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PubMed1980

The effect of electrical stimulation in the hypothalamus on the monosynaptic jaw closing and the disynaptic jaw opening reflexes in the cat.

The effects of electrical stimulation in the hypothalamus on the monosynaptic jaw closing and the disynaptic jaw opening reflexes were investigated in cats anaesthetized with chloralose. The hypothalamic electrodes were located by observation of behavioural attack responses in the unanaesthetized animal and by means of Horsley-Clarke coordinates. The locations were verified in histological serial sections. Hypothalamic conditioning with trains of 3--10 pulses, 0.5 ms duration, 0.5 mA, 500 Hz, evoked a strong facilitation of the jaw closing reflex and a facilitation followed by an inhibition of the jaw opening reflex. These effects differed from those elicited from the cerebral cortex. The hypothalamic effects had a longer latency (11--13 ms) and required a longer train of conditioning stimuli than was the case with those evoked from the cortex. Bilateral ablation of the sensorimotor cerebral cortex or lesion of the pyramids at the lower pontine level diminished but did not abolish the hypothalamic effects. They did, however, disappear after lesions including the ventral midbrain tegmentum. The stimulus positions eliciting the largest hypothalamic effects on the jaw reflexes were located in a region extending medio-laterally from the perifornical area to the entrance of the ansa lenticularis in the lateral hypothalamus. Rostro-caudally the location was found at the level of the ventromedial hypothalamic nucleus and the anterior hypothalamus just rostral to this nucleus. The region corresponds to those parts of the hypothalamus from which agonistic and feeding responses have been evoked. It is suggested that the observed hypothalamotrigeminal mechanism may exercise a tonic influence on the trigeminal motoneurones, thereby controlling the set point of the biting force. The implications of this hypothesis on the etiology of bruxism and the myofascial pain dysfunction are discussed.

Animals↗
PubMed1983

Reflex sensitivity of human jaw-closing muscles during the silent period following a jaw jerk.

Two successive force impulses were exerted upon the mandible in the opening direction with intervals of 20 to 120 ms. Electromyographic responses were recorded from the right temporal and masseter muscles and from the anterior belly of the right digastric muscle. Mandibular movement was recorded in the sagittal plane. The first-force impulse evoked a jaw jerk followed by a silent period. The jaw jerk following the second-force impulse was depressed when the interval between the force impulses was shorter than a certain value. The depression was total for at least 20 ms after the first jaw jerk. It is suggested that the silent period is the result of more than one inhibitory mechanism. From comparison of the resulting mandibular movement with movements resulting from single-force impulses, it is concluded that the jaw jerk may contribute to a small but significant extent to the stiffness of jaw-closing muscles.

Adult↗
PubMed2004

Glutamate evoked neck and jaw muscle pain facilitate the human jaw stretch reflex.

OBJECTIVE: Although pain and neuromuscular function are clearly linked in several clinical conditions manifested in the craniofacial and cervical regions, it is unclear if pain in these regions influences reflexly evoked activity in the jaw or neck muscles in humans. The aim of the present study was to test the effects of glutamate-evoked jaw or neck muscle pain on the jaw stretch reflex recorded in both jaw and neck muscles. METHODS: Nineteen healthy men participated in the study. Electromyographic (EMG) recordings were made from the left masseter (MAL) and right masseter (MAR) muscles and the right sternocleidomastoid (SCM) and splenius (SP) muscles. Glutamate (1 M) or isotonic saline was injected into the MAR or right SP in random order and then the other solution was injected 1-3 weeks later. Pain intensity was scored on a 10 cm visual analogue scale. Stretch reflexes were evoked by standardized jaw stretches before, during and 15 min after the end of the experimental muscle pain. Twenty trials were averaged in each condition. RESULTS: Pain evoked by MAR or SP glutamate injections was associated with a significant increase in the stretch reflex amplitude recorded in both MAR and SCM. The onset and offset times and duration of the stretch reflex did not change in any muscle during the various pain conditions. Injection of isotonic saline into the MAR or SP did not produce any significant change in the reflex parameters in any of the muscles. CONCLUSIONS: The results indicate the close interplay between the craniofacial and cervical regions in the neuromuscular changes that may result from musculoskeletal pain in either region. SIGNIFICANCE: The changes in neuromuscular activity documented in this study may be involved in the clinical occurrence of altered muscle activity in the orofacial and cervical regions as a result of deep tissue trauma and pain.

