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PubMed1980

Jaw muscle activity during chin-tapping.

Electromyographic (EMG) activity was recorded from the masseter, the anterior temporal and the anterior digastric muscle on the right side of ten dental students when taps were administered upwards or downwards to the chin. The experiment was performed both with relaxed jaw muscles and with contracting depressor muscles. Pairs of intracutaneous platinum hook electrodes were used for the masseter and temporal muscles while concentric needle electrodes were inserted into the anterior digastric muscles. The mean latency of the jaw-jerk elicited in the relaxed masseter muscle when tapping downwards on the chin was 7.8 msec and in the temporal muscle 8.4 msec. The corresponding values of the latency during jaw opening against resistance from the investigator's finger was 8.2 msec and 9.0 msec. During upward tapping on the chin recordings from the anterior digastric muscle showed obvious changes in EMG activity, the latency ranging from 13 to 34 msec. Thus, compared to the latency of the jaw-jerk in the masseter and temporal muscles, which contain numerous muscle spindles, recordings from the anterior digastric muscle, where muscle spindles are thought to be either lacking or few in number, showed no signs of a monosynaptic reflex.

Adult↗
PubMed1978

Reflex activation of extrinsic tongue muscles by jaw closing muscle proprioceptors.

Depression of the mandible in the decerebrate cat induced retraction of the tongue. The mechanism of this jaw-tongue reflex was analyzed by recording electromyographic activity from the temporal and styloglossal muscles as representative masticatory and extrinsic tongue muscles, respectively. Tongue muscle activity was elicited when the mouth was opened beyond 10 degrees while the threshold for the masticatory muscle activities was around 2 degrees. Neither sectioning of the masseteric nerve nor anesthetization of the temporomandibular joint capsule affected the tongue muscle activities. In contrast, exfoliation of the temporal muscle from the temporal bone greatly reduced the effects of jaw depression. When the isolated coronoid process of the mandible was stretched downwards, activities were evoked in the tongue muscle. Repetitive electrical stimulation at a frequency of 100 Hz to the temporal nerve activated the tongue muscle, and the threshold of reflex activation was between 1.3 and 1.7 times threshold of the temporal nerve. Vibratory stimuli applied to the mandible at frequencies below 130 Hz were also effective in evoking tongue muscle activity. However, when the frequency was above 135Hz, tongue muscle activity was not induced although activity was still observed in the masticatory muscles. These results indicate that the jaw-tongue reflex is elicited mainly by proprioceptors in the temporal muscle, and that they may probably be the Golgi tendon organs and the secondary endings rather than the primary endings of the muscle spindle.

Animals↗
PubMed1988

cAMP, myosin dephosphorylation, and isometric relaxation of airway smooth muscle.

The temporal relationships among increases in adenosine 3',5'-cyclic monophosphate (cAMP) levels, myosin dephosphorylation, and relaxation were investigated to clarify the mechanisms of airway muscle relaxation. Canine tracheal muscles isometrically contracted (82% of maximum force) with 10(-6) M methacholine were relaxed by adding either 4 x 10(-7) M atropine or 4 x 10(-5) M forskolin. Atropine had no effect on cAMP levels; myosin phosphorylation and force, however, decayed at the same rates and these two parameters returned to their basal pre-methacholine levels within 5 min. Forskolin treatment results in about a 10-fold increase in cAMP levels; myosin phosphorylation and force decayed simultaneously to their respective steady-state levels by 10 min but neither parameter returned to its pre-methacholine level. The addition of forskolin to muscles maximally contracted with 10(-4) M methacholine leads to about a 30-fold increase in cAMP levels. However, there are minimal decreases in myosin phosphorylation and force in these muscles. Thus myosin dephosphorylation appears to be essential for airway muscle relaxation, whereas an increase in cAMP in the absence of myosin dephosphorylation is insufficient to cause relaxation. Moreover, myosin dephosphorylation appears to be a common step in the cAMP-independent and cAMP-dependent mechanisms for airway muscle relaxation.

Animals↗
PubMed1999

Ca2+ -induced Ca2+ desensitization of myosin light chain phosphorylation and contraction in phasic smooth muscle.

