Muscle Function mechanical properties

Inside the typical smooth muscle cell, the cytoplasmic filaments course around the nuclei filling most of the cytoplasm between the nuclei and the plasma membrane. There are two filamentous systems in the smooth muscle cell which run lengthwise through the cell. The first is the more intensively studied actin-myosin sliding filament system. This is the system to which a consensus of investigators attribute most of the active mechanical properties of smooth muscle. It will be discussed in detail below. The second system is the intermediate filament system which to an unknown degree runs in parallel to the actin-myosin system and whose functional role has not yet been completely agreed upon. The intermediate filaments are so named because their diameters are intermediate between those of myosin and actin. These very stable filaments are functionally associated with various protein cytoarchitectural structures, microtubular systems, and desmosomes. Various proteins may participate in the formation of intermediate filaments, e.g., vimentin. 

Because of the qualitative similarities of the mechanical properties in smooth and striated muscles, much research over the past several decades has focused on determining whether the functional behavior of these muscles can be explained on the basis of simUar mechanisms. However, the unique structural features of smooth muscle are likely to underly some aspects of its contractile properties which differ significantly from those of striated muscles. In addition, smooth muscle tissues possess a number of distinctive functional properties that are not easily accounted for on the basis of models developed to account for the properties of striated muscles. 

Fung, Y.C. (1981). Biomechanics Mechanical Properties of Living Tissues. Springer-Verlag, New York. Cans, C. (1982). Fiber architecture and muscle function. Exerc. Sport Sci. Rev. 10 160-207. 

IF proteins assemble into a filament with a diameter of 8-12 nm which is the intermediate size between those of microtubules (25 nm) and microfilaments (7-9 nm). Whereas microtubules and microfilaments are more likely to be related to many basic cellular functions [44, 45], intermediate filaments play a key role in mechanical properties of tissues and cells, such as the stiffness and maximum strain, and the mechanical integrity of various tissues such as muscle, liver, and skin [44, 46]. 

Knowledge of the instantaneous and local functional distribution f(y,t) throughout the LV wall is required for the calculation of various cardiac phenomena (Beyar and Sideman, 1984b). This entails accounting for the anatomic microscopic orientation of the muscles fibers which hold a direct relation to the distribution of the mechanical properties. A 3-D dynamic model f(r,6,cp) is needed for a detailed description of the geometry of the cardiac chambers, and to account for the distributed parameters within the myocardium in the spatial inhomogeneities associated with certain diseases, like myocardial infarction. 

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