Ulnar Nerve. When your thumbs point outward from your body, the bones of the forearm open: the ulnar side has the nerve from the elbow (the funny bone sensation). The roots are in the neck, the fibers forom the c-8 & t-1 exit, and form the nerve on the other sie of the brachial plexus. Stretching anywhere along the nerve causes numbness.
Nerve problem. Numbness can occur from various reasons. Some potential causes include vitamin deficiency, nerve damage, nerve compression, alcohol over consumption, side effects of different medications, or as a result of different systemic medical conditions such as diabetes. Get evaluated by a professional to determine the diagnosis. Treatment is based on the diagnosis.