Tensor tympani muscle: strange chewing muscle

This work seeks to alert medical and odontological staff to understanding and using interdisciplinary handling for detecting different pathologies common otic symptoms. It offers better tools for this shared symptomatology during therapy s conservative phase. Tensor tympani muscle physiology and function in the middle ear have been veiled, even when their dysfunction and anatomical relationships may explain a group of confused otic symptoms during conventional clinical evaluation. Middle ear muscles share a common embryological and functional origin with chewing and facial muscles. This article emphasizes that these muscles share a functional neurological and anatomical dimension with the stomatognathic system; these muscles increased tonicity ceases to be a phenomenon having no logical connections. It offers functionality and importance in understanding referred otic symptoms in common with other extra-otical symptom pathologies. Tinnitus, vertigo, otic fullness sensation, hyperacusia, hypoacusia and otalgia are not only primary hearing organ symptoms. They should be redefined and related to the neighboring pathologies which can produce them. There is a need to understand temporomandibular disorders and craniofacial referred symptomatology from neurophysiologic and muscle-skeletal angles contained in the stomatognathic system. Common symptomatology is frequently observed in otic symptoms and temporomandibular disorders during daily practice; this should be understood by each discipline from a broad, anatomical and clinical perspective.     

Zygomaticomandibularis muscle

The aim of this study was to elucidate the precise anatomy of the zygomaticomandibularis muscle through cadaveric dissection and magnetic resonance imaging (MRI). Five fresh human cadavers and 10 fixed cadavers were dissected. Nine preserved human cadavers were used for the MRI study. Four volunteers took MRIs of their head as well. Zygomaticomandibularis muscle was found in all the cadaveric specimens. It is a fan shaped muscle. The length of the muscle is 25.1 +/- 4.6 mm, and the width at the zygomatic arch is 16.6 +/- 4.2 mm. The thickness is approximately 4.8 +/- 1.9 mm. It originates from the deep layer of the deep temporal fascia approximately 1 cm above the zygomatic arch and is inserted into the superior border and outer surface of the mandible between the coronoid process and mandibular notch. The deepest layer of the masseter muscle covers the lateral surface of zygomaticomandibularis. We believe that this muscle functions as coordinator of the temporalis and masseter in mammals with strong masticatory power but is a degraded or rudimentary muscle in humans.     

Jaw-opening muscle contracts more economically than jaw-closing muscle in rat

Mandibular movement is achieved by coordinated actions of the jaw muscles. To understand the assigned functional role (e.g., motor or postural role) of each jaw muscle, we characterised not only their contractile and energy-consumption properties but also their compositions of myosin heavy chain (MHC) isoforms. The Ca(2+)-dependent isometric tension development and ATPase activity were simultaneously measured in chemically skinned fibers harvested from rat jaw-closing (masseter and temporalis) and jaw-opening (digastric) muscles. After the measurements of isometric tension development and ATPase activity, the MHC compositions in each preparation were determined by SDS-gel electrophoresis. The Ca(2+)-sensitivity of isometric tension development and ATPase activity was significantly (P<0.001) higher in the digastric fibers than in the masseter and the temporalis fibers. The tension cost (ATPase activity/tension) was significantly (P<0.0001) lower in the digastric fibers than in the masseter and the temporalis fibers. The MHCs in the digastric fibers consisted of a mixture of slow type I and fast type II isoforms, while mostly fast type II isoforms in the masseter and temporalis fibers. These results suggest that in rat the jaw-opening muscle contracts more efficiently in terms of the energy use (i.e., more efficient ATP consumption for tension generation) than the jaw-closing muscle.     

Tongue muscle regeneration

Rat's tongues were injured by cold and the reactive processes were observed by light and electron microscopy. Injured animals and untreated controls were injected with aurothiomalate and the cells in tongue muscles which contained gold were observed after increasing injection-sacrifice time intervals. In the very rapid regeneration, gold-containing macrophage-like cells fused with each other and with well preserved parts of myofibers. The selectivity of gold localization suggested, at least morphologically, a macrophage to myoblast development. The possible factors affecting the rate of muscle regeneration have been discussed with special reference to the nature of the injurious stimulus and the type of cellular response.     

Classification of muscle spindle afferents innervating the masseter muscle in rats

