That’s the difference between gray matter and white matter. Gray matter readily communicates with it’s crowding neighbors and can retain information, while white matter is myelinated so it can send messages over distances. Gray matter extends from our brains down our spinal cords.
Muscles are dumb meat who take their orders from the nervous system. They have no capacity for memory. But training can create reflexes at the spinal cord level which some refer to as “muscle memory,” except it’s not the muscle that should get the credit here.
I never thought muscle memory was “stored” in the muscles. The same way a memory of a smell is not stored in the nose. I was quite confused to see this as a common misconception but it makes sense from the name