Question: where is the cell body of the neuron that directly causes sa node cells to depolarize faster

title: Sinoatrial node
text: The cells of the SA node are spread out within a mesh of connective tissue , containing nerves , blood vessels , collagen and fat . Immediately surrounding the SA node cells , are paranodal cells . These cells have structures intermediate between that of the SA node cells and the rest of the atrium . The connective tissue , along with the paranodal cells insulate the SA node from the rest of the atrium , preventing the electrical activity of the atrial cells from affecting the SA node cells . The SA node cells are smaller and paler than the surrounding atrial cells , with the average cell being around 8 micrometers in diameter and 20 - 30 micrometers in length ( 1 micrometer = 0.000001 meter ) . Unlike the atrial cells , SA node cells contain fewer mitochondria ( the power plant of the cell ) , fewer myofibers ( the contractile machinery of the cell ) , and a smaller sarcoplasmic reticulum ( a calcium storage organelle that releases calcium for contraction ) . This means that the SA node cells are less equipped to contract compared to the atrial and ventricular cells .