Neurotoxins in the neurobiology of pain.

Migraine is a common, chronic, incapacitating, neurovascular disorder that affects an estimated 12% of the population. Understanding the basic mechanisms of pain is important when treating patients with chronic pain disorders. Pain, an unpleasant sensory and emotional experience, is usually triggered by stimulation of peripheral nerves and often associated with actual or potential tissue damage. Peripheral nerve fibers transmit pain signals from the periphery toward the spinal cord or brain stem. The different diameter pain fibers (A and C) vary in the speed of conduction and the type of pain transmitted (eg, sharp versus dull). When stimulated, peripheral pain fibers carrying sensory input from the body enter at different layers of the dorsal horn, which is then propagated toward the thalamus via the spinothalamic tract within the spinal cord. Conversely, sensory input from the face does not enter the spinal cord but enters the brain stem via the trigeminal nerve. This review describes in detail the neurobiological mechanisms and pathways for pain sensation, with a focus on migraine pain.