AMPA (a-amino-3-hydorxi-methyl-4-isoxazolepropionic acid) receptors are ionotropic glutamatergic receptors responsible for the fast component of excitatory synaptic transmissions. They are ligand-gated ion-channels activated by the binding of the neurotransmitter glutamate, permeable to sodium and potassium ionic currents. AMPA receptors are thought to constitute the main substrate for synaptic LTP and LTD. [Animation by Pete Bilderback]


NMDA (N-methyl-D-aspartate) receptors are ionotropic glutamatergic receptors. Compared to AMPA receptors, these have a much slower kinetics of activation. A unique feature of NMDA receptors is their sensitivity to a Mg2+ block. The Mg2+ block is voltage-dependent, being relieved when the neuron is depolarized. The necessity of concomitant presynaptic (release of glutamate) and postsynaptic (depolarization) activities makes the NMDA receptors coincidence detectors. In addition, they are highly permeable to calcium ions, which are important mediators of different metabolic cascades. These properties are important for their role in synaptic plasticity and activity-dependent development. [Animation by Pete Bilderback]


Back-propagating action potentials are observed in a broad variety of cell types in the central nervous system. It is observed that, when an action potential is generated, it not only propagates down the axon, but also travels back into the dendrites. The back-propagating action potential plays an important theoretical role of delivering the information on the postsynaptic firing activity to the synapses. Such information is essential for any type of associative (Hebbian-type) learning rules. [Animation by Pete Bilderback]