Stapedius Research Articles

Acoustic-reflex responses in patients with insulin-dependent diabetes mellitus

Purpose: patients with insulin-dependent diabetes mellitus (IDDM) are especially susceptible to microangiopathic complications such as nephropathy, retinopathy, and neuropathy. Microangiopathic changes are also the most important findings in histopathologic studies of the inner ear and central nervous systems in diabetic subjects. No previous studies have measured acoustic-reflex latencies (ARL) or amplitudes (ARA) in patients with IDDM. ARL and ARA reflect the function of the acoustic-reflex arch. Furthermore, possible changes in the tympanic membrane, ossicular chain, and stapedius muscle may affect the shape of acoustic-reflex. Subjects and Methods: Acoustic-reflex thresholds, latencies, and amplitudes were studied in 53 patients with IDDM and 42 randomly selected nondiabetic control subjects, aged between 20 and 40 years, using the Madsen Model ZO 73 Impedance Bridge (Madsen Electronics, Copenhagen, Denmark). Subjects with an abnormal tympanic membrane, conductive hearing loss, and known cause for hearing impairment eg, noise damage, were excluded from the study. Results: There were no differences between control and diabetic subjects in the contralateral acoustic-reflex thresholds. In contrast, patients with IDDM had longer ARLs and decreased ARAs compared with those of control subjects. ARA amplitude had linear correlation with the amplitude of tympanogram, whereas ARL had no linear correlation with auditory brainstem latencies in the same study subjects. Acoustic-reflex responses in insulin-dependent diabetic patients were not associated with the duration of diabetes, metabolic control, microangiopathy, or neuropathy. Concluslons: Prolonged ARLs and decreased ARAs in patients with insulin-dependent diabetes are probably caused more by the stiff middle ear system than disturbances in the brainstem.

Ossification patterns of the tympanic facial canal in the human fetus and neonate

Dehiscences in the bony facial canal are comparatively common in the human adult. The highest incidence occurs in the tympanic segment of the facial nerve near the region of the oval window. Thirty-three fetal temporal bones, ranging from 16 to 40 weeks' gestation, and four from 1, 2, 4 and 12 weeks' postpartum neonates, were studied to evaluate the normal patterns of ossification of the fallopian canal of the tympanic facial nerve segment in the human. The tympanic facial nerve segment elongates three-fold during this period (from 1 mm to 3 mm). The ossification starts at 21 weeks' gestation anteriorly from apical otic ossification centers and at 26 weeks from canalicular ossification centers near the stapedius muscle. The ossification proceeds in an anterior-to-posterior direction as two periosteal shelves of bone surround the facial nerve. The superior periosteal bony ledge contributes 75% of the circumference of the fallopian canal. The anterior ossification center forms over 83% of the fallopian canal length. The two centers fuse post partum near the region of the oval window. The anatomic location of the facial nerve, nerve branching, and neural vasculature precede ossification. In 80% of the paired temporal bones, this ossification pattern appears to be symmetrical. The patterns and incidence of bony dehiscences within the tympanic fallopian canal segment can be explained by these observations. This study demonstrates that fallopian canal dehiscences are not congenital anomalies, but variations of normal developmental anatomic processes.

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.

Three‐dimensional reconstruction of the temporal bone from a case of e trisomy syndrome

Computer-assisted three-dimensional reconstruction was performed from histologic sections of the left temporal bone removed from a case of E trisomy syndrome. The reconstructions included structures such as the bony and membranous labyrinths, ossicles, ossicular muscles, tympanic membrane, and facial and eighth nerves. The structures could be observed individually or simultaneously in combination. Prominent abnormalities observed in these reconstructions included enlargement of the utricle, absence of the posterior semicircular canal, slight hypoplasia of the cochlea, anomaly of the stapes, abnormally shaped stapedius muscle, abnormal course of the facial nerve, and flattening of the tympanic membrane. The results were useful for the visual and stereoscopic understanding of abnormal configurations and the spatial orientations of these abnormalities.

Urinary incontinence in the community--analysis of a MORI poll.

