Electromyographic activity of intrinsic and extrinsic muscles of the human tongue.

In healthy human subjects, electromyographic activities (EMG) were obtained from various tongue muscles. Main actions such as protrusion, retraction, and changing of the shape of the tongue can be correlated with the EMG activity of the respective muscles. Amongst all tongue muscles the paired genioglossus (protruder) is of greatest importance since it prevents a relapse of the tongue with occlusion of the airways and the attendant risk of suffocation. To counteract the relapse of the tongue, the tonic activity of the genioglossus is markedly increased in the supine position; this activity is further increased with cervical flexion. In addition, the genioglossi are activated during respiration, particularly during the inspiratory phase. These activity patterns reflect the important role the genioglossus plays in the mechanics of maintaining an open air passage to the lungs.     

Mechanical function of hyoid muscles during spontaneous breathing in cats

We assessed the mechanical behavior of the geniohyoid and sternohyoid muscles during spontaneous breathing using sonomicrometry in anesthetized cats. When the animals breathed O2, the hyoid muscles either became longer or did not change length (but never shortened) during inspiration. During progressive hyperoxic hypercapnia, transient increases in geniohyoid muscle inspiratory lengthening occurred in many animals; however, at high PCO2 the geniohyoid invariably shortened during inspiration (mean 4.9% of resting length at the end of CO2 rebreathing; P less than 0.001). The PCO2 at which geniohyoid inspiratory lengthening changed to inspiratory shortening was significantly higher than the CO2 threshold for the onset of geniohyoid electrical activity (P less than 0.01). For the sternohyoid muscle, hypercapnia caused inspiratory lengthening in 13 of 17 cats and inspiratory shortening in 4 of 17 cats; on average the sternohyoid lengthened by 1.6% of resting length at the end of CO2 rebreathing (P less than 0.01). Sternohyoid lengthening occurred in spite of this muscle being electrically active. These results suggest that the relationship between hyoid muscle electrical activity and respiratory changes in length is very complex, so that the presence of hyoid muscle electrical activity does not necessarily indicate muscle shortening, and among the geniohyoid and sternohyoid muscles, the geniohyoid has a primary role as a hypopharyngeal dilator in the spontaneously breathing cat, with the sternohyoid muscle acting in an accessory capacity.     

Functional relationship between the foot intrinsic and extrinsic muscles in walking

The intrinsic and extrinsic muscles are considered to stabilize the foot and contribute to propulsion during walking. This study aimed to clarify the functional relationship between intrinsic and extrinsic muscles during walking. Thirteen healthy men participated in this study. The muscle activities of the intrinsic muscles (quadratus plantae and abductor hallucis), and the extrinsic muscles (flexor hallucis longus, flexor digitorum longus, and tibialis posterior) were measured using fine-wire and surface electromyography during walking. The muscle onset timing after foot contact was calculated and compared among muscles using the one-way ANOVA. The stance phase was divided into early and late braking, and early and late propulsion phases. Muscle activity among phases was compared using repeated-measures ANOVA. The onset time of the abductor hallucis was significantly earlier than those of the flexor digitorum longus and tibialis posterior. The quadratus plantae demonstrated significantly earlier onset than that of the tibialis posterior. In the late propulsion phase, the activity of extrinsic muscles decreased, whereas intrinsic muscles were continuously active. Early activation of the intrinsic muscles may stabilize the foot for efficient torque production by the extrinsic muscles. Furthermore, the intrinsic muscles may contribute to the final push-off after the deactivation of extrinsic muscles.     

Age effects on force produced by intrinsic and extrinsic hand muscles and finger interaction during MVC tasks.

Finger-pressing forces are produced by activation of the intrinsic hand muscles, which are finger specific, and the extrinsic muscles that connect to multiple fingers. We tested a hypothesis of greater weakening of intrinsic hand muscles with age and quantified associated indexes of finger interaction such as enslaving (force production by unintended fingers) and force deficit (loss of finger force in multifinger tasks compared with single-finger tasks). Twelve young (23-35 yr old) and 12 elderly (70-95 yr old) men and women performed single-finger and four-finger maximal pressing tasks, in which force was applied at the proximal phalanges (PP, the intrinsic muscles are major focal force generators) and at the distal phalanges (DP, the extrinsic muscles are focal force generators). The decline in the peak force with age was greater at PP (30%) than at DP (19%). Larger indexes of finger interaction were observed at PP (enslaving = 17.2 +/- 9.4%, force deficit = 36.1 +/- 11.1%) than at DP (enslaving = 14.9 +/- 8.8%, force deficit = 27.7 +/- 10.8%) across ages and genders. We conclude that intrinsic hand muscles show disproportionate weakening with age. The greater indexes of finger interaction in PP tests with greater involvement of intrinsic hand muscles suggest that the finger interactions are predominantly of a central origin across ages and genders.     

