Differences in loading of the temporomandibular joint during opening and closing of the jaw

Kinematics of the human masticatory system during opening and closing of the jaw have been reported widely. Evidence has been provided that the opening and closing movement of the jaw differ from one another. However, different approaches of movement registration yield divergent expectations with regard to a difference in loading of the temporomandibular joint between these movements. Because of these diverging expectations, it was hypothesized that joint loading is equal during opening and closing. This hypothesis was tested by predicting loading of the temporomandibular joint during an unloaded opening and closing movement of the jaw by means of a three-dimensional biomechanical model of the human masticatory system. Model predictions showed that the joint reaction forces were markedly higher during opening than during closing. The predicted opening trace of the centre of the mandibular condyle was located cranially of the closing trace, with a maximum difference between the traces of 0.45 mm. The hypothesis, postulating similarity of joint loading during unloaded opening and closing of the jaw, therefore, was rejected. Sensitivity analysis showed that the reported differences were not affected in a qualitative sense by muscular activation levels, the thickness of the cartilaginous layers within the temporomandibular joint or the gross morphology of the model. Our predictions indicate that the TMJ is loaded more heavily during unloaded jaw opening than during unloaded jaw closing.     

Dynamic visual cues induce jaw opening and closing by tiger beetles during pursuit of prey

In dynamic locomotory contexts, visual cues often trigger adaptive behaviour by the viewer, yet studies investigating how animals determine impending collisions typically employ either stationary viewers or objects. Here, we describe a dynamic situation of visually guided prey pursuit in which both impending prey contact and escape elicit observable adaptive behaviours in the pursuer, a predatory beetle. We investigated which visual cues may independently control opening and closing of the beetle''s jaws during chases of prey dummies. Jaw opening and closing typically occur when prey is within the 60° binocular field, but not at specific distances, angular sizes or time-to-collision. We show that a sign change in the expansion rate of the target image precedes jaw opening (16 ms) and closing (35 ms), signalling to the beetle that it is gaining on the target or that the target is getting away. We discuss the ‘sloppiness'' of such variation in the lag of the behavioural response, especially jaw closing, as an adaptation to uncertainty about target position due to degradation of the target image by motion blur from the fast-running beetle.     

Computational model of the movement of the human muscles of mastication during opening and closing of the jaw

Muscle fibre bundles comprising the four major muscles of mastication in the human being were studied in cadavers. Markers were placed along each muscle fibre bundle by means of serial dissections. The 3D coordinates of each marker were tabulated and imported to Cinema 4D, a software animation program. Origins and insertions of each fibre bundle were also digitized and imported, as were the coordinates of the surface of the skull, the mandible and temporomandibular joint. It was then possible to visualize the movement of all relevant fibre bundles during the passive motions of the mandible. An animated film depicts the positions of all relevant muscle fibres during passive movement of the mandible. The properties of the masseter muscle were documented as a prototype for the eventual study of all the muscles of mastication. One can now proceed to study the inverse problem, namely the forces within each fibre bundle that actively generate mandibular motion. It is hoped that these studies will aid in the management of conditions affecting the temporomandibular joint.     

A dynamic model of mouth closing movements in clariid catfishes: the role of enlarged jaw adductors

Some species of Clariidae (air breathing catfishes) have extremely large (hypertrophied) jaw closure muscles. Besides producing higher bite forces, the enlarged muscles may also cause higher accelerations of the lower jaw during rapid mouth closure. Thus, jaw adductor hypertrophy could potentially also enable faster mouth closure. In this study, a forward dynamic model of jaw closing is developed to evaluate the importance of jaw adductor hypertrophy on the speed of mouth closure. The model includes inertia, pressure, tissue resistance and hydrodynamic drag forces on the lower jaw, which is modelled as a rotating half-ellipse. Simulations are run for four clariid species showing a gradual increase in jaw adductor hypertrophy (Clarias gariepinus, Clariallabes longicauda, Gymnallabes typus and Channallabes apus). The model was validated using data from high-speed videos of prey captures in these species. In general, the kinematic profiles of the fastest mouth closure from each species are reasonably well predicted by the model. The model was also used to compare the four species during standardized mouth closures (same initial gape angle, travel distance and cranial size). These simulations suggest that the species with enlarged jaw adductors have an increased speed of jaw closure (in comparison with the non-hypertrophied C. gariepinus) for short lower jaw rotations and when feeding at high gape angles. Consequently, the jaw system in these species seems well equipped to capture relatively large, evasive prey. For prey captures during which the lower jaw rotates freely over a larger distance before impacting the prey, the higher kinematic efficiency of the C. gariepinus jaw system results in the fastest jaw closures. In all cases, the model predicts that an increase in the physiological cross-sectional area of the jaw muscles does indeed contribute to the speed of jaw closure in clariid fish.     

