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 in every direction, so that the myocardium functions as a single contractile unit. This property allows rapid, synchronous depolarization of the myocardium. While advantageous under normal circumstances, this property can be detrimental, as it has potential to allow the propagation of incorrect electrical signals. These gap junctions can close to isolate damaged or dying tissue, as in a myocardial infarction (heart attack). Embryologic evidence of generation of the cardiac conduction system illuminates the respective roles of this specialized set of cells. Innervation of the heart begins with a brain only centered parasympathetic cholinergic first order. It is then followed by