Skeletal muscle movement

Another area of NEMS that is receiving tremendous attention is the mimicry of biological systems, aptly referred to as biomimetics. For instance, in the development of linear molecular muscles that undergo contraction and extension movements. Initial work in this field utilized transition metal complexes containing rotaxanes and catenanes, due to the nondestructive redox processes occurring on the metal centers.Though these complexes were actuated by a chemical reaction, the movement was in a noncoherent manner. In order to better mimic skeletal muscle movement, one has to look at the mode of motion within the most efficient molecular machines - in our human bodies. 

Figure 6.69. A biomimetic approach toward skeletal muscle movement. Shown is (a) the stacked protein filaments of the sarcomere and (b) a redox-controlled molecular analogue. Adapted with permission from Liu, Y. Flood, A. H. Bonvallet, P. A. Vignon, S. A. Northrop, B. H. Tseng, H.-R. Jeppesen, J. O. Huang, T. J. Brough, B. Bailer, M. Magonov, S. Solares, S. D. Goddard, W. A. Ho, C.-M. Stoddart, J. F. J. Am. Chem. Soc. 2005, 727, 9745. Copyright 2005 American Chemical Society.

The somatic nervous system controls skeletal muscle movement through motor neurons. Alpha motor neurons extend from the spinal cord and terminate on indi-... 

Voluntary skeletal muscle movements are initiated by the motor cortex in the brain. Then signals travel down the spinal cord to the alpha motor neuron to result in contraction. However, not all movement of skeletal muscles is voluntary. Certain reflexes occur in response to dangerous stimuli, such as extreme heat. Reflexive skeletal muscular movement is controlled at the level of the spinal cord and does not require higher brain initiation. Reflexive movements are processed at this level to minimize the amount of time necessary to implement a response. 

Cardiac Similar to skeletal muscle Similar to skeletal muscle Movement of blood by... 

Acetylcholine is the neurotransmitter produced by neurons referred to as cholinergic neurons. In the peripheral nervous system acetylcholine plays a role in skeletal muscle movement, as well as in the regulation of smooth muscle and cardiac muscle. In the central nervous system acetylcholine is believed to be involved in learning, memory, and mood. 

Dawes GS. The central control of fetal breathing and skeletal muscle movements. J Physiol 1984 346 1-18. 

FIGURE 17.23 The mechanism of skeletal muscle contraction. The free energy of ATP hydrolysis drives a conformational change in the myosin head, resulting in net movement of the myosin heads along the actin filament. Inset) A ribbon and space-filling representation of the actin—myosin interaction. (SI myosin image courtesy of Ivan Rayment and Hazel M. Holden, University of Wiseonsin, Madison.)... 

The PNS is further divided into the somatic nervous system and the autonomic nervous system. The somatic branch of the PNS is concerned witii sensation and voluntary movement. The sensory part of the somatic nervous system sends messages to the brain concerning die internal and external environment, such as sensations of heat, pain, cold, and pressure The voluntary part of die somatic nervous system is concerned witii die voluntary movement of skeletal muscles, such as walking, chewing food, or writing a letter. 

Schneider, M.F. Chandler, W.K. (1973). Voltage dependent charge movement in skeletal muscle A possible step in excitation-contraction coupling. Nature 242,244-246. 

Proteins play an important role in movement at both the organ (eg, skeletal muscle, heart, and gut) and cellular levels. In this chapter, the roles of specific proteins and certain other key molecules (eg, Ca ) in muscular contraction are described. A brief coverage of cyto-skeletal proteins is also presented. 

The spinocerebellum influences muscle tone and coordinates skilled voluntary movements. It receives sensory input from interneurons in the spinal cord transmitting somatic information, in particular from muscle and joint proprioceptors providing data regarding body movements and positions that are actually taking place. It also receives input from the cortical motor areas providing information regarding intended or desired movement. The spinocerebellum then compares these inputs. If the actual status of a body part differs from the intended status, the spinocerebellum transmits impulses back to the motor areas of the brain to make appropriate adjustments in activation of the associated skeletal muscles. 

Descending tracts. Voluntary movement of skeletal muscles is controlled by two types of descending tracts. Neurons in these tracts terminate on and influence activity of alpha motor neurons in the ventral horn. The two types of tracts include ... 

Although skeletal muscle comprises the bulk of muscle tissue in the body, smooth muscle is far more important in terms of homeostasis. Most smooth muscle is found in the walls of tubes and hollow organs. Contraction and relaxation of the smooth muscle in these tissues regulates the movement of substances within them. For example, contraction of the smooth muscle in the wall of a blood vessel narrows the diameter of the vessel and leads to a decrease in the flow of blood through it. Contraction of the smooth muscle in the wall of the stomach exerts pressure on its contents and pushes these substances forward into the small intestine. Smooth muscle functions at a subconscious level and is involuntary. It is innervated by the autonomic nervous system, which regulates its activity. 

