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PubMed1978

The biphasic acoustic reflex: a new perspective.

The anatomic, neurologic, and physiologic characteristics of the middle ear structures have created confusion concerning the nature of the intraaural muscle reflex. After reviewing the relevant literature, we correlated this information with our studies of human temporal bones and computer analyses of the acoustic reflex responses of individuals with normal hearing. Our hypothesis is that although the stapedius is the initiator of the reflex and the primary contributor to ossicular chain fixation, the tensor tympani is responsible for the major observed response. The negative deflection present in normals tested on the impedance bridge is caused by the stapedius, whereas the large positive deflection is the result of the tensor tympani contraction. We postulate that proprioceptive feedback mechanisms located within the stapedius muscle and tendon permit and/or initiate tensor tympani contraction during acoustic stimulation.

Acoustic Stimulation↗

PubMed1983

An immunohistochemical study of the middle ear muscles of some carnivores and primates, with special reference to the IIM and slow-tonic fibre types.

The middle ear muscles of several species of carnivores (cat, dog, fox, ferret and stone-marten) and some New World monkeys (Callithrix, Saimiri) and Old World monkeys (Cercopithecus, Macaca) were examined. The fibre type compositions of these muscles were determined by a combination of the standard histochemical myofibrillar ATPase method, and immunohistochemical techniques using myosintype-specific antisera. Immunohistochemically slow-tonic fibres were found in the stapedius muscles of only two carnivores, the ferret and stone-marten. In all the carnivores and the New World monkeys, tensor tympani muscle contained IIM, slow-tonic and slow-twitch fibres, but in the Old World monkeys it resembled stapedius muscle, and contained only Type I (slow-twitch) and IIA fibres. Thus, because all the species examined had IIM fibres in the jaw-closer muscles, this means that the common embryological origin of tensor tympani muscle and the jaw-closers does not necessarily result in tensor tympani muscle containing this fibre type even though IIM fibres occur only in first branchial arch muscles. This fact, together with other species differences in the fibre type composition of these muscles, shows that there is no typical composition of middle ear muscles in general, and suggests that the differences are related to very different functional requirements.

Animals↗

PubMed1990

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 anesthesia. 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.

Animals↗

PubMed2002

Detection of intracochlear and intracranial pressure changes with otoacoustic emissions: a gerbil model.

Increased intracranial pressure (ICP) is known to affect the phases and levels of lower-frequency distortion-product otoacoustic emissions (DPOAE) in a characteristic manner suggestive of an increase in the stiffness of the stapes system, likely in relation to an attendant increased intracochlear pressure (ICoP). DPOAEs may thus provide an easy non-invasive means of gaining access to the otherwise elusive ICoP. However, the mechanisms by which DPOAEs actually relate to ICoP are unclear and may involve changes in the stiffness of the annular ligament, stapedius muscle and even some indirect contributions of other parts of the middle ear such as the tensor tympani. A systematic study of the role of each middle-ear element on ICoP-to-DPOAE relationships as a function of frequency was undertaken in gerbils under direct control of ICP via an intracranial catheter (from 0 to 500 daPa). After the bulla was widely opened, the tendons of the stapedius and tensor tympani muscles were severed in turn. A standard electroacoustic analog model of the middle ear was used for predicting the forward and reverse middle-ear transfer-functions changes under different experimental manipulations and their consequences on DPOAEs. The observed DPOAE changes chiefly consisted in a phase-lead peaking around 2.15 kHz in closed-bulla, and 1.2 kHz in open-bulla conditions. It was proportional to ICP increase provided ICP exceeded a threshold of about 50 daPa. The profiles of DPOAE shifts matched those derived from the premise that ICoP mainly induced a change in the stiffness of the stapes system. The possible involvement of the stapedius muscle was ruled out by the absence of any effect of cutting its tendon so that the intrinsically non-linear stiffness of the annular ligament must have been the main factor. A relatively minor contribution from the tensor tympani was observed, possibly in relation to the detection of ICoP-induced displacement of the ossicular chain by neuromuscular spindles.

Animals↗

PubMedDate not supplied

Middle ear muscle activity during vocalization in normal speakers and stutterers.

Although it has been established that the middle ear muscles contract prior to vocalization, it is not known which muscle is mainly responsible for this activity. Also, there have been contradictory reports about whether this activity in stutterers differs from that of normal speakers. To tackle these questions, extratympanic pressure measurements prior to vocalization are reported for normal speakers and stutterers. This measure allows activity deriving from the two middle ear muscles to be differentiated and for the temporal course to be followed more accurately than by impedance measurement. To establish which muscle is primarily responsible for the pre-vocalization activity, the measured pressure changes prior to vocalization are compared with activity measured in tasks known to involve the stapedius or tensor tympani alone. These data show that in normal speakers and stutterers, the activity that is measured prior to vocalization resembles that of the tensor tympani. Contrary to other reports, there is no difference between normal speakers and stutterers in the time course of this activity.

