This is a working model of a serotonin synapse. It is still under construction and incomplete, so be sure to check back in a few weeks to see if I have made any progress!
Press "Start" below the model to get things going. You will see the serotonin molecules (blue with a tail) move around the presynaptic nerve terminal (in yellow), at random. Serotonin is occasionally released in to the synaptic space (blue), and you will see the serotonin molecules begin to accumulate here. They cannot cross the membrane to re-enter the presynaptic neuron directly. However, if they encounter a reuptake pump (red cylinders in the presynaptic membrane) they are forcibly pumped back into the presynaptic neuron. This results in an equilibrium, with about 4 or 5 serotonin molecules in the synapse.
Occasionally, the serotonin molecules will encounter Serotonin Receptors (green barrels) on the postsynaptic neuron membrane. This activates intracellular machinery (illustrated with gears).
Note: in reality molecules of serotonin and other neurotransmitters are contained in small membrane bound vesicles, and are released by fusion of such vesicles with the presynaptic membrane. This was too complicated to illustrate in the model at this time.
First, stop the model by pressing the "Stop" button at the bottom. (There is a bug here, you may have to press "Stop" several times to get it to work.)
Next, select the HAND TOOL (with the pointing finger) at the left side of the model.
Now, with the hand tool selected, click on the medicine bottle. Six antidepressant molecules will appear in the synapse.
Watch as the antidepressant molecules bind to the reuptake pumps, blocking their ability to reuptake the serotonin. As this occurrs, more and more serotonin molecules will accumulate in the synapse. This is called a shift in equilibrium. In turn, this increases the chances of the postsynaptic receptors being occupied, and more gears will turn. In reality, a "second messenger system" is activated which, in the short run, may depolarize the cell and create an action potential to transmit the message to the next series of neurons (not shown). In the long run it may bring about other changes which alter synaptic connections themselves.
Prozac is gradually metabolized (disappears in the model), and the equilibrium will reverse as you watch the model run. You can speed this process by clicking on the small "organic waste disposal unit) to the right of the medicine bottle with the hand tool still selected.
You can remove antidepressant molecules or serotonin molecules with the eraser tool. Be careful, the eraser will remove other elements of the model. You can also select the pencil and the serotonin molecules or antidepressant molecules at the top of the screen; clicking in the intracellular space will now add them individually. If things get goofed up, just re-load the page with your browser. (I find I have to re-close and open Netscape to get the program to re-load properly.) Some of the other tools such as the hammer do not do anything.
I am thinking of trying to illustrate synaptic vessicles, postsynaptic membrane depolarization, and action potentials.
Stay tuned!