动作电位

Pain Signal And Our Products www.new1212.com An action potential arrives at the presynaptic terminal causing voltage-gated calcium ion channels to open, increasing the calcium ion permeability of the presynaptic terminal cell membrane. Calcium ions (Ca) enter the presynaptic terminal and cause vesicles to release their neurotransmitter, acetylcholine (ACh), from the synaptic vesicles into the presynaptic cleft. Diffusion of acetylcholine across the synaptic cleft and binding of acetylcholine to acetylcholine receptors on the postsynaptic muscle fiber membrane causes an increase in the permeability of ligand-gated sodium ion channels. The movement of sodium ions (Na) into the muscle cell results in depolarization of the postsynaptic membrane. Once threshold has been reached, a postsynaptic action potential is generated and is propagated over the muscle cell membrane. Acetylcholine is rapidly broken down to acetic acid and choline in the synaptic cleft by the enzyme acetylcholinestera