Examination of extrinsic foot muscles during running using mfMRI and EMG.

Over-pronation has been cited as a key contributor to many types of running injuries. However, the roles of the extrinsic foot muscles during running have not been adequately identified. The purpose of this study was to examine the muscle functional (mf) MRI and EMG responses to perturbations of the foot by running in varus, neutral and valgus wedged shoes. Ten males ran at 3.6 m/s in specially constructed shoes for 5 min with T2-weighted mfMRI collected before and after each run. The change in T2 from before to after each run characterized the level of metabolic activity in each of muscle. Kinematic and EMG data were also collected while subjects ran on a treadmill. There were no T2 differences across the three shoe conditions. In contrast, there was significantly less EMG activity in the tibialis anterior and soleus while wearing the neutral shoe. Overall, the results did not support the theory that muscle activity would increase as the degree of eversion increased. It also appears that surface EMG was more sensitive to differences between conditions than mfMRI. However, this study illustrated that mfMRI may be a useful tool for quantifying muscle activity in cases where surface EMG is inadequate.     

Pituitary adenylate cyclase-activating polypeptide in intrinsic and extrinsic nerves of the rat pancreas

Pituitary adenylate cyclase-activating polypeptide (PACAP) is the latest member of the vasoactive intestinal polypeptide (VIP) family of neuropeptides present in nerve fibres in many peripheral organs. Using double immunohistochemistry, with VIP as a marker for intrinsic innervation and calcitonin-gene related peptide (CGRP) as a marker for mainly extrinsic innervation, the distribution and localization of PACAP were studied in the rat pancreas. PACAP was demonstrated in nerve fibres in all compartments of the pancreas and in a subpopulation of intrapancreatic VIP-containing ganglion cells. PACAP and VIP were co-stored in intra- and interlobular nerve fibres innervating acini, blood vessels, and in nerve fibres within the islets of Langerhans. No PACAP immunoreactivity was observed in the islet cells. Another population of PACAP-immunoreactive nerve fibres co-localized with CGRP innervated ducts, blood vessels and acini. PACAP/CGRP-positive nerve fibres were also demonstrated within the islets. Neonatal capsaicin reduced the PACAP-38 concentration by approximately 50%, and accordingly a marked reduction in PACAP/CGRP-immunoreactive nerve fibres in the exocrine and endocrine pancreas was observed. Bilateral subdiaphragmatic vagotomy caused a slight but significant decrease in the PACAP-38 concentration compared with controls. In conclusion, PACAP-immunoreactive nerve fibres in the rat pancreas seem to have dual origin: extrinsic, most probably sensory fibres co-storing CGRP; and intrinsic, constituting a subpopulation of VIP-containing nerve cell bodies and fibres innervating acinar cells and islet cells. Our data provide a morphological basis for the reported effects of PACAP in the pancreas and suggest that PACAP-containing nerves in the rat pancreas may have both efferent and sensory functions.     

Bid activation during induction of extrinsic and intrinsic apoptosis in eosinophils

Eosinophils readily undergo apoptosis when removed from a physiological environment via activation of the intrinsic cell death pathway. This can be further enhanced by certain chemicals (for example, glucocorticoid), or by extrinsic means (that is, Fas receptor engagement). In this investigation, we examined the relative importance of these pathways in cultured human peripheral blood eosinophils in the context of expression and activation of the BH3-only Bcl2 homologue Bid. Bid activation was examined under conditions where programmed cell death was either stimulated (via Fas engagement or glucocorticoid treatment) or inhibited (interleukin-5 (IL-5)) relative to control. Full-length Bid was found to be highly expressed in eosinophils, and processed to a similar extent during either agonist anti-Fas or glucocorticoid treatment. IL-5 blocked intrinsic Bid activation during factor withdrawal or glucocorticoid treatment, and partially attenuated that caused by Fas activation. Caspase 8 (but not caspase 9) antagonism partly but significantly affected receptor-mediated Bid activation and cell death; these processes were not altered by either caspase inhibitor during simple factor withdrawal or glucocorticoid treatment. Bid processing appears to be central to both intrinsic and extrinsic pathways of cell death in eosinophils. The role of IL-5 in blocking the intrinsic pathway of eosinophil apoptosis is underscored. Results of specific inhibition support the existence of Bid activation pathways in eosinophils other than those mediated by the classic initiator caspases.     

