with Nucleus electrode arrays and stimulated with biphasic current pulse trains (250 pps) via a Cochlear Corporation CI24M stimulator. Typical EMG recordings (obtained with bipolar microwire electrodes) contained easily detectable unit potentials up to 300 microV in amplitude. Growth response curves (obtained from threshold-crossing counts or rms of the EMG signal) were typically monotonic with dynamic ranges spanning 700 microA or 8 dB. Based on adaptation and temporal properties, the stimulus protocol (500 ms duration with 4-5 s interstimulus intervals) was adequate for producing independent responses. The data presented are consistent with ESR characteristics (acoustic impedance technique) of cochlear implant recipients and with EMG properties of acoustically stimulated guinea pigs. Use of the EMG for characterizing the ESR may eventually be applied to human cochlear implant recipients as a guide in setting the upper limit of the dynamic range.

Action Potentials↗

PubMed1983

[Stapedius reflex. 1. Stapedius reflex threshold and recruitment].

UNLABELLED: The stapedius reflex threshold and pure tone threshold of 173 patients with normal hearing and cochlear disorders were examined (using Madsen ZO 73 equipment). CONCLUSIONS: 1. The aetiology of the cochlear hearing disorders does not influence the stapedial reflex threshold. 2. A linear regression between hearing loss and threshold difference was found in cochlear hearing disorders. 3. No correlation could be found between individual pure tone threshold and stapedial reflex threshold.

Adolescent↗

PubMed1992

Acoustic reflex frequency selectivity in single stapedius motoneurons of the cat.

1. The sound frequency selectivities of single stapedius motoneurons were investigated in ketamine anesthetized and in decerebrate cats by recording from axons in the small nerve fascicles entering the stapedius muscle. 2. Stapedius motoneuron tuning curves (TCs) were very broad, similar to the tuning of the overall acoustic reflexes as determined by electromyographic recordings. The lowest thresholds were usually for sound frequencies between 1 and 2 kHz, although many TCs also had a second sensitive region in the 6- to 12-kHz range. The broad tuning of stapedius motoneurons implies that inputs derived from different cochlear frequency regions (which are narrowly tuned) must converge at a point central to the stapedius motoneuron outputs, possibly at the motoneuron somata. 3. There were only small differences in tuning among the four previously described groups of stapedius motoneurons categorized by sensitivity to ipsilateral and contralateral sound. The gradation in high-frequency versus low-frequency sensitivity across motoneurons suggests there are not distinct subgroups of stapedius motoneurons, based on their TCs. 4. The thresholds and shapes of stapedius motoneuron TCs support the hypothesis that the stapedius acoustic reflex is triggered by summed activity of low-spontaneous-rate auditory nerve fibers with both low and high characteristic frequencies (CFs). Excitation of high-CF auditory nerve fibers by sound in their TC "tails" is probably an important factor in eliciting the reflex. 5. In general, the most sensitive frequency for stapedius motoneurons is higher than the frequency at which stapedius contractions produce the greatest attenuation of middle ear transmission. We argue that this is true because the main function of the stapedius acoustic reflex is to reduce the masking of responses to high-frequency sounds produced by low-frequency sounds.

Acoustic Stimulation↗

PubMed1999

Motoneuron axon distribution in the cat stapedius muscle.

Stapedius-motoneuron cell bodies in the brainstem are spatially organized according to their acoustic response laterality, as demonstrated by intracellular labeling of physiologically identified motoneurons [Vacher et al., 1989. J. Comp. Neurol. 289, 401-415]. To determine whether a similar functional spatial segregation is present in the muscle, we traced physiologically identified, labeled axons into the stapedius muscle. Ten labeled axons were visible in the facial nerve and five could be traced to endplates within the muscle. These five axons had 39 observed branches (others may have been missed). This indicates an average innervation ratio (> or = 7.8) which is much higher than that obtained from previous estimates of the numbers of stapedius motoneurons and muscle fibers in the cat. One well-labeled stapedius motor axon innervated only a single muscle fiber. In contrast, two labeled axons had over 10 endings and innervated muscle fibers spread over wide areas in the muscle. Two of the axons branched and coursed through two primary stapedius fascicles, indicating that the muscle zones innervated by different primary fascicles are not functionally segregated. In another series of experiments, retrograde tracers were deposited in individual primary nerve fascicles. In every case, labeled stapedius-motoneuron cell bodies were found in each of the physiologically identified stapedius-motoneuron regions in the brainstem. These observations suggest there is little, if any, functional spatial segregation based on separate muscle compartments in the stapedius muscle, despite there being functional spatial segregation in the stapedius-motoneuron pool centrally.

Animals↗

PubMed1990

Vocalization-related stapedius muscle activity in different age chickens (Gallus gallus), and its role in vocal development.

