Scanning Electron Microscopic Observation of Myodural Bridge in the Human Suboccipital Region.

STUDY DESIGN: A scanning electron microscopic study performed on three cadaveric specimens focused on the human suboccipital region, specifically, myodural bridge (MDB). OBJECTIVE: This study showed the connection form of the MDB among the suboccipital muscles, the posterior atlanto-occipital membrane (PAOM) and the spinal dura mater (SDM), and provided an ultrastructural morphological basis for the functional studies of the MDB. SUMMARY OF BACKGROUND DATA: Since the myodural bridge was first discovered by Hack, researches on its morphology and functions had been progressing continuously. However, at present, research results about MDB were still limited to the gross anatomical and histological level. There was no research report showing the MDB's ultrastructural morphology and its ultrastructural connection forms between PAOM and SDM. METHODS: A scanning electron microscope (SEM) was used to observe the connection of myodural bridge fibers with PAOM and SDM in atlanto-occipital and atlanto-axial interspaces, and the connection forms were analyzed. RESULTS: Under the SEM, it was observed that there were clear direct connections between the suboccipital muscles and the PAOM and SDM in the atlanto-occipital and atlanto-axial spaces. These connections were myodural bridge. The fibers of the myodural bridge merged into the spinal dura mater and gradually became a superficial layer of the spinal dura mater. CONCLUSION: MDB fibers merged into the SDM and became part of the SDM in the atlanto-occipital and atlanto-axial space. MDB could transfer tension and pulling force to the SDM effectively, during the contraction or relaxation of the suboccipital muscles. LEVEL OF EVIDENCE: N/A.

Effects of physical training on sarcomere lengths and muscle-tendon interface of the cervical region in an experimental model of menopause.

The aim of this study was to describe the structural and ultrastructural aspects of the myotendinous junction (MTJ) and the proximal and distal sarcomeres of the sternomastoid of aged Wistar rats subjected to an experimental model of menopause and swimming training. A total of 20 female elderly rats were divided into the following four groups (n=5 in each group): sedentary/no-menopausal (SNM), trained/no-menopausal (TNM), sedentary/menopausal (SM), and trained/menopausal (TM). The MTJ samples were dissected and analyzed using transmission electron microscopy. We showed that the TNM Group rats exhibited changes in morphological characteristics as a consequence of physical exercise, which included an increase of 36.60% (P<0.001) in the evagination length of the MTJ and a reduction in the length of the distal (77.38%) (P<0.0001) and proximal (68.15%) (P<0.0001) sarcomeres. The SM Group exhibited a reduction of about 275.93% (P<0.001) in the muscle-tendon interface and in the lengths of distal sarcomeres (55.87%) (P<0.0001) compared with SNM Group. Our results suggest that the swimming training under experimental model of menopause promoted tissue reorganization and increased muscle-tendon interaction with a drastic development in the length and thickness of the sarcoplasmatic invaginations and evaginations. In addition, the sarcomeres exhibited different lengths and a reduction in both groups subjected to swimming training.

Effect of ageing on the myosin heavy chain composition of the human sternocleidomastoid muscle.

The myosin heavy chain (MyHC) composition of ageing limb muscles is transformed into a slower phenotype and expresses fast-twitch fibre type atrophy, presumably due to age-related motor unit remodelling and a change in the patterns of physical activity. It is not known if ageing affects the sternocleidomastoid muscle (SCM) in a similar way. The goal of the study was to analyze the MyHC composition and the size of muscle fibres in the ageing SCM by immunohistochemical methods and quantitative analysis and stereology using our own software for morphometry. We hypothesize that with ageing the MyHC composition of SCM transforms similarly as in ageing limb muscles, but the size of the muscle fibres is less effected as in limb muscles. The study was performed on the autopsy samples of the SCM in 12 older males. The results were compared with those published in our previous study on 15 young adult males. An ageing SCM transforms into a slower MyHC profile: the percentage of slow-twitch fibres is enhanced (numerical proportion 44.6 vs. 31.5%, P<0.05; area proportion 57.2 vs. 38.4%, P<0.05). The share of hybrid 2a/2x fibres is diminished (numerical proportion 14.1 vs. 26.8%, P<0.05), the area proportion of all fast-twitch fibres expressing MyHC-2a and 2x is smaller (50.6 vs. 63.5%, P<0.05), and the area proportion of fibres expressing the fastest myosin isoform MyHC-2x is smaller too (19.0 vs. 34.5%, P<0.05). The slower phenotype with the preferential reduction of the fibres expressing the fastest MyHC-2x provide circumstantial evidence for: (i) more fast-twitch than slow-twitch motor units being lost; and (ii) reinnervation by the surviving motor units. There appears to be no significant influence on muscle fibre size, which is congruent with relatively unchanged SCM activity during life.