Humans↗

PubMed1984

Freeze-replica observations of guinea pig middle ear muscles.

The histological characteristics of the middle ear muscles, Musculus tensor tympani and M. Stapedius, of the guinea pig were studied using freeze-fracturing technique. No gap junction was observed but the tight junction was found in the tensor tympani muscle, possibly between muscle cells. No distinct difference was found between the size distributions of the apertures and caveolae on the fracture face of the sarcolemma of the two kinds of muscles.

Animals↗

PubMedDate not supplied

Bony auditory tube and otitis media with effusion.

The author has for 25 years manually probed the malleus handle for indications of middle ear pathology. Dissection of the bony auditory tube (BAT) and isthmus comprised 120 fresh autopsy and 26 anatomically prepared temporal bones. The semicanal lamina was not completely ossified in all infants and children and 52% of adults. The tensor tympani muscle was edematous and prolapsed into the superior portion of the BAT in eight ears with otitis media with effusion. Infants and children have the tendon of the tensor tympani muscle inserting into the neck of the malleus at an angle of 60 degrees or greater, possibly explaining the relatively large muscle bulk. It is suggested from these autopsy findings that the BAT and isthmus lumen is a functional 2-way channel for air superiorly and mucus streaming inferiorly. Manual palpation of the cartilaginous auditory tube in infants did not suggest malacia.

Adolescent↗

PubMed1986

Central auditory function in a hearing-impaired white mouse.

The dysfunction of the stria vascularis in the viable dominant spotting mutant mouse results in the reduction or the absence of the endocochlear potential. However, these mutants respond to an intense acoustic stimulus with a Preyer reflex (pinna twitch). This study used 14C autoradiography and electromyography to investigate central auditory responses in this mutant. There were three main findings: autoradiography demonstrated an increase in the metabolic rate within each of the central auditory nuclei during noise exposure compared with silence; electromyographic recordings indicated that there was no tensor tympani muscle reflex; the mutants were found to be susceptible to audiogenic seizures. It was concluded that the central auditory pathway of the viable dominant spotting mutant could be activated despite the abnormal strial function. Absence of the tensor tympani muscle reflex, together with auditory deprivation, might contribute to the susceptibility to audiogenic seizures.

Acoustic Stimulation↗

PubMedDate not supplied

Dynamic tympanometry.

Tympanometry was performed under the contraction of the middle ear muscles (dynamic tympanometry). A tympanogram of lesser compliance was observed under a stapedius reflex which was produced by contralateral acoustic stimulation. In patients with reversed (downward) stapedius reflex, the dynamic tympanogram showed either a higher peak amplitude or a shift of conventional tympanogram to the negative pressure side. Voluntary contraction of the tensor tympani produced a lesser compliance with positive pressure, whereas there was an apparent increase of compliance with negative pressure in the external auditory meatus. A shift of the dynamic tympanogram to the negative pressure side was interpreted as being due to contraction of the tensor tympani muscle. Dynamic tympanometry may also be utilized as a recording of reflex decay.

Acoustic Impedance Tests↗

PubMedDate not supplied

Localization of motoneurons innervating the Eustachian tube muscles in cat.

The localizations of the motoneurons supplying the tensor tympani muscle (TTM), tensor veli palatini muscle (TVPM) and levator veli palatini muscle (LVPM) were determined by retrograde transport of horseradish peroxidase (HRP) in the cat. TTM motoneurons were found ipsilaterally outside the trigeminal motor nucleus in an area just ventral to it. TVPM motoneurons were distributed mainly in the ventral part of the ipsilateral trigeminal motor nucleus. They were more compactly distributed in the rostral part of the nucleus than in the caudal part. LVPM motoneurons were found in the ipsilateral nucleus ambiguus. There were no HRP-labelled cells in the contralateral nucleus ambiguus.

Animals↗

PubMed1988

[The fixation theory of middle ear muscle function].

The still unidentified function of the middle ear muscles might be explained by the fixation theory. However, this idea, which is being favoured nowadays, namely, that the action of the muscles controls the position of the ossicles for optimal transmission, has never been investigated experimentally except for a few studies 50 and 100 years ago. In 25 temporal bone preparations, the air pressure-induced movements of the ossicles were microscopically measured, at first without and then with a 10 g. load on the tensor tympani muscle and a 5 g. load on the m. stapedius. The fixation hypothesis could not be confirmed, since with increasing pressure the movement-reducing effect of the middle ear muscle pull decreased. This inability of the muscles to compensate higher static air pressures is also demonstrated theoretically. A 10 g. pull of the tensor tympani muscle can only withstand a suction of 30 mm H2O in the ear canal. Hence, further evaluations are discussed that seem to enforce our hypothesis of the joint-preserving function of the middle ear muscles. The required antagonism of the pull of the muscle is accomplished by the change of the direction of movement in the gliding incudo-malleal joint.

