Effect of sensory input from the tongue on jaw movement in normal feeding in the opossum

Opossums were presented with solid and liquid foods. The movements of the jaw and tongue were recorded cineradiographically together with recordings of the EMG activity in muscles opening the jaw and moving the base of the tongue (hyoid). The jaw opening in each cycle was in two stages--01 and 02; 01 had a constant amplitude irrespective of the food ingested. Ingestion of liquid (which involved continuous accumulation of a liquid bolus in the valleculae prior to swallowing) was associated with cycles of oral movement in which 02 was small; tongue retraction was associated with this opening. In contrast, solid and semisolid food ingestion was associated with large angles of jaw opening in 02 that also coincided with the tongue retraction. In this latter case a characteristic pattern of EMG activity, in which all the muscles moving the hyoid were simultaneously active, was added to the pattern seen in lapping; this additional activity had an EMG pattern that was consistent with a jaw opening reflex. The findings contrast with other reports that the jaw opening reflex is suppressed in mastication. Experimentally induced tongue contact with a variety of solid surfaces during lapping (an activity involving accumulation of a liquid bolus in the valleculae) induced neither increased jaw opening nor the additional EMG pattern. However, in situations when there was no bolus in the valleculae, additional jaw opening activity was elicited when the tongue contracted solids intra- or extra-orally. It is suggested that the ability of sensory input, from the anterior tongue, to elicit a jaw opening reflex and to change the type of jaw/tongue cycle was dependent upon the extent of bolus accumulation in the valleculae and therefore indirectly upon the consistency of the food.     

Proposal of a new analgesia test based on the observation of nociceptive behavior induced by electric stimulation of dental pulp in the rat

Dental pulp was electrically stimulated in the awake rat. When the stimulus intensity was progressively increased the following four nociceptive reactions successively appeared: jaw opening reflex, scratching, head rotation, vocalization. The threshold of these four reactions was observed before and after administration of three antalgic drugs. No action of the three drugs was observed for the jaw opening reflex. However each drug showed different actions on the other three reactions.     

Inhibition of jaw opening reflexes by stimulation of the central gray matter and raphe nuclei in cats

The effect of stimulation of the mesencephalic central gray matter and raphe nuclei on jaw opening reflexes evoked by excitation of high-threshold (dental pulp) and low-threshold (A-alpha) fibers of the infraorbital nerve afferents was studied in cats anesthetized with chloralose and pentobarbital. The jaw opening reflex evoked by stimulation of the dental pulp was shown to be effectively suppressed by conditioning stimulation of the central gray matter and raphe nuclei. The reflex evoked by stimulation of low-threshold infraorbital nerve afferents also was depressed (but less deeply and for a shorter period than the reflex evoked by stimulation of the dental pulp) during stimulation of the raphe nuclei and caudal zone of the central gray matter, but was unchanged after stimulation of the points located in the rostral zone of the central gray matter. Application of single stimuli or bursts of five stimuli with a frequency of 100 Hz had no effect on the reflexes studied. Short-term stimulation with a burst of 10–20 stimuli with a following frequency of 200–400 Hz led to inhibition of the reflexes, which lasted 450–1000 msec. Long-term stimulation of the central gray matter and raphe nuclei for 30 sec with a frequency of 50 Hz caused inhibition of jaw opening reflexes evoked by stimulation of both high- and low-threshold afferents for 60 min. Impulses from the central gray matter and raphe nuclei thus have a mainly inhibitory action on the jaw opening reflex evoked by stimulation of high-threshold afferents, but they act less effectively on the reflex evoked by stimulation of low-thres-hold afferents. The duration of inhibition depends essentially on the parameters of stimulation.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 16, No. 3, pp. 374–387, May–June, 1984.     

Studies on the hemodynamic changes in the perfused hindlimb induced by the electrostimulation of the sinus nerve in the dog

The effects of intravenous administration of guanethidine and guanethidine plus atropine on the reflex vasodilatation induced in the perfused hindlimb by the electrostimulation of the sinus nerve were studied in dogs.Guanethidine induced a marked decrease in the reflex response of the perfused hindlimb. Moreover, the following administration of atropine completely abolished the hemodynamic response to the sinus nerve stimulation.These findings suggest that the cholinergic system is involved, along with the sympathetic and the histaminegic system, in the genesis of the reflex vasodilatation produced by the electrostimulation of the sinus nerve.     

