Originally Posted by Ken Cox
The nerves to the hand and fingers run from the head through the neck, and then through the shoulders, elbows, wrists and palm.
The cause of the tingling can come from any of those places, but usually from the neck.
Sometimes people will get a taller stem or riser bars in order to put themselves in a more erect position, thinking they have addressed the tingling by taking weight off of their hands; when, in reality, they have straightened out their neck so that they don't pinch the nerves in their neck which go to and from their hands.
Impingement at the neck doesn't typically cause isolated hand numbness. If compressed in the neck, the nerve is affected at the spinal root or at the cords/branches in the brachial plexus (eg. thoracic outlet syndrome), distal compression typically involves motor signs and/or dysesthesias in a dermatomal pattern of the root affected or in the distribution of the peripheral nerve supplied if it's compressed more distally. Impingement in the neck or at the thoracic outlet would be much more likely to show more widespread sensory changes than isolated hand numbness. The median nerve, the nerve supplying most of the cutaneous sensory innervation to the hand given that it's susceptible to compression at the wrist/hand and is a far more likely explanation for hand numbness than compression in the neck.
No nerves run from the head to innervate the upper extremity. Nerves from the head are more usually called cranial nerves, and have a variety of function of innervation including innervation of the face and anterior scalp.