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PubMed1989

Histological properties and biological significance of pouch in red kangaroo, Macropus rufus.

2 embryos, 4 youngs, 4 older youngs and the pouch of 2 mothers of the red kangaroos were examined. The results obtained are as follows: 1. The initial muscle spindles are already observed light microscopically in the vertebral, dorsal neck and forelimb muscles of the newborn baby and a little bit later in the masticatory muscles of the young of 68 mm in craniorump length and 28 g in body weight. 2. In the skin with less hair lining the inner surface of the pouch, abundant apocrine large sweat glands are observed, especially surrounding the basal region of the nipple and in the pleat formation of the skin. 3. The lactiferous mammary gland is enlarged, the lobules being divided by the interlobular muscle fiber tissue and enwrapped by the muscular capsule. The milk is squirted automatically by the muscle fiber contraction from the gland to the nipple, to which the baby attaches itself. 4. The musculature of the pouch wall is developed to form the sphincter muscle in the pouch orifice. The sphincter muscle plays an important role in conditioning the optimum temperature for the naked baby inside the pouch. 5. The apocrine perfume plays an important role in guiding the baby on the journey to the pouch after birth and the apocrine products also in maintaining the optimum humidity of the pouch to accomodate the baby. 6. During the long period of stay in the pouch, the masticatory and locomotive systems and their neuromuscular mechanism related to the herbivorous mastication become fully established and then the young leaves the pouch to feed on the animal's proper diet.

Abdominal Muscles↗

PubMed2001

Jaw-muscle spindle afferent pathways to the trigeminal motor nucleus in the rat.

Neural pathways conveying proprioceptive feedback from the jaw muscles were studied in rats by combining retrograde and intracellular neuronal labeling. Initially, horseradish peroxidase was iontophoresed unilaterally into the trigeminal motor nucleus (Vmo). Two days later, 1-5 jaw-muscle spindle afferent axons located in the mesencephalic trigeminal nucleus were physiologically identified and intracellularly stained with biotinamide. Stained mesencephalic trigeminal jaw-muscle spindle afferent axon collaterals and boutons were predominantly distributed in the supratrigeminal region (Vsup), Vmo, dorsomedial trigeminal principal sensory nucleus (Vpdm), parvicellular reticular formation (PCRt), alpha division of the parvicellular reticular formation (PCRtA), and dorsomedial portions of the spinal trigeminal subnuclei oralis (Vodm), and interpolaris (Vidm). Numerous neurons retrogradely labeled with horseradish peroxidase from the trigeminal motor nucleus were found bilaterally in the PCRt, PCRtA, Vodm, and Vidm. Retrogradely labeled neurons were also present contralaterally in the Vsup, Vpdm, Vmo, peritrigeminal zone, and bilaterally in the dorsal medullary reticular field. Putative contacts between intracellularly stained mesencephalic trigeminal jaw-muscle spindle afferent boutons and trigeminal premotor neurons retrogradely labeled with horseradish peroxidase were found in the ipsilateral Vodm, PCRtA, and PCRt, as well as the contralateral Vsup, Vmo, Vodm, PCRt, and PCRtA. Thus, multiple disynaptic jaw-muscle spindle afferent-motoneuron circuits exist. These pathways are likely to convey long-latency jaw-muscle stretch reflexes and may contribute to stiffness regulation of the masticatory muscles.

Afferent Pathways↗

PubMed1996

The relationship between inclination of the occlusal plane and jaw closing path.

The occlusal plane is determined according to morphologic guides such as Camper's plane and the position of the retromolar pad. However, there is no information available about the functional orientation of the occlusal plane. The purpose of this study was to investigate the relationship between the inclination of the occlusal plane and jaw closing movement path in the sagittal plane. Data from 38 young dentate subjects were obtained with a system that measures jaw movements. It was found that the occlusal plane and the masticatory closing path were consistent in maintaining an almost perpendicular relationship regardless of the variation in the inclination of the occlusal plane. This finding appears to be based on the functional formation of the occlusal plane according to the growth and change of masticatory muscles. The correlation between the inclination of the occlusal plane and masticatory closing movement could serve as the background for the functional significance of the occlusal plane.