Kinematic and Diffusion Tensor Imaging Definition of Familial Marcus Gunn Jaw-Winking Synkinesis

Background

Marcus Gunn jaw-winking synkinesis (MGJWS) is characterized by eyelid ptosis, which disappears during jaw movement. Familial MGJWS is an extremely rare condition. Some authors suggested that MGJWS is due to neural misdirection in the brainstem whereas others suggested that aberrant reinnervation or ephapse may be responsible for synkinetic activity. Pathogenesis of this condition is therefore still unclear.

Methodology/Principal Findings

To investigate pathogenetic mechanism in familial MGJWS we performed neurophysiological (EMG, Blink Reflex, Recovery cycle of the R2 component of the blink reflex, Masseter inhibitory reflex, BAEPS and kinematic analysis) and neuroradiological (MRI, Diffusion Tensor Imaging) investigations in a member of a multigenerational family with autosomal dominant Marcus Gunn jaw-winking synkinesis (MGJWS). Kinematic analysis of eyelid and jaw movements disclosed a similar onset and offset of the eyelid and jaw in both the opening and closing phases. The excitability of brainstem circuits, as assessed by the blink reflex recovery cycle and recovery index, was normal. Diffusion Tensor Imaging revealed reduced fractional anisotropy within the midbrain tegmentum.

Conclusions/Significance

Kinematic and MRI findings point to a brainstem structural abnormality in our familial MGJWS patient thus supporting the hypothesis of a neural misdirection of trigeminal motor axons to the elevator palpebralis muscle.     

Functional significance of the coupling between head and jaw movements

When humans open or close the jaw they also move the head. Unintentionally, it rotates backwards when the jaw opens and returns upon jaw closure. We hypothesized that this mutual movement coupling is related to the muscles in the floor of the mouth. A biomechanical model was applied to comprehend the functional significance of this movement coupling. As the jaw opened the jaw opening muscles shortened and became less forceful. Meanwhile they had to stretch the jaw closing muscles. The simulations showed that a simultaneous head extension facilitated jaw opening. A possible functional significance for the coupling between head and jaw movements is that it can extend jaw gape. Head extension can contribute to a wider jaw gape by on the one hand a reduced shortening of the jaw opening muscles and on the other hand by a reorientation of these muscles so that they obtain a more favorable position for jaw opening.     

Electrophysiologic identification and evaluation of stylohyoid and posterior digastricus muscle complex.

PURPOSE: To identify the function of stylohyoid and posterior digastricus (STH-PD) muscle complex by the EMG techniques. METHODS: Unaffected sides of the faces of 30 patients with facial paralysis or hemifacial spasm were investigated. A concentric needle electrode was inserted to the STH-PD muscle complex and another concentric needle electrode was inserted to the orbicularis oris (OO) muscle. Simultaneous recording were obtained from two muscles using electrical stimulation (ES) (in 25 cases) and magnetic coil stimulation (MS) (in 15 cases); and both in 10 cases. Afterwards, the function of STH-PD was studied such as whistling, lip pursing, swallowing, jaw opening and closing. RESULTS: (1) The motor latency of compound muscle action potential (CMAP) of the STH-PD muscle was shorter than that of OO. (2) When the facial nerve was stimulated more distally than the stylomastoid foramen, the CMAP elicited from the STH-PD muscle complex immediately disappeared. (3) Ipsilateral MS was able to elicit the motor evoked potential (MEP) from STH-PD either at intracranially (half of cases) or at the extracranially. While OO muscle was always stimulated intracranially by MS. (4) The STH-PD muscle complex could not be basically recruited by the mimicry except lip pursing. The main recruitment were provided by swallowing and jaw opening. Cortical MS were facilitated during swallowing (5) Late reflex responses appeared in the STH-PD muscle complex during infraorbital-trigeminal and facial nerve ES. CONCLUSION: The STH-PD muscle complex is identified electrophysiologically. Although it is innervated by the facial nerve, its functions are mainly related with jaw opening and oropharyngeal swallowing. However, it is activated by the lip pursing.     

