Q:

How can the CNS possibly need recovery after a strength workout?

In the last days I have read here and there some comments about CNS (central nervous system) fatigue produced by heavy lifting, and about allowing recovery for the CNS, not only the muscles.
It does not seem quite intuitive. I understand that the brain gives the orders and the nerves carry signals to/from the muscles. I don't understand how can they need recovery, since the work is done by the muscles, not by the cables transporting the signals or the guy in command of the machine.
Could anyone explain a little bit on this, or perhaps provide some links?

A:

I'm not aware of any concrete studies on the matter, but basically CNS fatigue can be summed up like this: it's the overall degradation of hormones and neurotransmitters that are required for sustained physical output. 
I wrote an answer a while back that gets into the fairly low level chemical actions that limit strength output, it's worth reading if you want to touch on the biochemical interactions that are happening when you're doing anything from pumping blood with your heart to deadlifting 1RM.
Your body uses a rather wide range of chemicals for signaling and movement, compounded by the chemical structures that are in place to do things like strip down inflamed and damaged tissue (the much maligned steroid cortisol). 
Your body only has so much chemical agent to work with, it has other tasks it needs to perform, and recovery takes time.   

