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PubMed1989

Co-contractions in antagonistic hindlimb muscles during simulated step cycle rates.

To determine whether the step cycle rate during locomotion may be limited by mechanical interactions of antagonistic muscles about the ankle, muscle activation patterns were simulated through electrical stimulation and muscle forces monitored in the rat lateral gastrocnemius-soleus (LGS) and tibialis anterior (TA) muscles. Simulations were made in acute experiments on Nembutal-anesthetized rats. Based on EMG data recorded from free-moving rats at 3 treadmill speeds, SOL mean cycle durations, cycles per second (eps), burst durations, and TA onset times following SOL EMG onset were determined. With muscle nerve stimulation based on these temporal patterns, muscle force was monitored from the detached tendons or directly at the approximate insertion sites. To investigate mechanical interactions attributed to the slow-twitch SOL muscle, forces were measured with the LGS intact, and after the SOL was denervated or the tendon was cut. With tendons detached, TA contraction force temporally overlapped with LGS or LG contraction force over periods ranging between 20 and 50 ms at 3.4 cps, 0-10 ms at 4.1 cps, and 0-10 ms at 4.6 cps. LGS force-time traces were asymmetrical, i.e. return time toward baseline force was more prolonged than the time to reach peak force. Without contributions to force from SOL activation, LG rate of relaxation was consistently increased and rate of rise and fall in force-time patterns were more symmetrical. Co-contractions were not observed when LGS contractions followed TA activation. At all cycle rates, forces remained above baseline (range 0.5-4.0 N) between contractions in LGS.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed2006

Spatial and temporal changes of upper trapezius muscle fiber conduction velocity are not predicted by surface EMG spectral analysis during a dynamic upper limb task.

The purpose of the study was to examine the temporal and spatial correlation between estimates of trapezius muscle fiber conduction velocity (CV) and surface EMG instantaneous mean power spectral frequency (iMPF) during dynamic movement of the upper limb. Surface EMG signals were detected from the upper division of the trapezius muscle in 13 healthy volunteers using linear arrays of eight electrodes at three locations in the cephalad-caudal direction. Subjects were asked to tap with their hands in a cyclic manner between targets positioned mid thigh and 120 degrees of shoulder flexion, to the beat of a metronome set at 88 beats per minute for 5 min. Muscle fiber CV and iMPF were estimated for each cycle at the time instant corresponding to 90 degrees of shoulder flexion. Non-significant correlations were identified between CV and iMPF initial values (R(2)=0.03-0.01), rate of change over time (R(2)=0.10-0.004) and normalized rate of change (R(2)=0.12-0.01) at all three locations on the upper trapezius muscle. These results demonstrate that both spatial and temporal variations in trapezius muscle fiber CV are not predicted by EMG spectral analysis during dynamic movement of the upper limb. This finding suggests that spectral analysis cannot be used to infer changes in the spatial and temporal behavior of muscle fiber CV during dynamic tasks.

Adult↗
PubMed1985

Temporalis muscle-galea flap in facial reanimation.

When substantial destruction of the facial nerve occurs as a result of trauma, measures to animate the face, such as transfer of masticatory muscles, must be considered. Unfortunately, these techniques have been limited by a difficult reeducation process for the patient and failure of these muscles to reach sufficiently large areas. A method of extending the temporalis muscle with galea allows rotation into important areas of the face. Case presentations illustrate specific indications, advantages, and disadvantages of this technique.

Adult↗
PubMed1990

Simultaneous 'dual system' rehabilitation in the treatment of facial paralysis.

Simultaneous dual system rehabilitation of facial paralysis involves using two independent reanimation techniques to optimize facial movement in both a quantitative and qualitative manner. These techniques involve the use of nerve grafting or crossover procedures combined with a dynamic muscle transfer. A group of 37 patients who underwent five different combinations of reanimation was analyzed. The techniques were evaluated using a standard rating scheme for judging success of reanimation procedures. The combination of a masseter muscle transfer to the lower region of the face and a cable graft of the upper facial nerve division appeared to offer excellent results in terms of independent motion of the upper and lower regions of the face and good eye closure, while allowing spontaneous mimetic function in 50% of cases. The advantages and disadvantages of the other techniques are described. The clinical situations in which these techniques have advantage over single reanimation techniques are outlined.

Facial Nerve↗
PubMed1990

Functional assessment of subfamily variation in maxillomandibular morphology among Old World monkeys.