The temporal relationship between Ca2+ -induced contraction and phosphorylation of 20 kDa myosin light chain (MLC) during a step increase in Ca2+ was investigated using permeabilized phasic smooth muscle from rabbit portal vein and guinea-pig ileum at 25 degrees C. We describe here a Ca2+ -induced Ca2+ desensitization phenomenon in which a transient rise in MLC phosphorylation is followed by a transient rise in contractile force. During and after the peak contraction, the force to phosphorylation ratio remained constant. Further treatment with cytochalasin D, an actin fragmenting agent, did not affect the transient increase in phosphorylation, but blocked force development. Together, these results indicate that the transient phosphorylation causes the transient contraction and that neither inhomogeneous contractility nor reduced thin filament integrity effects the transient phosphorylation. Lastly, we show that known inhibitors to MLC kinase kinases and to a Ca2+ -dependent protein phosphatase did not eliminate the desensitized contractile force. This study suggests that the Ca2+ -induced Ca2+ desensitization phenomenon in phasic smooth muscle does not result from any of the known intrinsic mechanisms involved with other aspects of smooth muscle contractility.

Animals↗
PubMed1986

Correlations between the cross-sectional area of the jaw muscles and craniofacial size and shape.

In adult human subjects, the correlations were determined between the cross-sectional areas of the jaw muscles (measured in CT scans) and a number of facial angles and dimensions (measured from lateral radiographs). Multivariate statistical analysis of the skeletal variables in a group of 50 subjects led to the recognition of six independent factors determining facial shape, i.e., cranial base length, lower facial height, cranial base flexure and prognathism, facial width, mandibular length, and upper facial height. In 29 of these subjects, the cross-sectional areas of the jaw muscles were determined, and correlations between these areas and the scores on the above-mentioned factors were calculated. It appeared that the cross-sectional areas of temporalis and masseter muscles correlated positively with facial width, whereas the areas of masseter and both pterygoid muscles did so with mandibular length. It has been shown experimentally that a decrease in jaw muscle size in various animals likewise has an effect on facial width and mandibular length. Our results therefore support the hypothesis that in man too the jaw muscles affect facial growth and partly determine the final facial dimensions. They also hint that the role of each muscle is different.

Adult↗
PubMed2006

Anomalous muscle adjacent to temporalis.

Temporalis is an important muscle of mastication. In recent years, there has been controversy about its detailed anatomy, and claims have been made about the existence of a variant muscle, sphenomandibularis. The present case report describes an anomalous muscle within the infratemporal fossa distinct from both temporalis and sphenomandibularis. Functionally the muscle could pull the buccinator laterally as the jaw closes.

Aged↗
PubMed1985

Form and function of the masticatory musculature in the tree sloths, Bradypus and Choloepus.

The tree sloths, Bradypus and Choloepus, show unusual masticatory specializations, compared to each other and to other mammals. Both have an incomplete zygomatic arch with descending jugal process, a complex superficial masseter, a large temporalis and medial pterygoid musculature, and a lateral pterygoid with two heads. In Choloepus the deep masseter and zygomaticomandibularis are typical when compared to other mammals. However, in Bradypus there is an ascending jugal process from which enlarged and vertically oriented deep masseter and zygomaticomandibularis muscles originate. Although both sloths are folivores, the anterior teeth in Choloepus are caniniform, while those of Bradypus have lost such elongation. In both sloths the glenoid cavity is similarly located; however, in Bradypus the craniomandibular joint is raised above the occlusal plane, and the pterygoid flanges are elongated. Prediction of the evolutionary sequence of cranial changes from Choloepus-like (primitive) to Bradypus-like (derived) morphology is based upon the most parsimonious model of masseter-medial pterygoid complex changes for masticatory efficiency improvement. The model proposes that the condylar neck in Bradypus was elongated and that this single change predicated a series of other structural changes. Mandibular movement patterns in both sloths showed anteromedially directed unilateral power strokes as in other mammals. Puncture-crushing, tooth-sharpening, and chewing cycles are distinct in Choloepus, less so in Bradypus. The masticatory rate is slow in sloths compared to other mammals of similar body size, averaging 590 ms per cycle for Choloepus and 510 ms for Bradypus.

Animals↗
PubMed1992

Jaw-muscle activity in ferrets, Mustela putorius furo.

