and which part of it exactly receives the foremost electron?
Probably the part that makes sure that voltage and power levels are stable before enabling the rest of the CPU. That might sound somewhat cheeky, but it's true! (It's called a power supervisor circuit)
EDIT: The part about receiving the foremost electron is somewhat nonsensical since it's not like in a water pipe where one molecule of water makes its way through the pipe. You establish the electric field first (propagates outwards first) and then electrons jostle themselves around in a fashion not unlike a Newton's cradle:
So the current starts up everywhere once the field is established. As for how the field propagates, well that goes along the length of the wire at some velocity a little less than the speed of light.
you might want to read an electrical engineering book on sequential circuits vs. combinatorial circuits (i.e., the concept of clocking)
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