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The presynaptic axon terminal, or synaptic bouton, is a specialized area within the axon of the presynaptic cell that contains neurotransmitters enclosed in small membrane-bound spheres called synaptic vesicles (as well as a number of other supporting structures and organelles, such as mitochondria and endoplasmic reticulum).
The releasable pool is located in the active zone and is bound directly to the presynaptic membrane. It is stabilized by proteins within the active zone and bound to the presynaptic membrane by SNARE proteins. These vesicles are ready to release by a single action potential and are replenished by vesicles from the reserve pool.
Both the presynaptic and postsynaptic sites contain extensive arrays of molecular machinery that link the two membranes together and carry out the signaling process. In many synapses, the presynaptic part is located on the terminals of axons and the postsynaptic part is located on a dendrite or soma.
Axon terminals (also called terminal boutons, synaptic boutons, end-feet, or presynaptic terminals) are distal terminations of the branches of an axon. An axon, also called a nerve fiber, is a long, slender projection of a nerve cell that conducts electrical impulses called action potentials away from the neuron's cell body to transmit those ...
The autoreceptor causes the inhibition of calcium channels (slowing calcium ion influx) and the opening of potassium channels (increasing potassium ion efflux) in the presynaptic membrane. These changes in ion concentration effectively diminish the amount of the original neurotransmitter released by the presynaptic terminal into the synaptic cleft.
A synapse during re-uptake. Note that some neurotransmitters are lost and not reabsorbed. Reuptake is the reabsorption of a neurotransmitter by a neurotransmitter transporter located along the plasma membrane of an axon terminal (i.e., the pre-synaptic neuron at a synapse) or glial cell after it has performed its function of transmitting a neural impulse.
The formation of the new membrane is a protein mediated process and can only occur under certain conditions. After an action potential, Ca 2+ floods to the presynaptic membrane. Ca 2+ binds to specific proteins in the cytoplasm, one of which is synaptotagmin, which in turn trigger the complete fusion of the synaptic vesicle with the cellular ...
Depolarization of the presynaptic membrane causes voltage gated Ca2++ to open in the axon terminals; Calcium diffuses into the axon terminal causing vesicles adjacent to axon terminals to fuse with the plasma membrane. Fusing results in release of the neurotransmitter into the synaptic cleft.