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At least 1,099 records · Page 61Linked to original sources
PubMed1996

Jaw muscles of Old World squirrels.

The jaw, suprahyoid, and extrinsic tongue muscles were studied in 11 genera, belonging to five tribes, of Old World squirrels. Significant variation in most of the adductor muscles is evident. The most primitive state of sciuromorphy is seen in the African tree squirrels Paraxerus and Funisciurus, especially as reflected in the anterior deep masseter. A derived state of sciuromorphy is found in five genera of Old World squirrels and perhaps evolved independently in each. Reduction of the temporalis muscle was observed in three genera, distantly related to one another. A unique arrangement of the superficial masseter is reported in the Asian giant tree squirrels, Ratufa. The arrangement of the masseter in the African pygmy squirrel, Myosciurus, is very similar to that of the South American pygmy squirrel, Sciurillus. We present hypotheses about the functional significance of these differences. In the derived state of sciuromorphy, which is found in three cases in squirrels that feed extensively on hard fruits, the anterior deep masseter is well positioned to increase the strength of the power stroke of the incisor bite. Among the pygmy squirrels, the position of the anterior deep masseter suggests that it plays a more significant role in molar chewing.

Anatomy, Artistic↗
PubMed1981

Adaptation of the masseter and temporalis muscles following alteration in length, with or without surgical detachment.

Histochemical properties, muscle fiber cross-sectional area, muscle fiber length, and the oxidative capacity of masticatory muscles of female rhesus monkeys were assessed following alteration in functional length by an intraoral appliance or by detachment of the muscle. Experimental groups received the appliance only (A); the appliance and subsequent detachment of the masseter (AD); the appliance and detached masseter, but with surgical reattachment of the masseter to the pterygomasseteric sling (ADR); no appliance, but detachment and reattachment of masseter (DR); or an appliance which was removed after 24 weeks to study posttreatment responses (PT). Animals were sacrificed and the muscles were studied at intervals from 4 to 48 weeks after initiation of the experimental period. The results of these studies led to the following conclusions: (1) Stretching the masseter and temporalis muscles within physiological limits did not significantly alter the proportion of fiber types, although oxidative capacity of the fibers was reduced. (2) Fibers with "intermediate" myofibrillar ATPase activity were no more prevalent in experimental than control muscles. (3) The cross-sectional area of Type I fibers of masseter muscles decreased following some experimental procedures, indicating that recruitment of these fibers is the most sensitive to altered jaw function. (4) Minimal alteration of muscle capillarity was induced by any of the experimental procedures. (5) The lengths of masseter muscle fibers in Group PT and of temporalis muscle fibers in groups AD and ADR were greater than in control animals.

Adaptation, Physiological↗
PubMed1990

Development of coordinated movement in chicks: I. Temporal analysis of hindlimb muscle synergies at embryonic days 9 and 10.

In this study, we examined electromyographic activity for an ensemble of hindlimb muscles during spontaneous activity in chick embryos to advance understanding of early motor coordination and its relationship to later emerging behaviors. Four-channel recordings were obtained from 6 muscles in ovo at embryonic Days 9 and 10. Analyses indicated that when muscles are repetitively active, patterns during embryonic motility are distinct from those for other behaviors. For example, unlike the muscle patterns for locomotion, extensor muscles and flexor muscles are synchronously activated at 50% of the extensor cycle period. Furthermore, flexor and extensor bursts are similar in duration and show little correlation with extensor cycle period. Finally, our data suggest that the ensemble of muscles active can vary from cycle to cycle. This study provides the basis for future studies that will examine neural and biomechanical interactions underlying the development of coordinated movement.

Animals↗
PubMed1984

Myofacial pain dysfunction syndrome: a clinical study of asymptomatic subjects.

