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At least 757 records · Page 42Linked to original sources
PubMed1978

[Action potentials of cat masseter muscle motor neurons evoked by stimulation of low-frequency infraorbital nerve afferents].

The responses of masseter motoneurons evoked by stimulation of the low-threshold infraorbital afferents by different number of stimuli were investigated in cats under chloralose-nembutal anesthesia. It is shown that 3-4 succesive stimuli (1.2 of threshold) evoked action potentials in masseter motoneurons if their frequency was above 300/s. Stimulation of the infraorbital nerve by paired stimuli produced action potentials in these motoneurons when the interval between the stimuli was 1.3-4.0 ms. With longer intervals only facilitation of the second EPSP was observed, the degree of facilitation varying from 0.2 to 1.0. A conclusion is made that the masseter motoneurons discharges can be produced by activation of the infraorbital nerve. A -fibres probably connected to rapidly adapting receptors of the vibrissae.

Action Potentials↗
PubMed1991

Ultrastructural changes in the masseter muscle of Macaca fascicularis resulting from intramuscular injections of botulinum toxin type A.

Intramuscular injections of botulinum toxin type A (Oculinum) is used to treat strabismus and focal dystonias affecting orofacial muscles. However, the toxin-induced morphological changes that underlie the therapeutic alterations of tone in the muscles of mastication have not been described. In this study, paired intramuscular injections of botulinum toxin (10 units) were made in three adult monkeys (Macaca fascicularis) allowed to survive 14, 28 and 63 days. Another monkey received multiple injection-pairs over 84 days. Animals were killed by deep pentobarbital anaesthesia before transcardiac perfusion-fixation. Tissue sampled from comparable regions of the injected masseter, the uninjected masseter and an uninjected animal was processed for ultrastructural analysis. Few changes were found 14 days post-injection. However, muscle fibres showed myofibrillar dissolution, aberrations in the Z-line, and enlarged mitochondria in the region of the I-band by 28 days. In the 63-day and 84-day animals, the injected muscle was considerably smaller than the uninjected, contralateral muscle. Regions of the injected muscle contained fibres with markedly reduced cross-sectional area. Internalization of myonuclei, loss of myofibrillar organization, and helical complexes were common. Toxin-induced changes, though similar to those that follow denervation by axotomy, were not accompanied by degeneration of neuromuscular junctions. Instead, morphological evidence for axonal sprouting in the region of the neuromuscular junction, possibly contributing to functional recovery, was seen as early as 14 days in toxin-treated muscles.

Actin Cytoskeleton↗
PubMed1994

A topographical analysis of spectral electromyographic data of the human masseter muscle under different functional conditions in healthy subjects.

In 20 healthy subjects, 16-channel surface electromyograms (EMG) were recorded with the mandible in its postural position, during compensation for forces applied from ipsilateral, contralateral and frontal positions, and during force-constant biting on a unilaterally placed force transducer. After artefact elimination, EMG power spectra were calculated on the basis of the original EMG curves via fast Fourier transformation. Using spectral EMG characteristics, EMG maps were computed by means of an interpolation algorithm and an imaging procedure. Spectral EMG maps were demonstrated for all the test conditions. Significant differences of myoelectrical activity were verified between the 16 electrode positions. Moreover, the levels and/or the topographical distributions of spectral EMG powers differed significantly between the test conditions. During biting as well as with contralaterally and frontally applied forces, the highest EMG activity was found in the inferior third of the masseter and the lowest in the superior third. With ipsilaterally applied forces, the topographical distribution of the total EMG power was completely changed. The power maximum was frequently demonstrated in the superior, especially the posterosuperior, third of the muscle, the minimum in the inferior third. In the postural position of the mandible, EMG activity decreased from the anterior to the posterior regions of the masseter. If the bite force or the horizontally applied forces were enhanced, EMG activity increased significantly but the EMG map structures were only changed in some details. The topographical distribution of myoelectrical activity demonstrated by EMG maps characterizes the intramuscular activation patterns of distinct masseter functions.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed2005

A study on synaptic coupling between single orofacial mechanoreceptors and human masseter muscle.