Ultrastructural features of the myotendinous junction of the sternomastoid muscle in Wistar rats: from newborn to aging.

The myotendinous junction (MTJ) is a major area for transmitting force from the skeletal muscle system and acts in joint position and stabilization. This study aimed to use transmission electron microscopy to describe the ultrastructural features of the MTJ of the sternomastoid muscle in Wistar rats from newborn to formation during adulthood and possible changes with aging. Ultrastructural features of the MTJ from the newborn group revealed pattern during development with interactions between muscle cells and extracellular matrix elements with thin folds in the sarcolemma and high cellular activity evidenced through numerous oval mitochondria groupings. The adult group had classical morphological features of the MTJ, with folds in the sarcolemma forming long projections called "finger-like processes" and sarcoplasmic invaginations. Sarcomeres were aligned in series, showing mitochondria near the Z line in groupings between collagen fiber bundles. The old group had altered "finger-like processes," thickened in both levels of sarcoplasmic invaginations and in central connections with the lateral junctions. We conclude that the MTJ undergoes intense activity from newborn to its formation during adulthood. With increasing age, changes to the MTJ were observed in the shapes of the invaginations and "finger-like processes" due to hypoactivity, potentially compromising force transmission and joint stability.

Incidence of humeral head of biceps brachii muscle: anatomical insight / Incidencia de la cabeza humeral del músculo bíceps braquial - visión anatómica

Biceps brachii is stated as one of the muscles that shows most frequent anatomical variations. Its most commonly reported anomaly is the presence of an accessory fascicle arising from the humerus which is termed as the humeral head of biceps brachii. Evidence shows a clear racial trend in the incidence of the humeral head of biceps brachii. Therefore, detailed knowledge of this variation in different populations is important for surgical interventions of the arm, nerve compression syndromes and in unexplained pain syndromes in the arm or shoulder region. The goal of this study was to elucidate the incidence and morphological features of this muscle in an adult Sri Lankan population. Upper extremities of the total of one hundred thirty five cadavers were dissected and studied for the presence of accessory heads of the biceps brachii muscle. The proximal and distal attachments of the humeral heads as well as their cranio-caudal, antero-posterior and medio-lateral dimensions were recorded. The incidence of humeral head of biceps brachii was found to be 3.7 percent. In all cases, it was found unilaterally and only in male subjects. The humeral head originated from the antero-medial aspect of the humeral shaft and descended and merged with the other two heads to form a common tendon. The results of the present study further highlight the racial variations in the incidence of humeral head of biceps brachii among Sri Lankans. Knowledge of the occurrence of humeral head of biceps brachii may facilitate preoperative diagnosis as well as the surgical procedures of the upper limb thus avoiding iatrogenic injuries.

El músculo bíceps braquial se conoce como uno de los músculos que muestra las variaciones anatómicas más frecuentes. Su anomalía más común es la presencia de un fascículo accesorio proveniente del húmero, que se denomina cabeza humeral del músculo bíceps braquial. La evidencia muestra una clara tendencia racial en la incidencia de la cabeza humeral del músculo bíceps braquial. El conocimiento acabado de esta variación, en las diferentes poblaciones, es importante para las intervenciones quirúrgicas del brazo, en los síndromes de compresión nerviosa y en los síndromes de dolor inexplicable en la región del brazo o del hombro. El objetivo de este estudio fue determinar la incidencia y las características morfológicas de este músculo en una población adulta de Sri Lanka. Fueron estudiados los miembros superiores en 135 cadáveres, disecados para evaluar la presencia de las cabezas del músculo bíceps braquial accesorio. Fueron registrados el origen e inserción de la cabeza humeral del músculo bíceps braquial, así como su dimensión cráneo-caudal, anteroposterior y mediolateral. La incidencia de la cabeza humeral del músculo bíceps braquial se encontró en el 3,7 por ciento de los miembros estudiados. En todos los casos, su presencia era unilateral y sólo presente en hombres. La cabeza humeral se originó en la región antero-medial de la diáfisis del húmero, descendió y se fusionó con las otras dos cabezas para formar un tendón común. Los resultados de este estudio resaltan aún más las variaciones raciales en la incidencia de la cabeza humeral del músculo bíceps braquial, entre los habitantes de Sri Lanka. El conocimiento de la presencia de la cabeza humeral del músculo bíceps braquial puede facilitar el diagnóstico preoperatorio, así como los procedimientos quirúrgicos del miembro superior, evitando las lesiones iatrogénicas.