Taylor et al. [Taylor, A., Durbaba, R., Rodgers, J.F., 1992a. The classification of afferents from muscle spindles of the jaw-closing muscles of the cat. J Physiol 456, 609-628] developed a method to classify muscle spindle afferents using succinylcholine (Sch) and ramp and hold stretches. They demonstrated that cat jaw muscle spindle afferents show high proportion of intermediate responses to ramp and hold jaw stretch. Together with observations on the responses to Sch their data suggests that the majority of jaw muscle spindle afferents are influenced by a combination of nuclear bag(2) and nuclear chain fibres. Relatively few are influenced solely by nuclear bag(1) fibres. The purpose of this study was to categorize jaw muscle spindle afferent in rodents in response to ramp and hold stretches. Several measures were used to classify spindle afferents including (1) conduction velocity, (2) coefficient of variation (C.V.) of the interspike interval during jaw opening, and (3) the dynamic sensitivity and the initial discharge of spindle afferents before and after succinylcholine infusion (Sch, 100mg/kg, i.v.). Consistent with observations in the cat jaw muscles, the distribution of the conduction velocity and the C.V. of Vmes masseter afferents were unimodal. Therefore, these parameters were of little value in functional classification of spindle innervation. Succinylcholine injection either markedly increased the dynamic sensitivity or produced no change in Vmes afferents. Unlike cat jaw muscle spindle afferents, the effect of Sch on the initial discharge was not clearly separable from those responding or not responding to Sch. These results suggest that rat jaw muscle spindle afferents, have physiological properties that are primarily intermediate in nature and are likely to reflect a predominance of influence from nuclear bag(2) and chain fibres. However, the distinction between bag(2) and chain fibres influences is not as clearly defined in the rat compared to the cat.     

Muscle hardness characteristics of the masseter muscle after repetitive muscle activation: comparison to the biceps brachii muscle

The purpose of this study was to compare hardness characteristics of the masseter muscle to those of the biceps brachii muscle during repetitive muscle movements. Seventeen asymptomatic female subjects participated in this study. Each subject, on separate days, undertook a 5-minute unilateral chewing gum task on the right side and a 5-minute flexion-extension exercise on the right hand with a 2kg dumbbell. Using a handheld hardness meter, muscle hardness was measured in the right masseter and in the biceps brachii muscle at eight time points (before the task, immediately after the task, and at 1, 3, 5, 10, 30, and 60 minutes after the task), and the data obtained before and after the task on each muscle were compared. Comparisons of the normalized data were also performed between the two muscles at each time point. As a result, a significant increase in muscle hardness was seen at 1 minute after the task in the biceps brachii muscle (p=0.0093). In contrast, the masseter muscle showed a tendency to lower hardness, with the lowest point of hardness occurring at 10 minutes after the task (p = 0.0160). Between the two muscles, there was a difference in the normalized data immediately after the task, and at 1, 5, and 10 minutes after the task (0.01 相似文献   

Malaris muscle, the lateral muscular band of orbicularis oculi muscle

Little is currently known about the variations in the muscular band around the orbicularis oculi muscle (OOc) region, and so the aim of the current study was to describe in anatomic terms the morphologic patterns of the lateral muscular bands of the OOc. Sixty-one hemifaces from embalmed Korean adult cadavers (34 males, 27 females; age range, 45-85 years; mean age, 62.6 years; 28 bilateral and 5 unilateral) were dissected to reveal the anatomic features of the region around the OOc. The lateral muscular band originating from the superficial temporal fascia lateral to the OOc was observed in 54.1% of cases. It terminated at the zygomatic arch region in 17 cases (type A, 27.9%), at the cheek region in 11 cases (type B, 18%), and at the angle of the mouth in 5 cases (type C, 8.2%). When the linear length from the lateral canthus to the tragion was set as 100, the length from the lateral canthus to the lateral edge of OOc was 34.0 (male, 34.1; female, 33.7), and the length between the lateral edge of OOc and the lateral muscular bands of OOc was 6.4 (male, 6.5; female, 6.2). The results of this study suggest that the lateral muscular bands of the OOc may play a significant role in facial animation and dimple formation. In addition, these data provide an index of suggested regions to be injected in patients with periorbital rhytides.     

Programming of antagonist muscle stiffness during masticatory muscle unloading in man

The activity of the masseter and digastric muscles was monitored carrying out a controlled, isometric biting task. In 7 out of 10 subjects, the level of activity in the digastric muscle, during the phase of isometric biting, was greater when the subjects expected the resistance between their teeth to yield suddenly than when they were confident that the resistance would not yield. It is therefore concluded that the co-activation of the digastric muscle which occurs during forceful isometric bites can be modified in accordance with the subject's expectation of the outcome of the bite.     

Role of muscle spindle afferents in the control of jaw-closing muscle activity

In order to understand how muscle spindle afferents contribute to the control of jaw-closing muscle activity, the following two experiments were performed in the urethane anesthetized rabbits; 1) EMG activities of the masseter muscle during chewing a test strip were compared before and after the trigeminal mesencephalic tract (Mes V) lesion. The Mes V, where the ganglion cells of jaw-closing muscle spindle afferents are located, was lesioned by thermal cauterization. Since the cells lying around the Mes V may also be damaged, it is possible that the effects of lesioning may partly be ascribed to the destruction of these cells. In order to circumvent this problem, kainic acid was injected into the Mes V one week before the lesioning. 2) Unit discharges were recorded from the Mes V during passive jaw-opening and during chewing a test strip. The response of these units to suxamethonium (SCh) administration was also examined. The results were as follows; 1) In the animals with the Mes V lesion, the facilitatory response of the masseter muscle during chewing the test strip was significantly reduced on the side ipsilateral to the Mes V lesion, while the contralateral masseteric activities were not affected. 2) The Mes V units were classified as the primary and secondary spindle afferents depending on the responses to SCh administration. During chewing, the Mes V units showed discharges locked to a certain phase of a single masticatory cycle. They were classified into 4 types, depending on the time relation between unit discharges and the jaw movement; 1) those fired predominantly on the jaw-opening phase, 2) those fired on the jaw-closing phase, 3) those excited at the beginning of both-jaw opening and power phases and 4) those fired within the period of the masseteric burst. The firing frequency of the third type units increased during the jaw-closing muscle burst induced by application of the test strip between the opposing molars. They were sensitive to SCh administration and supposed to be the primary spindle afferents. It is concluded that the muscle spindles of jaw-closing muscles (presumably primary endings) contribute to the enhancement of jaw-closing muscle activities during chewing.     