The stapedius muscle activity associated with vocalization was analyzed in young and adult roosters. Our results show that remarkable differences in the behavior of vocalization-related stapedius muscle activity exist between these two ages. Unlike young roosters, electrical stimulation in the midbrain of adult cocks yields vocalizations associated with stapedius muscle EMG responses that always show a higher threshold and a longer latency than those of the vocalization induced. Moreover, the maximal amplitude of the stapedius muscle EMG response is consistently lower than that detected in young roosters, despite the fact that the maximal vocalization amplitude of the adult birds is much higher. On the whole our results demonstrate that vocalization-related stapedius muscle activity is strongly reduced in adulthood. The possibility that stapedius muscle may play a role during the vocal development was verified by comparing the crow of normal roosters with that of cocks from which the stapedius muscle had been removed shortly after hatching. Strong differences exist in the amplitude/frequency distribution of the crowing of normal and stapedectomized roosters, suggesting that the stapedius muscle exerts an important role in auditory feedback modulation, and that this feedback is used for normal vocal development.

Aging↗

PubMed1988

Anatomical and functional segregation in the stapedius motoneuron pool of the cat.

1. Electromyographic activity (EMG) is detectable in the feline stapedius muscle 6-10 ms after the onset of an intense sound presented to either ear. Stapedius reflexes evoked by ipsilateral and contralateral sound were measured electromyographically before and after brain stem lesions were made. In some cases, stapedius motor axons were cut; in others, brain stem regions containing motoneuron cell bodies were destroyed electrolytically. 2. Electrolytic lesions that contacted an anatomically separate cluster of stapedius motoneurons (the ventromedial perifacial group) greatly reduced responses to contralateral sound without noticeably affecting responses to ipsilateral sound. 3. Electrolytic lesions in other brain stem areas had different effects; one appeared to reduce responses to ipsilateral sound selectively, whereas others reduced both responses or had little effect. 4. After subsets of stapedius motor axons were cut at the facial colliculus in the floor of the fourth ventricle, responses to contralateral sound were almost eliminated, while substantial responses to ipsilateral sound remained. 5. The results are consistent with the hypothesis that inputs from the two cochleas are distributed inhomogeneously across the stapedius motoneuron pool in such a way as to produce a segregation of function, with motoneurons in one brain stem region responding preferentially (or exclusively) to contralateral sound and motoneurons in other regions responding preferentially (or exclusively) to ipsilateral sound. This topographic organization of acoustic input to the stapedius motoneuron pool produces a "central partitioning" in the acoustic stapedius reflexes similar in some respects to the partitioning observed in proprioceptive spinal reflexes.

Acoustic Stimulation↗

PubMed1990

Central distribution of the stapedius motoneurons in the rat--a study of topographical anatomy and HRP transport experiments.

A detailed anatomical description of the stapedius muscle area in the rat was given and on this basis the central distribution of the neurons innervating the stapedius muscle was investigated by the horseradish peroxidase transport method. The stapedius muscle showed a circum-pennate structure with a para-centrally located tendon and was composed of about 500 muscle fibers. It contained no special sensory structures and was innervated by a single branch of the facial nerve consisting of myelinated axons. Horseradish peroxidase experiments provided the following findings. The stapedius muscle received few sensory components. The stapedius motoneurons resided in the brainstem ipsilaterally in a column-like region ventromedial to the facial motor nucleus. Some of them (up to 6%) were scattered rostrally as far as the level of the facial nerve exit. Almost all the stapedius motoneurons showed fusiform morphology with significantly smaller mean diameter and lesser size variation than the facial nucleus motoneurons. The number of the stapedius motoneurons per animal on one side amounted about 150 which was about the same as that of axons in the stapedius nerve. Their axons except for those of rostrally scattered ones shared the intramedullary route with axons of the facial nucleus motoneurons.

Animals↗

PubMed1989

Neuronal organization of the stapedius reflex pathways in the rat: a retrograde HRP and viral transneuronal tracing study.

The location of stapedius motoneurons in the rat was determined with horseradish peroxidase (HRP) retrograde tracing techniques. After injection of free HRP or wheat germ agglutinin-horseradish peroxidase (WGA-HRP) in the stapedius muscle on one side, labeled neurons were seen ipsilaterally in a region ventromedial to the rostral half of the facial motor nucleus (VII), extending rostrally to the caudal part of the superior olivary complex (SOC). These labeled neurons, located outside the SOC and facial motor nuclei themselves, constitute the pool of stapedius motoneurons, in agreement with previous descriptions for other species. In order to identify the origin of some inputs to the stapedius motoneurons, injections of herpes virus suis were performed in the stapedius muscle. After replication in the motoneurons, the viruses are transported transneuronally to some premotor neurons, as previously reported in other systems. The presence of the virus was detected by immunofluorescence in neurons corresponding to the stapedius motoneurons labeled with HRP or WGA-HRP. In addition, infected neurons were seen bilaterally at the level of the SOC, in the mediotrapezoid region, where no labeled cells were observed following HRP or WGA-HRP injections in the stapedius muscle. These neurons were considered as infected transneuronally and therefore providing inputs to the pool of stapedius motoneurons. No virus could be detected in cochlear nucleus neurons. These data are consistent with previous observations in the rabbit based on lesion experiments, suggesting that neurons at the level of the SOC are involved in the reflex arc of middle ear muscles.

