Function Skeletal Muscle Extracellular Matrix

What Is The Structure And Function Of The Skeletal Muscle Extracellular Matrix. Answer: Introduction The body integumentary system is composed of the skeletal and muscular systems. Muscles are divided into skeletal, cardiac and smooth muscle. The skeletal muscle anchors on the skeletal tissue.3,6 Skeletal muscle is voluntarily controlled. The muscle has contractile proteins; actin and myosin. Muscle fibres make up the muscular system. Each fibre is a unicellular model of a multinucleated, long, cylindrical cell surrounded by a sarcolemma. Contractile proteins are invested in the fibres forming myofibrils. 7The sarcomere is the functional unit of skeletal muscle and contracts and generates force when electrically stimulated.7 Sliding of the thick and thin filaments during contraction constitute the sliding filament theory. Non-contractile portions (troponin and tropomyosin) remain static. The sarcolemma has tubular invaginations called Transverse tubules which are associated with the sarcoplasmic reticulum. The sarcoplasm is the cytoplasm of the muscle cells and excludes the myofibrils.5,8 Skeletal muscle receives innervation of the Central Nervous System (CNS). The axons from the CNS form multiple synapses on the sarcolemma forming a motor end plate. The neuromuscular junction synapses have a presynaptic and a post synaptic knob.9The presynaptic knob has synaptic vesicles with Acetylcholine (Ach). The nervous stimulus cause acetylcholine in vesicles to be released into the synaptic gap. The action potential initiates an electric action potential in the sarcolemma.10 The Ach released from the initiation of the action potential binds the nicotinic receptors at the motor end plate allowing Na= influx this depolarizing the sarcolemma. Impulse from the resultant action potential spread rapidly through the transverse tubules especially on the terminal cisternae where dihydropyridine (DHP) receptors are triggered.6,8,10 The sarcoplasmic reticulum releases Calcium ions stored in the sarcoplasm. Calcium ions bind troponin changing conformation and allowing movement of tropomyosin from the active site on actin. Exposed actin results in myosin binding on its active site.5 The binding of actin to myosin forms a cross bridge which stimulates ATPase activity thus power stroke occurs, this is the ‘pulling’ of actin towards the Management line by pivoting of the myosin head. In the power stroke the myosin head moved from a high energy state to a low energy state.7 ATP serves to break the cross bridge and repositioning of myosin. The repeat of the contraction occurs until the impulse is stopped of depletion of ATP occurs; this called fatigue. Muscle fatigue after progressive contraction are caused by depletion of ATP stores, glucose, and buildup of lactic acid and exhaustion motor plate Ach. On the other hand, muscle twitch occurs due to rapid muscle contraction in response to a single stimulus. The mechanism involves progressive latency, contraction and relaxation. Muscles also obey the ‘all or none law’ of graded responses. The law indicates that an impulse can either generate an action potential or not at all. In temporal summation an increase in frequency of stimulatory impulse results in more contraction. Tetany may occur during contraction. Incomplete tetanus involve partial relaxation between contractions while complete tetany has no relaxation between contractions thus maximum sustained contraction. Varying numbers of muscle cells may also contract depending on motor units in spatial summation. Sometimes additional motor units in a single muscle are activated thus an increase in the contractile strength of the muscle.6 Materials And Methods Materials; LabChart 7 software – Toad Muscle Settings 2012 PowerLab Data Acquisition Unit Bridge Pod Force Transducer Small weight between 5–50 grams Safety glasses Retort Stand Micropositioner and clamps One toad (Bufo marinus), double pithed, per 2 groups of student Wash bottle with Ringer’s solution Dissection tools. Muscle Stimulation Equipment: Animal Nerve Stimulating Electrode ,Stand clamp for the electrode ,Femur clamp Procedure The power lab device is turned off and USB connected to a computer. The force transducer cables are connected and electrodes placed on outward panel. The force transducer and micro positioner and then set on a stand. The force transfer is then calibrated from millivolts to force in Newtons (N). The bridge pod is then opened of the lab chart and recordings made. Known weights are placed after five second recording intervals. The data is recorded on the lab chart software. The toad is then dissected and the leg removed from the hip joint. A thread is attached to the