Localization of neurons innervating masticatory muscle spindle and periodontal receptors in the mesencephalic trigeminal nucleus and their reflex actions

The mesencephalic trigeminal nucleus was studied in anaesthetized and curarized rabbits by recording the unitary activity through extracellular microelectrodes and identifying the constituent cell types. Two types of units were found, namely primary afferents supplying jaw raising muscle spindles and periodontal or gingival mechanoreceptors. These two groups of neurons exhibited a rostrocaudal somatotopy: the former occupied the entire rostral portion of the nucleus (A7-P2.3; trochlear decussation being taken as an arbitrary 0 level), the latter was located caudally (P3-P4.5) while the somata of both types of afferent fibres were present between P2.2 and P3. No evidence was found for representation of both tendon organs of jaw muscles and joint receptors. Among the units innervating muscle spindles, secondary afferents were largely more numerous than the primary ones. Among periodontal and gingival mechanoreceptor afferents, incisors were the most widely represented, followed by interalveolar gingiva and molars; the axonal conduction velocity ranged between 9 and 40 m/sec and between 8 and 16 m/sec for ipsilaterally and contralaterally projecting neurons, respectively. The motor responses obtained by electrical stimulation of discrete areas of the MTN confirmed the presence of a high degree of segregation between the two different populations of neurons. In fact, jaw raising movements are obtained when stimulating the area within A7 and P2 containing the somata of spindle afferent neurons, while only jaw opening movements are elicited by stimulation of the caudal levels of the nucleus. These data also show that the periodontal neurons whose somata are located in the MTN participate in the jaw opening reflex, just as the more numerous periodontal mechanoreceptors whose somata are located in the Gasser ganglion. Soma-somatic and soma-axon hillock gap junctions were found among the neurons of the MTN, particularly in the caudal third of the nucleus.     

Differences in loading of the temporomandibular joint during opening and closing of the jaw

Kinematics of the human masticatory system during opening and closing of the jaw have been reported widely. Evidence has been provided that the opening and closing movement of the jaw differ from one another. However, different approaches of movement registration yield divergent expectations with regard to a difference in loading of the temporomandibular joint between these movements. Because of these diverging expectations, it was hypothesized that joint loading is equal during opening and closing. This hypothesis was tested by predicting loading of the temporomandibular joint during an unloaded opening and closing movement of the jaw by means of a three-dimensional biomechanical model of the human masticatory system. Model predictions showed that the joint reaction forces were markedly higher during opening than during closing. The predicted opening trace of the centre of the mandibular condyle was located cranially of the closing trace, with a maximum difference between the traces of 0.45 mm. The hypothesis, postulating similarity of joint loading during unloaded opening and closing of the jaw, therefore, was rejected. Sensitivity analysis showed that the reported differences were not affected in a qualitative sense by muscular activation levels, the thickness of the cartilaginous layers within the temporomandibular joint or the gross morphology of the model. Our predictions indicate that the TMJ is loaded more heavily during unloaded jaw opening than during unloaded jaw closing.     

Effect of hypoxia on the excitability of two cranial reflexes in unanaesthetized fetal sheep

In fetal sheep acute hypoxia causes a decreased incidence of breathing movements and motor activity, and the excitability of polysynaptic reflexes in the hindlimbs is depressed. To determine whether this inhibitory effect extends to other areas in the fetal CNS, we have studied the effect of hypoxia on two reflexes with cranial pathways. The digastric (jaw opening) reflex was elicited by stimulation of the dental nerve through a pair of stainless steel electrodes implanted into the mandible (4 fetuses). The thyroarytenoid muscle of the larynx was reflexly activated by stimulation of the superior laryngeal nerve by a cuff electrode (4 fetuses). Low level stimulation at 1.5-2 X threshold was repeated at approximately 2 min intervals for 3-4 h; the stimulation did not alter the pattern of electrocortical activity, breathing movements, or cause arousal. The amplitude of the digastric reflex was greatest during low voltage electrocortical activity; conversely, the amplitude of the thyroarytenoid reflex was greatest during high voltage electrocortical activity. Isocapnic hypoxia lasting 30-60 min (16 trials), in which the PaO2 was reduced to 12-14 mmHg, did not reduce the amplitude of either reflex. The reduction of thyroarytenoid reflex amplitude which normally occurred during low voltage electrocortical activity was not present during hypoxia. These experiments show that the inhibitory effects of hypoxia on spinal reflexes, breathing movements and motor activity do not include these cranial pathways.     

Organization of reflex sympathetic influence on rate and force of cardiac contraction]

In acute experiments on 21 cats it was proved that the change of afferent impulse on vagus nerves by means of either freeze-block or electrostimulation of their central ends results in differential reflex influences on rhythm and force of the cardiac contractions caused by sympathetic nervous system. The cut of the lower cardiac nerves may cause 'break-up' of the observed reflex, removing or inverting its ino- or chronotropy component. The given phenomenon was revealed in the experiments with high arterial pressure and with absence of tonic chronotropy influences of the left lower cardiac nerve.     

