Action potentials are normally carried in only one direction: from the axon hillock toward the axon terminals. What would happen if you experimentally depolarize the middle of the axon to threshold, using an electronic probe? Choice $1$ of $5$:no action potential will be initiated. Choice $2$ of $5$:an action potential will be initiated and proceed only in the normal direction toward the axon terminal. Choice $3$ of $5$:an action potential will be initiated and proceed only back toward the axon hillock. Choice $4$ of $5$:two action potentials will be initiated, one going toward the axon terminal and one going back toward the hillock. Choice $5$ of $5$:an action potential will be initiated, but it will die out before it reaches the axon terminal.