Héroux, M. E., Stubbs, P. W., and Herbert, R. D. (2016). Behavior of human gastric and gastrointestinal muscle fascicles during increased submaximum isometric contractions. Physiol. Rep. 4:e12947. doi: 10.14814/phy2.12947 Muscles exposed to a high eccentric load suffer greater damage with overload (for example.
B during muscle building or strength training) than with a concentric load. When eccentric contractions are used in strength training, they are usually called negative. During a concentric contraction, the muscle myofilaments slide over each other and contract the Z lines. During an eccentric contraction, the myofilaments slide on top of each other in the opposite direction, although the actual movement of the myosin heads during an eccentric contraction is not known. Exercise with a strong eccentric load can actually support more weight (muscles are about 40% stronger in eccentric contractions than in concentric contractions) and also leads to greater muscle damage and delayed muscle pain one to two days after exercise. Exercises involving both eccentric and concentric muscle contractions (i.e. With strong contraction and controlled weight reduction), can lead to greater force gains than concentric contractions alone.   While unusual strong eccentric contractions can easily lead to overtraining, moderate exercise can provide protection from injury.  Intense muscle activity results in oxygen debt, which is the amount of oxygen needed to compensate for ATP produced without oxygen during muscle contraction. Oxygen is needed to restore ATP and creatine phosphate levels, convert lactic acid to pyruvic acid, and convert lactic acid into glucose or glycogen in the liver. Other systems used during exercise also require oxygen, and all these processes combined lead to an increase in respiratory rate that occurs after exercise.
Until the oxygen debt is satisfied, oxygen absorption is increased, even after the training is stopped. Creatine phosphate is a molecule that can store energy in its phosphate bonds. In a resting muscle, excess ATP transfers its energy to creatine and produces ADP and creatine phosphate. This acts as an energy reserve that can be used to quickly generate more ATP. When the muscle contracts and needs energy, creatine phosphate transfers its phosphate to ADP to make ATP and creatine. This reaction is catalyzed by the enzyme creatine kinase and occurs very quickly; Thus, ATP derived from creatine phosphate causes the first few seconds of muscle contraction. However, creatine phosphate can only provide energy worth about 15 seconds, after which another energy source must be used (Figure 10.12). The end of the crossbridge cycle (and the exit of the muscle in the latch state) occurs when the light-chain phosphatase of myosin removes phosphate groups from myosin heads. Phosphorylation of 20 kDa myosin light chains is well correlated with the speed of shortening of smooth muscles.
Meanwhile, there is a rapid eruption of energy consumption, measured by oxygen consumption. A few minutes after their appearance, calcium levels drop significantly, phosphorylation of 20 kDa myosin light chains decreases, and energy consumption decreases; However, the strength of the tonic smooth muscles is preserved. During muscle contraction, rapidly changing transverse bridges form between activated actin and phosphorylated myosin, creating strength. He hypothesizes that force maintenance results from dephosphorylated « locking bridges » that circulate slowly and maintain force. A number of kinases such as rhokinase, DAPK3 and protein kinase C are thought to participate in the prolonged phase of contraction, and the flow of Ca2+ may be significant. Maganaris, C., Baltzopoulos, V., and Sargeant, A. (1998). In vivo measurements of complex triceps-surae architecture in humans: implications for muscle function. J. Physiol. 512, 603–614.
doi: 10.1111/j.1469-7793.1998.603be.x The contractile activity of smooth muscle cells can be tonic (persistent) or phasic (transient) and is influenced by multiple inputs such as spontaneous electrical activity, neuronal and hormonal inputs, local changes in chemical composition and stretching.  This contrasts with the contractile activity of skeletal muscle cells, which is based on a single neuronal input. Some types of smooth muscle cells are able to spontaneously generate their own action potentials, which usually occur after pacemaker potential or slow wave potential. These action potentials are generated by the influx of extracellular Ca2+ and not Na+. Like skeletal muscles, cytosolic Ca2+ ions are also needed for the transverse bridge cycle in smooth muscle cells. Azizi, E., Deslauriers, A. R., Holt, N.C., and Eaton, C. E. (2017).
