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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↗
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↗
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↗
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↗
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↗
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↗
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↗
PubMed1987

Asymmetries in the acoustic reflexes of the cat stapedius muscle.

Electromyographic activity (EMG) was used to monitor contractions of the stapedius muscle evoked by both ipsilateral and contralateral sound in ketamine-anesthetized or decerebrate cats. After the onset of a continuing tone, stapedius EMG often had bursts of activity at regular intervals; similar bursts were also observed in the EMG from the tensor tympani muscle. Plots of the r.m.s. amplitude of stapedius-EMG versus sound level usually had a steep rising phase (small dynamic range) and a plateau at high sound levels. For sound stimulation at 1 kHz, the crossed stapedius reflex had a lower maximum amplitude (ave. amplitude ratio: 0.37) and a higher threshold (ave. 8 dB) than the uncrossed reflex. Since the uncrossed reflex evokes considerably more stapedius EMG than does the crossed reflex, it probably produces correspondingly greater changes in middle-ear sound transmission.

Acoustic Stimulation↗
PubMed1979

The noise protection effect of the stapedius reflex.

The purpose was to estimate the attenuation and protection effect of the acoustic stapedius reflex on the inner ear. The acoustic stapedius reflex was recorded by means of extratympanic manometry (ETM). This method was used, as it is able to differ between the stapedius and the tensor reflex. Patients with unilateral Bell's palsy were investigated during palsy time and after recovery. The amplitude of the contralateral acoustic stapedius reflex was used as a relative measure of the excitation of the cochlea on the affected side. The attenuation effect, 20 dB above the reflex threshold, was approximately 15 dB for all tested patients. After the ETM investigation a temporary threshold shift was shown on the affected side (average 34 dB). The hearing threshold on the healthy side was unchanged. Thus the attenuation effect of the acoustic stapedius reflex protects the inner ear from an acoustic damage. A protection effect of the tensor tympani was not demonstrated.

Audiometry↗
PubMed1977

Normal values of the ipsilateral acoustic stapedius reflex threshold.

It is frequently taken for granted that the acoustically evoked stapedius reflex is bilaterally symmetrical. Contrary to this, Møller described an asymmetry of the acoustic stapedius reflex with an ipsilaterally 2--14 dB lower threshold. The determination of normal values of the ipsilateral acoustic stapedius reflex threshold with a large number of patients is difficult as the intensity of the stimulus depends considerably on the position of the probe in the acoustic meatus and is therefore not defined with sufficient accuracy. For this reason we determined the values of the ipsilateral threshold by applying a stimulus sound of high intensity to the deaf ear of unilaterally completely deaf patients with a normal headphone, which can be calibrated much more accurately. After subtraction of the individual cross hearing loss, the exact ipsilateral intensity was obtained. By this method a stapedius reflex could be evoked with 49 of the 62 patients. By mathematical consideration of the data of the positive cases, as well as the maximum available intensities with the negative cases, determination of the median value of the ipsilateral threshold was possible: at 0.5 kHz 59 dB; at 1kHz 62.5 dB; at 2 kHz 67 dB; at 4 kHz approx. 67 dB. The difference between ipsilateral and contralateral stapedius reflex threshold was in the range of 15 dB. A new definition of the normal value for the ipsilateral measured Metz recruitment appears necessary.

Auditory Threshold↗
PubMedDate not supplied

Eardrum displacement following stapedius muscle contraction.

Simultaneous monitoring in human subjects on the same ear of eardrum displacement by tympanomanometry, and impedance with the electroacoustic bridge, provided information concerning contraction of the stapedius muscle and its effect on eardrum displacement. Extensive control procedures were employed to elicit only the stapedius reflex; lower intensity auditory stimulation, electrocutaneous stimulation of the homolateral external ear canal, and anesthetization of nerves leading to the tensor tympani. Following these procedures the following results were obtained: (1) Extremely small biphasic and monophasic eardrum movements were seen in the stapedius--only ear to auditory and electrocutaneous stimulation; the form of the response was much less predictable to auditory stimulation. (2) At high sound intensities relatively large inward and biphasic movements of the eardrum occurred in the normal ear, unquestionably due to contraction of the tensor tympani. These results were further validated in a group of stapedectomized ears, without the stapedius but with normal tensor tympani. (3) Biphasic responses did not occur in the tensor tympani--only ear, only monophasic inward responses. (4) Upon air-jet stimulation to the orbit of the eye, these subjects had an accentuated tensor response in that large inward movements of the eardrum occurred as compared with those in normal ears, suggesting that there is an alteration of the tensor response by the presence of the stapedius muscle. Estimates of the actual eardrum displacement were calculated based on a model of the external ear canal and eardrum.

