Mandibular movements and their control inHomarus gammarus

Summary The skeletal morphology, musculature and innervation of the mandible of the common lobster,Homarus gammarus, are described as a basis for the functional study included in the two subsequent papers.Although the mandible articulation takes the form of a hinge with movement in a single plane, the musculature of the mandible is complex. The main muscles are similar to those ofAstacus (Schmidt, 1915) but some smaller, previously undescribed muscles were found.As forAstacus (Keim, 1915) andCambarus (Chaudonneret, 1956) the mandibular muscles are innervated by two nerve trunks, the inner and outer mandibular nerves. However, differences occur in the branching of these nerves and the muscles which they innervate.A group of sensory cells associated with the posterior stomach nerve (omn 4) are described. It is suggested that these form a proprioceptive organ associated with the hypodermis overlying the lateral mandible articulation.An interesting group of neurones lying at the confluence of nerve branches from omn 2, omn 3, and omn 4 is described.     

The functional significance of morphological variation of the human mandible and masticatory muscles

A review is given of what is known about the functional significance of variation of the morphology of the human mandible and jaw muscles. First, the mandible is a lever transferring muscular forces to the teeth. The angle between corpus and ramus and the width of the ramus are particularly relevant in this respect as they determine the mechanical advantage of the lever system and the capacity for sagittal (open-close) movement. The stability of the mandible in asymmetric bites is especially affected by the ratio between the intermolar and intercondylar distances. The repertoire of bite forces that can be generated at any tooth and the loading pattern of the temporomandibular joint are strongly dependent on the relative size of the masseter, temporalis and medial pterygoid muscles. Second, executing its function as a lever, the mandible is subjected to shearing, bending and torsional forces. The bony parts harbouring the teeth, joints and muscle attachments serve to counter these forces; additional strength is needed in three areas i.e. in the symphysis, the condylar neck and in the transition area between corpus and ramus. In human populations there are clear-cut patterns of correlation between some facial skeletal traits, jaw joint morphology and strength and line of action of the jaw muscles. As a result, facial morphologies can be distinguished with marked differences in mechanical performance of their masticatory apparatus. It is suggested that they emerge as a result of diverging environmental influences during postnatal growth.     

Interrelationships Between Bones,Muscles, and Performance: Biting in the Lizard Tupinambis merianae

The origins of and potential constraints on the evolution of phenotypic diversity remain one of the central questions in evolutionary biology. The vertebrate skeleton is governed by historical, developmental, architectural, and functional constraints that all play a role in establishing its final form. Whereas the factors underlying shape variation in single bones are fairly well understood, this is less so the case for complex assemblages of bones as observed in the cranium or mandible. It is often suggested that the final phenotype must reflect the mechanical constraints imposed by the loading of the skeleton as bones remodel to withstand loading. Yet, in the cranium, in contrast to the mandible, the final phenotype is likely constrained by demands other than loading including the protection of sensory systems and the brain. Architectural design constraints may further limit the final form of complex units like the vertebrate cranium. Here we use geometric morphometric approaches to quantify the shape of the cranium and mandible in a lizard and test whether the observed shape co-varies with both the muscles attaching to these structures as well as functional traits such as bite force. Our results show that co-variation between the cranium and mandible is significant and likely driven by the muscles that link the two systems. Moreover, our results show that the patterns of co-variation are stronger between the mandible and ventral side of the cranium. Muscular cross sectional areas, bite force, and the ventral side of the cranium, also co-vary more than the dorsal side of the cranium does with muscle properties and function. Finally, our results show sex-specific patterns of co-variation with males showing a stronger degree of integration between the cranium, mandible, muscles and bite force suggesting that constraints on bite force drive the evolution of cranial shape to a greater extent in males compared to females.     

Functional morphology of the jaw muscles of two species of imperial pigeons, Ducula aenea nicobarica and Ducula badia insignis

