Why do small alpha motor neurons produce an action potential before larger alpha motor neurons?
Triggering an action potential requires depolarization of the initial segment of an alpha motor neuron to the action potential threshhold. The initial segment is the region of a neuron with the highest concentration of voltage-gated sodium channels per unit of surface. This high concentration of voltage-gated channels makes the initial segment the action potential generating region of a neuron. Once an action potential starts in the initial segment, the rest of the alpha motor neuron, the dendrites, and the axon follow. The amount of depolarizing current reaching the initial segments is related to the degree of depolarization that occurs in the rest of the alpha motor neuron body. The degree of depolarization of the alpha motor neuron body (voltage difference between the outside and the inside of the neuronal membrane) depends on the current that reaches an alpha motor neuron and the resistance of the alpha motor neuron body. The resistance of an alpha motor neuron depends on the total