Electromyographical (EMG) activity was recorded bilaterally from the masseter and temporalis muscles of alert ferrets (Mustela putorius furo) during mastication and crushing. Electromyographic activity was also recorded during biting while a bite-force transducer placed between the carnassial teeth registered forces ranging from 1.5 to 48.8 N. Linear regression analysis demonstrates that temporalis and masseter EMG activity are linearly related to bite force. Electromyographic activity from the balancing-side muscles is nearly equal to EMG activity of the working-side muscles during bone crushing with the carnassial teeth. It is hypothesized that a high percentage of balancing-side muscle activity in ferrets can be recruited during carnassial biting because the postglenoid process prevents ventral displacement of the working-side mandibular condyle.

Animals↗
PubMed1988

Expression of fiber type specific proteins during ontogeny of canine temporalis muscle.

The canine masticatory muscles contain a unique adult fiber type composition and different contractile protein isoforms than do adult limb muscles. To determine when these characteristic proteins are expressed during development, samples from canine temporalis (masticatory) and pectineus (limb) muscles were compared between 55 days gestation and 60 days postpartum by histochemical, biochemical, and immunocytochemical analysis. At 55 days gestation and 3 days postpartum, both muscles contained identical histochemical type 2C fibers, native myosin isozymes, and myosin light and heavy chains. By 14 days postpartum, fiber-type expression in these muscles diverged, with resultant formation of type 1 and type 2M fibers in the temporalis muscle and type 1 and 2A fibers in the pectineus muscle. The distinctive myosin isoforms, light chains, and heavy chain of the temporalis muscle were also expressed 2 weeks postpartum. Based on the methods used in this study, we conclude that (1) the temporalis muscle develops from embryonic fibers that initially contain a myosin indistinguishable from embryonic limb muscle fibers, suggesting they have a common precursor, and (2) the myosin light chains and heavy chain unique to the temporalis muscle are initially expressed 2 weeks postpartum.

Animals↗
PubMed1988

Immunocytochemical and electrophoretic analyses of changes in myosin gene expression in cat posterior temporalis muscle during postnatal development.

Changes in myosin gene expression during the postnatal development of the homogeneously superfast kitten posterior temporalis muscle were examined using immunocytochemical techniques supplemented by pyrophosphate gel electrophoresis and gel electrophoresis-derived enzyme linked immunosorbent assay (GEDELISA) of myosin isoforms. The antibodies used were polyclonals directed against the heavy chains of superfast and foetal myosins and monoclonals against the heavy chains of slow and fast myosins. The fibres of the posterior temporalis in the newborn kitten stained almost uniformly with the anti-foetal myosin antibody and the largest of these fibres stained strongly for superfast myosin. A subpopulation of fibres staining for superfast myosin also stained lightly for slow myosin. These slow staining fibres were evenly distributed in the centres of muscle fibre bundles, reminiscent of primary fibres in limb fast muscle. During subsequent development, slow myosin staining disappeared and superfast myosin replaced foetal myosin so that by 50 days the muscle was virtually homogeneously superfast as in the adult. Fast myosin was never expressed at any stage. It is proposed that fibres staining transiently for slow myosin are superfast primary fibres which are homologous to fast primary fibres recently described in regions of limb muscles devoid of slow fibres in the matured animal. Other jaw-closing muscles have significant populations of slow fibres in the mature animal and it is postulated that there exists in these muscles a second class of jaw primary fibres, the slow primary fibres, in which slow myosin synthesis would be sustained in the adult. It is suggested that the myogenic cells of jaw-closing and limb muscles are of two distinct types preprogrammed to express different muscle genes.

Animals↗
PubMed1984

Canonical correlations between masticatory muscle orientation and dentoskeletal morphology in children.

