This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Conducting System of Hea, Subject name: Physiology
TRUE statement regarding the AV node: 
Select and explain. 
A. The path length is greater in the "N" region, B. The path length is greater in the "N-H" region, C. Impulse velocity is slowest in the "A-N" region, D. Impulse velocity is slowest in the "N" region
D: Impulse velocity is slowest in the "N" region
Answer: D: Impulse velocity is slowest in the "N" region 
Explanation: There are 3 regions of the AV node: A-N region -the junction between atrial fibers and nodal tissue N region - the major pa of the nodal tissue N-H region - where nodal fibers merge into His bundle The path length, for impulse propagation, is longest in the A-N region. The velocity of impulse is slowest in the N region. The N region has fibers which depolarize very slowly Most of the AV blocks occur in AN and N regions.