The peripheral nerves in your arms and legs are mobile structures. Think of them as very thin, small Chinese finger traps. Just like that device, they can stretch when elongated.

Try an experiment.  Take your finger and touch your nose.  Now bring your hand all the way out to your side and stretch it out as far as it will go.  Now tilt your head away from your outstretched hand (if it's your right hand, bend your head left).  Do you notice a pulling sensation in your hand and arm with your head bent?   Now try to bring the head towards the hand, does it go away?  You've just demonstrated nerve tension.  There is no muscle that goes from your neck to the hand.   Since bending your head away from the hand tightens the nerves that go from your neck to your hand, you feel pulling (and sometimes numbness and tingling, although that's not normal). 

The nerves in your body have a normal range of motion like the joints.   Nerve glides are stretches that help get back that normal movement.  There are a few physical therapists in the country that understand how to treat this type of problem.  You should ask your therapist, "Have you taken any courses in nerve glides or adverse neural tension?".  If you get a blank stare and you have a problem with paresthesias down into the hand, find a new therapist. A handful of chiropractors have training in this area as well.