The masticatory system under varying functional load. Part 1: Structural adaptation of rabbit jaw muscles to reduced masticatory load.

Skeletal muscle fibres can change their myosin heavy-chain (MyHC) isoform and cross-sectional area, which determine their contraction velocity and maximum force generation, respectively, to adapt to varying functional loads. In general, reduced muscle activity induces transition towards faster fibres and a decrease in fibre cross-sectional area. In order to investigate the effect of a reduction in masticatory load on three functionally different jaw muscles, the MyHC composition and the corresponding cross-sectional area of fibres were determined in the superficial masseter, superficial temporalis, and digastric muscles of male juvenile New Zealand White rabbits that had been raised on a soft diet (n=8) from 8 to 20 weeks of age and in those of normal diet controls (n=8). Differences between groups were tested for statistical significance using a Mann-Whitney rank sum test. The proportion and cross-sectional area of fibres co-expressing MyHC-I and MyHC-cardiac alpha were significantly smaller in the masseter muscles of the animals that had been fed soft food than in those of the controls. In contrast, the proportions and cross-sectional areas of the various fibre types in the temporalis and digastric muscles did not differ significantly between the groups. The results suggest that reducing the masticatory load during development affects the contraction velocity and maximum force generation of the jaw-closing muscles that are primarily responsible for force generation during chewing. These muscles adapt structurally to the reduced functional load with changes in the MyHC composition and cross-sectional area mainly within their slow fibre compartment.

A tissue velocity ultrasound imaging investigation of the dorsal neck muscles during resisted isometric extension.

Persons with neck pain exhibit altered patterns of muscle patterning, but limited investigations have been carried out on these alterations or muscle patterning in healthy volunteers. This study investigated the tissue motion of the dorsal neck muscles at the C4 segmental level in 15 healthy subjects during manually resisted head extension. Doppler-based tissue velocity ultrasound imaging (TVI) was used to detect regional tissue deformation, providing indirect evidence of inter-muscular movement patterning. The deep muscles, multifidus and semispinalis, had different muscular movement patterning than the superficial muscles, especially the trapezius muscle. The semispinalis cervicis (SSCerv) was the first deformed upon exercise initiation, followed by multifidus and semispinalis capitis (SSCap). The semispinalis muscles, notably capitis, exhibited a high rate of deformation during the exercise. The trapezius muscle exhibited the least and lowest deformation rate. In conclusion, TVI provided detailed information on regional tissue activity and muscle movement patterning among the dorsal neck muscles. In future studies, data from patients with neck disorders will have to be matched to data from healthy volunteers in a variety of situations and activities.

Effects of increased occlusal vertical dimension on daily activity and myosin heavy chain composition in rat jaw muscle.

Mammalian skeletal muscles change their contractile-protein phenotype in response to mechanical loading and/or chronic electrical stimulation, implying that the phenotypic changes in masticatory muscles might result from new masticatory-loading conditions. To analyze the effects of increased occlusal vertical dimension (OVD) on daily activities and fibre-type compositions in jaw muscles, we measured the total duration of daily activity (duty time) and the myosin heavy chain (MyHC) compositions in the masseter and digastric muscles of freely moving control and bite-opened rats. In the control state, the duty time of the digastric muscle was higher than that of the masseter muscle at activity levels exceeding 5 and 20% of the day's peak activity. The opposite was true at activity levels exceeding 50 and 80% of the day's peak activity. The MyHCs consisted of a mixture of fast and slow types in the digastric muscle. The masseter consisted of mostly fast-type MyHC. The increment of OVD increased not only the duty time at activity levels exceeding 5, 20, 50 and 80% of the day' peak activity in both muscles but also the proportion of MyHC IIa in the masseter muscle and MyHC I in the digastric muscle at the expense of that of MyHC IIb. These results suggest that the increment of OVD changes masseter and digastric muscles towards slower phenotypes by an increase in their daily activities.