Resistance to radial expansion limits muscle tension and work. Biomech model. Mechanobiol. 16, 1633–1643. doi: 10.1007/s10237-017-0909-3 The area where the thick and thin filaments overlap has a dense appearance because there is little space between the filaments. This area, where thin and thick filaments overlap, is very important for muscle contraction because it is where the movement of the filament begins. Thin filaments anchored at their ends through the Z disks do not extend completely into the central zone, which contains only thick filaments anchored to their bases in a place called the M line. A myofibril consists of many sarcomeres that run along its length; Thus, myofibrils and muscle cells contract when sarcomeres contract. Bolsterlee, B., D`Souza, A., and Herbert, RD (2019). Reliability and robustness of muscle architecture measurements obtained using diffusion tensor imaging with anatomically limited tractography. J.
Biomech 86, 71–78. doi: 10.1016/j.jbiomech.2019.01.043 Figure 3. A sarcomere is the area from one Z line to the next Z line. Many sarcomeres are present in a myofibrill, which leads to the characteristic scratch pattern of skeletal muscles. Figure 1. The body contains three types of muscle tissue: skeletal muscle, smooth muscle and heart muscle, which are visualized here with optical microscopy. Smooth muscle cells are short, tapered at each end and have only one bulging nucleus in each. Heart muscle cells are branched and scratched, but short. The cytoplasm can branch out, and they have a nucleus in the middle of the cell. (Source: NCI Work Change, NIH; Scale bar data by Matt Russell) Roberts, T.
J., Eng, C.M., Sleboda, D. A., Holt, N.C., Brainerd, E. L., Stover, K. K., et al. (2019). The multi-scale and three-dimensional nature of skeletal muscle contraction. Physiology 34, 402–408. doi: 10.1152/physiol.00023.2019 Which of the following claims about muscle contraction is true? The relaxation of skeletal muscle fibers and finally skeletal muscle begins with the motor neuron, which stops releasing its chemical signal, ACh, into the synapse at the NMJ. The muscle fiber will repolarize, which closes the doors in the SR where Ca++ has been released. ATP-controlled pumps will move Ca++ from the sarcoplasm to the SR.
This leads to a « shielding » of the actin binding sites on thin filaments. Without the ability to form transverse bridges between thin and thick filaments, the muscle fiber loses its tension and relaxes. Hill, A. V. (1938). The heat of shortening and the dynamic constants of the muscles. Proc. R. Soc.B 126, 136-195. doi: 10.1098/rspb.1938.0050 Excitation-contraction coupling in heart muscle cells occurs when an action potential of pacemaker cells in the sinus node or atrioventral node is initiated and conducted via lacunar junctions to all cells of the heart. The action potential moves along the surface membrane in the T tubules (the latter are not observed in all types of heart cells) and depolarization causes the entry of extracellular Ca2+ into the cell via L-type calcium channels and possibly sodium-calcium exchangers (NCX) at the beginning of the plateau phase. Although this influx of Ca2+ represents only about 10% of the Ca2+ needed for activation, it is relatively larger than that of skeletal muscles.
This influx of Ca2+ causes a small local increase in intracellular Ca2+. The increase in intracellular Ca2+ is detected by RyR2 in the membrane of the sarcoplasmic reticulum, which releases Ca2+ in a positive physiological feedback response. This positive feedback is called calcium-induced calcium release and leads to calcium sparks (Ca2+ sparks ). The spatial and temporal sum of about 30,000 Ca2+ sparks results in an increase in cytoplasmic calcium concentration at the cell level.  The increase in cytosolic calcium after calcium flows through the cell membrane and sarcoplasmic reticulum is moderated by calcium buffers, which bind to much of the intracellular calcium. As a result, a large increase in total calcium leads to a relatively small increase in free Ca2+.  Winters, T.M., Takahashi, M., Lieber, R. L., and Ward, S. R. (2011). Whole muscle length-tension relationships are accurately modeled as scaled sarcomeres in the muscles of the rabbit`s hind leg. J.
Biomech 44, 109–115. doi: 10.1016/j.jbiomech.2010.08.033 After depolarization, the membrane returns to its resting state. This is called repolarization, in which voltage-dependent sodium channels close. Potassium channels remain at 90% conductivity. Since the sodium-potassium atPase plasma membrane always carries ions, the resting state (negatively charged inside relative to the outside) is restored. The period immediately after the transmission of an impulse into a nerve or muscle, in which a neuron or muscle cell regains its ability to transmit another impulse, is called the refractory period. .