Adult↗
PubMed2003

Effects of TMJ anesthesia and jaw gape on jaw-stretch reflexes in humans.

OBJECTIVE: To study the roles of afferent sensory inputs in the temporomandibular joint (TMJ) and of muscle length in the modulation of the jaw-stretch reflex in humans. METHODS: Reflexes were evoked in both the masseter and temporalis muscles under standardized conditions in 11 young women. The study was performed in two sessions; experimental conditions were jaw gape and injection of local anesthetics. For jaw gape, 4, 14, and 24 mm were used in random order. One milliliter TMJ injections (carbocaine, 10 mg/ml, versus isotonic saline, 0.9%) were given in a randomized, double blind manner. When a participant received carbocaine during the first session, isotonic saline was injected during the second one. A total of 480 reflexes were evoked in every participant. RESULTS: No significant differences were found between carbocaine and isotonic saline. ANOVA and post hoc paired t tests did show, however, a significant effect of jaw gape for the left masseter and anterior temporalis muscles, with the 14 mm gape having the highest amplitude. CONCLUSIONS: Blocking the afferent sensory input (including the mechanoreceptors) from the TMJ seems to have no influence on the sensitivity of the human jaw-stretch reflex. Instead, muscle spindles are the most likely receptors to be responsible for the reflex modulation that was observed in the present study.

Adult↗
PubMed1997

Reflex jaw motions and jaw stiffness pertaining to whiplash injury of the neck.

Because a so-called mandibular whiplash injury requires the absence of short-latency jaw-closing reflexes in order to explain the postulated mechanism of injury (excessive jaw opening); the authors studied the presence and absence and more importantly, the kinematics (duration, displacement, velocity, acceleration) of monosynaptic and possibly, polysynaptic myotatic (stretch) reflexes in the jaw elevator muscles. In six healthy adults jaw jerk maneuvers were elicited through a brisk tap on the chin, and surface electromyography identified elevator reflexes while translational electrognathography identified the kinematics of the reflexes. The maneuvers were done while maintaining the rest position (3% MVC) and moderate clenching of the teeth (30% MVC). Electromyography was also used to identify phasic elevator excitations during a passive brisk neck extension maneuver. A sudden and unexpected elongation of the jaw elevators released autogenic reflex responses that, in conjunction with augmented tissue elasticity (stiffness), elevated the mandible into centric occlusion within approximately 150 milliseconds. In 86% of trials, the responses occurred regardless of the prevailing resting and clenching contractile activities. There was no evidence of a depressor force that consistently would and could anchor the mandible in a position of extreme or moderate depression, the theoretical linchpin of the mandibular whiplash injury. It was concluded that the mandibular locomotor system is very efficient in maintaining the rest and intercuspal positions of the mandible. This study found no evidence corroborating the mechanism claimed to release a so-called mandibular whiplash injury.

Acceleration↗
PubMed1996

Tongue, jaw, and lip muscle activity and jaw movement during experimental chewing efforts in man.

The electromyographic (EMG) activity of the human genioglossus (GG) muscle during chewing efforts is not fully understood. In this study, the EMG activity of the human GG muscle during unilateral gum chewing was illustrated and correlated with the activities in the anterior temporalis (AT), the anterior digastric (DG), and the inferior orbicularis oris (OI) muscles. GG muscle activity was measured with customized surface electrodes, while other muscles were recorded with conventional surface electrodes. EMG activities during tongue displacement and the articulation of long vowels, recorded by the customized electrodes, were consistent with the recordings obtained by fine wire electrodes placed in the GG muscle. Jaw displacement was monitored by means of a kinesiograph with a transducer attached to the mandibular central incisors. Mean normalized GG muscle activity showed an onset in the last one-fifth of the intercuspal phase, gradually increasing during jaw-opening, and at its greatest immediately before the maximum jaw-opening position. It then decreased during jaw-closing and ceased in intercuspation but showed a small rebound in the third fifth of the intercuspal phase. The GG muscle burst showed phase lags with the DG and OI muscles and an opposite phase with the AT muscle (all P < 0.0001). All correlations were statistically significant (all P < 0.0001, r values between 0.88 and 0.97). The results suggest central coordination of the timing of the activities of the jaw, lip, and tongue muscles in chewing.

