Where Nerves End

With support from PSC's biomedical group and the Salk Institute, many research labs around the world use MCell and DReAMM, powerful software for simulating and visualizing chemical reactions that occur as molecules diffuse within, around and between cells. In recent work, PSC scientist and MCell/DReAMM co-developer Joel Stiles used MCell to simulate the mechanism of a degenerative neuromuscular disease. His studies predicted a never-before-seen defect in a protein involved in nerve-muscle communication, leading to experiments that verified his computational finding.

This image - from an MCell simulation - represents a closeup of a nerve-muscle junction and shows neurotransmitter molecules (small blue spheres) releasing from a synaptic vesicle (large white sphere, upper center). The valley represents a cleft in the geometry of the muscle cell. The colored markers indicate receptor proteins embedded in the muscle-cell wall. They're shown in four different states of interaction with the neurotransmitters, ranging from unbound (purple), to intermediately bound (red), fully bound (green) and activated (yellow). Other markers (white and black) represent an enzyme that breaks down the transmitter to a non-transmitter molecule (small red spheres). In a normal muscle membrane, yellow becomes predominant at later times as receptors open and make current to stimulate the muscle cell.