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The sliding filament theory explains the mechanism of muscle contraction based on muscle proteins that slide past each other to generate movement. [1] According to the sliding filament theory, the myosin ( thick filaments ) of muscle fibers slide past the actin ( thin filaments ) during muscle contraction, while the two groups of filaments ...
The termination of muscle contraction is followed by muscle relaxation, which is a return of the muscle fibers to their low tension-generating state. [ 1 ] For the contractions to happen, the muscle cells must rely on the change in action of two types of filaments : thin and thick filaments.
Smooth muscle is grouped into two types: single-unit smooth muscle, also known as visceral smooth muscle, and multiunit smooth muscle. Most smooth muscle is of the single-unit type, and is found in the walls of most internal organs (viscera); and lines blood vessels (except large elastic arteries), the urinary tract , and the digestive tract .
An impulse from a nerve cell causes calcium release and brings about a single, short muscle contraction called a muscle twitch. If there is a problem at the neuromuscular junction, a very prolonged contraction may occur, such as the muscle contractions that result from tetanus. Also, a loss of function at the junction can produce paralysis. [5]
It allows the motor neuron to transmit a signal to the muscle fiber, causing muscle contraction. [2] Muscles require innervation to function—and even just to maintain muscle tone, avoiding atrophy. In the neuromuscular system, nerves from the central nervous system and the peripheral nervous system are linked and work together with muscles. [3]
The action of myosin along the actin filaments causes the shortening and lengthening of the sarcomere; responsible for muscle contraction and relaxation, respectively. Motor proteins are the driving force behind most active transport of proteins and vesicles in the cytoplasm .
During muscle contraction, tropomyosin shifts to expose the myosin-binding site on an actin filament, allowing the interaction between actin and myosin microfilaments to occur. The initiation of contraction involves calcium ions binding to troponin, prompting a reaction that displaces tropomyosin from the actin filament binding sites.
T-tubules (transverse tubules) are extensions of the cell membrane that penetrate into the center of skeletal and cardiac muscle cells.With membranes that contain large concentrations of ion channels, transporters, and pumps, T-tubules permit rapid transmission of the action potential into the cell, and also play an important role in regulating cellular calcium concentration.
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