Adolescent↗
PubMed1993

Alterations of muscle activities and jaw movements after blocking individual jaw-closing muscles in the miniature pig.

Although the inactivation or removal of motoneurones and muscles are known to affect development and growth of the craniofacial skeleton and masticatory muscles, the effect of these on functional activity patterns is not clear. The goal of this study was to evaluate the immediate responses of masticatory muscle activities to temporary nerve blocks of individual jaw-closing muscles. Nineteen experiments were made with four miniature pigs (Sus scrofa). Electromyograms of the masticatory muscles and jaw movements were recorded during natural chewing. Then, the function of individual jaw-closing muscles was removed unilaterally by local anaesthesia, and the recording repeated. The results showed a general increase in the activities of the other jaw-closing muscles, particularly those that were synergistic with the blocked muscle in producing lateral movements. Furthermore, the lateral pterygoid showed stronger activity, and accordingly the lateral movement was increased. Digastric muscle activity and the magnitude of jaw opening also tended to increase. Thus, the response to loss of a muscle is a strong, immediate compensation by synergists.

Animals↗
PubMed1982

A new method for recording temporomandibular joint sounds and electrical jaw muscle activity in relation to jaw opening degree.

A system for continuously quantifying of jaw movements in terms of jaw angle was tested in combination with a previously tried method for simultaneous recording of temporomandibular joint (TMJ) sounds and electromyographic (EMG) activity. The system was used to measure the degree of rotation of the lower jaw in the sagittal plane in relation to the upper jaw. It was tested on a group of healthy subjects and patients with TMJ clicking and found useful to record EMG activity and TMJ clicking in relation to opening degree and velocity of jaw movement in open-close cycles.

Adult↗
PubMed1989

Interactions between jaw-muscle recruitment and jaw-joint forces in Canis familiaris.

Electromyographic activity from the jaw-adductor muscles was recorded during mastication and bone crushing in domestic dogs (Canis familiaris). During mastication, balancing-side temporalis electromyographic activity was much less than that of the working side while masseter muscle electromyographic activities were of similar amplitude. Despite the large bite forces that were produced during bone crushing, balancing-side masseter and temporalis electromyographic activities were always smaller than the working-side electromyographic amplitudes. Based upon geometric modelling, it is proposed that balancing-side muscle activity is reduced because of its tendency to produce mechanically disadvantageous jaw-joint forces. This hypothesis was tested by correlating bone strain adjacent to the jaw joint measured during manipulations of the mandibular condyle with bone strain recorded during the simulation and stimulation of jaw-adductor muscle activity. Working-side muscle activity produced bone strain that correlated with a compressive joint loading, while balancing-side muscle activity, with an occlusal fulcrum at the carnassial teeth, produced bone strain indicative of an anteroventral movement of the working-side mandibular condyle which eventually ruptured the joint capsule. When the temporalis and masseter muscles were stimulated bilaterally with a carnassial bite point, bone strain indicative of a ventrally directed and potentially damaging condylar movement was produced. It is proposed that working-side muscle activity exceeds balancing-side muscle activity during carnassial biting to maintain jaw-joint stability.

Animals↗
PubMed1995

Premotor neurons for trigeminal motor nucleus neurons innervating the jaw-closing and jaw-opening muscles: differential distribution in the lower brainstem of the rat.