Histological and histochemical effects after occlusion alteration in suprahyoid muscles.

This study verified the effect of unilateral teeth extraction on the suprahyoid muscles in gerbils (Meriones unguiculatus). Ten adult male gerbils weighing about 50g had induced occlusal alterations by upper molar teeth extraction on the left side while the other ten animals were only subjected to surgical stress, control group. After 60 days, animals of both groups, experimental and control had the suprahyoid muscles removed and processed for histological and histochemical (adenosine triphosphatase (ATPase), nicotine adenine dinucleotide tetrazolium reductase (NADH-TR) and succinate dehydrogenase (SDH)) purposes. The fiber type area was estimated in % according to Weibel method (point-counting method) using a test-system. The myosinic ATPase pH 4.7 activity in the control group of the digastric, milohyoid and geniohyoid muscles presented a small area of type I fiber and a larger area of type IIa fibers; in the experimental group, significant contractile capacity alteration was not observed. Samples of the digastric, milohyoid and geniohyoid muscles, after SDH activity, showed a small area with high metabolic activity fibers, and a large area with intermediary and low metabolic activity fibers in the control group. The milohyoid muscle of the experimental group presented low metabolic fibers in a reduced area, in both sides, however without significant difference. In the experimental group, high metabolic fibers were observed on the left side in a reduced area in the geniohyoid muscle, but without statistical significance. Thus, the geniohyoid muscle did not change the metabolic activity after occlusal alteration. In conclusion, 60 days of unilateral malocclusion induced was able to alter the fibers oxidative activity of the suprahyoid muscles, however, it does not affect the contractile property of the fibers. The digastric muscle has adequate fibers to produce fast contraction and able to resist to fatigue in intermediate degrees, but became more fatigable after unilateral exodontia.

Effect of unilateral extraction of molar teeth on suprahyoid muscles: macroscopic and ultrastructural aspects.

Anatomical and physiologic components are parts of the stomatognathic system and their interaction results in integrated functional activities. Important alterations in the masticatory system originated by dental loss affect the bone, oral mucosa and muscular function. Dental arch structures specifically designed to receive and expose teeth allow performance of their functions. But the distinction between bony and soft tissues is lost when teeth are removed since there is not a specific function to be completed. The aim of this study was to evaluate the macroscopic and ultrastructural effects of the unilateral extraction of molar teeth on the suprahyoid muscles function, using twenty young male gerbils (Meriones unguiculatus) as the experimental animal model. They were divided in experimental malocclusion (n=10) and control (n=10) groups. The experimental malocclusion group was submitted to exodontia of the left upper molars and the control group was not submitted to this procedure and served as sham-operated. For macroscopic analysis of the suprahyoid muscle, the skin was uplifted and the muscles dissected individually and removed for weight analysis according to Scherle method. The electron microscopy analysis was made in ultra thin sections of small suprahyoid muscle fragments from the experimental and control groups, examined in a Jeol 1010, 880 Kv transmission electron microscope. Several micrographs at magnifications of 3000x, 6000x, 30,000x were randomly selected for the qualitative analysis of the muscle fiber ultrastructures. Sixty days after the induced unilateral occlusal alteration no macroscopic morphologic changes was detected in the suprahyoid muscles and the muscle volume differences between the right and left sides and between groups were not significant. However, in the ultrastructural analysis suprahyoid muscles showed characteristics of specific adaptation to the unilateral occlusal alteration, by the reduced density of subsarcolemmal mitochondria and the shorter and less numerous ramifications in intermyofibrilar mitochondria localized between electronlucid myofibrils. It is concluded that unilateral exodontia of all the upper left molars affect the ultrastructural morphology of suprahyoid muscle fibers.

