Jaw-opening Phase Research Articles

Discharge patterns of neurons in the medial pontobulbar reticular formation during fictive mastication in the rabbit.

In this study, we describe functional characteristics of neurons forming networks generating oral ingestive motor behaviours. Neurons in medial reticular nuclei on the right side of the brainstem between the trigeminal and hypoglossal motor nuclei were recorded in anaesthetized and paralysed rabbits during two types of masticatory-like motor patterns induced by electrical stimulation of the left (contralateral) or right (ipsilateral) cortical masticatory areas. Sixty-seven neurons in nucleus reticularis pontis caudalis (nPontc), nucleus reticularis parvocellularis (nParv), and nucleus reticularis gigantocellularis (Rgc) were studied. These were classified as phasic or tonic depending on their firing pattern during the fictive jaw movement cycle. Phasic neurons located in the dorsal part of nPontc were active during the jaw opening phase, whilst those in dorsal nParv tended to fire during the closing phase. In most neurons, burst duration and firing frequency changed between the two motor patterns, but there was little change in phase of firing. Tonic units were mainly recorded in the ventral half of nPontc, and at the junction between Rgc and caudal nParv. Cortical inputs with short latency from the contralateral masticatory area were more frequent in phasic (82%) than tonic (44%) neurons, whilst inputs from the ipsilateral cortex were equal in the two subgroups (57% and 56%). Phasic neurons had significantly shorter mean contralateral than ipsilateral cortical latencies, whilst there was no difference among tonic neurons. Intra- and perioral primary afferent inputs activated both types of neurons at oligo-synaptic latencies. Our results show that subpopulations of neurons in medial reticular nuclei extending from the caudal part of the trigeminal motor nucleus to the rostral third of the hypoglossal motor nucleus are active during the fictive masticatory motor behaviour. Unlike masticatory neurons in the lateral tegmentum, the medial subpopulations are spatially organized according to discharge pattern.

Modulation of H reflex of pretibial and soleus muscles during mastication in humans.

A previous study in our laboratory demonstrated that the soleus H reflex was facilitated during mastication in humans. In the present study, we investigated whether there was any modulation of the magnitude of the pretibial H reflex during mastication in five healthy adult volunteers. The pretibial H reflex was significantly facilitated during mastication, and there was no significant difference in the facilitation between jaw-closing and jaw-opening phases; that is, the gain of the H reflex was modulated tonically but not in a phase-dependent manner during mastication. Furthermore, in the same subjects, we confirmed that the soleus H reflex was facilitated during mastication. Based on our findings, we conclude that the H reflexes in both the pretibial and soleus muscles undergo a nonreciprocal facilitation during mastication. It is suggested that mastication contributes to stabilization of postural stance in humans.

Development of a three-dimensional jaw-tracking system implanted in the freely moving mouse

A high-resolution mandibular tracking system was designed and tested in a freely moving mouse. A sensor unit, which consisted of four small magnetic sensors, was employed to trace small magnet movements in the three-dimensional space. After the sensor's output-to-displacement transformation equations were obtained from a multiple regression analysis of pre-experimental calibration data, the magnet and the sensors were transferred to the mouse, being kept at the same configuration as determined in the calibration system. In order to measure the three-dimensional jaw movements, the magnet was glued on the mandibular surface of the mouse and the sensor unit was implanted in the nasal bone. Jaw-movement trajectories were obtained as electrical signals from the sensors after being compensated by the output-to-displacement transformation equations of the sensors with a personal computer. This sensor system, applied to the freely moving mouse, could trace the jaw trajectories with an accuracy of better than 20 μm in three-dimensional space. Consequently, the typical pattern of the rhythmical jaw movements of the mouse during mastication was obtained. The mouse protruded the mandible to the most anterior position in the jaw-opening phase and retruded to it the most posterior position in the jaw-closing phase. This tracking system may also be applied to other small animals.

Genioglossus muscle activity during rhythmic open-close jaw movements.

