When we do so, the under side of the arm and the little finger feel very numb and strange.

This is why you call this part of the elbow the "funny" or "crazy bone." The cells of the spinal cord also send out branches to the body and to other cells in the brain.
~10.

How we Feel.~--If we cut or burn ourselves we suffer pain.

Can you tell why it hurts us to prick the flesh with a pin, or to pinch or burn or bruise it?
It is because the flesh contains a great many nerve-branches from the brain.

When we hurt the skin or the flesh, in any way, these nerves are injured.