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Metabotropic receptors on the other hand activate second messenger cascade systems that result in the opening of ion channel located some place else on the same postsynaptic membrane.
These allow Ca2 ions to diffuse through these channels and bind with synaptic vesicles within the terminal boutons.
The Hodgkin–Huxley model of an action potential in the squid giant axon has been the basis for much of the current understanding of the ionic bases of action potentials.
Briefly, the model states that the generation of an action potential is determined by two ions: Na and K .
Synaptic plasticity in both excitatory and inhibitory synapses has been found to be dependent upon postsynaptic calcium release Two molecular mechanisms for synaptic plasticity (researched by the Eric Kandel laboratories) involve the NMDA and AMPA glutamate receptors.
Opening of NMDA channels (which relates to the level of cellular depolarization) leads to a rise in post-synaptic Ca2 concentration and this has been linked to long-term potentiation, LTP (as well as to protein kinase activation); strong depolarization of the post-synaptic cell completely displaces the magnesium ions that block NMDA ion channels and allows calcium ions to enter a cell – probably causing LTP, while weaker depolarization only partially displaces the Mg2 ions, resulting in less Ca2 entering the post-synaptic neuron and lower intracellular Ca2 concentrations (which activate protein phosphatases and induce long-term depression, LTD).