Identify the steps that show how an action potentialproduced in the motor end-plate of the neuromuscularjunction eventually results in contraction of the muscle fiber.
Identify the steps that show how an action potential
produced in the motor end-plate of the neuromuscular
junction eventually results in contraction of the muscle fiber.
The muscular system comprises three major types of muscle cells - smooth muscle, cardiac muscle, and skeletal muscle. The skeletal muscles have a striated appearance, and these muscle tissues are under the voluntary control of the central nervous system. The mechanism of contraction in the fibers of skeletal muscles begins at the site of the neuromuscular junction. The flow of Ca2+ ions towards the inside leads to the release of acetylcholine (a chemical, neurotransmitter molecule) at the site of the neuromuscular junction. This chemical then moves to the postsynaptic membrane of the synapse at the myofiber. The postsynaptic membrane of the myofiber is also termed the motor endplate. Acetylcholine molecules attach themselves to the nicotinic receptors present at the motor endplate, and this binding results in its depolarization, which in turn generates the action potentials in the skeletal muscle fiber. The steps that finally lead to contraction of the muscle fiber after the production of the action potential are as follows –
- The sarcoplasmic reticulum releases calcium ions.
- The calcium ions interact with the troponin complex, which results in the shifting of the actin myofilaments. This shifting exposes the myosin-binding sites.
- The cross-bridges formed by the myosin proteins attach and detach, which eventually pulls the thin filaments of actin towards the center. This step requires ATP molecules.
- The cyclic events of cross-bridges eventually lead to the contraction of the muscle fiber.
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