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Depiction of smooth muscle contraction. Muscle contraction is the activation of tension-generating sites within muscle cells. [1] [2] In physiology, muscle contraction does not necessarily mean muscle shortening because muscle tension can be produced without changes in muscle length, such as when holding something heavy in the same position. [1]
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 ...
Sliding filament model of muscle contraction. Cardiac sarcomere structure featuring myosin. Myosin II (also known as conventional myosin) is the myosin type responsible for producing muscle contraction in muscle cells in most animal cell types. It is also found in non-muscle cells in contractile bundles called stress fibers. [18]
Relaxation of ciliary muscle causes paralysis of accommodation (cycloplegia) and impaired near vision; Raised intraocular pressure; Gastrointestinal tract: Inhibition of motility; Other smooth muscle Relaxation of bronchial smooth muscle; Biliary and urinary tract smooth muscle only slightly affected, might precipitate urinary retention
For example, non-muscle myosin II bipolar thick filaments provide the force of contraction needed to divide the cell into two daughter cells during cytokinesis. In addition to myosin II, many other myosin types are responsible for variety of movement of non-muscle cells.
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]
Sherrington, one of the founding figures in neurophysiology, observed that when the central nervous system signals an agonist muscle to contract, inhibitory signals are sent to the antagonist muscle, encouraging it to relax and reduce resistance. This mechanism, known as reciprocal inhibition, is essential for efficient movement and helps ...
This ring, aptly called the "contractile ring", uses a similar mechanism as muscle fibers where myosin II pulls along the actin ring, causing it to contract. [66] This contraction cleaves the parent cell into two, completing cytokinesis. [66] The contractile ring is composed of actin, myosin, anillin, and α-actinin. [67]