Lymphatic capillaries join together to form larger lymphatic vessels that have valves within them to ensure the one-way flow of lymph. The lymph is moved along by two mechanisms. Automatic, rhythmic waves of contraction of the smooth muscle in the walls of these vessels are the primary mechanism by which lymph is propelled through the system. Second, the contraction of skeletal muscles causes compression of lymphatic vessels. As in the veins, this pumping action of the surrounding skeletal muscles contributes to movement of the lymph. Ultimately, the lymph is returned to the blood when it empties into the subclavian and jugular veins near the heart. 

The first molecule, the Ca2+ channel, is required for coupling at the triad. Skeletal muscle contains higher concentrations of this L-type Ca2+ channel that can be accounted for on the basis of measured voltage-dependent Ca2+ influx because much of the Ca2+ channel protein in the T-tubular membrane does not actively gate calcium ion movement but, rather, acts as a voltage transducer that links depolarization of the T-tubular membrane to Ca2+ release through a receptor protein in the SR membrane. The ryanodine receptor mediates sarcoplasmic reticulum Ca2+ release. The bar-like structures that connect the terminal elements of the SR with the T-tubular membrane in the triad are formed by a large protein that is the principal pathway for Ca2+ release from the SR. This protein, which binds the... 

Rapid, often continuous contraction of a bundle of skeletal muscle fibers which does not produce a purposeful movement (twitching). 

Anatomically, the nervous system is divided into the central nervous system (CNS) consisting of the brain and the spinal cord and the peripheral nervous system comprised of neural cells forming a network throughout the body. The peripheral system is itself subdivided into two sections the somatic system, where control of skeletal muscles allows movement and breathing, and the autonomic system which controls the actions of smooth muscle, cardiac muscle and glandular tissues. Further subdivision of the autonomic system based on anatomical and biochemical factors creates the sympathetic and parasympathetic nervous systems. 

Skeletal muscle, also known as striated muscle because of the microscopic appearance, is responsible for locomotion and those fine, voluntary movements of the body which are under conscious control. Smooth muscle exerts automatic, involuntary... 

Skeletal muscle Is composed of bundles of tissue, with a tendon at either end. Usually the fixed end is referred to as the tendon of origin, the end that moves, the tendon of insertion. Muscles produce force through the process of contraction. Stretching of a muscle is passive and performed by contraction of an antagonist. For this reason, at least two muscles are necessary for free movement of joints. The principle of flexion and extension of the elbow joint by two antagonistic muscles is shown in Fig. 1. 

What we commonly call movement depends on mnscle cells. There are several types of muscle in the hnman body heart mnscle striated skeletal muscle, which includes the large muscles of the body and smooth mnscle of the stomach, intestines, arteries and veins, and nterns. There is a fnndamental difference between striated and smooth muscle. You can control the former bnt not the latter. Yon can pretty mnch will what yon do with yonr arms and legs, for example. The activities of your stomach, veins and arteries, and intestines are pretty mnch beyond yonr ability to control by force of will. Heart is an exception heart mnscle is basically a striated muscle but we are at a loss to willfully control the rate or force of its contractions. 

Smooth muscle is composed of spindle-shaped cells rather than fibres. It lacks striations since adjacent myofibrils are out of register. Power output is lower than that from skeletal muscle it is responsible for the gentler, involuntary movements including, for example, those that cause movement of the intestine and those that change the diameter of blood vessels. 

The major role of skeletal muscle is movement, which is described and discussed in Chapter 13). Nevertheless, since muscle comprises 40% of the body it is large enough to play a part in control of the blood concentrations of the major fuels glucose, fatty acids, triacylglycerol and some amino acids. Skeletal muscle contains the largest quantity of protein in the body, which is used as a source of amino acids under various conditions (e.g. starvation, trauma, cancer see above). It plays an important part in the metabolism, in particular, of branched-chain amino acids, glutamine and alanine, which are important in the overall metabolism of amino acids in the body (discussed below). 

Movement is an essential component of life. If something moves, it is assumed to be alive. External movement depends upon skeletal muscle whereas internal movement depends upon smooth and cardiac muscles. The latter muscles are discussed in other chapters. The term physical activity is another term for external movement. Hence, it depends on skeletal muscle. This chapter contains a discussion of the biochemistry of skeletal muscle, including its involvement in everyday activities. This leads into the biochemistry underlying both the benefits and hazards of physical activity. In addition, the biochemical bases of the common problem of fatigue and the debilitating condition of chronic fatigue are discussed. 

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