[Ultrastructural analysis of mouse levator auris longus muscle intoxicated in vivo by botulinum neurotoxin type A]. / Análisis ultraestructural del músculo levator auris longus de ratón intoxicado in vivo por la neurotoxina botulínica tipo A.

We studied the short and long term ultrastructural changes produced by botulinum neurotoxin type A injected in vivo, at a sublethal dose, in mouse levator auris longus muscle. The neurotoxin had a temporary effect on nerve terminals which consisted in a generalized paralysis, that affected the following features of the neuromuscular sample's morphology: size of the nerve terminals, vesicle population, mitochondrial appearance, Schwann cell's morphology, development and distribution of post-synaptic membrane folds, and nuclear morphology of the different elements of the motor end plate. Besides, the amount of endomysial connective tissue was significantly greater compared to non-intoxicated cases, and these changes were more notorious during the first couple of weeks. 20 to 25 days after the injection, during the recovery phase, we observed nerve terminals with a variable appearance: some completely degenerated, enveloped by Schwann cell processes, and new contacts characterized ultrastructurally for their small size, scarce vesicles, partially enveloped by Schwann cells, early myelinized axons and barely developed synaptic folds. Sixty days after the injection, the axon terminal recovered its normal appearance: synaptic vesicles filled the axon's cytoplasm, and the mitochondria showed normal appearing cristae and electronic densities. We conclude that botulinum neurotoxin type A produces changes related to denervation of the nerve terminals and affects the motor end plate components. Schwann cells play an important role both in the morphofuntional recovery of nerve terminals and in their degradation.

Morphological and immunohistochemical changes in muscle tissue in association with mandibular distraction osteogenesis.

PURPOSE: Studies of changes in the surrounding soft tissue in association with distraction osteogenesis in the maxillofacial region, where various different kinds of tissue are tightly packed, are rare. In this study, we performed morphological and immunohistochemical investigations of muscle tissue during mandibular distraction osteogenesis. MATERIALS AND METHODS: Japanese white rabbits were divided into 2 groups. In 1 group, the mandibular bone was distracted at a rate of 1 mm/day (DO group), whereas in the other group it was advanced by 10 mm all at once (O group). The cross-section of the anterior belly of the digastric muscle was examined using hematoxylin and eosin, periodic acid-Schiff (PAS), and proliferating cell nuclear antigen (PCNA) staining methods, as well as scanning electronmicroscopy (SEM). RESULTS: In the DO group, the cross-section of muscle bundle revealed no remarkable changes. In PAS staining, type II fibers gradually disappeared with distraction, but eventually reappeared after a period of consolidation. In the SEM photographs, striation-like laminated structures were evident in the control and the 3-mm distraction, ambiguous in the 6-mm distraction, and not evident in the 10-mm distraction. In contrast, the structure appeared to be restored in the consolidation for 1 week thereafter. In the PCNA immunostaining, the numbers of PCNA-positive nuclei increased during periods of distraction, but subsequently tended to decrease gradually. CONCLUSIONS: Although minute injuries were induced in muscle fibers in association with distraction osteogenesis, it is suggested that muscle fibers regenerate starting in the distraction period and thus can adapt to the environment.

Defective neuromuscular synapses in mice lacking amyloid precursor protein (APP) and APP-Like protein 2.

Biochemical and genetic studies place the amyloid precursor protein (APP) at the center stage of Alzheimer's disease (AD) pathogenesis. Although mutations in the APP gene lead to dominant inheritance of familial AD, the normal function of APP remains elusive. Here, we report that the APP family of proteins plays an essential role in the development of neuromuscular synapses. Mice deficient in APP and its homolog APP-like protein 2 (APLP2) exhibit aberrant apposition of presynaptic marker proteins with postsynaptic acetylcholine receptors and excessive nerve terminal sprouting. The number of synaptic vesicles at presynaptic terminals is dramatically reduced. These structural abnormalities are accompanied by defective neurotransmitter release and a high incidence of synaptic failure. Our results identify APP/APLP2 as key regulators of structure and function of developing neuromuscular synapses.

Craniofacial morphology and growth in the ferret: effects from alteration of masticatory function.