Nociceptive afferent blockade by percutaneous peripheral stimulation in the cat]

Experiments have been performed in order to study the effects of percutaneous peripheral stimulation (PCPS) both on the transmission of messages elicited by recruiting sensory units of the tooth pulp at the thalamic Centrum Medianum Level and on the jaw opening reflex (JOR). Both evoked potentials and JOR were inhibited by stimuli applied to the limbs by means of percutaneous (needle) electrodes. Observed inhibitory effects were not immediate: there was a latency period and progressive induction of these phenomena. The site of the inhibition is still unknown, nevertheless, the demonstration that PCPS was able to inhibit both evoked potentials in Centrum Medianum and JOR support the hypothesis that the analgesic effects may be due to descending inhibition blocking transmission of nociceptive information through the spinal cord.     

Intralimbic evoked potentials in the formation of an instrumental food conditioned reflex to hippocampal electrostimulation in dogs]

In dogs with the electrodes implanted in the hippocampus, amygdala, septum and hypothalamus an instrumental alimentary conditioned reflex (CR) was elaborated to electrostimulation of the hippocampus. Intralimbic evoked potentials (EPs) were studied during the elaboration and extinction of this reflex and during stimulations of limbic structures conducted with the purpose of CR generalization checking. Late EP components in the lateral hypothalamus and central nucleus of the amygdala changed during CR elaboration and extinction and in the hippocampus during amygdala testing. In both cases the amplitude of trace positivity and of slow negative wave was less, when during stimulation of the structure an instrumental movement was initiated than at its absence.     

Preweaning feeding mechanisms in the rabbit.

Muscle contraction patterns and mandibular movements of infant rabbits during suckling and chewing were compared. Oral muscle activity was recorded by fine-wire electromyography, while jaw movements and milk bottle pressure were registered. Suckling and mastication have a comparable cycle duration and share a common pattern of oral muscle activity which consists of a succession of a jaw closer burst, during which the jaw closes and undergoes a power stroke (in mastication), a suprahyoid burst with a stationary or slightly opening jaw and a digastric burst with fast jaw opening (the power stroke of suckling). Compared to suckling, mastication shows decreased jaw opener activity, increased jaw closer activity, development of jaw closing activity in the lateral pterygoid, and increased asymmetry in the masseter by development of a new differentiated motor pattern on the working side. The study shows that the suckling motor pattern enables the infant rabbits to change to chewing with just a few modifications.     

The Striatum and Pain Modulation

The aim of this review was to give a general aspect of the sensorial function of the striatum related to pain modulation, which was intensively studied in our laboratory. We analyse the effect of electrical and chemical stimulation of the striatum on the orofacial pain, especially that produced by tooth pulp stimulation of the lower incisors. We demonstrated specific sites within the nucleus which electrical or chemical stimulation produced inhibition of the nociceptive jaw opening reflex. This analgesic action of the striatum was mediated by activation of its dopamine D₂ receptors and transmitted through the indirect pathways of the basal ganglia and the medullary dorsal reticular nucleus (RVM) to the sensorial nuclei of the trigeminal nerve. Its mechanism of action was by inhibition of the nociceptive response of the second order neurons of the nucleus caudalis of the V par.     

Passive force characteristics of an architecturally complex muscle

In architecturally complex muscles with large attachment areas, it can be expected that during movement different muscle regions undergo different amounts of length excursions. As a consequence, the amount of passive force produced by the regions will differ. Therefore, we tested the hypothesis that during movement the vector of the passive force of such a muscle, which defines the magnitude, position and orientation of the resultant force of the various regions, has no fixed position, between the muscle's center of origin and insertion. As a model for an architecturally complex muscle we used the masseter muscle. It was expected that during jaw opening anterior muscle regions are more stretched than posterior regions, leading to an anterior shift of the passive force vector. A three-component force transducer was used to measure both the position and magnitude of passive force in the masseter muscle of 9 rabbits. Forces were recorded during repeated cycles of stepwise opening and closure of the jaw. The muscle exhibited a clear hysteresis: passive force measured during jaw opening was larger than that during jaw closing. With an increase of the jaw gape there was an approximately exponential increase of the magnitude of the passive muscle force, while simultaneously the passive force vector shifted anteriorly. Moment arm length of passive force increased by about 100%. This anterior shift contributed substantially to the increase of the passive muscle moment generated during jaw opening. It can be concluded that in architecturally complex muscles the increase of the passive resistance moment which is associated with muscle lengthening might not only be due to an increase of the magnitude of passive muscle force but also to an increase of the moment arm of this force.     

