Once the chemical / neurotransmitter signal has been translated into an electrical signal, the postsynaptic receptors need to be "cleared" very quickly so that they can receive new transmitters from new signals (otherwise you'd end up with neurotransmitter traffic worse than any traffic you've ever experienced on the freeway!). The membrane of the postsynaptic neuron contains a few channels (receptors) that control how a neurotransmitter can be translated into an electrical signal. ![]() The neurotransmitters can now "swim" (diffuse) through the synaptic cleft, until they reach the postsynaptic neuron. Once these channels are open, calcium ions from the surrounding extracellular environment rush into the presynaptic terminal.Īs the calcium ions encounter the vesicles, the membrane of the vesicles fuse with the membrane of the presynaptic terminal, right at the synaptic cleft.Īs the vesicles fuse with the membrane, the neurotransmitters are "expelled" into the synaptic cleft. When the electrical signal reaches the presynaptic terminal, it opens some channels in the membrane (these are called voltage gated Ca 2+ channels). The small groups of neurotransmitters are released into the synaptic cleft when they receive an order from Ca 2+ ions to do so. In neurobiological terms, we say that the neurotransmitters need to be packaged into vesicles. Once the neurotransmitters are synthesized, they need to be put into "small groups" ready to be "launched" across the synaptic cleft. The smaller amines/amino acids can generally be synthesized at the presynaptic terminal itself. The large peptides are synthesized in the cell body of the neuron and are transported to the synaptic terminal through the axon. There are two general classes of neurotransmitters: large neuropeptides or smaller amines/amino acids. neurotransmitter is either reabsorbed by presynaptic cell, and repackaged for future release, or broken down metabolically. Due to thermal shaking, neurotransmitter molecules will break loose from receptorsĨ. The binding of neurotransmitter causes receptor molecule to be activatedħ. Some escapes, but some binds to chemical receptor molecules located on the membrane of the postsynaptic cell.Ħ. The neurotransmitter diffuses within the cleft. These proteins change shape, causing membranes of some "docked" vesicles to fuse with membrane of presynaptic cell, thereby opening vesicles & dumping neurotransmitter contents into synaptic cleft, the narrow space between membranes of pre- and postsynaptic cells.ĥ. high Ca concentration activates calcium-sensitive proteins attached to vesicles that contain a neurotransmitter chemical. C+ flow through presynaptic membrane, rapidly increasing Ca concentration in interior.Ĥ. ![]() ![]() electrical depolarization of membrane at synapse causes channels to open that are permeable to calcium ions.ģ. Begins w/ wave of electrochemical excitation = action potential traveling along membrane of presynaptic cell, until reaches the synapse.Ģ.
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