INTRODUCTION: Our hypothesis is that any effects on craniofacial growth and morphology induced by altering the masticatory function will vary according to the species involved. The general aim of this thesis was to test the possible effects of altering the masticatory function on craniofacial growth and morphology, as well as features of masticatory muscles in ferrets. To better elucidate these mechanisms involved, the anatomy of the skull, craniofacial growth pattern and development of occlusion in the ferret were investigated to serve as baseline data. MATERIALS AND METHODS: The description of the anatomy and the radiographic features of the skull was based on observations of 100 skulls of adult ferrets of both sexes. The craniofacial growth pattern was studied in 16 young ferrets of both sexes using serial cephalograms taken on 5 occasions according to age: 25 days, 35 days, 55 days, 80 days and 300 days. To follow the development of occlusion, these animals underwent dental examinations every other day. Forty male ferrets were divided into two groups from the age of 5 weeks. One group was fed hard pellets (hard-diet group), and the other the same diet but softened with water (soft-diet group). After six months, specimens of masticatory muscles were dissected and analysed histochemically, and cephalograms were analysed cephalometrically. RESULTS: The ferret skull is relatively elongated with a short facial region, being longer and broader in males than in females. The viscero- and neurocranium follow an orderly pattern of expansive growth. The growth of the mandible is mainly characterized by an anteroposterior body elongation, and enlargement of the coronoid process. Craniofacial growth in ferrets ceases earlier in female than in male animals. The deciduous teeth erupted between the 19th and 31st postnatal day, and exfoliated approximately between days 51 and 76. The time of eruption of the permanent teeth ranged from 42 to 77 days. The female ferrets were generally ahead of the males regarding the eruption age of permanent teeth. The alteration of the masticatory function by feeding the animals a soft diet caused a hard palate plane more distant from the cranial base plane, smaller inter-frontal and inter-parietal widths, and a slenderer zygomatic arch, as well as a generally shorter and narrower coronoid process. Variations of most variables are greater in animals fed on soft diet. The mean cross-sectional area of type I and type II fibres in the temporalis and the masseter, and type II fibres in the digastricus, as well as the number of capillaries per fibre were significantly smaller in the soft-diet animals. CONCLUSION: Altered masticatory function has induced changes in masticatory muscles and certain effects on craniofacial growth in ferrets. These changes are not the same as those reported in other species (e.g. rats). It appears that reduced masticatory function leads to smaller fibres in the elevators and transverse skull dimensions. The different effects are presumably related to the differences in craniofacial anatomy and growth pattern, as well as the masticatory system, in the various species studied previously.

Development of a mammalian series-fibered muscle.

This study examines the processes by which multiply innervated, serially fibered mammalian muscles are constructed during development. We previously reported that primary myotubes of such a muscle, the guinea pig sternomastoid muscle, span from tendon to tendon and are innervated at each of the muscle's four innervation zones. Secondary myotubes form later, in association with each point of innervation (Duxson and Sheard, Dev. Dyn., 1995; 204:391-405). We now describe the further growth and development of the muscle. Secondary myotubes initially insert onto and grow along the primary myotube. However, as they reach a critical length, they encounter other secondary myotubes growing from serially adjacent innervation zones and may transfer their attachment(s) to these serially positioned secondary myotubes. Other secondary myotubes maintain attachment at one or both ends to their primary myotube. Thus, an interconnected network of primary and secondary myotubes is formed. Patterns of reactivity for cell adhesion molecules suggest that early attachment points between myotubes are the embryonic precursors of adult myomyonal junctions, characterized by the expression of alpha7Bbeta1 integrin. Finally, the results show that secondary myotubes positioned near a tendon are generally longer than those lying in the mid belly of the muscle, and we suggest that the environment surrounding the tendinous zone may somehow stimulate myotube growth.

Myosin heavy-chain isoform composition of human single jaw-muscle fibers.

Diversity in muscle contractile properties is based on the variability of contractile properties of single muscle fibers which in turn is related to the presence of different myosin heavy-chain (MyHC) isoforms. Human jaw muscles are featured by many hybrid fibers expressing more than one MyHC isoform. The purpose of this study was to determine the proportion of each isoform within these fibers for evaluation of the fiber's capacity of producing a large diversity in contractile properties. Electrophoretic separation of MyHC isoforms was performed on 218 single fibers of the temporalis and digastric muscles. Of these fibers, 100 were classified as hybrid fibers. Most hybrid fibers co-expressed MyHC-IIA and -IIX (n = 62); a smaller number co-expressed MyHC-I and -IIA (n = 14), MyHC-I and -IIX (n = 12), and MyHC-I, -IIA, and -IIX (n = 12). The proportions of the individual MyHC isoforms in the hybrid fibers varied highly, suggesting a large range of contractile properties among these fibers.