Animals↗

PubMed1994

[Effect of anesthesia on the intraoperative elicited stapedius reflex].

Evaluation of the intraoperative electrically evoked stapedius reflexes during cochlear implant surgery has two purposes: (1) The functioning of the device and the peripheral auditory pathways can be proven immediately and (2) The data of reflex threshold can be used for the prediction of later threshold (T)- and maximum comfortable (C) levels. This is especially useful for the later fitting of the speech processor in very young children. When trying to use the stapedius reflex data for the prediction of T- and C-levels it must be considered that during surgery the drugs used for general anaesthesia influence the values of the stapedius reflex. Depending on the drug, the stapedius reflex threshold can be increased or the reflex can even be totally blocked. This is not only due to relaxants but also to anaesthetics. To investigate this influence we first determined the acoustically evoked stapedius reflex threshold in normal hearing adults under general anaesthesia with 7 different anaesthetics without additional relaxation. It was found that especially with Dormicum and Brevimytal the stapedius threshold increased only very lightly or did not change at all. In a second investigation the electrically evoked stapedius reflex thresholds were obtained in adults who underwent a cochlear implant surgery using the same anaesthetics for anaesthesia. The intraoperatively evaluated reflex data were compared with postoperatively obtained data. It was found that both reflex thresholds were similar if evaluated in Dormicum or Brevimytal anaesthesia. This suggests that only with the use of the right anaesthetics the data of the electrically evoked stapedius reflex obtained intraoperatively can be used for predicting T- and C-levels.

Anesthesia, General↗

PubMed1985

Number and distribution of stapedius motoneurons in cats.

Cell bodies of stapedius motoneurons were identified by retrograde transport of horseradish peroxidase (HRP) following injections into the stapedius muscle. Large injections were made in an attempt to label all stapedius motoneurons. To control for labeling of non-stapedial neurons resulting from spread of HRP, we determined the locations of brainstem neurons labeled by HRP applied to the facial nerve, the chorda tympani nerve, the auricular branch of the vagus nerve, the tensor tympani muscle, and the cochlea. In three cats analyzed in detail, 1,133-1,178 neurons projecting to the stapedius muscle were identified. Arguments are given which suggest that in these three cats all stapedius motoneurons were labeled. The labeled stapedius neurons may all be motoneurons because they all stain positively for acetylcholinesterase and have medium-coarse Nissl bodies. Most stapedius motoneurons were located around the motor nucleus of the facial nerve. Staphedius motoneurons were also found near the descending limb of the facial-nerve root, in the peri-olivary neuropil, and in the reticular formation with the ascending fibers of the facial-nerve root.

Animals↗

PubMed1989

Brainstem facial-motor pathways from two distinct groups of stapedius motoneurons in the cat.

To determine the brainstem origins and axonal routes of stapedius motoneurons, we labeled motoneurons by injecting cat stapedius muscles with horseradish peroxidase. Some injections were made in normal cats and some in cats in which the middle segment of the internal facial genu had been cut. By tracing labeled axons and by comparing the locations of labeled cell bodies in normal and lesioned cats, we divided stapedius motoneurons into two groups: "perifacial" and "accessory." Perifacial stapedius motoneurons have cell bodies located around the motor nucleus of the facial nerve and axons which follow the classical course of facial motor axons through the internal genu of the facial nerve. Accessory stapedius motoneurons have cell bodies near the descending facial motor root and axons which ascend to the rostral tip of the internal facial genu, abruptly reverse direction, and then join the descending facial motor root. The sharply hooked course of axons of accessory stapedius motoneurons is similar to the course of axons from other accessory nuclei of cranial nerves V-VII. Our present results, with those of McCue and Guinan (J. Neurophysiol. 60:1160-1180, '88), demonstrate that cats have two groups of stapedius motoneurons which can be separated anatomically by the locations of their cell bodies or by the courses of their axons, and which, on the average, have different response properties.

Animals↗

PubMed1995

Speech discrimination in patients with Bell's palsy and a paralysed stapedius muscle.