1. The functional morphological study of the jaw muscles of 2 species of Imperial Pigeons, Ducula aenea nicobarica and Ducula badia insignis has revealed that the structural variations of the bill, osteological and connective tissue elements, and muscles of the jaw apparatus may be correlated to functional diversity in the fruit-eating adaptation of these birds. 2. Both the species of Ducula possess moderately long, thick and stout bill with flexion zones inside, elongated orbital process of the quadrate, stout pterygoid, broad palatine and wide mandibular ramus on either side with increased retroarticular space. Such skeletal modifications together with increased orbital space indicate wide attachment-sites for the muscles, aponeuroses, tendons, and ligaments. 3. The morphology of the quadrato-mandibular joints suggests possible 'coupled kinesis' of the upper jaw, along with depression of the lower jaw. However, in a rhynchokinetic upper jaw as possessed by these birds, the kinesis is just moderate. Hence the gape of the mouth is mainly effected by the depression of the lower jaw, rather less so by the protraction of the upper jaw. 4. Among the functional groups of muscles, M. depressor mandibulae, M. adductor mandibulae externus, M. pseudotemporalis profundus, and M. pterygoideus are especially well developed. The various components of these muscles are provided with stiff as well as wide aponeuroses and tendons (much stronger than those observed in Columba), indicating forceful opening and closure of the beaks for plucking off the fruit, grasping it hard and manipulating it with the help of the beaks before swallowing. 5. The fleshy insertion of the outer slip of M. pseudotemporalis profundus extends ventrally over the dorsolateral surface of the mandible much more than it does in Columba. Further, 2 short and stiff aponeuroses at the rostral insertion of the inner slip of the muscle increase the force of adduction on the mandible. 6. M. adductor mandibulae posterior has not only wider origin and insertion, but also greater mass of fibres than that observed in Columba. 7. M. adductor mandibulae externus and M. pterygoideus form muscle-complexes with the predominance of bipinnate and multipinnate arrangements of fibres and with occasional joining fibres between their components. Such arrangements of fibres indicate sustained force-production, rather than faster movements of the jaw apparatus. 8. M. pterygoideus ventralis lateralis has a well developed 'venter externus' slip which has its thick and fleshy insertion on the outer lateral angular and articular mandible.(ABSTRACT TRUNCATED AT 400 WORDS)     

Shark Pharyngeal Muscles and Early Vertebrate Evolution

This study provides a new classification of shark pharyngeal muscles, leading to a re-interpretation of the evolutionary history of these muscles. It begins with Edgeworth's developmental classification but also incorporates phylogenetic and functional information. The two basic groups of pharyngeal muscles are (1) branchial (including deep interbranchials and superficial constrictors) and (2) spinal (including epaxial and hypobranchial muscles). Most of the branchial muscles are also present anteriorly in the mandibular and hyoid segments, indicating that these were once typical branchial segments. The extrabranchial cartilages and gill septa are used as landmarks for dividing the interbranchials from the superficial constrictors. These landmarks reveal that the most important expiratory muscles in the anterior pharynx (most parts of "constrictor hyoideus", interhyoideus, levator palatoquadrati, spiracularis, and intermandibularis) are actually enlarged interbranchial muscles that have taken on a surface location. "Shrinking" these enlarged interbranchials and returning them to a deep location produces a simple, metameric reconstruction of the pre-gnathostome pharynx that fits what is known about thelodonts and other fossil agnatha related to gnathostomes. Finally, the pharyngeal muscles of bony fishes are considered, and concluded to have evolved from a sharklike condition through an acanthodian-like intermediate. © 1997 The Royal Swedish Academy of Sciences. Published by Elsevier Science Ltd.     

A biomechanical model for analysis of muscle force,power output and lower jaw motion in fishes

Fish skulls are complex kinetic systems with movable components that are powered by muscles. Cranial muscles for jaw closing pull the mandible around a point of rotation at the jaw joint using a third-order lever mechanism. The present study develops a lever model for the jaw of fishes that uses muscle design and the Hill equation for nonlinear length-tension properties of muscle to calculate dynamic power output. The model uses morphometric data on skeletal dimensions and muscle proportions in order to predict behavior and force transmission mediated by lever action. The computer model calculates a range of dynamic parameters of jaw function including muscle force, torque, effective mechanical advantage, jaw velocity, bite duration, bite force, work and power. A complete list of required morphometrics is presented and a software program (MandibLever 2.0) is available for implementing lever analysis. Results show that simulations yield kinematics and timing profiles similar to actual fish feeding events. Simulation of muscle properties shows that mandibles reach their peak velocity near the start of jaw closing, peak force at the end of jaw closing, and peak power output at about 25% of the closing cycle time. Adductor jaw muscles with different mechanical designs must have different contractile properties and/or different muscle activity patterns to coordinate jaw closing. The effective mechanical advantage calculated by the model is considerably lower than the mechanical advantage estimated from morphological lever ratios, suggesting that previous studies of morphological lever ratios have overestimated force and underestimated velocity transmission to the mandible. A biomechanical model of jaw closing can be used to interpret the mechanics of a wide range of jaw mechanisms and will enable studies of the functional results of developmental and evolutionary changes in skull morphology and physiology.     

山溪鲵头部肌肉大体解剖

通过染色、解剖、观察和绘图对山溪鲵头部肌肉做了详细描述.山溪鲵头部肌肉包括头侧肌肉、头腹肌肉、眼部肌肉及喉部肌肉.其肌肉组成与有尾类头部肌肉的一般构成基本一致.从第二鳃弓游离端内侧发出一细条状肌纤维,附着在三角骨外侧末端,此种情况在以前其他有尾类肌肉系统研究中未见报道.     