Adult↗

PubMed1997

[Myositis ossificans of the pterygoid and temporal muscles with metachronous contralateral involvement].

After reviewing the literature, the authors report a case of myositis ossificans of the right pterygoid and temporalis muscles in a patient undergoing surgery to remove the left medial pterygoid muscle owing to the same pathology. The metachronous localisation in contralateral masticatory muscles compared to the primary site leads the authors to emphasize the post-traumatic and iatrogenic etiology of this rare pathology. In the light of their experience, they underline the importance of a precise diagnosis and surgical exeresis, followed by cautious rehabilitation with the least trauma, if necessary backed by appropriate medical treatment.

Adult↗

PubMed1998

Food properties that influence neuromuscular activity during human mastication.

The rate of breakdown of food in mastication depends on the ratio of two mechanical properties of the food--the toughness and modulus of elasticity (Agrawal et al., 1997)--a result which can be predicted by an analysis of the energetics of fracture. The work input to produce food fragmentation is provided by the masticatory muscles, the activity levels of which depend on sensory feedback from the mouth. Here, we test the hypothesis that the activity of a representative of this musculature is modulated by the above combination of food properties. The surface electrical activity (EMG) of the anterior temporalis muscles of ten human subjects was recorded while subjects chewed standardized volumes of 15 food types. The integrated EMG in these muscles was highly significantly related to the square root of the ratio of the above two food properties. Significant correlations were found between this food property index and integrated EMG, both when data for all chews and all subjects were lumped together (r = -0.86; p < 0.0001) and when correlation coefficients between the index and EMG were plotted for each chew made by each subject. Except for two subjects in the first chew, these coefficients reached and maintained highly significant levels throughout the masticatory sequence. Thus, a clear relationship between the electrical activity of a jaw-closing muscle and the mechanical properties of food has been found for the first time.

Adult↗

PubMed1983

Identification of motoneurons innervating the tensor tympani and tensor veli palatini muscles in the cat.

The somatotopic arrangement of the motoneurons associated with the two non-masticatory muscles innervated by the trigeminal motor nerve, tensor tympani (TT) and tensor veli palatini (TVP), was determined in the cat using retrograde transport of horseradish peroxidase. The motoneurons of the TT are distinct and separate, ventral and ventral-lateral to the rostral two-thirds of the trigeminal motor nucleus. The cells are smaller than those of the motor nucleus and constitute a parvocellular division. Based on functional and morphological criteria, TT motoneurons may be considered as an accessory trigeminal nucleus. The somatotopic arrangement of TVP motoneurons has been described for the first time. These motoneurons are located in the rostral two-thirds of the ventromedial division of the cat trigeminal motor nucleus. The location of motoneurons associated with TT and TVP does not fit the parcellation of the cat trigeminal motor nucleus as described by previous investigators. The motoneurons of these muscles can now be assigned to areas either within (TVP) or adjacent to (TT) the rostral two-thirds of the motor nucleus.

Animals↗

PubMed2006

Inflammation increases the excitability of masseter muscle afferents.