Among Old World monkeys, subfamily variation in maxillomandibular form is commonly attributed to divergent dietary and social behaviors. However, our knowledge of any musculoskeletal adaptations for gape in cercopithecines, and folivory in colobines, is incomplete. Such data are requisite to a more informed perspective on the evolutionary morphology of these taxa. Structural analyses of gape and biomechanical efficiency were applied to a representative sample of adult cercopithecids. Factors pertaining to the biomechanical scaling of cranial structures were evaluated with least-squares bivariate regression techniques. To assess subfamily differences in masticatory efficiency, analyses of covariance were made between relevant factors. Cercopithecines achieve increased gape and relative canine size mainly with strong positive allometry of the facial skull, combined with a larger gonial angle. Colobines possess a relatively long masseter lever arm and short facial skull, as well as an enlargened masseter-medial pterygoid complex. Subfamily differences in temporalis lever arm scaling are negligible. Biomechanical comparisons within and between subfamilies suggest that the mechanical advantage of the temporalis is relatively greater than that of the masseter, while the mechanical advantage of both muscles increases with face length. Evidence is presented to stress the need for adequate consideration of the dependent variable in allometric investigations of skull form.

Analysis of Variance↗
PubMed1994

Morphological adaptation to diet in platyrrhine primates.

Morphological features of the jaws and teeth are examined in eight species of platyrrhine monkeys that coexist in the Suriname rainforest. Z-scores calculated from geometric predictions for several features of the feeding apparatus thought to have some functional significance (e.g., tooth dimensions, jaw robusticity, leverage of primary jaw elevators) are compared to a profile of the naturalistic dietary behavior of these species (i.e., proportions of fruit mesocarp, seeds, leaves, and fauna eaten). Several features are found exclusively in those platyrrhines whose dietary preferences are the most limited. Such specializations appear to be associated with a particular protein source exploited by a species to supplement a largely frugivorous diet. Ateles paniscus, which feeds primarily on the mesocarp of ripe fruit, has an adaptive morphology that emphasizes broad incisors. Chiropotes satanas (and to a slightly lesser extent, Pithecia pithecia) is a frugivore/seed predator with large upper and lower canines and a robust mandible. The frugivore/folivore Alouatta seniculus has a relatively large total molar area and effective mandibular condyle height. In all four of these strictly vegetarian species, the leverage of the masseter muscle is greater than that of temporalis. Of the omnivorous species, Cebus apella and C. nigrivittatus exploit both fauna and seeds for protein and exhibit an array of many of the above features, such as large teeth and thick mandibles. Saimiri sciureus, not particularly known for seed predation, departs from Cebus in having less robust canines and a more gracile mandible. All three cebid omnivores have a temporalis with greater leverage than the masseter, indicating a requirement for resisting anteriorly directed forces, for example, using the jaws for vigorous foraging. The lack of any enlarged features, other than incisors, in the omnivorous Saguinus midas may be attributable to the functional constraints of small body size. Because the small size of the gape limits the size of the food parcel ingested, a requirement to enlarge other dentomandibular structures for trituration is alleviated.

Adaptation, Physiological↗
PubMed1982

Further evaluation of the superficial and deep tendons of the human temporalis muscle.

The superficial and deep tendons of the human temporalis muscle and their fasciae were examined for specific attachments. It was found that as they pass inferiorly along the ramus of the mandible, a structure consisting of tendon and fascia (herein referred to as the fascial-tendinous complex of FTC) is projected anteromedially and inferiorly. The FTC is a unifying structure in the oral-buccal area, serving as a common point of attachment for three muscles of mastication (temporalis, masseter, and medial pterygoid) as well as the buccinator, superior pharyngeal constrictor (SPC), and the mylohyoid muscles, and their corresponding fasciae. The FTC creates a defined fascial space containing loose connective tissue, the buccal nerve, and corresponding blood vessels between the posterior buccal region and the anterior ramus and posterior body of the mandible. The FTC has two components: (1) a medial part which merges into the posterior buccal region in the area of the pterygomandibular depression and (2) a lateral part which continues inferiorly to the posterior area of the body of the mandible. A distinct slip of the medial pterygoid muscle was found to attach to the FTC which caused the lingual nerve to be sandwiched between this slip and the main bulk of the medial pterygoid as it inserts into the mandible. The pterygomandibular raphe, as previously described, was not found. Because of the FTC, the buccinator and SPC do not have simple hamulus-raphe-mylohyoid line attachments. The exact relationship of the buccinator and SPC is dependent upon the extent of the FTC. The larger the FTC, the greater are the muscle attachments and vice versa. In large FTCs a separate muscle (Hamular-FTC muscle) was found attaching from the hamulus to the FTC. The pterygomandibular fold was found not to coincide with the "raphe." The concavity of the pterygomandibular depression upon depression of the mandible was found to be the result of the FTC.

Adult↗
PubMed1988

Quantitative electromyography of the masticatory muscles of Pteropus giganteus (Megachiroptera).