Air Pressure↗

PubMed1986

Effect of middle ear modification on umbo vibration. Human temporal bone experiments with a new vibration measuring system.

The effects of aditus blockage, decrease of tympanic cavity volume, and resection of the tensor tympani muscle on umbo displacement were studied in human temporal bones using a new non-contacting video measuring system. This system, combined with stroboscopic illumination, allowed measurement of umbo vibration down to 0.3 micron in the 0.1- to 4.5-kHz frequency range for a constant 124-dB sound pressure level at the tympanic membrane. Aditus blockage caused a mean increase of 5.4 dB with a peak at 2.8 kHz and a mean decrease of 3.4 dB below 1.6 kHz. Decrease of the tympanic cavity volume by 30% to 42% showed an improvement of 2.2 dB in the 1.4- to 3-kHz range and a similar loss below 1 kHz. Resection of the tensor tympani muscle produced a slight improvement of 1.7 dB at 1.8 kHz.

Bone Conduction↗

PubMed1989

[Movement of the ear ossicles by middle ear muscle contraction].

Up to now, the function of the middle ear muscles has mainly been investigated from an acoustical point of view. However, the primary function of the middle-ear muscles, namely the induction of ossicular movements, has never been investigated systematically. For this purpose, the displacements of the ossicles, as induced by simulated muscle contractions, were measured microscopically in 13 fresh temporal bone preparations. Both muscles move all ossicles. The tensor tympani muscle pulls the umbo inwards about 100 microns. Due to the gliding motion in the malleus-incus joint, the stapes is thus pushed inwards by at the most 10 microns and, additionally, displaced anteriorly, antagonistic to the pull of the stapedius muscle. This muscle pulls the stapes backwards, lifting the anterior crus outwards and pushing the posterior crus inwards. This reduces the pressure on the cochlear fluids significantly as compared to our former concepts of the movement of the footplate, tilting outwards as a whole around an axis at the posterior pole. Furthermore, this outward displacement of the stapes is not prerequisite for the outward movement of the malleus-drumhead complex, which typically appears at the contraction of the stapedius muscle. The basic motion of the stapes is the movement backwards, which is 5 times greater and which matches the anatomic direction of the pull of the stapedius muscle. This explains the otherwise unlogical position of the stapedius muscle parallel to the footplate. Due to the gliding movement in the malleus-incus joint, this motion changes at the umbo into outward rotation, counteracting the tensor tympani muscle.(ABSTRACT TRUNCATED AT 250 WORDS)

Ear Ossicles↗

PubMed1989

[The functional significance of the suspending ligaments of the ear ossicle chain].

The contraction of the tensor tympani muscle has not enough force to stabilise the drum membrane-malleus complex against a negative pressure in the external ear nor against a hyperpressure in the middle-ear, as in sneezing, Valsalva's manoeuvre, etc. The ossicular ligaments must therefore perform this task. It was shown in experiments with fresh temporal bone preparations that the superior malleolar ligament diminishes the pressure-induced displacements of the malleus. This proves that this often neglected ligament has true functional significance. The most important ligament, which retains the malleus against an outward displacement, however, is the sturdy connective tissue between the cochleariform process and the malleus' handle, enveloping the tendon of the tensor tympani muscle and crossing the middle-ear cleft together with the tendon. These connective tissue strands are much too strong for a simple sheath of tendon, as can be seen histologically. In consideration of the fact that the functional significance surpasses the function of a pure tendon sheath, this ligamentous structure can be called the malleo-cochleariform ligament.

Ear Ossicles↗

PubMed1990

The innervation of the middle ear muscles of the rat.

The innervation of the tensor tympani muscle and the stapedius muscle in the rat was studied. This was done by acetylcholinesterase in toto staining of the tympanic bullae and of muscles dissected separately, acetylcholinesterase staining of serial cross-sections of the muscles, silver impregnation of serial sections of complete tympanic bullae, serial semithin sections stained according to Laczko & Levai and electron microscopy of both muscles. The gross innervation of the muscles and the relation to other nerves in the bulla are described. It is shown that both muscles are innervated by very thin nerve fibres which form a well-organised elaborate network in the muscles, with very short branches that connect with motor endplates. Electron microscopically there are indications that the endplates in the stapedius muscle seem to enable faster activation of the muscle fibres than those of tensor tympani muscle. No morphological evidence for any sensory innervation of the muscles could be detected in the muscles themselves, in the connective tissue related to the muscles, or in the contents of the bulla tympanica. It is postulated that the afferent input of the acoustic middle ear muscle reflex is sound alone and that sensory information from the muscles themselves or from other structures in the tympanic bulla do not contribute to the reflex.