Muscle strength and mineral densities in the mandible

Bone mineral density (BMD) in the femoral neck and lumbar spine was measured for 355 postmenopausal 48- to 56-year-old women and the BMD in five different regions in the mandible for 77. All 355 women were also classified according to the size of the masseter muscle. Both skeletal measures and the BMD of the buccal cortex distally from the foramen mentale were compared with the size of the masseter muscle. This study indicates that functional stress, caused by the masseter muscle, is involved in maintaining bone mineral density in edentulous regions of the mandible. Those individuals who are physically active or are bruxists may lose less mineral, after extractions of teeth, from those regions of the jaw bones where the muscles are attached.     

Quantitative method for comparison of skeletal muscle architectural properties.

A numerical method is presented which calculates the architectural difference index between two muscles. This index is based upon the parameters, identified using statistical discriminant analysis, which best characterize the various muscles. This index can be used to reduce multiple architectural properties into a single value and may be useful in selecting donor muscles which are required to perform a substitute function for another muscle which has been lost or injured.     

Jaws that snap: control of mandible movements in the ant Mystrium

Ants of the genus Mystrium employ a peculiar snap-jaw mechanism in which the closed mandibles cross over to deliver a stunning blow to an adversary within about 0.5 ms. The mandible snapping is preceded by antennation and antennal withdrawal. The strike is initiated by contact of the adversary with mechanosensory hairs at the side of the mandible, and is powered by large yet slow closer muscles whose energy is stored by a catapult mechanism. Recording of closer muscle activity indicates that the mandibles are not triggered by any fast muscle. Instead, we suppose that activity differences between the left and right mandible muscles imbalance a pivot at the mandible tip and release the strike. The likelihood for the strike to occur can be modulated by an alarm pheromone. The presence of specialized sensilla and of a complex muscle receptor organ shows that the mandibles are also adapted to functions other than snapping and suggests that the force of the mandible can be finely adjusted for other tasks.     

An atypical Bronze Age mandible from Żerniki Górne,Poland

The unusual anatomical features of a Bronze Age mandible are described. Of particular interest were the shelf-like ridges which were located approximately midway along the rami. These ridges probably formed the insertion areas for the masseter muscles. Of two possible explanations presented to account for the unusual morphological variations, the more likely is the congenital absence of the superficial portions of the masseter muscles. However, an alternative explanation is presented suggesting the presence of shortened superficial portions of the masseter muscle which could explain the contour of the shelf.     

Anatomical anomaly of human digastric muscles

In the submandibular region an anatomical anomaly of muscle arrangement was found. Between the left and right digastric muscles, asymmetric accessory digastric muscles were detected, which all arose from the mandible and were attached to the hyoid bone. Furthermore, the right anterior digastric muscle had an accessory belly. These anomalies of digastric muscles may be anatomical manifestations of a functional support of the mylohyoid muscle.     

A method to predict muscle control in the kinematically and mechanically indeterminate human masticatory system

A method is proposed to generate muscle activation patterns for goal-directed movements of the human masticatory system. This system is special because apart from a larger amount of muscles than degrees of freedom its joints do not restrict its movements a priori. Therefore, each muscle is able to influence all six degrees of freedom which makes the system kinematically and mechanically indeterminate. Furthermore, its working space is principally determined by the dynamical properties of its muscles and not by passive constraints.The presented method determines the contribution of each degree of freedom to a movement of a reference point on the mandible. It avails of straightforward mathematical techniques like Linear Programming. It does not require a separate trajectory planning step. It was applied in a six degrees of freedom dynamical mathematical model of the human masticatory system. This model which was based upon rigid-body dynamics incorporating skull morphology and muscle architecture including dynamical properties. Movements were exclusively defined by a goal position of the mandibular reference point.The method proved to be robust in generating muscle activation patterns for both feasible and infeasible movement tasks. Generally, they were accomplished faster than habitually observed. If the task was infeasible the movement stopped at the outer boundary of the working space at the side of the unreachable goal. The method, therefore, enables to explore the working space of the mandible and the factors that are relevant for its boundaries.     

Hardware and software for EMG recording and analysis of human respiratory muscles

This paper presents a new hardware and software system that allows not only recording the EMG of different groups of the respiratory muscles but also performing its amplitude-frequency analysis to determine the change in the contribution to the function of breathing of the respiratory muscles and detect early signs of fatigue of the respiratory muscles. The presented system can be used for functional diagnostics of breath in patients and healthy subjects and athletes.     