To investigate the prevalence of urinary incontinence among people living at home, their responses to it, and its emotional and social effects. Random sample of 4007 adults interviewed in their own homes. Random sample of 178 constituency sampling points throughout Great Britain. 1883 men, 2124 women aged 30 and over. Responses to questionnaire. 6.6% (125) men and 14.0% (297) women had been incontinent of urine at some time--2.8% (52) men and 7.5% (159) women in the previous two months and 61% (124) of these for more than four years. 52% (108) had consulted their general practitioner at the onset of incontinence and a further 31% (65) later. Doctors commonly took a urine sample (163, 54%), referred the patient to a specialist (127, 42%), and prescribed tablets (109, 36%); only 22% (66) carried out an abdominal, rectal, or vaginal examination. Patients were not embarrassed in seeing their doctor and most thought they were treated sympathetically. 60% (265) of all those affected were concerned or worried about their incontinence, and in almost half incontinence limited their daily social activities. More people with incontinence seem to be consulting their doctors about it than has been found in previous studies, but the procedures carried out by general practitioners still seem to be suboptimal. Urinary incontinence has a profound effect on the day to day lives of most of those who suffer from it.

Detection of Hearing Impairment with the Acoustic Stapedius Reflex

The acoustic stapedius reflex (ASR) is the sound-evoked contraction of the stapedius muscle. The ASR is mediated by a neural network, receiving its afferent input from the VIIIth cranial (auditory) nerve and sending its efferent output to the VIIth cranial (facial) nerve. Several centers in the brain stem comprise the central portion of the reflex pathway. The stapedius muscle in each ear responds to ipsilateral, contralateral, and binaural stimulation. The normal ASR threshold is 90 to 95 dB SPL for tones and 70 to 75 dB SPL for wideband noise. In ears with sensorineural hearing loss, ASR thresholds are elevated more for wideband noise than for tones. These bandwidth-related changes form the basis for detection of hearing loss from ASR data. A number of methods have been proposed which differ in the nature of the outcome. Some try to quantitatively estimate hearing loss, whereas others categorize outcomes as pass or fail. In general, methods that attempt quantitative estimation of hearing loss do so at the expense of higher error rates. With adequate recording techniques, the ASR has been shown to effectively detect hearing losses exceeding 30 dB in adult subjects. Although ASR recording in newborns requires a higher probe frequency than the commonly used 226 Hz, ASR thresholds in newborns appear to be similar to those in adults. Limited information exists on the use of the ASR for detection of hearing loss in the infant population. With adequate attention to methodological requirements of testing infants, the ASR may offer a cost-effective method for the early detection of hearing loss.

Ultrastructure of Nerve Endings in the Stapedius Muscle of the Squirrel Monkey

The stapedius muscle of the squirrel monkey (Saimiri sciureus) was studied electron microscopically with regard to neuromuscular junctions, muscle-tendon junctions and tendons. Two types of neuromuscular junctions were identified. The first type which was predominant in number showed well-developed primary and secondary synaptic clefts. They were almost the same with those of other mammalian skeletal muscles. The second type showed a flat-shaped junction with fewer secondary synaptic clefts. Muscle-tendon junctions were characterized by many interdigitations between the muscle fibers and tendon. The tendon was composed of collagen fibers, approximately 70-100 nm in diameter. Muscle spindles were not present, while nerve endings resembling the Golgi tendon organ were found adjacent to the tendon and the muscle-tendon junctions. These findings suggest that a feedback system may exist and regulate the fine contractile function of this muscle.

Familial stapes superstructure fixation

Congenital stapes superstructure fixation was found in a mother in both ears and her daughter in one ear. The head of the stapes was fixed to the pyramid by a bony bar which lay immediately superior to a normal stapedius muscle. Removal of the bony bar resulted in normal hearing, which has been maintained. We believe that these are the first reported cases of this abnormality.

Hypothetical roles of middle ear muscles in the guinea-pig

The attenuation of incoming sounds induced by acoustic reflex triggering was evaluated from the cochlear microphonic response to test tones in 45 awake guinea-pigs. Although control electromyographic measurements proved that the stapedius muscle was contracting, neither impedance changes nor attenuation induced by contralateral reflex-eliciting sounds were detectable in 30 cases out of 45. For ipsi- and bilateral stimulations, an attenuation was detectable for 7 guinea-pigs out of 10. In the guinea-pigs for which a reflex-induced change was found on CM, the mean attenuation was weak i.e. of the order of 2 dB at 20 dB above reflex threshold. These results were quite different from those obtained during control experiments in the rabbit for which CM attenuation was much larger. However, large attenuations associated with middle ear muscle contractions were found in the guinea-pig in other circumstances, i.e. during self-vocalization or when spontaneous muscle contractions occurred during anaesthesia. It is concluded that middle ear muscle can have several different functions, and that even when it exists, attenuation of loud sounds might not be their primary role.

