Skeletal muscle description

An increasing number of studies on lipid metabolism in human skeletal muscle using localized MR proton spectroscopy have been performed since the first description of the phenomenon that proton NMR spectroscopy allows the differentiation of two distinct lipid compartments and the experimental confirmation that one of these compartments is attributed to the IMCL pool. The non-invasiveness and the high sensitivity even to low lipid concentrations under physiological conditions denote the uniqueness of this modality and allow examinations of large numbers of healthy volunteers and follow-up metabolic intervention studies. 

Skeletal muscle fibers have dilferent mechanical and metabolic properties, and fiber classification schemes are based on these differences. All fibers within a muscle unit are similar (but not identical) with respect to twitch characteristics, as these are largely determined by the innervation, and all fibers in a muscle unit are innervated by the same a-MN. However, even within a muscle unit, there may be appreciable interfiber differences in metabolic profile. Consequently, the following classifications should be viewed as useful simplified categories rather than a literal description of populations of fibers. 

The synapses using acetylcholine (ACh) as the transmitter substance are the target for a wide variety of pesticides and therefore need a more detailed description. Acetylcholine is used as a transmitter substance in nearly all animal phyla, but at different parts of the nervous system. It is also present in single-cell animals and even in plants. Enzymes that catalyze the hydrolysis of acetylcholine, the cholinesterases, are also present in various organisms not having a nervous system. In insects and other arthropods, ACh is the transmitter of messages from sensory neurons to the central nervous system (CNS) and within the CNS, but not from motor neurons to skeletal muscles, where the transmitter is glutamate. In annelids, the excitatory transmitter for the body wall muscles is acetylcholine, as at the neuromuscular junctions in vertebrates. 

Anomalous rectification for K+ has been found in the membranes of skeletal muscle cells " and cardiac muscle cells. It is therefore of interest to see if the Ij -V curves for muscle cell membranes are adequately described by (14) for appropriate values of Cq, C , n, and V. The shapes of the curves are similar, but (14) is not a good quantitative description primarily because the curvature of the experimental relation is too large. This can be shown by rewriting (14) for K+ ions and taking the limit of as approaches + oo ... 

In fact, the ATPase of skeletal muscle exhibits a commonly recognizable structural feature for the ATP bound state. So in an initial illustration (Fig. 1.6), we approach ATPases with the most simplistic cycle, that of an idling motor. Then, in Chapter 2 we take a first step toward useful function by attachment to and detachment from a surface and progress from there to more complete depictions. Once the basic science is laid out in Chapter 5, a detailed molecular description is given in Chapter 8. 

Fig. 9.8. Description of muscle mechanics experimental contraction modes of a skeletal muscle...

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