if I can move specific muscle in my toe via brain command, does this mean that in spinal cord there is a specific fiber that extends from brain to that toe? And let's say if in a lab rat we cut that single CNS fiber, the muscle affected will stop working without any other consequences to the organism? Or is this mental model in fact completely wrong so that let's say CNS does time domain multiplexing (or packet addressing? or some other form of multiplexing?), allowing it to send commands to multiple muscles through a single "cable" / fiber?