Effect of contralateral acoustic stimulation on active cochlear micromechanical properties in human subjects: dependence on stimulus variables

1. Outer hair cells (OHCs) have active micromechanical properties that are thought to be the origin of evoked otoacoustic emissions (EOAEs). In the present study, click-evoked otoacoustic emissions were recorded in humans with or without various contralateral acoustic stimulations. A previous study, concentrating on contralateral stimulation with broadband noise, had shown a decrease of the EOAE amplitude in humans. Results support a role for the efferent system in cochlear mechanics; indeed, medial efferent neurons of the olivocochlear bundle terminate on the OHCs. To obtain a better understanding of the medial efferent system functioning in humans, the present study looked at the contralateral suppressive effect as a function of stimulus parameters. 2. The study of the input-output function of the EOAE amplitude with and without a 50-dB SPL contralateral broadband noise showed that the suppressive effect was equivalent to a mean reduction of 3.77 dB. 3. For the EOAEs to tone pips, the contralateral suppressive effect was strongest when the contralateral ear stimuli were narrow bands that were centered around the central EOAE frequency. This frequency specificity disappeared for contralateral narrow band noise levels greater than 50 dB SPL. 4. The contralateral suppressive effect was also observed with transient contralateral sounds (nonfiltered clicks). Significant reductions of the EOAE amplitude were seen with contralateral click levels as low as 17.5 dB SL. Above this level, the EOAE amplitude decreased as the contralateral stimulus level increased. This effect was still present in subjects without any stapedial reflex, but absent in total unilateral hearing-loss subjects. Therefore this suppressive effect is unlikely to be due to alteration of the middle ear function or to transcranially conducted sound. 5. When the contralateral interclick interval exceeded 14.2 ms. the suppressive effect was smaller. With contralateral stimulus level maintained subjectively constant, the effect was found to disappear when the interclick interval was greater than 49.9 ms. A saturation of the contralateral suppressive effect was observed for click rates greater than 70/s (interclick interval less than 14.2 ms). 6. Our study confirms and specifies the contralateral sound suppression effect on cochlear mechanisms in humans, assessing the equivalent reduction, showing a frequency specificity and extending these findings to contralateral transient sounds. Any influence of the acoustic crosstalk was eliminated. A role played by middle ear muscles cannot be absolutely ruled out but is not necessary to produce such a contralateral suppressive effect (the effect being found in subjects after surgical removal of the stapedius muscle) and could not explain the frequency specificity.(ABSTRACT TRUNCATED AT 400 WORDS)

一側顔面痙攣症におけるアブミ骨筋の病態

Hemifacial spasm (HFS) is characterized by involuntary contructions of the mimetic muscles, and it is usually accompanied by synkinesis. When spasm and synkinesis spread to the stapedius muscle, tympanic noise (tinnitus due to the stapedius muscle contruction)arise. In the present study,57 patients with HFS who had normal tympanogram and stapedius reflex were examined by impedance audiometry to determine the spasm and synkinesis of the stapedius muscle before and after microvascular decompression. Only 18patients complained of tympanic noise, but 54 showed the stapedius muscle spasm and synkinesis. After operation, in all cases tynpanic noise disappeared and 50 patients showed neither spasm nor synkinesis of the stapedius muscle. During the operation,5 of these patients were also recorded by electrical stimulation on supraorbital nerve using needle electrodes inserted through the external auditory meatus. Synkinetic responses of the stapedius muscles could be recorded in 4 cases, and these abnormal potentials disappeared after intraoperative procedures. These results suggests that spasm and synkinesis spreads to the stapedius muscle even in patients without tynpanic noise, and these disappear during the microvascular decompression operation.

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.

Enzymes of transmitter and energy metabolism in cat middle ear muscles

Activities of the enzymes choline acetyltransferase (ChAT) and acetylcholinesterase (AChE), which metabolize the neuromuscular transmitter acetylcholine, and malate and lactate dehydrogenase (MDH and LDH), enzymes of oxidative and glycolytic energy metabolism, respectively, were measured in the middle ear muscles of the cat. For comparison, the same enzyme activities were measured in extraocular muscle tissue and in three hindlimb muscles rich in either slow oxidative (soleus), fast glycolytic (white part of vastus lateralis), or fast oxidative glycolytic (plantaris) muscle fibers. ChAT and AChE activities were much higher in middle ear muscles than in hindlimb muscles, consistent with a denser neuromuscular innervation, as in extraocular muscles. By contrast, MDH and LDH activities were remarkably low in the middle ear muscles, lower than in any of the hindlimb muscles or the extraocular muscles. Denervation of the stapedius muscle by peripheral transection of the facial nerve resulted in decreases in all four enzyme activities without associated changes in the tensor tympani. Surgical ablation of the peripheral facial nerve supply to the stapedius muscle appears to be a feasible option for producing its denervation. The results suggest some rather specialized chemical characteristics for the middle ear muscles.

