This program models the AMPA and NMDA receptors found in the Hippocampus, which appear to be involved in LTP. This process is suggested to be the cellular mechanism for memory formation. In order for the NMDA receptor to be activated two conditions must be met: presynaptic binding of glutamate to its receptor site and presynaptic depolarization. The glutamate binding activates the receptor. Calcium (Ca2+) cannot pass unless depolarization occurs, which will expel the magnesium (Mg2+) ion that is in the channel. Depolarization occurs when the AMPA receptor has been activated by glutamate binding and Na+ influx depolarizes the membrane sufficiently. Ca2+ influx signals the induction of LTP and is believed to activate 2nd messenger systems, which will ultimately alter RNA and protein synthesis. These activities likely result in the synaptic strengthening that is observed after repeated LTP.
In this program, both conditions must be met for Mg2+ to be expelled. First, there must be glutamate bound at the receptor site. Second, there must be enough intracellular Na+, which will depolarize the membrane. The glutamate that binds to the AMPA and NMDA receptors are distinguished in this model. In real biological systems this is not true, but this allows the user to manipulate individual receptor's activity and view the result.
The SETUP button will setup the program, creating the receptors, chemicals and ions. The GO button runs the program and allows you to visually experience the activity of the AMPA and NMDA receptors. You may want to play around with the sliders in the program to get a better feel of how the receptors function. Eliminating glutamate that can bind to the AMPA receptor will disallow Na+ from being able to pass the membrane, not allowing depolarization, which will render the NMDA receptor unable to become active. Decreasing the amount of Na+ will either not allow depolarization to occur or slow the time that the neuron takes to become depolarized. Eliminating glutamate that can bind to the NMDA receptor will not allow the Mg+ to become expelled because, although the cell is able to become depolarized, it is unable to become activated by the glutamate bound to its receptor site.
The program will end after the Mg2+ returns to the receptor. This signals the end of one cycle. To view additional cycles, press SETUP and then GO.
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