Functional significance of the coupling between head and jaw movements

When humans open or close the jaw they also move the head. Unintentionally, it rotates backwards when the jaw opens and returns upon jaw closure. We hypothesized that this mutual movement coupling is related to the muscles in the floor of the mouth. A biomechanical model was applied to comprehend the functional significance of this movement coupling. As the jaw opened the jaw opening muscles shortened and became less forceful. Meanwhile they had to stretch the jaw closing muscles. The simulations showed that a simultaneous head extension facilitated jaw opening. A possible functional significance for the coupling between head and jaw movements is that it can extend jaw gape. Head extension can contribute to a wider jaw gape by on the one hand a reduced shortening of the jaw opening muscles and on the other hand by a reorientation of these muscles so that they obtain a more favorable position for jaw opening.     

Phosphorylation by Nek1 regulates opening and closing of voltage dependent anion channel 1

VDAC1 is a key component of the mitochondrial permeability transition pore. To initiate apoptosis and certain other forms of cell death, mitochondria become permeable such that cytochrome c and other pre-apoptotic molecules resident inside the mitochondria enter the cytosol and activate apoptotic cascades. We have shown recently that VDAC1 interacts directly with never-in-mitosis A related kinase 1 (Nek1), and that Nek1 phosphorylates VDAC1 on Ser193 to prevent excessive cell death after injury. How this phosphorylation regulates the activity of VDAC1, however, has not yet been reported. Here, we use atomic force microscopy (AFM) and cytochrome c conductance studies to examine the configuration of VDAC1 before and after phosphorylation by Nek1. Wild-type VDAC1 assumes an open configuration, but closes and prevents cytochrome c efflux when phosphorylated by Nek1. A VDAC1-Ser193Ala mutant, which cannot be phosphorylated by Nek1 under identical conditions, remains open and constitutively allows cytochrome c efflux. Conversely, a VDAC1-Ser193Glu mutant, which mimics constitutive phosphorylation by Nek1, remains closed by AFM and prevents cytochrome c leakage in the same liposome assays. Our data provide a mechanism to explain how Nek1 regulates cell death by affecting the opening and closing of VDAC1.     

Nature and fate of the ureteric membrane closing the primitive ureterovesical opening.

83 albino rat embryos were used to investigate and ascertain the presence of the ureteric membrane closing the mouth of the primitive ureterovesical opening. The membrane is found to be derived from the stratified etithelium lining the urogenital sinus and later the developing urinary bladder. It progressively thins out and bulges in the bladder cavity as a result of the increasing functional differentiation and activity of the developing kidney, where the excreted urine dilates the lower end of the ureter till it forms a small cyst-like dilatation before the membrane finally ruptures. The destruction of the ureteric membrane occurs caudal to its center and is immediately followed by dilatation of the bladder cavity and differentiation of mits musculature and lining epitherlium.     

The rate of opening and closing of the DNA gate for topoisomerase II

Type II DNA topoisomerases can catalyze the transport of one DNA segment through a transient break in another DNA segment by a complex mechanism of ATP hydrolysis. According to the hydrolysis process of two ATPs, a multi-state model is proposed to investigate the work cycle of DNA topoisomerase II. The rate of the opening and closing of the DNA topoisomerase gate is evaluated by determining the release rate of inorganic phosphates. The calculated results show that, under the condition of the high concentration of ATP, the work cycle of DNA topoisomerase II is about 0.84 s which is in agreement with the experimental data.     

Inhibition of jaw opening reflexes by stimulation of the central gray matter and raphe nuclei in cats

The effect of stimulation of the mesencephalic central gray matter and raphe nuclei on jaw opening reflexes evoked by excitation of high-threshold (dental pulp) and low-threshold (A-alpha) fibers of the infraorbital nerve afferents was studied in cats anesthetized with chloralose and pentobarbital. The jaw opening reflex evoked by stimulation of the dental pulp was shown to be effectively suppressed by conditioning stimulation of the central gray matter and raphe nuclei. The reflex evoked by stimulation of low-threshold infraorbital nerve afferents also was depressed (but less deeply and for a shorter period than the reflex evoked by stimulation of the dental pulp) during stimulation of the raphe nuclei and caudal zone of the central gray matter, but was unchanged after stimulation of the points located in the rostral zone of the central gray matter. Application of single stimuli or bursts of five stimuli with a frequency of 100 Hz had no effect on the reflexes studied. Short-term stimulation with a burst of 10–20 stimuli with a following frequency of 200–400 Hz led to inhibition of the reflexes, which lasted 450–1000 msec. Long-term stimulation of the central gray matter and raphe nuclei for 30 sec with a frequency of 50 Hz caused inhibition of jaw opening reflexes evoked by stimulation of both high- and low-threshold afferents for 60 min. Impulses from the central gray matter and raphe nuclei thus have a mainly inhibitory action on the jaw opening reflex evoked by stimulation of high-threshold afferents, but they act less effectively on the reflex evoked by stimulation of low-thres-hold afferents. The duration of inhibition depends essentially on the parameters of stimulation.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 16, No. 3, pp. 374–387, May–June, 1984.     