The purpose of this study was to examine genioglossus muscle activity during rhythmic open-close jaw movements. The electromyographic activity of the genioglossus muscle was recorded with a bipolar fine-wire electrode in six healthy males. The electromyographic activities of the ipsilateral masseter and digastric muscles were simultaneously recorded with bipolar surface electrodes. The subjects were instructed to perform rhythmic open-close jaw movements in time with a metronome set at 23, 27, 33, 42 and 50 beats/min. In all of the subjects, rhythmic electromyographic activity of the genioglossus muscle was recorded in both the jaw-opening and jaw-closing phases. The activity of the genioglossus muscle was predominantly recorded in the jaw-opening phase in two subjects, and in the jaw-closing phase in two subjects. The burst duration of the electromyographic activity of the genioglossus muscle changed linearly in accordance with the cycle duration. However, the latency from the onset of the electromyographic activity of the masseter or digastric muscle to that of the genioglossus muscle was almost constant, independent of the cycle duration. Based on these findings, we conclude that the activity of the human genioglossus muscle is closely linked to that of masticatory muscles under the control of a closely related central pattern generator.

Evidence for functional compartmentalization of trigeminal muscle spindle afferents during fictive mastication in the rabbit.

Primary afferent neurons innervating muscle spindles in jaw-closing muscles have cell bodies in the trigeminal mesencephalic nucleus (NVmes) that are electrically coupled and receive synapses. Each stem axon gives rise to a peripheral branch and a descending central branch. It was previously shown that some spikes generated by constant muscle stretch fail to enter the soma during fictive mastication. The present study examines whether the central axon is similarly controlled. These axons were functionally identified in anaesthetized and paralysed rabbits, and tonic afferent firing was elicited by muscle stretch. For the purpose of comparison, responses were recorded extracellularly both from the somatic region and from the central axon in the lateral brainstem. Two types of fictive masticatory movement patterns were induced by repetitive stimulation of the masticatory cortex and monitored from the trigeminal motor nucleus. Field potentials generated by spike-triggered averaging of action potentials from the spindle afferents were employed to determine their postsynaptic effects on jaw-closing motoneurons. Tonic firing of 32% NVmes units was inhibited during the jaw-opening phase, but spike frequency during closing was almost equal to the control rate during both types of fictive mastication. A similar inhibition occurred during opening in 83% of the units recorded along the central branch. However, firing frequency in these was significantly increased during closing in 94%, probably because of the addition of antidromic action potentials generated by presynaptic depolarization of terminals of the central branch. These additional spikes do not reach the soma, but do appear to excite motoneurons. The data also show that the duration and/or frequency of firing during the bursts varied from one pattern of fictive mastication to another. We conclude that the central axons of trigeminal muscle spindle afferents are functionally decoupled from their stem axons during the jaw-closing phase of mastication. During this phase, it appears that antidromic impulses in the central axons provide one of the inputs from the masticatory central pattern generator (CPG) to trigeminal motoneurons.

Regulation of human jaw tapping force with visual biofeedback.

The purpose of this study, which made use of visual biofeedback, was to determine whether jaw tapping force reproduction is related to the strength of tapping and to investigate how jaw tapping force affects the tapping movement curve. Nine healthy examinees were asked to reproduce jaw tapping force. We found that the ease and method of regulating jaw tapping force differed depending on the target force. We also found that jaw tapping force was regulated by alteration of the jaw opening distance, the duration of the tooth contact phase, the duration of the jaw closing phase, the maximum jaw opening velocity, and the maximum jaw closing velocity. However, the duration of the jaw opening phase and cycle time was not affected by force regulation under our experimental conditions.

Flexure deformation of the temporomandibular joint disk in pseudodynamic magnetic resonance images.

The purpose of this study was to determine correlation of flexure disk deformation during jaw movement with other findings on magnetic resonance images and with clinical signs and symptoms in patients with anterior displacement of the temporomandibular joint disk. T(1)-weighted magnetic resonance images and gradient recalled acquisition in steady state magnetic resonance images were obtained in 62 subjects with flexure deformed disk in the jaw opening phase. Each disk deformation observed on a pseudodynamic image during jaw opening was classified as an upward or downward flexure deformation. The relationships between type of disk deformation, clinical signs and symptoms, and other findings on the magnetic resonance images were statistically analyzed by chi(2) test.Results. Of 80 delineated joints, 30 showed upward deformation and 50 showed downward deformation. There were significant differences between the upward and downward deformations in TMJ sound, TMJ pain, restricted jaw opening, extent of anterior displacement, and presence of disk reduction. The type of disk deformation appeared to correlate with the clinical signs and symptoms and with the progress of internal derangement.