The diagnosis of myofacial pain dysfunction (MPD), commonly called temporomandibular joint syndrome, has traditionally been made on the presence of a group of clinical symptoms that produce pain and limitation of movement. The cause of this common illness has been the subject of controversy for over half a century. There has been a lack of agreement on diagnosis, a cause, and treatment. Advanced bioelectronic technology now makes an accurate diagnosis possible, based not merely on clinical symptoms, but on reproducible scientific data. A cause of MPD is discernable and reliable treatment possible, as well as long lasting resolution objectively monitorable with the Mandibular Kinesiograph (MKG 5-R) and Bioelectric Processor (EMIR). A study of mandibular movement and masticular muscle function of 26 "normal" subjects (i.e., clinically asymptomatic) revealed that the overwhelming majority did indeed have dysfunction of the muscles which move and posture the mandible. The significance of this study is twofold. First it demonstrates a valid testing procedure for measuring mandibular movement and muscle function. Second it establishes the fact that most individuals have a physical predisposition to MPD. Changes in the adaptive capacity of the neuromusculature by physical or emotional trauma could then precipitate MPD.

Adult↗
PubMed1991

Expression of superfast myosin in aneural regenerates of cat jaw muscle.

We investigated whether innervation is necessary for the expression of superfast myosin in regenerating cat jaw-closing muscle. Strips of jaw muscle were permitted to regenerate bilaterally in the beds of a fast limb muscle with innervation on one side being prevented surgically. Immunocytochemical analyses using anti-myosin heavy chain antibodies were done at various times postoperatively, the latest being after 78 days. We found little difference between innervated and uninnervated regenerates up to 27 days postoperatively. All regenerating myotubes expressed fetal myosin. In addition, some myotubes stained for superfast or slow myosin, while others stained for both superfast and slow myosins. Subsequently, uninnervated myotubes became atrophic but continued to express fetal, slow, and superfast myosins while innervated myofibers suppressed fetal and slow myosin expression. These results are consistent with the notion that satellite cells of jaw-closing muscles are committed to express superfast myosin during myogenesis, and that the expression of this program is independent of innervation.

Animals↗
PubMed1992

Development of coordinated movement in chicks: II. Temporal analysis of hindlimb muscle synergies at embryonic day 10 in embryos with spinal gap transections.

Spinal neural circuits can recruit muscles to produce organized patterns of activity early in embryonic development. In a previous study, using multichannel electromyographic (EMG) recordings, we characterized burst parameters for these patterns in the legs of chick embryos during spontaneous motility in ovo at embryonic days (E) 9 and E10 (Bradley and Bekoff, 1990). Results of the study suggested both neural and biomechanical factors play an important role in the development of coordinated limb movements. In this study, to explore the contribution of descending neural inputs to the control of leg movements during motility, we applied similar methods to characterize motor patterns produced by the spinal cord in the absence of descending inputs. Thoracic spinal gap transections were performed at E2 and EMG patterns were recorded at E10. Several EMG features for chronic spinal embryos were similar to those for normal embryos and demonstrate that lumbar spinal circuits can be correctly assembled to control limb movements in the absence of connectivity with more rostral neural structures during early differentiation processes. However, certain aspects of the EMG patterns in chronic spinal embryos were different from patterns in normal embryos and provide support for conclusions drawn earlier by Oppenheim (1975). Specifically, our data support the view that propriospinal and/or supraspinal inputs function to regulate the timing of cyclic limb movements controlled by spinal neural circuits. Finally, we consider the possible long-term effects of chronic spinal gap transections as compared to acute spinal transections on the development of motility.

Animals↗
PubMed1996

Spatial and temporal pattern of smooth muscle cell differentiation during development of the vascular system in the mouse embryo.

The initial phase of smooth muscle differentiation in the vascular system of the mouse embryo was observed immunohistochemically with monoclonal antibody against alpha-smooth muscle actin. Few smooth muscle cells were detected in the vascular system of the 9.5-day embryo, where only the dorsal aorta and umbilical artery showed signs of smooth muscle differentiation. In the 10.5-day embryo, smooth muscle cells were observed in the dorsal aorta, ventral aorta, omphalomesenteric artery and vein, umbilical artery and vein, internal carotid artery, aortic arches III and IV, and subclavian artery. The extent of smooth muscle differentiation varied among these vessels and among regions of a vessel. At 11.5 days of gestation, smooth muscle cells appeared in the basilar artery, vertebral artery, aortic arches VI, intersomitic artery, ductus venosus, and caudal artery. Smooth muscle cells were absent from the venous system characteristic of the embryo at the stages examined. Alpha-smooth muscle actin-positive cells were also observed in allantoic mesoderm in the placenta at 9.5 days, when the umbilical vessels were not surrounded by smooth muscle cells. Vascular smooth muscle cells appear to arise independently from mesenchyme at multiple sites in the vascular system.

