Biology · Nervous System

In the nervous system, the action potential is generated at the axon hillock under physiological conditions and conducted to the terminal end of the axon. The location-specific origin of the action potential and its direction-specific conduction are explained in the following statements: A. The membrane of the axon hillock has the highest threshold for the generation of an action potential. B. The membrane of the axon hillock contains a large number of voltage-gated Na+ channels, making it more excitable. C. The propagating action potential in the middle of the axon cannot generate another action potential in the direction of the cell body because a large fraction of voltage-gated Na+ channels in the preceding portion is voltage-inactivated. D. As the number of voltage-gated Na+ channels is less in the preceding portion of the axonal membrane, the propagating action potential in the middle of the axon cannot generate another action potential in the direction of the cell body. Which one of the following combinations represents both correct explanations?