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Body Systems: The Basics
Published in Karen L. LaBat, Karen S. Ryan, Human Body, 2019
Other cell structures are part of the muscle fiber, like nuclei (plural of nucleus, the control center of a cell) and connections from the nervous system to individual striated muscle fibers. Nerve signals and chemical changes within the muscle fiber trigger movement of the actin and myosin (levels 1 and 2) and the muscle fiber contracts. Individual muscle fibers (level 3) are separated by thin connective tissue coverings. Groups of muscle fibers surrounded by another outer layer of fine connective tissue strands form muscle fascicles (level 4) which in turn are bound together by more connective tissue into a muscle (level 5). When muscle fibers (level 3) contract at the same time throughout a muscle, the whole muscle contracts and its contours change (level 5). This muscle activity offers an opportunity for development of products to monitor muscle function.
Applications of Biomaterials in Soft Tissue Replacement
Published in Yaser Dahman, Biomaterials Science and Technology, 2019
Muscle tissue functions by transforming chemical energy into mechanical energy. It can be differentiated into three types: skeletal, smooth, and cardiac (Marieb, 2006). Skeletal muscle tissues have long, striated, and multinucleate cells. They attach to bones and help in the movement and stabilization of the skeleton. Each muscle consists of many muscle fascicles (bundle of cells), and each fascicle consists of many muscle fibers (cell). Each muscle fiber consists of many myofibrils, which consist of the functional unit of the muscle (actin and myosin). Smooth muscle tissue consists of short, spindle-shaped, non-striated cells. Smooth muscle is involuntary, and can be found in the organs of the visceral region of the body such as stomach and intestines where they allow these organs to contract and expand. Cardiac muscle tissue consists of short, striated, branched cells. Cardiac muscle is only found in the heart and is responsible for the circulation of blood (Marieb, 2006).
A finite element muscle building block derived from 3D ultrasound: application to the human gastrocnemius
Published in Computer Methods in Biomechanics and Biomedical Engineering: Imaging & Visualization, 2020
M. Alipour, K. Mithraratne, R. D. Herbert, J. Fernandez
While passive muscle behaviour is captured from observing muscle fascicle deformations during passive dorsiflexion movements and knowing the applied dorsiflexion torque, the active force is a Hill type contraction model applied computationally in addition to the passive behaviour. The active contractile force is added to the direction of the muscle fascicles causing the continuum to contract and deform along these fascicle lines. Appendix A summarises the implementation of active muscle force in the model.
Aponeurosis behaviour during muscular contraction: A narrative review
Published in European Journal of Sport Science, 2018
I hope the studies on aponeurosis behaviour that I have presented here motivate future work to track how aponeurosis dimensions are altered after injury, surgery, disuse and training. It is currently unknown if the aponeurosis remodels at the same rate as the muscle or free tendon in humans and if this is muscle- or contraction-type specific (Franchi et al., 2018), and there is only limited evidence that aponeurosis stiffness is increased in animal muscles with a larger force-producing capacity (Scott & Loeb, 1995). A first step to improve our understanding of how aponeurosis dimensions change following disuse or training could be to investigate aponeurosis widths and lengths of bi-pennate muscles pre- and post-intervention with 3DUS imaging, as bi-pennate muscles typically have a clearly definable central aponeurosis. Such studies could also provide further information on how muscle fascicle strains are distributed medio-laterally and proximo-distally if submaximal fixed-end contractions are performed, as 3DUS imaging allows the muscle volume to be resliced and viewed in multiple reconstructed parasagittal planes. The aponeurosis and fascicle strain data could then be used to inform, optimise and validate the finite element models mentioned above that have investigated muscle injury susceptibility. Such models are important because they permit changes in both muscle width and muscle thickness during contraction, as opposed to one-dimensional Hill-type muscle models, and finite element models can therefore be implemented in simulations examining if transverse strains influence the mechanical output of muscle. More simple musculoskeletal Hill-type models could also be beneficial to investigate whether a SEE stiffness that is modulated by MTU length and force can improve the agreement between experimental and modelling results during human locomotion (Arnold, Hamner, Seth, Millard, & Delp, 2013). For the human tibialis anterior at least, our recent data (Raiteri et al., 2018) suggest that fascicle length and velocity predictions would be incorrect if a constant SEE stiffness was assumed in the model. The improved understanding of muscle–aponeurosis interaction gained from such simulations would be a valuable design factor for robotic prostheses that aim to enhance the function of the musculoskeletal system. Because robotic prostheses typically have series elastic actuators with constant series compliance (Rao et al., 1998), the findings from such simulations could have a significant impact on future prosthetic designs if a variable SEE stiffness is shown to have a mechanical advantage during walking or running.