Actins↗
PubMed1992

Correlations between an autoregressive model coefficient of the electromyogram of human jaw-closing muscles and maximum clenching time at the intercuspal position.

During maximum clenching in the intercuspal position, surface electromyograms of both masseters and both anterior temporales in seven healthy subjects with intact natural dentitions were sampled to generate a four-order, autoregressive model of the myoelectrical signal. The correlation coefficients and the linear regression between the model coefficients and the clenching time were calculated. The first-order autoregressive coefficient had the greatest negative correlation on average. In this model the first-order coefficient relates to muscular fatigue and the slope of the regressive equation relates to the length of time the isometric contraction can be maintained.

Adult↗
PubMed1993

Fibre type distribution in the muscle spindles of cat jaw-elevator muscles.

Small samples of the masseter and temporalis muscles of six adult male cats were dissected free, snap-frozen and cryosectioned. Serial sections from areas with muscle spindles were histochemically stained for myofibrillar ATPase after incubation in acid and alkali buffer, and for reactivity to two different myosin isoform-specific antibodies. Differential reactivity to these four stains identified bag1, bag2 and chain intrafusal fibre types. The most typical distribution of fibres within the spindle was 1 bag1, 1 bag2 and 3-4 chains. Although a few spindles were found in the anterior area of the temporalis that attaches to the coronoid process of the mandible and in the anterior area of the superficial masseter, the vast majority were found in the deepest portion of the masseter. Here spindles were characteristically with a number of simple spindles fused together into complex units.

Adenosine Triphosphatases↗
PubMed1993

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

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

Animals↗
PubMed1994

Disclusion time measurement studies: stability of disclusion time--a 1-year follow-up.

Six of seven women were recalled after 1 year to remeasure their right- and left-side working disclusion times. Before the occlusal adjustment technique known as immediate complete anterior guidance development (ICAGD), these patients presented lengthy mean disclusion times (> 1.0 second) and multiple chronic myofascial pain dysfunction syndrome (MPDS) symptoms. After ICAGD, these patients presented with short mean disclusion times (< 0.7 second) and no chronic MPDS symptoms were observed. At 1-year follow-up, there was no statistical difference between present measurements of disclusion time and those of 1 year earlier. In addition, all six posttreatment patients demonstrated no observed chronic MPDS symptoms. However, the symptom of nocturnal bruxism appeared to recur with some chronic regularity. These results suggest that, for this population, disclusion time was stable over the 1-year period of observation, and the short disclusion time appears to allow normal daily muscle function with significantly lessened appearance of chronic myofacial pain dysfunction symptoms.

Analysis of Variance↗
PubMed1990

Histochemical analysis of the masseter and temporalis muscles in macaca mulatta after mandibular advancement using rigid or nonrigid fixation.

This study compared the histochemical characteristics of the temporalis and masseter muscles in monkeys who underwent mandibular advancement with and without immobilization of the mandible. The results showed, when compared with controls, that the animals who underwent maxillomandibular fixation (MMF) following advancement of the mandible had significant atrophy in both temporalis and masseter muscles. In contrast, much less myoatrophy was noted in the animals who underwent rigid internal fixation and no MMF following advancement of the mandible.

Analysis of Variance↗
PubMed1991

Temporal pattern of skeletal muscle changes in lambs fed cimaterol.