Temporomandibular disorder is a major health problem associated with chronic orofacial pain in the masticatory muscles and/or temporomandibular joint. Evidence suggests that changes in primary afferents innervating the muscles of mastication may contribute to temporomandibular disorder. However, there has been little systematic study of the mechanisms controlling the excitability of these muscle afferents, nor their response to inflammation. In the present study, we tested the hypotheses that inflammation increases the excitability of sensory neurons innervating the masseter muscle of the rat and that the ionic mechanisms underlying these changes are unique to these neurons. We examined inflammation-induced changes in the excitability of trigeminal ganglia muscle neurons following intramuscular injections of complete Freund's adjuvant. Three days after complete Freund's adjuvant injection acutely dissociated, retrogradely labeled trigeminal ganglia neurons were studied using whole cell patch clamp techniques. Complete Freund's adjuvant-induced inflammation was associated with an increase in neuronal excitability marked by a significant decrease in rheobase and increase in the slope of the stimulus response function assessed with depolarizing current injection. The increase in excitability was associated with significant decreases in the rate of action potential fall and the duration of the action potential afterhyperpolarization. These changes in excitability and action potential waveform were associated with significant shifts in the voltage-dependence of activation and steady-state availability of voltage-gated K(+) current as well as significant decreases in the density of voltage-gated K(+) current subject to steady-state inactivation. These data suggest that K(+) channel subtypes may provide novel targets for the treatment of pain arising from inflamed muscle. These results also support the hypothesis that the underlying mechanisms of pain arising from specific regions of the body are unique suggesting that it may be possible, if not necessary to treat pain originating from different parts of the body with specific therapeutic interventions.

4-Aminopyridine↗

PubMed1975

[The dynamic complex of the temporomandibular meniscus].

The existence of meniscocapsular insertions of the temporal, masseter and external pterygoid muscles complicates the scheme of capsulo-meniscal dynamics. Our findings do indeed agree with those of DUBECQ (Bordeaux); but we think that the insertions of the masseter and the temporal are not only fine tracts. In the embryon, the meniscus is the preglossal mekelian conjunctival blastema, which receives the 3 masticatory muscles on its anterior border. In the adult, menisco-capsulo-muscular relationships are not modified; inspite of considerable functional adaptation of the articulation to varied stimuli, the menisco-capsular apparatus seems to be triply controlled by 3 musculo-masticatory bands, owing to the anterior premeniscal tendinous lamina, in histological continuity with the meniscus and rich in corpuscles of deep sensitivity. The resultant of the tridirectional muscular traction of the masseter, external pterygoid and temporal is a force in the postero-anterior oblique direction, downwards and forwards, which allows the meniscus to stretch, as was shown by Pr Delaire, and thus to have a sub-temporal sliding pathway of 8 to 12 mm. The three muscle bundles external pterygoid, temporal and masseter constitute the dynamic complex of the meniscus.

Cartilage, Articular↗

PubMed1990

[Morphological and functional analysis of dento-orofacial complex in monozygotic twins with Duchenne type muscular dystrophy].

The form of dento-orofacial complex and masticatory muscle function of monozygotic twins with Duchenne type muscular dystrophy were investigated. They had no environmental difference. Morphological analysis were performed on the dental casts and cephalograms. EMG recordings were derived from the bipolar surface electrodes on the masseter muscle and the anterior belly of digastric muscle on the left side. Each consisted of the data for three years. Results obtained are as follows: 1) Based on the average data, these patients showed an elongated dental arch in the maxilla and mandible, which might be caused by enlarged tongues. There were little difference in the tooth and dental arch sizes between them. 2) Cephalometric findings indicated that the elder brother showed a clockwise rotation of the mandible with larger gonial angle than the younger brother. Both of them showed a larger gonial angle based on the mean values. 3) Analysis of EMG recordings revealed an elongated silent period induced by teeth tapping and chin tapping, and a variable masticatory rhythm compared with that of normal sample. Moreover an annually increased imbalance between masseter muscle and digastric muscle was evident, which were parallel to the change of the blood creatine kinase value. Differences in the form and function of orofacial complex between them might be caused by their polygene heredity and the large size of DMD gene (XP 21).

Adolescent↗

PubMed2000

Effect of carticaine on the sarcoplasmic reticulum Ca2+-dependent adenosine triphosphatase.