A model relating patterns of human jaw movement to biomechanical constraints

After testing the effects of the ways in which several different ligaments and bony constraints would influence movements of the human mandible in three dimensions, a mathematical model based on constraints due to the articular eminences, temporomandibular ligaments and sphenomandibular ligaments has been constructed. The effects of these constraints on jaw movements during opening and lateral movements are analysed. The model predicts the observed translation of the human condyle during jaw opening and Bennett shift during lateral jaw movements. The model is refined to account for observed irregular movements of the condyle during opening and to predict a locus for the instantaneous centre of rotation. The model can also be used to predict the new position taken up by any point on the mandible after the jaw has been opened and/or moved laterally a given amount.     

Further evaluation of an EMG technique for assessment of the deep cervical flexor muscles

A novel surface electromyographic (EMG) technique was recently described for the detection of deep cervical flexor muscle activity. Further investigation of this technique is warranted to ensure EMG activity from neighbouring muscles is not markedly influencing the signals recorded. This study compared deep cervical flexor (DCF) muscle activity with the activity of surrounding neck and jaw muscles during various anatomical movements of the neck and jaw in 10 volunteer subjects. DCF EMG activity was recorded with custom electrodes inserted via the nose and fixed by suction to the posterior mucosa of the oropharynx. Surface electrodes were placed over the sternocleidomastoid, anterior scalene, masseter and suprahyoid muscles. Positioned in supine, subjects performed isometric cranio-cervical flexion, cervical flexion, right and left cervical rotation, jaw clench and resisted jaw opening. Across all movements examined, EMG amplitude of the DCF muscles was greatest during neck movements that would require activity of the DCF muscles, particularly during cranio-cervical flexion, their primary anatomical action. The actions of jaw clench and resisted jaw opening demonstrated significantly less DCF EMG activity than the cranio-cervical flexion action (p < 0.05). Across all other movements, the neighbouring neck and jaw muscles demonstrated greatest EMG amplitude during their respective primary anatomical actions, which occurred in the absence of increased EMG amplitude recorded from the DCF muscles. The finding of substantial EMG activity of the DCF muscles only during neck actions that would require their activity, particularly cranio-cervical flexion, and not during actions involving the jaw, provide further assurance that the majority of myoelectric signals detected from the nasopharyngeal electrode are from the DCF muscles.     

Morphological and biomechanical changes of the feeding apparatus in developing southern flounder,Paralichthys lethostigma

The feeding biomechanics of premetamorphic, metamorphic, and postmetamorphic southern flounder, Paralichthys lethostigma, were investigated to better understand the origin and design of adult pleuronectiform feeding mechanisms. Larval P. lethostigma were sampled from culture tanks every day from first feeding through metamorphosis. Fish were then fixed, cleared, and double stained for cartilage and bone. Postmetamorphic juvenile and adult fish were obtained from aquaculture facilities, fixed, and the muscles and bones of the head dissected. All fish were digitally photographed from both sides of the head. Measurements from digital images included head depth, head length, and quadratal angle (a measure of articular‐quadrate position). Measurements were also made of closing in‐lever, opening in‐lever, and out‐lever moment arm lengths for the determination of lower jaw opening and closing mechanical advantage. In premetamorphic larvae, quadratal angle increased from 40° to 80°, opening lever ratio increased from 0.10 to 0.37, and closing lever ratio increased from 0.06 to 0.40. From these measurements and observations of cleared and double‐stained specimens, it was determined that lower jaw depression and elevation changed from a hyoid‐based to an opercular‐based mechanism prior to the onset of metamorphosis. With migration of the right eye to the left side of the head, quadratal angle remained relatively unchanged at 72° to 84°, opening lever ratio decreased from a high of 0.32 to a low of 0.14, and closing lever ratio decreased to as low as 0.17. Postmetamorphic fish exhibited little change with a quadratal angle of 83° to 84°, an opening lever ratio of 0.19, and a closing lever ratio of 0.17 to 0.19. Paired measurements made on the left (ocular) and right (blind) sides of the head indicated that quadratal angle was asymmetrical during metamorphosis (P = 0.003, α = 0.017). Mechanical advantage for lower jaw elevation was also bilaterally asymmetrical following metamorphosis (P = 0.002, α = 0.013). Because mechanical advantage for lower jaw depression was not directionally asymmetrical in metamorphic or postmetamorphic P. lethostigma, functional asymmetry (lateral jaw flexion) is not predicted for jaw opening. These results suggest differences in the design and function of feeding mechanisms for premetamorphic, metamorphic, and postmetamorphic P. lethostigma. J. Morphol., 2008. © 2008 Wiley‐Liss, Inc.