Evolution of skull and mandible shape in cats (Carnivora: Felidae)

The felid family consists of two major subgroups, the sabretoothed and the feline cats, to which all extant species belong, and are the most anatomically derived of all carnivores for predation on large prey with a precision killing bite. There has been much controversy and uncertainty about why the skulls and mandibles of sabretoothed and feline cats evolved to become so anatomically divergent, but previous models have focused on single characters and no unifying hypothesis of evolutionary shape changes has been formulated. Here I show that the shape of the skull and mandible in derived sabrecats occupy entirely different positions within overall morphospace from feline cats, and that the evolution of skull and mandible shape has followed very different paths in the two subgroups. When normalised for body-size differences, evolution of bite forces differ markedly in the two groups, and are much lower in derived sabrecats, and they show a significant relationship with size and cranial shape, whereas no such relationship is present in feline cats. Evolution of skull and mandible shape in modern cats has been governed by the need for uniform powerful biting irrespective of body size, whereas in sabrecats, shape evolution was governed by selective pressures for efficient predation with hypertrophied upper canines at high gape angles, and bite forces were secondary and became progressively weaker during sabrecat evolution. The current study emphasises combinations of new techniques for morphological shape analysis and biomechanical studies to formulate evolutionary hypotheses for difficult groups.     

Multiple Profile Models Extract Features from Protein Sequence Data and Resolve Functional Diversity of Very Different Protein Families

Functional classification of proteins from sequences alone has become a critical bottleneck in understanding the myriad of protein sequences that accumulate in our databases. The great diversity of homologous sequences hides, in many cases, a variety of functional activities that cannot be anticipated. Their identification appears critical for a fundamental understanding of the evolution of living organisms and for biotechnological applications. ProfileView is a sequence-based computational method, designed to functionally classify sets of homologous sequences. It relies on two main ideas: the use of multiple profile models whose construction explores evolutionary information in available databases, and a novel definition of a representation space in which to analyze sequences with multiple profile models combined together. ProfileView classifies protein families by enriching known functional groups with new sequences and discovering new groups and subgroups. We validate ProfileView on seven classes of widespread proteins involved in the interaction with nucleic acids, amino acids and small molecules, and in a large variety of functions and enzymatic reactions. ProfileView agrees with the large set of functional data collected for these proteins from the literature regarding the organization into functional subgroups and residues that characterize the functions. In addition, ProfileView resolves undefined functional classifications and extracts the molecular determinants underlying protein functional diversity, showing its potential to select sequences towards accurate experimental design and discovery of novel biological functions. On protein families with complex domain architecture, ProfileView functional classification reconciles domain combinations, unlike phylogenetic reconstruction. ProfileView proves to outperform the functional classification approach PANTHER, the two k-mer-based methods CUPP and eCAMI and a neural network approach based on Restricted Boltzmann Machines. It overcomes time complexity limitations of the latter.     

Model sensitivity and use of the comparative finite element method in mammalian jaw mechanics: mandible performance in the gray wolf

Finite Element Analysis (FEA) is a powerful tool gaining use in studies of biological form and function. This method is particularly conducive to studies of extinct and fossilized organisms, as models can be assigned properties that approximate living tissues. In disciplines where model validation is difficult or impossible, the choice of model parameters and their effects on the results become increasingly important, especially in comparing outputs to infer function. To evaluate the extent to which performance measures are affected by initial model input, we tested the sensitivity of bite force, strain energy, and stress to changes in seven parameters that are required in testing craniodental function with FEA. Simulations were performed on FE models of a Gray Wolf (Canis lupus) mandible. Results showed that unilateral bite force outputs are least affected by the relative ratios of the balancing and working muscles, but only ratios above 0.5 provided balancing-working side joint reaction force relationships that are consistent with experimental data. The constraints modeled at the bite point had the greatest effect on bite force output, but the most appropriate constraint may depend on the study question. Strain energy is least affected by variation in bite point constraint, but larger variations in strain energy values are observed in models with different number of tetrahedral elements, masticatory muscle ratios and muscle subgroups present, and number of material properties. These findings indicate that performance measures are differentially affected by variation in initial model parameters. In the absence of validated input values, FE models can nevertheless provide robust comparisons if these parameters are standardized within a given study to minimize variation that arise during the model-building process. Sensitivity tests incorporated into the study design not only aid in the interpretation of simulation results, but can also provide additional insights on form and function.     

Classification ofBacillus thuringiensis strains

An updated classification ofB. thuringiensis strains according to flagellar antigens is presented. Twenty-seven antigenic groups and seven subgroups have enabled us to distiguish 34 serovars. Biochemical tests are unable to separate these serovars. The significance of serovars is discussed in comparison with pathogenicity and with reference to the Bacteriological Code.