Stephen J Smith Stephen J Smith Stephen J Smith is a Senior Investigator at the Allen Institute for Brain Science. Previously, Dr. Smith was Professor of Molecular and Cellular Physiology at the Stanford University School of Medicine. In 1990, Smith published an article in the journal "Science", which proposed that certain glial cells in the human brain known as astrocytes would be able to communicate through chemical signals, rather than electrical. By utilizing the neurotransmitter glutamate, he was able to show that these cells, which had once been perceived as inert tissue between neurons, in fact were actively communicating with the rest of
Electrical conduction system of the heart well as to the endocardium at the apex of the heart, then finally to the ventricular epicardium; causing its contraction. These signals are generated rhytmically, which in turn results in the coordinated rhythmic contraction and relaxation of the heart. On the microscopic level, the wave of depolarization propagates to adjacent cells via gap junctions located on the intercalated disc. The heart is a "functional syncytium" (not to be confused with a true "syncytium" in which all the cells are fused together, sharing the same plasma membrane as in skeletal muscle). In a functional syncytium, electrical impulses propagate freely between cells