Task: Question Answering
Input (English): Question: The action potential starts in the membrane of the initial segment of the axon by: 
 Options:  <1> Be the place where the synapse occurs. <2> Have a higher excitation threshold. <3> Present high concentration of voltage-dependent channels. <4> Present Na + channels regulated by ligand <5> Start there the axon myelin sheath.
Output (English): 3