In order to identify associations between the orientation of the superficial masseter and temporalis muscles and dentoskeletal morphology in a sample of fifty-five children with various malocclusions, eight muscle-orientation variables (relative to the occlusal plane) and twenty-three dentoskeletal variables were evaluated from lateral head films. The thirty-one measurements were reduced to six muscle-orientation and sixteen dentoskeletal variables by a principal component analysis. Three canonical correlations were identified between the muscle orientation and dentoskeletal variable groups at the 0.05 level of significance and canonical loadings were determined for each set of variables. The first canonical correlation (r1 = 0.931) represents a growth-related correlation factor between the masticatory muscle insertion positions relative to the occlusal plane and the dimensional and positional changes of craniofacial structures during growth. The second canonical correlation (r2 = 0.846) may account for an operational artifact in the geometric measurement process, and the third canonical correlation (r3 = 0.813) suggests an association between superficial masseter muscle orientation relative to the occlusal plane and mandibular form. This report confirms the usefulness of multivariate statistical methods to extract latent associations between muscle orientation and craniofacial morphology; the results obtained suggest a contribution from the geometric orientation of the masticatory muscles to the development and maintenance of the dentoskeletal system.

Adolescent↗
PubMed1985

An electromyographic analysis of the temporalis function of normal occlusion.

Electromyographic (EMG) activity was recorded from the anterior, middle, and posterior regions of the temporalis muscle in ten subjects with normal occlusion of the teeth and with the mandible at rest and during exertion of increased biting force, using bipolar intramuscular electrodes. Results show that the posterior part of the temporalis muscle maintains the mandibular posture. Although there is no statistically significant difference in EMG recordings between the three divisions of the temporalis muscle during intercuspal biting, individual variations in EMG pattern exist. During exertion of increased biting force the EMG activity increases proportionally in all parts of the muscle. During retruded biting force the posterior temporalis predominates. The EMG activity of the temporalis muscle is correlated to the form and position of the mandible.

Action Potentials↗
PubMed1982

Contractile properties of the muscles of mastication of rhesus monkeys (Macaca mulatta) following increase in muscle length.

The hypothesis was tested that increasing the resting length of the masseter and temporalis muscles by a bite-opening appliance with or without detachment and re-attachment of the masseter would not affect the contractile properties of these muscles. Appliances opened the bite of 10 adult female monkeys 20 mm. Five received the appliance alone (Group A); five received the appliance and in addition the masseter was detached and re-attached (Group ADR). Comparisons were made 48 weeks later. Small bundles of fibres were excised from the masseter and temporalis muscles of experimental animals and from 8 control animals. Isometric and isotonic contractile properties were measured in vitro and fibre classification and fibre areas were determined histochemically. No significant differences were observed within either masseter or temporalis muscles between animals in Groups A and ADR. In both groups, the bundles of fibres from the masseter had prolonged contraction and relaxation times compared to control masseter muscles but no difference was observed in the percentage of Type II fibres. As detachment and re-attachment had no significant effect on morphological or physiological characteristics, other than those due to lengthening, this procedure may be useful in decreasing the passive tension induced when orthognathic surgery increases muscle length. The significant prolongation of the contractile response of the masseter is similar to the adaptation induced by long-term stimulation at low frequency.

Adaptation, Physiological↗
PubMed1988

Analysis of electromyographic signals in human jaw closing muscles at various isometric force levels.

The effect of sustained isometric contraction on surface electromyograph (EMG) and force signals derived from these muscles was examined. Premolar-molar region force was measured with a small unilaterally positioned force transducer. Subjects produced and sustained 25, 50, 75 and 100 per cent isometric force levels, and measurements were made at the beginning and end of these efforts. There was no significant change in the resulting EMG/force ratio at any of the force levels. The EMG signal did exhibit a significant shift in its frequency both as the force level increased and during the sustained effort. Neuromuscular fatigue, when defined as a change in the EMG/force ratio, was not demonstrated even though there was a consistent change in the frequency of the EMG signal.

Adult↗
PubMed1980

Quantitative electromyographic diagnosis of myofascial pain-dysfunction syndrome.

The slopes of the V/T curves of masticatory muscles were determined in patients with MPD syndrome, and the changes in the slopes were observed prior to and during electrical muscle stimulation and splint therapy. The slopes of the V/T curves in patients with MPD syndrome were significantly steeper than those of the healthy subjects. In patients with MPD the slopes were decreased by electrical muscle stimulation of moderate duration and by insertion of the splint. These findings suggest that the most simple procedure for the diagnosis of MPD syndrome is to compare the slopes in MPD patients with those of healthy subjects. The observation of the changes in slopes during electrical muscle stimulation and splint therapy permits a more quantitative diagnosis of MPD syndrome. It also permits a quantitative measurement of improvement of symptoms in patients with MPD syndrome.

Adult↗