CNS/PNS Confusion... It's Elementary

So, I have seen this same stupid picture in several articles which mention the CNS.
Motor Units have to do with the Peripheral Nervous System (PNS) NOT the Central Nervous System (CNS) which is basically just your Brain and Spinal Cord!

And, “CNS Recovery” … what the HAY?
Is this addressing chemical deficiencies created in the brain b/c of lifting, or something?

I do know that “Muscle Memory” and Muscle Fiber Recruitment are important factors in strengh training,
however search feature has just led to lemons and bad apples… nothing worth reading.

So, on to my question…
Can someone address Signal Transduction Pathways, “Muscle Memory”, or anything else pert. to Muscular Recruitment Efficiency in an intelligent manner?

Perhaps, a few links to articles as well?