The distribution of premotor neurons for trigeminal motor nucleus neurons innervating the jaw-closing and jaw-opening muscles was examined in the lower brainstem of the rat by using retrograde and anterograde labeling techniques. First, Fluorogold, a fluorescent retrograde tracer, was injected into the dorsolateral or ventromedial division of the trigeminal motor nucleus, each of which contains motoneurons innervating the jaw-closing or jaw-opening muscles, respectively. Second, Phaseolus vulgaris-leucoagglutinin, an anterograde tracer, was injected into each of the lower brainstem sites, where clusters of retrogradely labeled premotor neurons had been seen in the first set of experiments. Third, after injection of the anterograde tracer into a lower brainstem site, followed by injection of the retrograde tracer cholera toxin B subunit into a masticatory muscle, termination of anterogradely labeled axons onto retrogradely labeled motoneurons was confirmed with the aid of a confocal laser-scanning microscope. It was found that the premotor neurons distributed in the mesencephalic trigeminal nucleus, medial part of the parabrachial region, supratrigeminal region, and dorsal parts of the principal sensory, oral spinal and interpolar spinal trigeminal nuclei project preferentially to the dorsolateral division of the trigeminal motor nucleus, whereas those in the lateral part of the parabrachial region, intermediate parts of the principal sensory, oral spinal and interpolar spinal trigeminal nuclei, and alpha part of the gigantocellular reticular nucleus project preferentially to the ventromedial division of the trigeminal motor nucleus. The dorsal and lateral parts of the medullary reticular formation and the medullary raphe nuclei contain premotor neurons of both types. Group k motoneurons, a cluster of trigeminal motoneurons that innervate the tensor tympani muscle, receive projection fibers predominantly from the dorsolateral part of the oral pontine reticular formation.

Animals↗
PubMed1985

Distribution of the human jaw stretch reflex response elicited by percutaneous, localized stretch of jaw-closing muscles.

In the present study homonymous and heteronymous projections of muscle spindle afferent fibers in the human jaw-closing system were investigated. Stretch reflex responses were elicited with percutaneous displacement stimuli applied to the belly of the anterior superficial divisions of temporalis and masseter muscles. The distribution of reflex responses in jaw-closing muscles was assessed. Reflex responses to this stimulus were observed in all jaw-closing muscles ipsilateral to the stimulated muscle, suggesting that the projection of spindle afferent fibers to jaw-closing muscles in humans is diffuse. Comparisons of homonymous and heteronymous reflex response amplitudes indicated that homonymous response amplitudes tended to be larger. However, the relative strength of heteronymous inputs to masseter motoneurons appeared to be stronger than those to temporalis motoneurons.

Adult↗
PubMed1998

Stimulation of the neostriatum induces jaw-opener muscle activity, but not jaw-closer muscle activity: an electromyographic study in the rat.

Microstimulation was carried out at 36 sites in the dorsal striatum in lightly anesthetized rats. Only at two sites, microstimulation of 40 microA induced a considerable EMG activity in the jaw-opener (anterior digastric muscle). No activity was evoked in the jaw-closers (masseter and temporalis muscles). The effective sites were confirmed to be localized in a small central region of the striatum at a level corresponding to the caudal end of the anterior commissure. The effect was ascribed to excitation of a small cluster of striatal neurons, rather than to antidromic activation of cerebral cortical neurons through their axons within the striatum. (1) The effect was abolished after destruction of neurons in the striatal region by injecting kainic acid. (2) The effect was not influenced by ablation of the neocortex. (3) Microinjection of kainic acid into the striatal region also induced the similar muscle activity in the jaw-opener, but not in the jaw-closers.

Animals↗
PubMed1993

The recording and analysis of EMG and jaw tracking. II. Reproducibility of jaw tracking.

In 10 male and 10 female adults jaw movements and muscle activity were monitored during chewing. Subjects had a Class I occlusion and fluent unrestricted jaw movements; non exhibited signs or symptoms of craniomandibular disorders. Recordings were made on two occasions separated by 2 weeks. Within each recording session the subjects carried out a number of tasks under direction, including eating nuts and gum. The jaw movements were monitored with a Sirognathograph which had been interfaced to a computer for data logging and analysis. A computer program identified each chewing stroke and after scrutiny a data base was constructed of measurements from a subset of 4447 suitable strokes. Mean values of 10 parameters selected to describe jaw movements during chewing were entered into an ANOVA. This indicated that the major contribution to variance was due to the subject from whom the data was recorded. This intersubject variability is well known, but can its separation from the other contributions to the variation within the data be assessed? To provide an estimate of the spread of data the variance for each parameter was calculated, transformed and these values entered into an analysis of variance. All subject differed significantly in their chewing movements from one another. But 15 of the 20 subjects showed a greater degree of consistency than the other five: they exhibited good inter- and intra-recording reproducibility. The food being eaten made a major contribution to the variability. The timing of the chewing strokes was also more consistent than the dimensions of the chewing envelope.