Experimental masticatory muscle pain

Ten female subjects with no history of temporomandibular disorders performed five exercises designed to induce masticatory muscle pain. Three of the exercises were replications of Christensen's tooth-clenching (1970) and tooth-grinding (1971) studies and Scott and Lundeen's mandibular protrusion (1980) study. The other two exercises were designed to induce specific unilateral masticatory muscle pain. The amount of muscle pain as well as the time of onset and the duration were assessed by a clinical palpation exam and a pain questionnaire. These five pain-inducing methods did not consistently produce masticatory muscle pain in non-pain subjects. However, certain individuals appeared to be very susceptible to developing pain during or after most of the exercises. These susceptible individuals demonstrated a bilateral muscle pain pattern after the unilaterally stressful exercises. None of the five exercises produced a statistically significant amount of site-specific masticatory muscle pain as determined by either the palpation examination or the pain questionnaire, even when the exercise was intended to produce such specificity. The fact that some subjects did develop masticatory muscle pain is indicative that muscle exercise and fatigue may lead to TMD-like symptoms.     

预成型肌功能矫治器早期肌功能矫治研究进展

儿童在生长发育期存在的不良习惯,可能导致其颌面部肌群的不平衡,增加了(牙合)系统发生错(牙合)畸形的风险。儿童的早期矫治与肌功能训练是为了去除能够造成错(牙合)畸形的病因和进行早期的肌功能训练,从而达到恢复正常颅颌面结构和咬合关系的目的。预成型肌功能矫治器是一类通过改变口面肌肉功能,促进(牙合)发育和颅颌面生长的矫治器,可以对患者的不良习惯及颅颌面畸形的危险因素进行早期的阻断治疗。预成型肌功能矫治器由于其预成型、疗效快、舒适等优点,近年来被广泛使用,该文对预成型肌功能矫治器进行综述。     

The pterygoideus proprius muscle

A bstract — An anomalous muscle was found in the infratemporal fossa of a male cadaver of advanced age. This formation passed between fixed bony attachments at the infratemporal crest (greater wing of the sphenoid) and the inferior part of the lateral pterygoid plate. The muscle was not atrophied but functional significance was not clear.     

体外培养的肌卫星细胞在肌肉冻伤模型中的修复作用研究

目的研究体外培养的肌肉卫星细胞在冻伤模型中的修复作用。方法使用改良的方法在体外获得高纯度卫星细胞,同时通过冻伤得到C57小鼠腓肠肌的冻伤模型。通过注射方法将卫星细胞移植到3周后的冻伤模型中。不同时间取材,通过组织学观察卫星细胞在冻伤模型中的修复能力。结果移植细胞早期表现为灶型的增殖,增殖的细胞呈现漩涡状扩展,周边的细胞迁移很远。细胞移植4周后的组织学证实卫星细胞已经相互融合形成肌管,肌肉体积增大。6周后出现功能恢复。组织学表现为再生的肌纤维有明确的功能性排列,结构更趋于正常组织。结论体外培养的卫星细胞可以修复冻伤的肌肉,表现出良好的修复能力。     

Developing muscle spindles in the mouse masseter muscle studied by electron microscopy

The morphogenesis of the muscle spindles of the masseter muscle was investigated by electron microscopy. The mice used in this study were those from the 16-day-old fetuses to the four-day-old young, and the three-month-old adult ICR mice. At the time of observation the formation of the masseter muscle spindle had already started in the 16-day-old fetus. In the 17-day-old fetus, the sensory nerve terminated not only in the myotube but also in the myoblast in which no myofilaments were yet formed. From the observations on the 16-day-old and 17-day-old fetuses, it is suggested that the myotubes of the intrafusal muscle fibers are formed by the fusion of the myocytes already containing the myofilaments. The gamma motor end-plate appeared two days later than the sensory nerve terminal formation in the muscle spindle. The initial inner capsule of the spindle was observed in the four-day-old young. The cell without the myofilaments appeared amidst the cluster of the intrafusal muscle fibers in the three-day-old young. It is considered that this cell may be the origin of the inner capsule cell. The periaxial space formation and the myelination of the masseteric nerve fiber occurred in the four-day-old young. The formation of the postsynaptic folds was observed in the extrafusal muscle fiber at the same stage. Thus, the muscle spindles, nerve fibers and the extrafusal muscle fibers showed a remarkable development at the same time in this early postnatal stage.