this is a simplified explanation

SMALL FIBER NEUROPATHY

Small fibers (C-fibers) provide mostly sensory and autonomic innervations. The sensory fibers (unmyelinated and thinly myelinated) perceive pain and temperature changes. The autonomic fibers controls for heart rate, blood pressure, sudomotor function and gut function. Small fiber neuropathy mostly involves thermal perception, which means that pain is in the form of cold, warm and hot. Clinical presentations of small fiber neuropathy include hyperesthesias ( increase in sensitivity to stimuli, such as pain out of all proportion to injury or even contact with an object), hyperalgesia (increased sensitivity to pain), excess sweating and impaired microcirculation.

LARGE FIBER NEUROPATHY

The large fibers are myelinated motor fibers. These fibers are responsible for motion control, touch (such as numbness), proprioception (knowing where your body is, such as if your feet are numb you will not know where they are on the floor or even their position) and vibration. The myelinated sensory fibers also perceive for touch, proprioception and vibration. The clinical presentation in patients with large fibers neuropathy are impaired vibration, gait instability, weakness, numbness, small muscle wasting and commonly radiating or cramping pain at night.