Adult↗
PubMed2004

[Serial 1 Development of jaws; over view--development of jaws in vertebrates].

Mouth is entrance to the alimentary canal of the animal. One of the most significant evolutionary advances made in the evolution of vertebrate was the development of jaws. The presence of jaws manipulated by muscles allows an organism to grasp feed firmly. From primitive amphibian to primitive reptile, there had only primary oral cavity, but an advanced mammal-like reptile was divided primary oral cavity between oral and nasal cavity. An advanced mammal-like reptile was able to maintain breathing easily while the mouth is functioning in eating, fore get the development of a secondary palate. In the development of vertebrate it made many characteristic forms of jaws. In this series we will discuss that development and morphological character of the jaws.

Animals↗
PubMed1989

Jaw fractures in the county of Stockholm (1978-1980). Jaw fractures in children and adolescents.

Jaw fractures are less frequent in children than in adults. Very few studies exclusively on jaw fractures in children have been reported. From an investigation earlier published about jaw fractures in the country of Stockholm during the years 1978, 1979 and 1980 the authors have selected all cases of jaw fractures in children and adolescents below the age of 20. One hundred and seventy-one patients were studied, 128 boys and 43 girls. The ratio between boys and girls was 3:1. The material was separated into 4 age groups: 0-5, 6-10, 11-15 and 16-20 years. Sixty percent of the fractures were found in the older age groups. The majority of the injuries (62%) occurred during the period May-September, mostly on Fridays and Saturdays, in the younger groups in day time, in the older group during the evening. Fractures due to falling and playing dominated in the younger age groups, but decreased with age. Even if all bicycle traffic accidents were excluded, this vehicle caused 31% of all play and sporting accidents. The relatively percentage of traffic accidents increased steadily from 17 to 42% in the age groups. In the oldest age group violence exceeded traffic as the dominating cause. Le Fort fractures were not found in the younger groups, were fractures of the mandibular condyle and maxillary alveolar process dominated. An erupted tooth in the fracture line was registered in 43% of the cases. Most patients received outpatient treatment.

Accidents↗
PubMed1994

Precision of the jaw tracking system JAWS-3D.

The purpose of this study was to measure, under laboratory conditions, the noise level of the optoelectronic jaw-tracking system JAWS-3D, which records the movement of the whole mandible from extraorally placed landmarks. Also, an assessment was made of its accuracy in measuring positions, angles, and velocities. The results showed that the accuracy of JAWS-3D decreased when the distance between the recorded point and the extraoral landmarks increased. The path of a point near to the landmarks was estimated with an error of 0.11%, whereas the error increased to 1.33% when the point was far from the landmarks. The maximum error in angle computation was 0.7 degrees. The velocities calculated by JAWS-3D corresponded closely to the actual ones: mean error of 3 mm/s for velocities up to 80 mm/s. Thereafter, the error increased to reach 26 mm/s at a speed of 210 mm/s.

Artifacts↗
PubMed1975

Lip and jaw motor control during speech: responses to resistive loading of the jaw.

Resistive loads were applied to the jaw during speech production. Loads were initiated during the jaw closing movement associated with the production of bilabial stops, creating a situation in which bilabial closure would be disrupted if motor control were independent of peripheral feedback. Three subjects were observed during control and experimental conditions. In all utterances in which a load was appropriately introduced, closure of the lips was achieved and the bilabial stop was adequately produced. To assess the nature of this control, displacement of the upper lip, lower lip, and jaw, in the inferior-superior dimension, were recorded along with EMG from medial pterygoid, anterior temporalis, masseter, and orbicularis oris superior muscles. Based on observation of these variables, it appears that the muscles of the lips and jaw are capable of on-line compensatory motor reorganization.

Adult↗
PubMed1986

Focal dystonia of the jaw and the differential diagnosis of unilateral jaw and masticatory spasm.

The clinical features, differential diagnosis and treatment of unilateral spasms of the jaw and masticatory muscles are discussed and illustrated by eight cases of unilateral jaw spasms of various aetiologies. These include focal dystonia of the jaw, hemimasticatory spasm with and without facial hemiatrophy, paroxysmal events in multiple sclerosis and tetany. Attention is particularly drawn to four cases of unilateral dystonia of the jaw which has not been described before.

Adult↗