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. A multi-step molecular process in muscle fiber begins when acetylcholine binds to receptors in the muscle fiber membrane. Proteins in muscle fibers are organized into long chains that can interact with each other and reorganize to shorten and relax.

When acetylcholine reaches the receptors on the membranes of muscle fibers, the membrane channels open and the process of contraction of a relaxed muscle fiber begins: a muscle that contracts and is the main muscle group responsible for movement is called an agonist or main motor. The muscle that relaxes is called an antagonist. One of the effects of regular strength training is an improvement in the level of relaxation that occurs in the opposing muscle group. Although the relationship between the agonist and the antagonist changes depending on the muscle responsible for the movement, each muscle group has an opposite muscle group. The ends of the muscle connect to the bone via a tendon. The muscle is connected to two bones to allow movement through a joint. When a muscle contracts, only one of these bones moves. The point at which the muscle is attached to a moving bone is called insertion. The point at which the muscle is attached to a bone that remains in a fixed position is called the origin.

The release of calcium ions triggers muscle contractions. Watch this video to learn more about the role of calcium. a) What are "T-tubules" and what role do they play? (b) Please describe how actin binding sites are provided for cross-bridging with myosin heads during contraction. In concentric contraction, muscle tension is sufficient to overcome the load, and the muscle shortens as it contracts. [8] This happens when the force generated by the muscle exceeds the load that prevents it from contracting. The process by which a signal is transmitted to a neuromuscular compound is shown in figure (PageIndex{2}). The sequence of events begins when an action potential is initiated in the cell body of a motor neuron and the action potential propagates along the neuron`s axon to the neuromuscular connection. Once the action potential reaches the end of the axonal termination, it causes the neurotransmitter acetylcholine (ACh) from synaptic vesicles in the axonal termination. ACh molecules diffuse through the synaptic cleft and bind to receptors in muscle fibers, initiating muscle contraction.

Muscle contraction is initiated by the depolarization of the sarcolemma, which is caused by the entry of sodium ions through the sodium channels associated with ACh receptors. Muscle contraction begins when the nervous system produces a signal. The signal, a pulse called the action potential, travels through a type of nerve cell called a motor neuron. The neuromuscular connection is the name of where the motor neuron reaches a muscle cell. Skeletal muscle tissue is made up of cells called muscle fibers. When the signal from the nervous system reaches the neuromuscular connection, a chemical message is released by the motor neuron. The chemical message, a neurotransmitter called acetylcholine, binds to receptors outside muscle fibers. This triggers a chemical reaction in the muscle. Unlike skeletal muscle, smooth muscle and heart muscle contractions are myogenic (meaning they are initiated by the smooth muscle or heart cells themselves, rather than being stimulated by an external event such as nerve stimulation), although they can be modulated by stimuli from the autonomic nervous system. The contraction mechanisms in these muscle tissues are similar to those of skeletal muscle tissue. Muscle contraction is the activation of tension-generating sites in muscle cells.

[1] [2] In physiology, muscle contraction does not necessarily mean muscle shortening, as muscle tension can be generated without a change in muscle length, for example when. B`a heavy book or dumbbell is held in the same position. [1] The end of muscle contraction is followed by muscle relaxation, which is a return of the muscle fibers to their low-tension state. [1] When motor neuron stimulation, which gives impetus to muscle fibers, stops, the chemical reaction that causes muscle fiber proteins to rearrange is stopped. As a result, the chemical processes in the muscle fibers are reversed and the muscle relaxes. The bridge cycle process is shown in (PageIndex{6}). A transverse bridge cycle begins when the myosin head binds to an actin filament. ADP and Pi are also related to the myosin head at this stage. Then, a power stroke moves the actin filament inwards to the center of the sarcoma, thereby shortening the sarcomere.

At the end of the strength stroke, ADP and Pi are released from the myosin head so that the myosin head remains attached to the thin filament until another ATP binds to the myosin head. .