Acoustic Stimulation↗
PubMed1992

Stapedius reflexes to electrical stimulation in the rabbit for the assessment of hearing.

The possibility of using electrically induced stapedius reflexes as a means of objective hearing evaluation was investigated in the rabbit as an animal model. The contralateral stapedius reflex to acoustic and electrical stimulation was measured in anesthetized rabbits. For electrical stimulation, the middle ear was opened surgically and stimulation was applied by a monopolar electrode placed at or into the round window. Contraction of the middle ear muscle was monitored by digital sampling and averaging of the impedance changes in the contralateral ear. Acoustically evoked reflexes were recorded within expected limits despite anesthesia. The level of the electrical stimulus was raised until mass reflexes of the neck muscles were observed. A contralateral stapedius reflex to electrical stimulation could not be demonstrated. In our experiment, monopolar electrical stimulation at the round window could not elicit contralateral stapedius reflexes.

Acoustic Stimulation↗
PubMed1979

The effect of the stapedius reflex on attenuation and poststimulatory auditory fatigue at different frequencies.

The effect of the stapedius reflex on attenuation was measured in patients with unilateral facial palsy (Bell's palsy) and stapedius muscle paralysis. Poststimulatory auditory fatigue was determined in the same patients and in a group of normal test subjects with a normal bilateral stapedius muscle function. The attenuation for a 0.5 kHz tone was found to begin at the reflex threshold, to increase about 7 dB per a 10 dB increase in the stimulus tone and to reach a maximum in the vicinity of 20 dB. When a 2.0 kHz tone was used, no attenuation of note appeared until the sound had risen to about 10 dB above reflex threshold. The attenuation reached a maximum at a little less than 10 dB. A properly functioning stapedius muscle significantly reduced poststimulatory auditory fatigue at 0.75 kHz while at 3.0 kHz, it could do so only if it was stimulated into action by low-frequency noise.

Acoustic Impedance Tests↗
PubMed1979

Physiological activation of the stapedius muscle in Gallus gallus.

The function of the avian middle ear muscle was investigated in the chicken, Gallus gallus (domesticus). The avian species offers excellent conditions for study of middle ear muscle function since it possesses a single middle ear muscle, the stapedius, which is located extracranially. Electromyograms (EMG), measurements of impedance change, and volume change in the middle ear cavity were used to assess the muscle's activity. The results showed that the middle ear muscle of Gallus does not exhibit an acoustic reflex. However, the stapedius is regularly activated during the animal's own vocalization. Measurements of the EMG and volume change showed the stapedial activity to increase systematically with increases in the vocal sound level. The use of volume change as a measure of stapedius function was found to be highly suitable in the present experiments in that it allows for measurements of the magnitude of the stapedius contraction without altering the intact physiological state of the middle ear, and is insensitive to the ambient noise and vocal sounds, that hamper the impedance technique.

Acoustic Impedance Tests↗
PubMed1979

Contraction properties and functional morphology of the avian stapedius muscle.

The influence of the stapedius muscle contraction on middle ear volume and acoustic impedance was investigated in the chicken, Gallus gallus. The time course of twitch responses to electrical stimulation (measured as volume and impedance changes) was found to be largely independent of the stimulus voltage, having a contraction time of 22 ms and a half-relaxation time of 22 ms. The stapedius muscle was therefore characterized as a fast twitch muscle. Slow contraction properties were also revealed: A summation of responses to repetitive stimulation beginning at 2.5 Hz and a slow decline to baseline were seen in volume and impedance change recordings. The morphological characteristics were consonant with that of a homogeneously fast muscle: Only fibres with high ATPase activity were identified and no fibres with "en grappe" or multiple innervation were observed. The slow characteristics were suggested to be due to visco-elastic elements in the middle ear. The chicken stapedius muscle is suggested to be analogous to both the stapedius and the tensor tympani of mammals.

Acoustic Impedance Tests↗