Mastication has been studied by cinematography and quantitative electromyography while flying foxes, Pteropus giganteus, were freely feeding on standardized pieces of apple, soaked raisin, and banana. The primarily orthal mandibular movements are caused by mainly bilaterally symmetrical firing of all the masticatory muscles. Asymmetric activity in the superficial and deep masseter and medial pterygoid causes slight protrusion early in opening. Slight lateral deviations at the end of opening and at the start of closing are caused by asymmetric and asynchronous activity in the pterygoids and digastrics, and by asynchronous firing of the deep temporalis and zygomaticomandibularis. Food consistency affects movement characteristics as well as characteristics of muscular activity. In this study electromyograms were digitized and the number of spikes and mean amplitude per interval (set by the filming rate) recorded. Although a significant correlation exists between descriptors, the product thereof appears to be the best predictor of certain kinematic variables (cycle length and maximum excursion of the mandible). On the other hand, the changes in magnitude of muscular activity as a function of the position of a cycle in the reduction sequence and as a function of food consistency are more translated in a variation of the mean amplitude than in a variation of the number of spikes per interval. Observed variation differs among muscles studied. It is most apparent in the superficial and deep masseter and least in the temporalis and zygomaticomandibularis. Late cycles of apple and raisin mastication are long and exhibit large gapes but almost no anterior movement. The adductor activity frequently shows a synchronized, pulsatile pattern leading to an unfused tetanus.

Animals↗
PubMedDate not supplied

Fiber type-specific autoantibodies in a dog with eosinophilic myositis.

Serum from a 2-year-old male Belgian sheepdog with eosinophilic myositis, which particularly affects the masticatory muscles, was tested for the presence of muscle-specific autoantibodies. Control type 2 temporalis muscle fibers were selectively stained following incubation with the patient's serum and staphylococcal protein A conjugated to horseradish peroxidase (SPA-HRPO). Likewise, type 2 fibers in the patient's temporalis muscle were selectively stained with SPA-HRPO. The same staining procedures applied to limb muscle did not result in fiber staining. Proteins isolated from the temporalis and triceps brachii muscles of a normal dog were separated under denaturing conditions by one-dimensional sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The separated proteins were transferred onto nitrocellulose paper and incubated with either sera from the patient, normal dogs, or neuromuscular disease controls. Subsequent incubation with peroxidase-conjugated goat anti-dog IgG demonstrated antibodies to at least four proteins of the temporalis muscle (myosin heavy chain and three unidentified proteins) when incubated with the patient's serum but not with the controls. Under all conditions, antibodies to the proteins of the triceps brachii were not detected. These findings establish the presence of autoantibodies to specific temporalis muscle proteins that may initiate the myonecrosis and inflammatory response as well as limit the distribution of the response.

Animals↗
PubMed1982

Limitation of jaw movement by antagonist muscle stiffness during unloading of human jaw closing muscles.

The unloading reflex in the jaw closing muscles in man was investigated with a view to correlating the jaw closing movement with the timing of the electrical activity of the agonist and antagonist muscles. When the resistance to the forceful isometric bite was suddenly and unexpectedly withdrawn, the closing movement of the mandible was always arrested before the teeth came together. The rapid arrest of the jaw closing movement was not adequately accounted for by the timing of the inhibition of the jaw closing muscles and reflex excitation of the jaw opening muscles. It was observed that the jaw opening muscles, as well as the jaw closing muscles, were always active during the phase of isometric biting on an object between the teeth. It is therefore concluded that the resulting stiffness of the antagonist muscles is the mechanism which is principally responsible for limiting the jaw closing movement after unloading of the agonist muscles.

Adult↗
PubMed1997

An anatomical study of the motor distribution of the mandibular nerve for a masseteric-facial anastomosis to restore facial function.

On account of the complex anatomy at the base of skull, surgery here may result in post operative cranial n. deficits. Facial palsy is often feared and its effects upon the patient's psychological and emotional well-being can be catastrophic. The modest results and the side effects of the facio-hypoglossal anastomosis used for facial rehabilitation have led us to consider an anastomosis between a motor branch of the trigeminal n. and the facial n. Dissection has allowed us to demonstrate that the masseteric n. offers the characteristics and the relationships which should make such an anastomosis feasible.

Cadaver↗
PubMed1989

The infratemporal fossa: a trial clarification.

The contents of the infratemporal fossa have been studied using CT scans, anatomical dissections and radiography of the anatomical specimens. On the strength of this, 3 distinct regions are discernable: the anterior part of the fossa contains the fat pad of the cheek and this area corresponds to the retromaxillo-zygomatic region; the region of the pterygoid m. contains vascular structures and lies behind the preceding region; the pterygopalatine fossa, formerly considered the deepest part, extends the infratemporal fossa superiorly and medially. These anatomical and radiographic findings could serve as a guide to maxillo-facial surgeons dealing with expanding lesions within the infratemporal fossa, or invading it from adjacent regions.

Adipose Tissue↗
PubMed2004

Long-term registration of daily jaw muscle activity in juvenile rabbits.