Concomitant mandibular and head-neck movements during jaw opening-closing in man.

To test the hypothesis of a functional relationship between the human mandibular and cranio-cervical motor systems, head-neck movements during voluntary mandibular movements were studied in 10 healthy young adults, using a wireless optoelectronic system for three-dimensional (3D) movement recording. The subjects, unaware of the underlying aim of the study, were instructed to perform maximal jaw opening-closing tasks at fast and slow speed. Movements were quantified as 3D movement amplitudes. A consistent finding in all subjects was parallel and coordinated head-neck movements during both fast and slow jaw opening-closing tasks. Jaw opening was always accompanied by head-neck extension and jaw closing by head-neck flexion. Combined movement and electromyographic recordings showed concomitant neck muscle activity during head-neck movements, indicative of an active repositioning of the head. No differences in 3D movement amplitudes could be seen with respect to speed. The head movement was 50% of the mandibular movement during jaw opening, but significantly smaller (30-40%), during the jaw closing phase. In repeated tests, the 3D movement amplitudes of the concomitant head movements were less variable during slow jaw movement and during the jaw opening phase, than during fast and jaw closing movements, suggesting speed- and phase-related differences in the mechanisms controlling the integrated mandibular and head-neck motor acts. The present results give further support to the concept of a functional trigeminocervical coupling during jaw activities in man.

Effects of food consistency on the modulatory mode of the digastric reflex during chewing in freely behaving rabbits

Effects of food consistency on the mode of the phase-linked modulation in the digastric reflex amplitude were examined in naturally chewing rabbits. Two test foods with different textures (bread as a soft food, pellet as a hard food) were used. The digastric reflex was elicited by electrical stimulation (10 train pulses at 2 kHz) of the inferior alveolar nerve. The amplitude of the digastric reflex measured was divided into three categories depending on the chewing phases in which the stimulus was delivered and each value was compared with the control response obtained when the animal was resting. The reflex was strongly inhibited in the jaw-opening phase and no difference was observed in the inhibitory effect between the foods. In the jaw-closing phase, larger digastric reflexes than those in the opening phase were elicited with both foods. This was the case in both the fast-closing and slow-closing phases. Reflex amplitude was significantly larger during chewing of the hard food than the soft food and, thereafter, inhibition of the reflex was observed only during chewing of the soft food in the closing phase. The results suggest the following: (1) food consistency may affect the central mechanism which regulates the digastric reflex and (2) the reflex may contribute to the regulation of masticatory force during chewing particularly hard food.

Transition from suckling to drinking at weaning: a kinematic and electromyographic study in miniature pigs.

The movements of the tongue, hyoid, and jaw were recorded cineradiographically in preweaning pigs as they suckled bariumized milk from a veterinary teat or drank it from a bowl. The movements were quantified by measuring the X, Y coordinates of radioopaque markers embedded in the tongue and attached to both jaws and to the hyoid. EMG activity in masseter, anterior digastric, geniohyoid, genioglossus, hyoglossus, sternohyoid, stylohyoid, and omohyoid muscles was recorded synchronously with cineradiography at 100 frames/sec. In both suckling and drinking, the movements were characterized by minimal movements of the jaw and hyoid but extensive movements of the tongue. In suckling, the movements were largely confined to the midposterior part of the tongue. A seal was formed between the posterior tongue and soft palate while a depression formed in the mid-tongue; this was associated with fluid moving into the depression probably because of a reduced intraoral pressure. The depression was associated with increased EMG activity in the genioglossus muscle and overlapping activity in digastric, geniohyoid, hyoglossus, and sternohyoid muscles. In drinking cycles, significant movement occurred in all parts of the tongue; milk ingestion was associated with tongue movements that combined elements characteristic both of suckling (mid-tongue depression with a posterior seal) and of lapping (extensive anteroposterior movements within the tongue itself). In drinking, compared to suckling, there was a major reduction in EMG activity in masseter, digastric, geniohyoid, and sternohyoid muscles. After milk had accumulated in the valleculae, swallows usually occurred in every other cycle during suckling and in every third or fourth cycle during drinking. The emptying of the valleculae was an event that was embedded in the early jaw-opening phase of an otherwise normal suckling or drinking cycle. Emptying of the valleculae was associated with posteriorly directed movement of the back of the tongue and increased EMG activity in hyoglossus, styloglossus, and omohyoid muscles. No differences were noted in the kinematics associated with swallowing in the two activities, but, in the normalized and averaged EMG data, there were significant differences in the timing of genioglossus activity and in the relative balance of hyoglossal and stylohyoid activity.