The intrinsic and extrinsic effects of TET proteins during gastrulation

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Vesicular glutamate transporter 1 immunoreactivity in extrinsic and intrinsic innervation of the rat esophagus

Encouraged by the recent finding of vesicular glutamate transporter 2 (VGLUT2) immunoreactivity (-ir) in intraganglionic laminar endings (IGLEs) of the rat esophagus, we investigated also the distribution and co-localization patterns of VGLUT1. Confocal imaging revealed substantial co-localization of VGLUT1-ir with selective markers of IGLEs, i.e., calretinin and VGLUT2, indicating that IGLEs contain both VGLUT1 and VGLUT2 within their synaptic vesicles. Besides IGLEs, we found VGLUT1-ir in both cholinergic and nitrergic myenteric neuronal cell bodies, in fibers of the muscularis mucosae, and in esophageal motor endplates. Skeletal neuromuscular junctions, in contrast, showed no VGLUT1-ir. We also tested for probable co-localization of VGLUT1-ir with markers of extrinsic and intrinsic esophageal innervation and glia. Within the myenteric neuropil we found, besides co-localization of VGLUT1 and substance P, no further co-localization of VGLUT1-ir with any of these markers. In the muscularis mucosae some VGLUT1-ir fibers were shown to contain neuronal nitric oxide synthase (nNOS)-ir. VGLUT1-ir in esophageal motor endplates was partly co-localized with vesicular acetylcholine transporter (VAChT)/choline acetyltransferase (ChAT)-ir, but VGLUT1-ir was also demonstrated in separately terminating fibers at motor endplates co-localized neither with ChAT/VAChT-ir nor with nNOS-ir, suggesting a hitherto unknown glutamatergic enteric co-innervation. Thus, VGLUT1-ir was found in extrinsic as well as intrinsic innervation of the rat esophagus.     

Changes in left ventricular geometry during spontaneous breathing

The purpose of these experiments was to determine the effects of a spontaneously generated inspiration on the size and shape of the left ventricle (LV) in anesthetized supine dogs. We implanted markers in the LV to establish three perpendicular axes and recorded the motion of these markers using biplane cinefluoroscopy at 60 Hz. The primary changes in LV size that accompanied inspiration occurred at end diastole (ED). The largest change in LVED dimension was a 2.46-mm narrowing of the septal-lateral wall dimension, but the apex-base dimension decreased also, by 0.74 mm. The anteroposterior dimension actually widened by 1.07 mm. The septal-lateral narrowing was caused by both a 1.0-mm narrowing of the distance between the septal marker and the apex-base axis, as well as by a 1.4-mm narrowing between the apex-base axis and the lateral wall marker. Narrowing of the septal portion seemed expected because of presumed enhanced right ventricular filling during inspiration. Narrowing of the lateral portion of the LV, while the anteroposterior dimension widened, was surprising because a change in LVEDV shape is implied. Assuming ventricular homogeneity, this change in LVED shape implies that the forces applied to the epicardial surface were not uniform. There must have been a retraction on the anterior and posterior surface that was not experienced by the lateral LV wall. The net effect of these dimensional changes of the LV at end diastole (estimated from the product of the three ED axes) was a 3.5-cm3 reduction in LVED volume.(ABSTRACT TRUNCATED AT 250 WORDS)     

Coordination of leg muscles during speed skating

Five speed skaters of elite performance level and six speed skaters of trained level were subjected to an inverse dynamical analysis during speed skating. Push-off forces were registered by means of special skates. Myoelectric activity (EMG) of ten leg muscles and cinematographic data were recorded. Linked segment modelling yielded net joint moments and joint powers. The speed skating technique is characterized by a typical horizontal position of the trunk and a suppression of a plantar flexion during the push-off. This technique, necessary to reduce external friction, constrains the transfer of rotation in joints to translation of the mass center of the body. In spite of constrained push-off, the EMG levels of the leg muscles show a proximo-distal temporal order which to a certain extent is comparable to that previously found in an unconstrained vertical jump. This proximo-distal sequence is also reflected by the time courses of the net moment and net power output in hip, knee and ankle joints. The temporal sequence in activation levels of activated muscles is not different between elite and trained speed skaters. The difference in performance level between these groups obviously has an origin in the ability of the elite speed skaters to realise larger net joint moments. Differences in net joint moments and in kinematics result in a higher power output and a lower air frictional force for the elite than for the trained speed skaters.     