Accuracy of elastic property measurement in mandibular cortical bone is improved by using cylindrical specimens

Ultrasonic determination of elastic properties in human craniofacial cortical bone is problematic because of a lack of information about the principal material axes, and because the cortex is often thinner than in long bones. This study investigated solutions that permit reasonable determination of elastic properties in the human mandible. We tested whether ultrasonic velocities could be reliably measured in cylindrical samples of aluminum and mandibular bone, and the effects of reduced specimen thickness. Results indicted that (1) varying shape had minimal effects on ultrasonic velocities or derived elastic properties, and (2) ultrasonic velocities have relatively increased measurement error as propagation distances decreased. The increased error in velocity measurements of mandibular cortical specimens of less than 1.2 mm in thickness should be considered when assessing the reliability of single measurements.     

Amygdaloid-induced jaw opening and facilitation or inhibition of the trigeminal motoneurons in the rat

1. Repetitive stimulation of the rat'se central amygdaloid (CAm) nucleus induced rhythmic masticatory jaw movements or continuous jaw opening. Both types of jaw movements were accompanied by coincidental activities of the mylohyoid (Myl) nerve. 2. The effects of CAm stimulation were examined on activities of bilateral Myl and masseteric (Mass) nerves or their motoneurons (Myl-Dig and Mass, respectively). 3. CAm stimulation induced contralaterally dominant facilitation of the Myl nerve activity as well as Myl-Dig motoneurons. These facilitatory effects were caused by EPSPs seen in Myl-Dig motoneurons. 4. One third of the Mass motoneurons were inhibited or hyperpolarized by contralateral CAm stimulation, while a few were facilitated and the majority unaffected.     

Overexpression of poplar cellulase accelerates growth and disturbs the closing movements of leaves in sengon

In this study, poplar (Populus alba) cellulase (PaPopCel1) was overexpressed in a tropical Leguminosae tree, sengon (Paraserianthes falcataria), by the Agrobacterium tumefaciens method. PaPopCel1 overexpression increased the length and width of stems with larger leaves, which showed a moderately higher density of green color than leaves of the wild type. The pairs of leaves on the transgenic plants closed more slowly during sunset than those on the wild-type plants. When main veins from each genotype were excised and placed on a paper towel, however, the leaves of the transgenic plants closed more rapidly than those of the wild-type plant. Based on carbohydrate analyses of cell walls, the leaves of the transgenic plants contained less wall-bound xyloglucan than those of the wild-type plants. In situ xyloglucan endotransglucosylase activity showed that the incorporation of whole xyloglucan, potentially for wall tightening, occurred in the parenchyma cells (motor cells) of the petiolule pulvinus attached to the main vein, although the transgenic plant incorporated less whole xyloglucan than the wild-type plant. These observations support the hypothesis that the paracrystalline sites of cellulose microfibrils are attacked by poplar cellulase, which loosens xyloglucan intercalation, resulting in an irreversible wall modification. This process could be the reason why the overexpression of poplar cellulase both promotes plant growth and disturbs the biological clock of the plant by altering the closing movements of the leaves of the plant.     

A simple method for measurement of the haemoglobin binding capacity of canine haptoglobin

The potential of a series of related compounds to induce haemolytic anaemia in dogs highlighted the need for a reliable and sensitive technique to identify changes in plasma haptoglobin concentration. An indirect method established for human samples was adapted for use with canine plasma. This method measures the haemoglobin binding capacity of plasma, which is directly proportional to the functional haptoglobin concentration. The efficacy of this technique was investigated on samples taken from Beagle dogs which had previously received small quantities of water intravenously. A substantial reduction in haemoglobin binding capacity was recorded before other haematological parameters were significantly affected. It was concluded that measurement of haemoglobin binding capacity by this method provides a valid reflection of haptoglobin status in the dog.     

Dielectric measurement of individual microtubules using the electroorientation method

Little is known about the electrostatic/dynamic properties of microtubules, which are considered to underlie their electrostatic interactions with various proteins such as motor proteins, microtubule-associated proteins, and microtubules themselves (lateral association of microtubules). To measure the dielectric properties of microtubules, we developed an experiment system in which the electroorientation of microtubules was observed under a dark-field microscope. Upon application of an alternating electric field (0.5-1.9 x 10(5) V/m, 10 kHz-3 MHz), the microtubules were oriented parallel to the field line in a few seconds because of the dipole moment induced along their long axes. The process of this orientation was analyzed based on a dielectric ellipsoid model, and the conductivity and dielectric constant of each microtubule were calculated. The analyses revealed that the microtubules were highly conductive, which is consistent with the counterion polarization model-counterions bound to highly negatively charged microtubules can move along the long axis, and this mobility might be the origin of the high conductivity. Our experiment system provides a useful tool to quantitatively evaluate the polyelectrolyte nature of microtubules, thus paving the way for future studies aiming to understand the physicochemical mechanism underlying the electrostatic interactions of microtubules with various proteins.