Final answer:
The FALSE statement is C, as the amplitude of the action potential is not based on the amplitude of the graded potential. Action potentials occur with a consistent magnitude, being all-or-nothing events.
Step-by-step explanation:
The FALSE statement among the options provided is C. They do not vary in amplitude; once the threshold is reached, they will always propagate with the same magnitude, regardless of the strength of the graded potential that triggered them. In contrast, graded potentials can vary in amplitude depending on the strength of the stimulus.
Statements A, B, and D all contain truths about neural conduction. Statement A is true because under normal conditions, action potentials in a given cell are indeed identical. Statement B is true as conduction between nodes of Ranvier is decremental only in the sense that the depolarization decreases due to the lack of voltage-gated channels in the myelinated sections of the axon. However, the action potential itself is not decremental as it 'jumps' from node to node in a process known as saltatory conduction, thus maintaining the integrity of the signal. Statement D is true as voltage-gated sodium and potassium channels do begin to open during depolarization.