Modulation of jaw muscle spindle discharge during mastication in the rabbit.

Discharges of jaw muscle spindles were recorded during chewing carrot from mesencephalic trigeminal nucleus (Mes V) in the awake rabbit to evaluate contribution of the muscle spindles to the development of complete sequences of masticatory movements. The Mes V spindle units were divided into two types according to the maximum firing rates during mastication, with a dividing line at 200 Hz; high-frequency units and low-frequency units. Although both types of units fired maximally during the jaw-opening phase of chewing cycles, their firing rates and pattern varied according to three sequential stages of mastication (stages I, IIa, and IIb). The high-frequency units often increased firing before the start of mastication and built up firing in the first few chewing cycles. Their maximal firing rate was sometimes lower during stage IIa (chewing stage) than during stage I (ingestion stage) and stage IIb (preswallowing stage), although the jaw movements were greater in stage IIa than in other stages. The phase relationship of the firing to a jaw movement cycle in stage IIa was consistent in individual units. The low-frequency units did not build up activity before the onset of movements. They fired mostly during the jaw-opening phase, but the peak of firing did not necessarily coincide with the time of maximal opening. It was concluded that the difference in the firing pattern among masticatory stages may be ascribed to a stage-dependent modulation of both fusimotor activity and jaw movement pattern.

Modification of mastication and respiration during swallowing in the adult human.

1. The normal interactions between respiration, mastication, and swallowing were studied in seated adult humans. Respiratory movements and movements of the larynx were recorded with mercury-elastic strain gauges placed around the rib cage and neck. A rigid body containing infrared-emitting diodes (IREDs) was attached to the forehead, and a single IRED was applied to the chin. Jaw and head movements were transduced using the OPTOTRAK spatial motion analysis system. Recordings were made before, during, and after the mastication of pieces of carrot. 2. Movements of the larynx were used as a marker for swallowing. Measurements were made of the duration of masticatory and respiratory cycles, and the phase relationship between the two rhythms was determined. Deviations in masticatory and respiratory movements during swallowing were detected; the phases of the masticatory and respiratory cycles in which the deviations occurred were determined, and the interval between each deviation and the swallowing marker was calculated. 3. Three characteristic swallowing patterns were observed: interposed, terminal, and spontaneous. Interposed swallows occurred within a masticatory sequence, terminal swallows ended the sequence, and spontaneous swallows occurred sporadically between masticatory sequences. 4. Results revealed that mastication could have a profound effect on the respiratory rhythm in some subjects. One subject, whose data were excluded from further analyses, became apneic for a long period, followed by short and shallow breaths near the end of the masticatory sequence. In most subjects, respiratory rate increased during mastication and then dropped below baseline as soon as mastication ended. The end-inspiration diameter of the rib cage tended to decrease in the preswallow period and increase postmastication relative to baseline. 5. There was a weak but significant tendency for inspiration to begin during the jaw opening phase of mastication, but phase coupling did not become stronger as swallowing was approached. 6. Deviations in respiration during swallowing occurred during the late expiratory phase of the breathing cycle. Swallows within a masticatory sequence occurred most frequently during the early opening phase of the masticatory cycle, and terminal swallows occurred after the end of the sequence with the mandible in the resting, postural position. Swallowing temporarily reset both the masticatory and respiratory rhythms. Most swallows prolonged the duration of one or two respiratory cycles, however; swallows were often repetitive, and in some subjects two or three swallows fell within a single respiratory cycle, prolonging it for several seconds. 7. A tight temporal relationship was observed between deviations in respiration and the swallowing marker: all deviations occurred before or coincident with the marker. The time of deviations in mastication relative to the swallowing marker depended on swallow type. There was no link between the start of pauses in the two rhythms, suggesting that the commands from the swallowing central pattern generator to the other two pattern generators are independent. 8. We suggest that disordered coordination of mastication and swallowing with respiration may cause prolonged apnea in susceptible individuals.