The sarcoplasmic reticulum Ca2+-ATPase (calcium-dependent adenosine triphosphatase) transports Ca2+ from the myoplasm to the reticulum lumen at the expense of free energy from ATP hydrolysis. Carticaine is a local anesthetic of frequent use in dentistry which is now entering other clinical fields. We studied the action of carticaine on the sarcoplasmic reticulum (SR) skeletal muscle Ca2+-ATPase. SR vesicles from rabbit fast skeletal muscle were used. Carticaine inhibits the enzymatic activity. The inhibition of the enzymatic activity depends on pH, [Ca2+] and the presence of calcimycin. Half-maximal carticaine concentration that inhibits the ATPase activity tends to a maximal value upon increasing [Ca2+]. Carticaine concentrations required to inhibit the enzymatic activity at myoplasmic calcium concentration are lower than usual clinical doses: Ki=6.0+/-1.4 mM carticaine (n=5) for 0.1 microM [Ca2+]. ATP-dependent calcium uptake is also inhibited by the local anesthetic: Ki=30.5+/-3.4 mM (n=4). Besides, carticaine inhibits the phosphorylation of the enzyme by inorganic phosphate (Pi): Ki=20.0+/-3.4 (n=5) - 33.2+/-4.6 (n=4) mM, for [Pi] 1-4 mM. Carticaine increases the membrane permeability to Ca2+. Ca2+ efflux from preloaded vesicles is prevented by Ca2+ and Mg2+. Our results suggest that the diffusion of the local anesthetic into muscle fibers might trigger undesired effects such as sustained contraction of the masticatory muscles.

Anesthetics, Local↗

PubMed1994

A comparison of human masseter muscle thickness measured by ultrasonography and magnetic resonance imaging.

Non-invasive imaging techniques such as computerized tomography, magnetic resonance imaging (MRI), and ultrasonography enable measurements of the cross-section and thickness of human jaw muscles in vivo, providing an indication of the maximal force a muscle can exert. In 15 adult Caucasian men the thickness of the masseter muscle was registered bilaterally on three different levels by ultrasonography. Scans were made on the contracted and relaxed muscle. A comparison was then made with measurements from serial MRI scans, using univariate analysis of variance for repeated measurements and Pearson's correlation coefficients. Variances of the repeated measurements were calculated for the different scanning levels and the different muscle conditions and tested for homogeneity. For both the ultrasound and MRI measurements there was no difference in thickness between the left and right muscle. The registration level with highest reproducibility was halfway between the origin and insertion. Measurements from the contracted muscle were more reproducible than those from the relaxed muscle. The relaxed muscle thickness measured by ultrasonography was smaller than that measured by MRI. The correlation between ultrasound and MRI was significant for the upper and middle level of scanning (p < 0.001). The highest correlation was found between MRI (relaxed) and ultrasound (contracted) at the middle level (R = 0.83, p < 10(-6)). The conclusion is that ultrasonography is an accurate and reproducible method for measuring the thickness of the masseter in vivo. It allows for large-scale longitudinal study of changes in jaw-muscle thickness during growth in relation to change in biomechanical properties of masticatory muscles.

Adult↗

PubMed1998

Development of fusimotor innervation correlates with group Ia afferents but is independent of neurotrophin-3.

Fusimotor neurons, group Ia afferents and muscle spindles are absent in mutant mice lacking the gene for neurotrophin-3 (NT3). To partition the effect of Ia afferent or spindle absence from that of NT3 deprivation on fusimotor neuron development, we examined the fusimotor system in a mutant mouse (NesPIXpNT3) that lacks Ia afferents and spindles, but has normal or elevated tissue levels of NT3 during embryogenesis. Fusimotor fibers were absent in lumbar ventral spinal roots, and limb muscles were devoid of Ia afferents and spindles in adult NesPIXpNT3 mice. In contrast, no deficiency in motoneuron numbers was observed in the trigeminal nucleus which contains cell bodies of motor axons innervating muscles of mastication. Spindles and Ia afferents were also present in the masticatory muscles. Thus, the development and/or survival of fusimotor neurons correlates with the presence of Ia afferents and/or spindles, and not with the amount of NT3 in the spinal cord or muscle.