The objectives of this study were to compare the efficacy of 3-week vs 6-week dietary administration of the beta-adrenergic agonist cimaterol on skeletal muscle growth, and to measure the changes in muscle nucleic acid and protein concentration and content to provide evidence regarding the mechanism(s) by which cimaterol stimulates muscle hypertrophy in growing ruminants. Two groups of 12 Dorset or Dorset-Finn cross ram lambs weighing 36 kg or 33 kg were assigned to treatment intervals of 3 or 6 weeks, respectively. Lambs within each weight group were randomly assigned to receive 0 or 10 ppm cimaterol in a complete mixed diet fed ad libitum. Initial live weights and treatment periods were chosen to achieve similar slaughter weights. Cimaterol increased the mass of three hind leg muscles 30% and 25% on average (both P less than .001) with 3- and 6-week administration, respectively, resulting in identical average muscle weights of treated lambs at both treatment intervals. The mean mass of these 3 muscles, expressed as a percentage of body weight, was increased 18.6% (P less than .001) at both treatment intervals. RNA concentration and content of the semitendinosus muscle were increased 24.8% (P less than .01) and 84.6% (P less than .001), respectively, after 3 weeks of treatment, but neither was significantly different from controls after 6 weeks. DNA concentration in the muscle was reduced 42% (P less than .05) with 3-week cimaterol administration, and was 25% less than controls (P greater than .05) in lambs fed cimaterol for 6 weeks. Total DNA content of the semitendinosus was unchanged at either treatment interval.(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenergic beta-Agonists↗
PubMed1998

The short-term effect of stabilization-type splints on local cross-sectional dimensions of muscles of the head and neck.

STATEMENT OF PROBLEM: Patients with temporomandibular disorders may have a cluster of joint and muscle disorders characterized primarily by pain, joint sounds, and irregular or deviating jaw function. PURPOSE: This study evaluated changes in local cross-sectional dimensions of muscles of the head and neck associated with short-term application of "splint therapy" using the diagnostic approach of high resolution gray-scale ultrasonography. MATERIAL AND METHODS: The study included 15 subjects with signs and symptoms of temporomandibular disorders, 10 in the internal derangement type (IDT) III-a group, and 5 in the myalgia type I (MT I) and myalgia type II (MT II) group. Ultrasonographic investigation was performed with a linear (B-scan) 7.5 MHz small-part transducer to visualize the anterior temporalis, anterior and deep masseter, anterior and posterior digastric, and sternocleidomastoid muscles. The absolute asymmetry index was used to assess local muscle asymmetry patterns and to evaluate the respective effect of occluding splints, with the mean maximum muscle diameter of the respective right and left sides calculated from 3 consecutive measurements before and after splint therapy. RESULTS: A comparison of pretreatment with 2-month follow-up values revealed a slight decrease in the overall mean local cross-sectional dimensions in the internal derangement type III-a group (0.3 mm) and a moderate decrease in the myalgia type I/II group (3.3 mm). With an overall mean pretreatment absolute asymmetry index of 1.3% for the internal derangement type III-a group and 0.5% for the myalgia type I/II groups, the 2-month follow-up showed the internal derangement type III-a group to be associated with a moderate (1.2%) and the myalgia type I/II groups with a slight (0.1%) decrease in the respective overall mean pretreatment absolute asymmetry indices. CONCLUSION: This study suggests that stabilization-type splints are effective in the reduction of local muscle thicknesses and asymmetries. Further studies are necessary to evaluate muscle-site specific effects in patient and nonpatient groups and to relate these effects to variables such as bite force, preferred chewing side, facial structure, and occlusion.

Adult↗
PubMed1999

Tongue muscle activity after orthodontic treatment of anterior open bite: a case report.

A case report of a Class I malocclusion with an anterior open bite and bimaxillary dental protrusion was presented. The patient had a tongue thrust swallow and slight lisping. After the treatment, significant adaptation in electromyographic pattern of genioglossus muscle activity during swallowing was determined. However, remarkable change in the electromyographic pattern of the genioglossus muscle did not occur during chewing.

Adult↗
PubMed1991

Bicoronal flap approach to the temporomandibular joints.

The bicoronal scalp flap provides an excellent approach to the temporomandibular joint, particularly in cases where bilateral operation is required. It is also indicated when wide exposure is required and when previous surgery may make more conventional techniques difficult. In this report, the anatomy and indications for this approach are reviewed, the operative technique is described and complications are discussed.

Ankylosis↗