JAW MOVEMENT DURING MASTICATION OF FIBROUS AND NONFIBROUS COMPOSITE FOODS BY ADULT SUBJECTS

ABSTRACTA cinematographic study was made of subjects during mastication of fibrous and nonfibrous foods. The motion of the jaw was analysed mathematically. Each cycle of the vertical movement of the jaw could be considered as a combination of a sinusoidal motion, chewing phase, and a linear one, jaw opening phase. The lateral movement was not so well defined. On average, females took longer to chew foods and had smaller jaw movements than males. Fibrous foods took longer to chew and the amplitudes were larger than nonfibrous foods. The maximum rate of jaw movement during chewing ranged from 15 mm s−1 to 30 mm s−1, with males chewing at faster rates than females.

Coordination of cortically induced rhythmic jaw and tongue movements in the rabbit

1. Rhythmic movements of the jaw, tongue, and hyoid that were induced by stimulation of the cortical masticatory area (CMA) were recorded cineradiographically in the anesthetized rabbit. Jaw movements were also recorded by a laser position detector. 2. The evoked jaw movements were classified into four types: small circular (type A), large circular (type B), large vertical (type C), and crescent-shaped (type D). Among these, types B and D resembled the jaw movements of the food transport cycle and those of the chewing cycle in a masticatory sequence. 3. Each type of jaw movement was associated with a particular pattern of tongue and hyoid movements. In general, the tongue protruded during jaw opening and retracted during jaw closure. The hyoid generally moved upward and forward during jaw opening but downward and backward during jaw closure. 4. Electromyograms (EMGs) were recorded from jaw muscles [masseter (Ma) and digastric (Di) muscles], extrinsic tongue muscles [styloglossus (Sg) and genioglossus (Gg) muscles], and hyoid muscles [sternohyoid (Sh) and geniohyoid (Gh) muscles] during cortically induced rhythmic jaw and tongue movements (CRJTMs). These muscles were classified into two groups: group 1 was activated mainly in the jaw opening phase, and group 2 was activated mainly in the jaw closing and power phases. The Di, Gg, and Gh were included in the former, and the Ma, Sg, and Sh were included in the latter. 5. The timings of EMG activation to a jaw movement cycle were relatively constant for the muscles of group 1, irrespective of the types of CRJTMs, whereas those for the muscles of group 2 altered considerably with the different types of CRJTMs. 6. Relationships of the integrated muscle activity between the Di and Gg and between the Di and Gh were significant, whereas those between the Ma and Sg and between the Ma and Sh were not. 7. When a small strip of polyurethane form of various degrees of hardness was inserted between the opposing molars during CRJTMs, EMG activity of the muscles of group 2 increased with the hardness of the strip. On the other hand, EMG activities of the muscles of group 1 were less affected by the same intraoral stimuli. 8. Two conclusions were reached: first, physiological properties of the CRJTMs and cortically induced rhythmic movements of the hyoid were essentially similar to those observed in natural mastication. This fictive mastication might thus be regarded as a suitable model for simulating natural mastication.(ABSTRACT TRUNCATED AT 400 WORDS)

Trigeminal premotor neurons in the bulbar parvocellular reticular formation participating in induction of rhythmical activity of trigeminal motoneurons by repetitive stimulation of the cerebral cortex in the guinea pig.

1. Single-unit activity was recorded from neurons in the bulbar parvocellular reticular formation (PCRF) dorsal and dorsolateral to the gigantocellular reticular nucleus near its caudal boundary, and the roles of these reticular neurons in induction of rhythmical activity of trigeminal motoneurons by repetitive stimulation of the cerebral cortex (the cortical masticatory area, CMA) were studied in the paralyzed guinea pig anesthetized with urethan or with ketamine and chlorpromazine. 2. One hundred nine PCRF neurons were activated antidromically by microstimulation in either the masseter (MA) or anterior digastric (AD) motoneuron pool in the ipsilateral trigeminal motor nucleus, and orthodromically by stimulation in the contralateral CMA. Repetitive CMA stimulation induced rhythmical burst activity in these PCRF neurons in association with the rhythmical field potential in the contralateral AD motoneuron pool induced by the same CMA stimulation. The burst was synchronous with the rhythmical AD field potential in 81 neurons, 44 and 37 of which responded antidromically to stimulation in the MA and AD motoneuron pools, respectively. The remaining 28 neurons antidromically responded to stimulation in the MA motoneuron pool, and their burst corresponded in time with the period between successive AD field potentials. 3. Spike-triggered averaging of the intracellular potentials of MA and AD motoneurons (MNs) by simultaneously recorded spontaneous spikes of the PCRF neurons, which showed rhythmical burst responses during the jaw-opening phase to repetitive CMA stimulation, revealed a monosynaptic inhibitory postsynaptic potential in MA.MNs in 12 of 34 tested pairs and a monosynaptic excitatory postsynaptic potential (EPSP) in AD.MNs in 14 of 26 tested pairs. An EPSP was also found in MA.MNs after a monosynaptic latency from triggering spikes in 11 of 37 tested PCRF neurons that showed burst activity during the jaw-closing phase. 4. We conclude that both excitatory and inhibitory premotor neurons projecting to MA.MNs as well as excitatory premotor neurons projecting to AD.MNs are located in the PCRF, and that these premotor neurons relay the output of the central rhythm generator for rhythmical jaw movements in the medial bulbar reticular formation to trigeminal motoneurons, and thus participate in induction of rhythmical activities of trigeminal motoneurons by repetitive CMA stimulation.