The connection between individual orofacial mechanoreceptive afferents and the motoneurones that innervate jaw muscles is not well established. For example, although electrical and mechanical stimulation of orofacial afferents in bulk evokes responses in the jaw closers, whether similar responses can be evoked in the jaw muscles from the discharge of type identified single orofacial mechanoreceptive afferents is not known. Using tungsten microelectrodes, we have recorded from 28 afferents in the inferior alveolar nerve and 21 afferents in the lingual nerve of human volunteers. We have used discharges of single orofacial afferents as the triggers and the electromyogram (EMG) of the masseter as the source to generate spike-triggered averaged records to illustrate time-based EMG modulation by the nerve discharge. We have then used cross correlation analysis to quantify the coupling. Furthermore, we have also used coherence analysis to study frequency-based relationship between the nerve spike trains and the EMG. The discharge patterns of the skin and mucosa receptors around the lip and the gingiva generated significant modulation in EMGs with a success rate of 40% for both cross correlation and coherence analyses. The discharge patterns of the periodontal mechanoreceptors (PMRs) generated more coupling with a success rate of 70% for cross correlation and about 35% for coherence analyses. Finally, the discharges of the tongue receptors displayed significant coupling with the jaw muscle motoneurones with a success rate of about 40% for both analyses. Significant modulation of the jaw muscles by single orofacial receptors suggests that they play important roles in controlling the jaw muscle activity so that mastication and speech functions are executed successfully.

Action Potentials↗
PubMed1991

Projections from neurons innervating the masseter muscle to the subnucleus oralis of the spinal trigeminal nucleus and adjacent lateral reticular formation in the rat.

The projection from the masseter to the subnucleus oralis of the spinal trigeminal nucleus (Vo) and adjacent parvicellular reticular nucleus (PCRt) was studied with retrograde and transganglionic transport of horseradish peroxidase (HRP) combined with fluorescent double labeling method. The labeled axons and terminals within the medulla showed a specific distribution. The field of labeling formed a continuous band from rostro-laterally to caudo-medially. At the level of caudal Vo the labeling region became the most expanded in the medulla, which occupied dorso-medial Vo (Vodm) and adjacent PCRt about half by half. The ratio of masseter primary afferent neurons in the mesencephalic trigeminal nucleus (Vme) to that in the trigeminal ganglion (TG) was found to be 7.7-8.5:1 following injection of HRP into the masseter nerve. However, the proportion between the Vme and the TG neurons which build up the pathway from the masseter to the Vodm and the adjacent PCRt was 8.7-10:1, revealed by means of fluorescent double labeling when different tracers were applied at the peripheral and central targets.

Animals↗
PubMed1995

Masseter muscle activity in diagnosed sleep bruxists compared with non-symptomatic controls.

All-night polysomnographic recordings were made of clinically diagnosed sleep bruxists (n = 23) and non-symptomatic controls (n = 6). The total duration of masseter contraction (MC) episodes during sleep was 11.6 minutes per night in bruxists and 6.6 in controls (P < 0.01). The mean frequency of MC episodes was 11.0 per hour of sleep in bruxists and 6.4 in controls (P < 0.05). The mean relative amplitude of MC episodes reflecting clenching strength was 0.81 in bruxists and 0.56 in controls (P < 0.01). The percentage distribution of mixed and phasic MC episodes was 94% among bruxists and 88% in controls. The remaining activity was classified as tonic in both groups. The subclassification of rhythmic jaw movements (RJM), defined as three or more separate rhythmic contractions during MC episode were also evaluated. The frequency of those MC episodes with RJM was 3.6 per hour of sleep in bruxists and 1.1 in controls (P < 0.001). The difference in the relative amplitude between the two study groups suggests that the amount of clenching force is the primary factor responsible for the harmful effects of sleep bruxism on the masticatory apparatus. The most significant difference was seen in those phasic and mixed MC episodes which also included the subclassification of rhythmic jaw movement. The result suggests that relative amplitude and rhythmicity of MC episodes can be used as a basis to confirm the diagnosis and to evaluate the treatment effects of suspected sleep bruxists.

Journal Article↗
PubMed1978

The masseter muscle flap.

This little-used muscle flap has four significant applications in radical ablation about the palate, pharynx, and mesopharynx that include the ascending ramus of the mandible, a portion of the tongue and lateral neck, and in radical operations on the parotid gland causing a facial paralysis: 1. It assists in the rehabilitation of the act of swallowing when it is sutured to the lateral hyoid arch, thus elevating the thyrohyoid complex and reinforcing this portion of the upper lateral neck. 2. This flap may be transposed over the upper portion of the internal carotid artery to provide protection for this vital structure. 3. This flap may be transposed into the internal nasopharynx and then dressed with a free split thickness skin graft to close this wound and to augment the nasopharynx, with improvement in speec and swallowing. 4. In facial paralysis it can be used to restore facial movement around the oral commissure and melolabial folds, thus improving appearance in repose and animation.

Face↗