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 rooster 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.

Enzymes of transmitter and energy metabolism in rat middle ear and extraocular muscles

To further investigate the peculiar characteristics of the middle ear and extraocular muscles, compared to the extensively studied skeletal muscles of the limbs, activities of enzymes of transmitter and energy metabolism were measured in homogenates of these muscles from albino and pigmented rats. These activities were compared to those for a masticatory muscle and for three hindlimb muscles chosen for their preponderance of either slow oxidative, fast glycolytic, or fast oxidative glycolytic fibers. Activities of the neuromuscular transmitter enzymes choline acetyltransferase and acetylcholinesterase were relatively very high in the extraocular and middle ear muscles. The activity of malate dehydrogenase, an enzyme of oxidative energy metabolism, was as high in the extraocular, masticatory and stapedius muscles as in the oxidative hindlimb muscles, but was lower in tensor tympani. The activity of lactate dehydrogenase, an enzyme of glycolytic energy metabolism, was remarkably low in both middle ear muscles. The results are consistent with high innervation density in the extraocular and middle ear muscles, and highly oxidative metabolism in the extraocular and stapedius muscles. Metabolic differences between the stapedius and tensor tympani suggest a relatively more active role for the former in the function of the rat middle ear.

Electrophysiological aspects of the middle ear muscle reflex in the rat: Latency, rise time and effect on sound transmission

The latency, the rise time and the influence of the acoustic reflex on sound transmission were investigated in the adult rat during ketamin anaesthesia. This was done by recordings of the cochlear microphonics (CM) and electromyographic (EMG) recordings of the reflex responses of the tensor tympani muscle. The acoustic reflex was elicited by contralateral acoustic stimuli of which the intensity and frequency was varied. Ipsilaterally, the effect on sound transmission was determined by estimating the change in amplitude of the CM's of ipsilateral administered subliminal stimuli. It was shown that both the tensor tympani muscle and the stapedius muscle contribute in the reflex. The latency as well as the rise time of the reflex determined by CM recordings showed to be short (minimal values: 12 and 7 ms respectively). The mean latency of the tensor tympani muscle reflex, measured by EMG, was about 7 ms. The attenuation of 0.25–8 kHz tone bursts upto 115 dB SPL is limited to a mean maximum of 15 dB SPL. The maximal attenuation was shown to occur at 1 kHz. Frequencies above 2 kHz appeared to be the best elicitor of the middle ear muscle reflex.

Immitance Audiometry

Immitance audiometry is a safe, simple, reliable, and relatively objective method of determining middle-ear function that provides advantages for examining the difficult patient because minimal cooperation is needed. Acoustic-immitance measurements obtain sophisticated data that give us valuable information about the middle ear mechanism as a whole. It can be used in a quiet office environment. Immitance audiometry can confirm a doubtful otoscopic diagnosis and screen for ear disease. There are limitations to observer reliability with otoscopy, which has good sensitivity but poor specificity, in contrast to immitance audiometry. The tympanogram can be classified into four different patterns on the basis of its characteristics. These patterns are diagnostic, distinguishing normal function from various types of middle ear pathology. Immitance audiometry has very high sensitivity and specificity. The acoustic reflex, a contraction of the stapedius muscle following an intense auditory stimulus, can be valuable in determining a conductive hearing loss and many other otologic diagnoses. As a screening tool, immitance audiometry is most valuable in populations at risk for middle ear effusion, primarily those aged 7 months to 5 years. Significant improvements in measurements of ear function also allow us to be more precise in the diagnoses of otosclerosis, perforation of the tympanic membrane, ossicular discontinuity, facial nerve dysfunction, and brain stem disorders.

Anatomic Variations of the Chorda Tympani Canal

The anatomic variations of the facial recess are of interest in certain otosurgical procedures. The medial border of the recess is the mastoid portion of the facial nerve canal, and the lateral border is the bony canal of the chorda tympani. These two structures were investigated in 64 polyester casts of temporal bone specimens. The point of exit of the chorda tympani canal from the facial canal was assessed together with the angle, formed between these two nerve channels. As a further way of describing the spaciousness at the facial recess, the distance between the sulcus of the stapedius muscle and the chorda tympani canal was evaluated.

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.

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.