Mastication and swallowing: an overview.

The cycles of jaw and tongue movement during feeding produce not only the breakage of food but its intra-oral transport; which activity predominates depends upon the physical characteristics of the food. When hard food is eaten and tooth-food-tooth contact is made during jaw closure, the velocity of closing is suddenly reduced, producing two clearly different phases of closure; during the second phase the activity of the jaw closing muscles is much increased. Conversely, in cycles with a mainly transport function (eating soft food), the antero-posterior movements of the tongue are much greater; this alters the time and rate at which the jaw opens. The pattern of jaw movement during closing and during opening consequently varies with food consistency. The evidence suggests that sensory input controls the form of the cyclical tongue and jaw movements. However the basic plan of movement is produced by the activity of a brainstem pattern generator which receives input from both cerebro-cortical and peripheral sources. The swallow that occurs in normal feeding consists of the equivalent of the classical second stage of swallowing inserted into the occlusal or initial jaw opening phase of an otherwise standard cycle. Although leakage of traces of food or saliva into the vallecula appears to be a peripheral sensory input of major importance in inducing such a swallow, the execution of the swallow is due to a pattern generator in the brainstem.

Hypoglossal neural activity during licking and swallowing in the awake rat.

1. Thirty-five neurons in the hypoglossal nucleus (mXII) of the rat were characterized during licking and swallowing in response to fluid stimulation in an awake, freely moving preparation. Simultaneously recorded electromyographic (EMG) recordings from a subset of oropharyngeal muscles were obtained to delineate both the lick cycle and the occurrence of swallows. Most mXII neurons discharged with rhythmic bursts in phase with licking. Twenty-six of the 35 mXII neurons had bimodal interspike interval (ISI) histograms, reflecting rhythmic bursts and the absence of spontaneous activity. Three mXII cells with unimodal ISI histograms were rhythmically active during licking but had some spontaneous activity. Of the remaining six cells with unimodal ISI histograms, five had nonbursting modes of activity. 2. Phase relationships between neural and EMG activity during licking were determined by cross-correlation and compared with distributions of cross-correlations between lingual and masticatory EMG activity. A bimodal distribution of cross-correlations was obtained by cross-correlating EMG activity between lingual protrudor muscles [genioglossus (GG) or geniohyoid (GH)] and masticatory jaw-opener activity [anterior digastric (AD)] and cross-correlating lingual retractor activity [styloglossus (STY)] with anterior digastric EMG. A similar bimodal distribution of cross-correlations obtained between mXII neuron activity and AD contractions suggested that the majority of mXII neurons (30/35) could be classified as protrudor- or retractor-related. Neurons classified as protrudor-related cells were located ventrally in mXII; cells classified as retractor-related were more dorsally located, consistent with anatomic and physiological descriptions of the myotopic organization of mXII. 3. Ten mXII protrudor-related neurons responded with a mean of 4.9 +/- 2.2 (SD) action potentials per lick cycle and preceded the peak jaw-opening phase of licking by a mean of 22.3 ms. In contrast, the activity of 20 retractor-related mXII neurons lagged the jaw-opening phase of licking by a mean of 55.9 ms, with a mean of 5.5 +/- 3.4 (SD) action potentials occurring per lick cycle. Five other mXII neurons exhibited nonrhythmic activity during licking and could not be classified as protrudor- or retractor-related on the basis of cross-correlations with the AD. 4. The occurrence of a swallow decreased the licking frequency by 21%, corresponding to an increase of approximately 43 ms in the period between AD contractions.(ABSTRACT TRUNCATED AT 400 WORDS)