Animals↗

PubMed1993

Immunohistochemical localization of intracellular Ca-ATPase in outer hair cells, neurons and fibrocytes in the adult and developing inner ear.

Intracellular isoforms of the enzyme Ca-ATPase were identified in the inner ear by immunostaining paraffin sections with a polyclonal antiserum against rabbit cardiac muscle Ca-ATPase. In the adult cochlea, intense staining was present at the lateral border of outer hair cells in regions corresponding with the distribution of the subsurface cisternal system. Other cell types containing high levels of Ca-ATPase were skeletal muscle fibers in the tensor tympani, vascular smooth muscle, spiral ganglion neurons and subpopulations of fibrocytes in the limbus, spiral ligament and underlying vestibular neurosensory epithelium. In neonatal gerbils, staining of tensor tympani muscle fibers was observed at 4 days after birth and approached adult levels by 8 days after birth. Ca-ATPase was first detected in other cell types between postnatal days 12 and 14 but immunostaining still remained well below the intensity seen in adults at 20 days after birth. The demonstration of abundant calcium pumps in the subsurface cisternae confirms the role of this organelle as an intracellular reservoir for Ca2+ in outer hair cells. The presence of high levels of Ca-ATPase in spiral ganglion neurons and in fibrocytes specialized for ion transport points to a role for the enzyme in regulating the activity of other cell types of importance to normal hearing.

Animals↗

PubMed2003

Effects of non-invasive ventilation on middle ear function in healthy volunteers.

OBJECTIVES: To evaluate the effects of non-invasive ventilation (NIV) with facial mask or helmet on middle ear (ME). DESIGN. Prospective, randomised study. SETTING: University hospital. PARTICIPANTS: Ten healthy subjects randomly allocated in two groups of five subjects each. INTERVENTIONS: NIV for 1 h, with helmet (group H) or facial mask (group M). Flow-triggered pressure support was 10 cmH(2)O, PEEP 5 cmH(2)O, FiO(2) 0.21. MEASUREMENTS AND RESULTS: Impedenzometry was performed before NIV and 5 min after NIV ended; it was repeated 60 min later. In group H the acoustic compliance increased after NIV from 2.0+/-.6 ml to 2.3+/-.6 ml ( P<.01), suggesting that the tympanic membrane became less stiff; 1 h later the compliance returned to basal values (2.0+/-.7 ml); in group M the compliance was unaffected (from 2.0+/-.5 ml to 2.0+/-.4 ml; 1.9+/-.4 ml 1 h later). The acoustic reflex, i.e., the contraction of the stapedial muscle in response to an auditory stimulus, involving the acoustic and facial nerves, was also evaluated during impedenzometry at 250 Hz, 500 Hz, 1,000 Hz, and 4,000 Hz; no significant change of the threshold was observed. CONCLUSIONS: The tympanic membrane is tighten by the tensor tympani and a reversible loosening suggests muscle fatigue in response to the application of intermittent positive pressure applied to the external ear during NIV with helmet. The loss of tensor tympani protective action could theoretically predispose the middle and inner ear to mechanical damage during NIV with helmet, suggesting the use of protective devices (ear plugs) in selective cases requiring long-term, high-pressure treatment.

Adult↗

PubMed1996

Effects of stapedial arch fractures on conductive hearing loss and stapedial reflexes.

OBJECTIVE: It has been stated in the clinical literature that stapedial fractures could produce a significant conductive hearing loss while leaving the contralateral stapedial reflex intact. The objective of this study is to test this hypothesis in an animal model. DESIGN: Nine hooded rats underwent acoustic-stapedial reflex (ASR) and cochlear microphonic (CM) threshold determinations before and after middle ear surgery. An argon laser was used to divide the tensor tympani tendon, the anterior stapedial curs, and the posterior stapedial crus, sequentially. The initial functional measures were repeated after each laser procedure to document its effect. RESULTS: Dividing the tensor tympani tendon and the anterior stapedial crus had variable and small effects on ASR and CM thresholds. Division of the second (posterior) crus eliminated stapedial reflexes and produced a significant hearing loss. CONCLUSIONS: This study refutes the hypothesis that fracture of one (anterior) stapedial crus will significantly alter ossicular sound transmission, but it supports the hypothesis that measured stapedial reflexes would not be significantly altered by a single crus fracture. Therefore, the surgeon exploring an ear for a conductive hearing loss with an intact contralateral stapedial reflex should look carefully for another source of the hearing loss if finding only a single stapedial arch fracture.

Animals↗