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Muscle Regions (muscle + regions)

Distribution by Scientific Domains

Medical Sciences	75%

Selected Abstracts

Differences in Local Environment Determine the Site of Physiological Angiogenesis in Rat Skeletal Muscle

EXPERIMENTAL PHYSIOLOGY, Issue 5 2003
I. Badr
The specificity in location of angiogenesis to either glycolytic or oxidative fibre types, or muscle regions, was examined in the tibialis anterior (TA) and extensor digitorum longus (EDL) muscles of rat. Angiogenesis was induced by mechanical means either with (chronic muscle stimulation) or without (muscle stretch by overload) changes in blood flow, treatments which invoked only minor changes in fibre type and fibre size. Proliferation estimated by PCNA labelling of cells co-localised with capillaries was very rare in control muscles, where it occurred mainly in the glycolytic regions, but was increased in both models of angiogenesis. However, when labelled capillaries were scored according to the type of surrounding fibres, only muscle stimulation significantly accentuated proliferation of capillaries surrounded by glycolytic fibres. We conclude that while mechanical stimuli are important for proliferation in glycolytic regions in both models, capillary growth occurs specifically around glycolytic fibres in that region when the angiogenic stimulus includes increased blood flow and/or increased metabolic demand. [source]

Differential activity patterns in the masseter muscle under simulated clenching and grinding forces

JOURNAL OF ORAL REHABILITATION, Issue 8 2005
H. J. SCHINDLER
summary, The aim of this study was to investigate (i) whether the masseter muscle shows differential activation under experimental conditions which simulate force generation during clenching and grinding activities; and (ii) whether there are (a) preferentially active muscle regions or (b) force directions which show enhanced muscle activation. To answer these questions, the electromyographic (EMG) activity of the right masseter muscle was recorded with five intramuscular electrodes placed in two deep muscle areas and in three surface regions. Intraoral force transfer and force measurement were achieved by a central bearing pin device equipped with three strain gauges (SG). The activity distribution in the muscle was recorded in four different mandibular positions (central, left, right, anterior). In each position, maximum voluntary contraction (MVC) was exerted in vertical, posterior, anterior, medial and lateral directions. The investigated muscle regions showed different amount of EMG activity. The relative intensity of the activation, with respect to other regions, changed depending on the task. In other words, the muscle regions demonstrated heterogeneous changes of the EMG pattern for the various motor tasks. The resultant force vectors demonstrated similar amounts in all horizontal bite directions. Protrusive force directions revealed the highest relative activation of the masseter muscle. The posterior deep muscle region seemed to be the most active compartment during the different motor tasks. The results indicate a heterogeneous activation of the masseter muscle under test conditions simulating force generation during clenching and grinding. Protrusively directed bite forces were accompanied by the highest activation in the muscle, with the posterior deep region as the most active area. [source]

Evidence for shutter-speed variation in CR bolus-tracking studies of human pathology

NMR IN BIOMEDICINE, Issue 3 2005
Thomas E. Yankeelov
Abstract The standard pharmacokinetic model for the analysis of MRI contrast reagent (CR) bolus-tracking (B-T) data assumes that the mean intracellular water molecule lifetime (,i) is effectively zero. This assertion is inconsistent with a considerable body of physiological measurements. Furthermore, theory and simulation show the B-T time-course shape to be very sensitive to the ,i magnitude in the physiological range (hundreds of milliseconds to several seconds). Consequently, this standard model aspect can cause significant underestimations (factors of 2 or 3) of the two parameters usually determined: Ktrans, the vascular wall CR transfer rate constant, and ve, the CR distribution volume (the extracellular, extravascular space fraction). Analyses of animal model data confirmed two predicted behaviors indicative of this standard model inadequacy: (1) a specific temporal pattern for the mismatch between the best-fitted curve and data; and (2) an inverse dependence of the curve's Ktrans and ve magnitudes on the CR dose. These parameters should be CR dose-independent. The most parsimonious analysis allowing for realistic ,i values is the ,shutter-speed' model. Its application to the experimental animal data essentially eliminated the two standard model signature inadequacies. This paper reports the first survey for the extent of this ,shutter-speed effect' in human data. Retrospective analyses are made of clinical data chosen from a range of pathology (the active multiple sclerosis lesion, the invasive ductal carcinoma breast tumor, and osteosarcoma in the leg) that provides a wide variation, particularly of Ktrans. The signature temporal mismatch of the standard model is observed in all cases, and is essentially eliminated by use of the shutter-speed model. Pixel-by-pixel maps show that parameter values from the shutter-speed analysis are increased by more than a factor of 3 for some lesion regions. This endows the lesions with very high contrast, and reveals heterogeneities that are often not seen in the standard model maps. Normal muscle regions in the leg allow validation of the shutter-speed model Ktrans, ve, and ,i magnitudes, by comparison with results of previous careful rat leg studies not possible for human subjects. Copyright © 2004 John Wiley & Sons, Ltd. [source]