gastrocnemius tendon, the tibiofibular bone is cut and clamping is done. The setup is then placed as follows; The exercises on Twitch recruitment, stretch and contraction, summation, tetany and fatigue are done and results obtained. The contractile force increases with increased stimulus to peak at around 0.6V then decreases gradually. This is because of maximum contraction and resultant fatigue.8 The force of the twitches increase with an increase in the force of the preload. This because of the recruitment of muscle and cross bridge formation.5 The force of the second peak increases with the increased stimulation interval. This is due to frequency summation. The force of the second peak increases with decrease in stimulation time. An increase in frequency results in increased contractile force. More motor plates are recruited.3 The contractile force increases and peaks at 1s, the contraction reduces gradually to baseline due to muscle fatigue from substrate exhaustion. Discussion An increase in the stimulus intensity results in an increase in the threshold of the action potential thus an increase in the number of recruited motor end plates.2,5,8,10 The increase in the preload results in an increase in the stretch, on isometric contraction, the tension is directly proportional to the numerical value of all cross-bridges between the myosin and the actin myofilaments. When as stretching force is applied, the overlap between the myofilaments decrease and in turn the number of cross bridges reduce. The resting length also decreases and the distance the actin filaments move is shortened resulting in a stronger contraction.3,7,9 There is a hyperbolic relationship between velocity and load. This indicates that the smaller the load the higher the velocity and the heavier the load the lower the velocity of the muscle fibres shortening. A heavy preload would result in engagement of numerus bridges this clearly seen in power output of muscle under tension.7 Summation occurs after continuous muscle summation or frequency summation. With multiple action potential on the given muscle fibres, the muscles twitch and summate increasing the tension developed .The higher the frequency of stimulation, the greater the tension. Close contractions result in tetany.4 Fatigue is the progressive loss of muscle contraction from prolonged use caused by ATP shortage and glucose depletion Smooth muscles unlike skeletal; muscle do not fatigue hence continuous contraction. The muscle evades fatigue through selective recruitment of muscle fibres and calcium storage.6,8 Conclusion Muscle is a crucial component of the human body. Skeletal muscle is the basis behind movements and spatial orientation in space. 3This is the basis from which the experiment was done. The sole aim of the experiment was to establish the dynamics of muscle contraction and the psychology adaptation to the functioning.5 It was established that muscle tissue is contractile, excitable, extensible and elastic. The mechanism of action of muscle that facilitates movement was also established. The objectives of the experiment were achieved and the understanding of experimentation, research and integration of knowledge made lucid.10 References Allen DG, Lamb GD, Westerblad H. Skeletal muscle fatigue: cellular mechanisms. Physiological reviews. 2008 Jan;88(1):287-332. Berridge MJ. Smooth muscle cell calcium activation mechanisms. The Journal of physiology. 2008 Nov 1;586(21):5047-61 Boron, Walter F., and Emile L. Boulpaep. Medical Physiology: A Cellular and Molecular Approach. 2012. Horowitz A, Menice CB, Laporte R, Morgan KG: Mechanisms of smooth muscle contraction. Physiol Rev 2012; 76:967-1003 Devasahayam SR. Skeletal Muscle Contraction. InSignals and Systems in Biomedical Engineering 2013 (pp. 225-252). Springer, Boston, MA Hall, John E., and Arthur C. Guyton. Guyton and Hall Textbook of Medical Physiology. Philadelphia, PA: Saunders Elsevier, 2011. . Kandel ER, Schwartz JH, Jessell TM, Siegelbaum SA, Hudspeth AJ (editors): Principles of Neural Science, 5th ed. McGraw-Hill, 2013 Linari M, Caremani M, Lombardi V. A kinetic model that explains the effect of inorganic phosphate on the mechanics and energetics of isometric contraction of fast skeletal muscle. Proceedings of the Royal Society of London Business: Biological Sciences. 2010 Jan 7;277(1678):19-27. Winegrad S. The intracellular site of calcium activation of contraction in frog skeletal muscle. The Journal of general physiology. 1970 Jan 1;55(1):77-88. Gillies AR, Lieber RL. Structure and function of the skeletal muscle extracellular matrix. Muscle & nerve. 2011 Sep 1;44(3):318-31

Function Skeletal Muscle Extracellular Matrix

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