What are the thin fibers of the human nervous system called?
a. nerves
b. brain
c. spinal cord
d. eye

The thin fibers of the human nervous system are called nerves. These fibers emanate from the brain and the spinal cord and branch to every part of the body. They convey impulses of sensation, motion, pain, etc and basically are responsible of transmitting signals between the brain or spinal cord and all other parts of the body. They are a critical part of the Nervous system.  

where is the diagram

the constitution gives congress the power to regulate commerce "among" the several states.