Understanding control of muscles during various tasks and their adaptive changes requires information on all motor behavior used throughout the day. The total duration of muscle activity depends on the magnitude of its activation and can change during maturation. Therefore, the purpose of this study was to examine the duration of muscle activity (i.e. duty time) exceeding various activity levels in maturing jaw muscles. A telemetric device was implanted into nine juvenile male New Zealand White rabbits to continuously record muscle activity during maturation weeks 9-14. Electrodes were inserted into digastric, superficial and deep masseter, medial pterygoid, and temporalis muscles. Duty times (expressed as a percentage of time) were calculated for activation exceeding different levels (5-90%) of EMG peak activity per 24-h period. At 10 weeks of age, for activation exceeding the 5% level, the duty time of the temporalis (20.0+/-5.2%) was statistically significantly higher than that of the medial pterygoid (11.2+/-1.5%), digastric (11.0+/-5.1%), superficial (12.6+/-5.6%), and deep masseter (8.6+/-5.5%). Duty times declined with increasing activity level. For activation exceeding the 40% level the duty times of the superficial masseter and medial pterygoid were significantly higher than those of the other muscles. During maturation none of the muscles showed a significant change in duty time. However, for activation exceeding the 5% level, the inter-individual variation in duty time decreased significantly for the digastric, and superficial and deep masseter.

Action Potentials↗
PubMed2001

Conditioning of heteronymous H reflex in human temporalis muscle by stimulation of perioral afferents.

A heteronymous H reflex in the temporalis muscle can be elicited by selective stimulation of the masseteric nerve. The present study aimed at defining the optimal amplitude of the H reflex to detect inhibitory changes induced by stimulation of the perioral afferents and at providing new information on the control of masticatory muscles. Sixteen healthy volunteers participated in the experiment. A conditioning stimulus (CS) to the perioral skin was applied at various delays before an ipsilateral selective masseteric nerve stimulation (test stimulus: TS) while the subject was clenching the teeth at 25% of the maximal voluntary contraction. Two intensities of CS and TS were employed, high and low. The peak-to-peak amplitude of the H reflex (TS) and the root-mean-square value of the preceding electromyography were measured and the data analyzed by three-way analysis of variance and Tukey's posthoc tests. For both intensities used the heteronymous H reflex in the temporalis muscle was significantly decreased by prior activation of perioral afferents for delays from 5 to 60 ms. With a delay of 5 and 35 ms the preceding EMG level was not changed, while it was reduced at 20 and 60 ms delay. The intensities used to elicit the heteronymous H reflex of the temporalis muscle were appropriate to detect a reduction in motoneuron excitability. The reduction in the H reflex without a change in the preceding EMG at 5 and 35 ms delays could be due to presynaptic inhibition of the masseteric afferents exerted by the ipsilateral perioral afferents.

Adult↗
PubMed1986

Inhibition of jaw-closing muscle activity by tactile air-jet stimulation of peri- and intra-oral sites in man.

There were two distinct periods of suppression in electromyograms of masseter and temporalis muscles in 8 subjects after light tactile stimulation (a puff of air) of the peri-oral zone; the latencies were 16 and 60 ms, respectively. These effects were similar to those induced by painful electrical stimulation. A single period of suppression with a latency of 50 ms, was evoked by tactile stimulation of the mucosa of the hard palate or of the tongue. Threshold for suppression was lower in mucosa than skin. Low-threshold and fast-adapting receptors are likely to be involved in this reflex inhibition.

Adult↗
PubMed1986

Inhibition of jaw-closing muscles by electrical stimulation of the ophthalmic division in man.

High-intensity stimulation of the supraorbital region elicits, together with a blink reflex, a reflex inhibition of the jaw-closing muscles in normal man. The response differs from the well known inhibition obtained by intra- and perioral stimulation in two main features. Firstly, it consists of a single late silent period (SP), only occasionally preceded by a short and partial decrease of the background EMG activity; secondly, the inhibitory response appears at a rather high threshold, requiring a stimulus intensity which is 4-fold the sensory perception threshold and 3-fold that required to evoke the blink reflex. Electrical and mechanical stimulation of the cornea failed to evoke a significant inhibitory reflex. The silent period and the blink reflex were similarly affected by local anaesthetic infiltration of the supraorbital skin, suggesting that the afferents subserving the two reflexes belong to the same fibre group; the higher threshold of the supraorbital inhibitory response may be explained by the need for a larger spatial summation. The considerable latency gain and relatively rapid habituation shown by the supraorbital inhibitory response imply a multisynaptic circuit, similar to that responsible for the second silent period which occurs following 'oral' stimulation. A common interneuronal net for these two reflexes is suggested by the results of interaction experiments employing combined supra- and infraorbital stimulation.

Adult↗