The contraction of the stapedius muscle results in a frequency dependant attenuation of sound through the middle ear. Idiopathic facial nerve paralysis (Bell's palsy) usually results in a paralysis of the stapedius muscle. This prospective study included 119 patients presenting with Bell's palsy over an 18-month period. After applying exclusion criteria, 80 patients with normal pure-tone audiograms underwent speech audiometry. This was performed on presentation and after recovery of the facial nerve palsy. Fifty-six patients (70%) with an absent stapedius reflex showed marked 'roll-over' from means of 98-49% on their speech audiogram. This resolved completely with recovery of the facial nerve palsy and return of the stapedial reflex. To determine whether this effect was due primarily to the paralysis of the stapedius muscle or to an associated polyneuropathy, a second study on six normal patients was done. These patients had both ears (12 in total) tested with speech filtered to simulate a paralysed stapedius muscle. This resulted in a mean 'roll-over' from 90.9 to 59.9%. The magnitude of this roll-over (31%) was only two-thirds of that seen in Bell's palsy patients (49%) with the difference between these means statistically significant (P < 0.05). This suggests that Bell's palsy, usually considered a mononeuropathy, involves certain of the auditory fibres of the eighth nerve and is a polyneuropathy. Stapedius function is important in speech discrimination at higher levels of sound intensity such as speech in noise and severing the stapedius tendon in stapes surgery may affect speech discrimination after successful surgery.

Adult↗

PubMed1989

Intracellularly labeled stapedius-motoneuron cell bodies in the cat are spatially organized according to their physiologic responses.

This study examines whether the locations of stapedius-motoneuron cell bodies are correlated with their responses to sound. Single-unit recordings and injections of horseradish peroxidase were made in axons of stapedius motoneurons in the fascicles which run from the facial nerve to the stapedius muscle in the cat. Single units were characterized physiologically by their responses to ipsilateral, contralateral, and binaural sounds. Labeled cell bodies (N = 28) were found in all of the brainstem regions previously identified as containing stapedius motoneurons. Motoneurons characterized as having similar response properties had cell bodies in relatively circumscribed locations. Most (eight of 12) motoneurons excited by sound in either ear had cell bodies in a narrow band around the facial nucleus. Most (seven of eight) motoneurons excited by ipsilateral but not contralateral sound had cell bodies in the cleft between the superior olivary complex and the facial nucleus. All four motoneurons excited by contralateral but not ipsilateral sound had cell bodies located ventromedial to the facial nucleus. The three motoneurons excited only by binaural sound had cell bodies located dorsal to the superior olivary complex. (Two of these were also in the cleft between the superior olivary complex and the facial nucleus.) The cell body of the one motoneuron showing activity in the absence of sound stimulation was located dorsolateral to the facial nucleus. These results show that the cell bodies of stapedius motoneurons with similar electrophysiologic properties tend to have similar locations in the brainstem. The results are consistent with the idea that the stapedius-motoneuron pool is divided into subgroups that are spatially segregated in terms of their patterns of input from the two ears.

Acoustic Stimulation↗

PubMed1993

Acoustic structure of vocalization and stapedius muscle activity during vocal development in chickens (Gallus gallus).

The link between stapedius muscle activity and acoustic structure of vocalization was analysed in cocks of age 20-30 to 90-100 days old. The results show that stapedius muscle activation depends on the acoustic structure of vocalization and changes during vocal development. This dependence was observed in spontaneous calls and in vocalizations elicited by stimulating the mesencephalic "calling area". In 30-day-old cocks stapedius muscle EMG response is never associated with vocalizations with an acoustic energy content which is always distributed at frequencies higher than 2000 Hz. The coupling between vocalization and stapedius muscle activity begins later, when birds produce vocalizations with acoustic energy shifted towards lower frequencies. Overall, stapedius muscle activity is related to a bird's production of high amplitude low frequencies. These results support the hypothesis that the primary role of the stapedius muscle during normal vocal development is to dampen the amplitude of low frequency energy that reaches the cochlea during vocalization.

Aging↗

PubMedDate not supplied

The activity of the stapedius muscle in man during vocalization.

The EMG of the stapedius muscle and visible movements in the stapedius tendon during the subject's own vocalization of an [a:] and during contralateral acoustic stimulation were studied in subjects with eardrum perforation. The threshold for stapedius activity was near the lowest vocal intensity that the subjects could produce. At normal vocal effort the stapedius muscle was activated to about 50% of its maximum value. The EMG often started before the vocal sound, indicating that the stapedius muscle can be activated from the central nervous system as a part of the vocalization process. It is suggested that the contraction of the stapedius muscle during vocalization reduces the masking caused by the low frequency components of the person's own voice even at normal vocal effort and thereby improves intelligibility of simultaneous external speech.

Acoustic Stimulation↗