Afferent and efferent lymph-collecting vessels of the submandibular nodes with special reference to the lymphatic route passing through the mylohyoid muscle.

BACKGROUND: Although metastasis of cancer in the oral region to the submandibular node is well described, there has been no anatomic representation of lymph vessels penetrating the oral floor and draining into the node. MATERIALS AND METHODS: Ninety specimens were obtained from formalin-fixed, donated cadavers. Histologic observations using serial sections followed the macroscopic observations. RESULTS: In 19 of 90 specimens, we found afferent collecting lymph vessels exiting from the mylohyoid surface and draining into the preglandular submandibular node. In 3 of the 19 specimens, collecting vessels passing through the narrow muscle gap with or without arteries, veins, and nerves were identified histologically. The postglandular submandibular node was not evident in the drainage route. CONCLUSIONS: Although it carries a low incidence, because of the direct lymphatic route or pathway between the oral region and preglandular submandibular node, the pathologically positive supraomohyoid node sometimes seems to be found even in elective neck dissection. However, we speculate that sentinel node investigation would reveal the much more critical role of the jugulodigastric node not only as the actual sentinel node but also as the common terminal node along the various drainage routes from the oral region.

Topographic variation of the sternocleidomastoid muscle in a just been born children

The sternocleidomastoid muscle was dissected in one just been born children with approximately nine months of age. The topographic variation of this muscle found in this work suggests your surgical importance and your influence in the appropriate surgical access to repair structures found in the neck.

Examination of intrafascicular muscle fiber terminations: implications for tension delivery in series-fibered muscles.

Mammalian skeletal muscles with long fascicle lengths are predominantly composed of short muscle fibers that terminate midbelly with no direct connection to the muscle origin or insertion. The manner in which these short fibers terminate and transmit tension through the muscle to their tendons is poorly understood. We made an extensive morphological study of a series-fibered muscle, the guinea pig sternomastoid, in order to define the full range of structural specializations for tension transmission from short fibers within this muscle. Terminations were examined in single fibers, teased small bundles of fibers, and in sections at both the light and electron microscopic level. In many cases, sites of fiber termination were defined by reactivity for the enzyme acetylcholinesterase, which also marks myotendinous junctions. Additionally, transport of the lipophilic fluorescent dye, DiI, or injection of Lucifer Yellow were used to visualize undisturbed fiber terminations in whole muscles using confocal and fluorescence microscopy. At the light microscopic level, we find that intrafascicularly terminating fibers end about equally often in either a long progressive taper, or in a series of small or larger blunt steps. Combinations of these two morphologies are also seen. However, when analyzed at higher resolution with confocal or electron microscopy, the apparently smooth progressive tapers appear also to be predominantly composed of a series of fine stepped terminations. Stepwise terminations in most cases join face-to-face with complementary endings of neighboring muscle fibers, some via an extended collagenous bridge and others at close interdigitating myomyonal junctions. These muscle-to-muscle junctions show many of the features of myotendinous junctions, including dense subsarcolemmal plaques in regions of myofibrillar termination and we suggest that they serve to pass tension from fiber to fiber along the longitudinal axis of the muscle. In addition, we observe regions of apparent side-to-side adhesion between neighboring fibers at sites where there is no apparent fiber tapering or structural specialization typical of myofibril termination. These sites show acetylcholinesterase reactivity, and large numbers of collagen fibers passing laterally from fiber to fiber. These latter connections seem most likely to be involved in lateral transmission of tension, either from fiber to fiber, or from fiber to endomysium. Overall, our results suggest that tension from intrafascicularly terminating fibers is likely to be passed along the muscle to the tendon using both in-series and in-parallel arrangements. The results are discussed in light of current theories of tension delivery within the series-fibered muscles typical of large, nonprimate mammals.