Where is the cell body of the neuron that directly causes SA node cells to depolarize faster? Solution The cell body of the nerve fibres which directly causes the depolarization of Sino Atrial node or SA node is located in the parasympathetic and sympathetic nerves of autonomous nervous system. This depolarization is spontaneous because the SA node is responsible for the cintraction of all the other muscles of the heart. Therefore the action potential which is generated at SA node passes down the other pacemeker cells like AV nodes and conduction of impuslse throughout the heart muscles..