LINGUIST 2PS3 Lecture Notes - Alpha Motor Neuron, Endoplasmic Reticulum, Myocyte

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Muscle contraction is initiated by the release of ach from the axon terminals of alpha motor neurons. Ach produces a large epsp in the postsynaptic membrane due to the activation of. Ach receptors which is sufficient to evoke an action potential in the muscle fiber. By the process of excitation-contraction coupling, this action potential (excitation) triggers the release of ca2+ from an organelle inside the muscle fiber, which leads to contraction of the fiber. Relaxation occurs when the ca2+ levels are lowered by reuptake into the organelle. Fusion of myoblasts in early development leads to the formation of multinucleated muscle fibers. Muscle fibers are enclosed by an excitable cell membrane called the sarcolemma. 13. 11): the arrival of an action potential in the t tubule membrane causes a conformational change in the tetrad, which opens the calcium release channel in the sr membrane. This leads to an increase in free ca2+ within the cytosol which causes the myofibrils to contract.

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