Medicala Physiology - Fundamental Mechanism of Muscle Contraction

Medical Physiology - Fundamental Mechanism of Muscle Contraction
The commencement and implementation of muscular contraction transpire in the subsequent sequential steps: 1. An action potential propagates along a motor neuron to its terminals on muscle fibers, where each terminal releases a minute quantity of the neurotransmitter acetylcholine. 2. Acetylcholine interacts with a specific region of the muscular membrane to activate acetylcholine-gated cation channels, permitting primarily sodium ions, along with calcium ions, to enter the muscle fiber, resulting in localized depolarization. The local depolarization subsequently causes the opening of voltage-gated sodium channels, culminating in an action potential. The action potential propagates over the muscle fiber membrane, prompting the sarcoplasmic reticulum to release calcium ions into the myofibrils that were previously stored in the sarcoplasmic reticulum. 4. Calcium ions instigate attractive interactions between the actin and myosin filaments, resulting in their sliding together; this constitutes the contractile process. 5. Calcium ions are continuously transported back into the sarcoplasmic reticulum, where they are stored until a muscular action potential occurs; this expulsion of calcium ions from the myofibrils results in the cessation of muscle
contraction.