Animals↗

PubMed2001

Motor evoked potentials from masseter muscle induced by transcranial magnetic stimulation of the pyramidal tract: the importance of coil orientation.

BACKGROUND: Reliable recording of motor evoked potentials (MEPs) of the masseter muscle by transcranial magnetic stimulation (TMS) has proved more difficult than from facial or intrinsic hand muscles. Up to now it was unclear whether this difficulty was due to methodological and/or anatomical reasons. METHODS: The mechanism of pyramidal cell activation in masseter MEPs was investigated by using magnetic and electric transcranial stimulation. Analysing the effect of magnetic coil positioning and orientation over the scalp, and scrutinizing the masseter recording technique to avoid compound motor action potential (CMAP) contamination from facial muscles, an optimized method of masseter MEPs was developed. RESULTS: In particular, an antero-lateral inducing current orientation in the stimulating coil, approximately paralleling the central sulcus, proved clearly more effective for the masseter muscles than the postero-lateral orientation (P=0.005) found optimal for intrinsic hand muscles. The thus evoked masseter MEPs by transcranial magnetic stimulation (TMS) were found to be identical in shape, amplitude and latency as those evoked by transcranial electric stimulation (TES), evidencing a direct rather than trans-synaptic activation of the pyramidal cells. CONCLUSIONS: We conclude that in TMS evoked MEPs of masseter muscles, the direct stimulation of the pyramidal tract is more easily achieved than the trans-synaptic activation, which is in contrast to the intrinsic hand muscles. We hypothesize that the presynaptic projections to pyramidal cells of the masticatory muscles are less abundant than in hand muscles, and are therefore less accessible to trans-synaptic stimulation.

Action Potentials↗

PubMed2003

Effects of interocclusal appliances on EMG activity during parafunctional tooth contact.

To test the hypothesis that a flat plane interocclusal appliance affects the electromyographic (EMG) activity of the temporalis and masseter muscles in pain-free individuals, maxillary splints were fabricated for 20 individuals who reported no history, signs or symptoms of myofascial pain or arthralgia as determined by two trained, independent examiners. Subjects were instructed to establish light tooth contact, maximum clenching, and moderate clenching with/without the splint in place (as determined by random assignment) while EMG data from the left and right temporalis and masseter muscles were recorded. A 5-min biofeedback training session to relax the masticatory muscles was followed by a repetition of the tooth contact/clenching tasks with/without the splint in place. With the splint in place, the activity of the temporalis muscles decreased for all tasks, significantly for the left and right temporalis under maximal clenching and for the right temporalis under moderate clenching. In contrast, the activity of the masseter muscles increased under light and moderate clenching (significantly for the left masseter under moderate clenching) and decreased slightly under maximal clenching. The effectiveness of interocclusal appliances may be due to mechanisms other than redistribution of adverse loading.

Bruxism↗

PubMed1989

Experimental studies on masseter muscle grafts in rats: comparison of donor muscles.

Experimental studies were performed in rats to explore the feasibility of using limb muscles to replace masticatory masseter muscles. The results showed that if several small fusiform muscles such as the extensor digitorum longus (EDL), soleus (SOL) and plantaris (PLT) were used for the grafting, the graft regenerated and matured fully in the masseter bed, although the weights were lower than those of contralateral control masseter muscles. If a multipennate muscle such as the gastrocnemius was used for the grafting, the graft also regenerated but later degenerated due to the lack of innervation. This is probably due to the excessive amount of connective tissue in the multipennate muscle. The connective tissue proliferates faster than the regeneration of muscle fibres and, thus, renders the innervation of muscle fibres difficult. Other factors pertinent to the possible clinical application of muscle transplantation in oral region are discussed.

Animals↗

PubMed1992

Neuromuscular transmission studies in the healthy dog: EMG and muscle force measurement after repetitive nerve stimulation.