ヒト外側翼突筋上頭・下頭の機能的相違について １． 各種基本運動時の活動様式ならびに解剖学的考察

We investigated functional roles of the superior and inferior heads of the human lateral pterygoid muscle (SUP. LPT and INF. LPT, respectively). In 6 subjects EMG activities were recorded from the both heads of the lateral pterygoid muscle and other masticatory muscles. The movements of the incisor and condyle points and biting force were measured. Three-dimensional structure of the temporomandibular joint (TMJ) was examined in 12 cadavers. The findings are summarized as follows.(1) Articular disk can rotate around the condyle backward, but not forward, on the axis of the lateral and medial poles of the condyle to which the articular disk is tightly attached.(2) The SUP. LPT was active primarily in the jaw closing phase and the INF. LPT in the jaw opening phase during chewing. The SUP. LPT and INF. LPT showed reciprocal EMG activities in various basic jaw movements.(3) The SUP. LPT showed the stretch reflex but the INF. LPT did not.(4) The SUP. LPT muscle activity increased rapidly at a lower biting force level, whereas the relationship between the biting force and the activity of the masseter and temporalis muscles changed in a manner quite different from that in SUP. LPT.(5) The SUP. LPT maintains a considerable activity level at the rest position and increases its activity during swallowing, chewing and clenching of the teeth.

Sensory and motor responses of trigeminal and reticular neurons during ingestive behavior in rats.

Activities of 53 neurons in the brain stem were recorded with chronically implanted fine wires in freely eating and drinking rats. Twenty units were isolated from the trigeminal mesencephalic nucleus; 18 were spindle afferents and 2 periodontal afferents. The spindle units were classified into 4 types: 5 units showed rhythmical activity related only to the jaw opening phase during both licking and chewing, 8 units discharged at jaw opening phase during licking, but both at jaw opening and jaw closing phases during eating, 2 units increased phasic activity at jaw opening phase during licking, but increased tonically independent of jaw movements during eating, and the remaining 3 units responded only at jaw closing phase both in licking and eating behavior. Nine units were assumed to be alpha motoneurons isolated from the trigeminal motor nucleus; 2 innervating the temporalis muscle, 3 the masseter muscle, 2 the digastric muscle, and the remaining 2 presumably the pterygoid muscles. These units, with a mean tonic spontaneous rate of about 10 impulses/s, showed phase-related rhythmical burst activities during licking and eating. Four units were isolated from the trigeminal main sensory nucleus. Sixteen units were isolated from the medullary reticular formation and 1 from the pontine reticular formation. Of these 16 units, 3 from the parvocellular part of the medullary reticular formation were presumably premotor interneurons, and 3 units in the "intertrigeminal region", 2 units in the "juxtatrigeminal region", and 8 units in the "supratrigeminal region" were responsive to multiple sensory modalities. These results demonstrate that almost all the units sampled showed characteristic rhythmic activities associated with the position of the tongue or mandible during rhythmical jaw movements.

An analysis of mandibular movement trajectories and masticatory muscle EMG activity during drinking in the guinea pig

Electromyographic (EMG) activity of the anterior digastric, lateral pterygoid, and deep masseter muscles as well as the associated jaw movements during drinking were studied in the awake guinea pig. Drinking was characterized by rhythmic, vertically directed jaw movements with little or no associated lateral movements. The jaw opening phase of each cycle was associated with bilaterally synchronized EMG activity in the digastric and lateral pterygoid muscles, and the jaw closing phase with bilaterally synchronized activity in the masseter muscles. The mean EMG burst durations (± 1 S.E.) in the digastric and masseter muscles were 164.2 ± 14.93 ms and 94.3 ± 26.44 ms, respectively. The digastric muscle EMG burst duration was significantly correlated with drinking cycle time and with masseter muscle EMG onset; on the other hand, masseter muscle EMG burst duration was not correlated with cycle time. These patterns of EMG activity and jaw movement trajectories are similar to those induced by apomorphine in the ketamine-anesthetized guinea pig.