Regional ventilation during spontaneous breathing and mechanical ventilation in dogs

We evaluated the effects of the different patterns of chest wall deformation that occur with different body positions and modes of breathing on regional lung deformation and ventilation. Using the parenchymal marker technique, we determined regional lung behavior during mechanical ventilation and spontaneous breathing in five anesthetized recumbent dogs. Regional lung behavior was related to the patterns of diaphragm motion estimated from X-ray projection images obtained at functional residual capacity (FRC) and end inspiration. Our results indicate that 1) in the prone and supine positions, FRC was larger during mechanical ventilation than during spontaneous breathing; 2) there were significant differences in the patterns of diaphragm motion and regional ventilation between mechanical ventilation and spontaneous breathing in both body positions; 3) in the supine position only, there was a vertical gradient in lung volume at FRC; 4) in both positions and for both modes of breathing, regional ventilation was nonlinearly related to changes in lobar and overall lung volumes; and 5) different patterns of diaphragm motion caused different sliding motions and differential rotations of upper and lower lobes. Our results are inconsistent with the classic model of regional ventilation, and we conclude that the distribution of ventilation is determined by a complex interaction of lung and chest wall shapes and by the motion of the lobes relative to each other, all of which help to minimize distortion of the lung parenchyma.     

Mechanical role of expiratory muscles during breathing in upright dogs

To examine the mechanical effects of the abdominal and triangularis sterni expiratory recruitment that occurs when anesthetized dogs are tilted head up, we measured both before and after cervical vagotomy the end-expiratory length of the costal and crural diaphragmatic segments and the end-expiratory lung volume (FRC) in eight spontaneously breathing animals during postural changes from supine (0 degree) to 80 degrees head up. Tilting the animals from 0 degree to 80 degrees head up in both conditions was associated with a gradual decrease in end-expiratory costal and crural diaphragmatic length and with a progressive increase in FRC. All these changes, however, were considerably larger (P less than 0.005 or less) postvagotomy when the expiratory muscles were no longer recruited with tilting. Alterations in the elastic properties of the lung could not account for the effects of vagotomy on the postural changes. We conclude therefore that 1) by contracting during expiration, the canine expiratory muscles minimize the shortening of the diaphragm and the increase in FRC that the action of gravity would otherwise introduce, and 2) the end-expiratory diaphragmatic length and FRC in upright dogs are thus actively determined. The present data also indicate that by relaxing at end expiration, the expiratory muscles make a substantial contribution to tidal volume in upright dogs; in the 80 degrees head-up posture, this contribution would amount to approximately 60% of tidal volume.     

Coordination of the leg muscles in backlift and leglift.

Net joint moments are often used to quantify the loading of structures (e.g. the intervertebral disc at L5S1) during lifting. This quantification method is also used to evaluate the loading of the knee, for instance, to determine the effect of backlifting as opposed to leglifting. However, the true loading of the joint as derived from net joint moments can be obscured by a possible co-contraction of antagonists. To unravel the mechanisms that determine the net joint moments in the knee, the leglift was compared to the backlift. Although a completely different net knee moment curve was found when comparing the two lifting techniques, it appeared to be closely related to the ground reaction force vector and its orientation with respect to the joint centre of rotation (R > 0.995). This close relation was established by co-contraction of both flexors and extensors of the knee. Furthermore, a close relation appeared to exist between the joint moment difference between hip and knee and the activity difference between rectus femoris muscle and hamstring (R = 0.72 and 0.83 in leglift and backlift, respectively). The knee-ankle joint moment difference and the activity of the gastrocnemius showed a close relation as well (R = -0.89 and 0.96 in leglift and backlift, respectively). These relations can be interpreted as a mechanism to distribute net moments across joints. It is concluded that during lifting tasks the intermuscular coordination is aimed at coupling of joint moments, such that the ground reaction force points in a direction that provides balance during the movement. The use of net joint moments as direct indicators for joint loading (e.g. knee) seems, therefore, questionable.