In 10 healthy anaesthetized female dogs the ulnar and the mandibular nerve were stimulated supramaximally by repetitive electric impulses according to a fixed programme. To evaluate the neuromuscular transmission system the course of the evoked compound muscle action potential and the near-isometric force of forelimb and masticatory muscles were studied respectively. The presented results are comparable to values obtained from small hand muscles of conscious, healthy human subjects. The simultaneous measurement of both the electrical and the force response may improve the diagnostic accuracy of the examination in presumed neuromuscular transmission failure in the dog, as it does in humans.

Action Potentials↗

PubMed2005

Mastication effort estimated by electromyography for cooked rice of differing water content.

The objective of this study was to quantify the mastication effort for cooked rice. We analyzed mastication patterns while normal subjects ate a spoonful of cooked rice that had been prepared by cooking with different amounts of water (1.5, 2.0, 3.0, and 4.0 times the water to rice weight). The rice samples were served with the same weight, same volume and same solid content, and electromyography (EMG) of the masticatory muscles was measured. The texture of the four cooked rice samples was instrumentally analyzed by the two-bite method. The number of chews, masticatory time, and jaw-closing muscle activities per chew evaluated by EMG were higher in the rice sample cooked with least water, which exhibited a high firmness value in the instrumental test. Rice cooked with 4.0 times the amount of water exhibited the longest jaw-opening duration, which was related to the adhesiveness value in the instrumental test. The ratio of jaw-opening muscle activity to the preceding jaw-closing muscle activity was lower for the rice containing least water, this corresponding to the area ratio (balance degree) in the instrumental test. Softer rice containing more water reduced the total mastication effort until swallowing because it required a shorter mastication time. It was not difficult for the softer rice with high density to be ingested in greater weight, decreasing the mastication effort for a certain amount.

Adult↗

PubMed2001

Effect of jaw muscle pain and soreness evoked by capsaicin before sleep on orofacial motor activity during sleep.

AIMS: Sleep bruxism, which is a form of orofacial motor activity (OMA), and jaw muscle pain and soreness have for a long time been thought to be mutually linked. The aim of this study was to investigate the effect of clinical and experimental jaw muscle pain and soreness on sleep OMA. METHODS: Twelve healthy subjects aged 21 to 31 years old participated in this study. All of them were aware of signs or symptoms of sleep OMA and were subdivided into a group with clinical pain complaints (n = 5) and a group without pain (n = 7). All subjects slept in the laboratory for 3 consecutive nights, including a habituation night, a baseline night, and an experimental night. Electroencephalographic (EEG) activity and electromyographic (EMG) activity from the masseter muscles were recorded during sleep. On the experimental night, before sleep, all subjects received an injection of capsaicin (0.1 mL, 100 micrograms/mL) into the masseter muscle that had demonstrated the most EMG activity during the previous recordings. The OMA events and episodes were quantified and were compared between the baseline night and the experimental night. Every evening and morning during the study period, pain intensity, unpleasantness, and soreness were scored by the subjects on a visual analog scale (VAS), and pain detection thresholds (PDTs) in the masseter muscles and maximal voluntary occlusal force (MVOF) were also measured. RESULTS: Pre-sleep injection of capsaicin did not cause significant differences between groups in peak pain intensity on the VAS. The PDT and MVOF did not show any significant differences between groups, injection and non-injection sides, or baseline and experimental nights and mornings. The number of EMG episodes/hour sleep, the number of bursts/hour sleep, and total area of all bursts and episodes during the baseline night were significantly higher in the subjects without pain than in the subjects with pain. However, the capsaicin injection did not cause any significant changes in these parameters. CONCLUSION: This study suggests that an acute pre-sleep painful stimulus does not have any effect on OMA during sleep, but the study extends previous findings that clinical jaw muscle pain and soreness are associated with less EMG activity in the masticatory muscles.

Adult↗