Table 1.
Definition of key terms
| Action potential: Rise and fall in the membrane potential of a cell leading to the transmission of electrical impulses along neurons |
| Allodynia: Pain evoked by painless stimuli |
| Analgesia: Lack of pain upon painful stimulus |
| Antidromic impulse: An impulse traveling in the opposite direction of regular action potential (i.e., from the central nervous system to the periphery), contributing to the release of neuroinflammatory mediators and peripheral sensitization |
| Ascending pathway: A neural circuit that carries sensory and nociceptive signals from peripheral receptors to the central nervous system |
| A-β fibers: Thickly myelinated fibers conducting the sensation of touch, vibration, and proprioception; they are referred to as fast-conducting fibers with a speed of ∼35-120 meters/second |
| A-δ fibers: Thinly myelinated fibers associated with acute pain and sensation of cold and pressure; their conduction velocity of action potentials is 5–30 meters/second |
| Axon reflex: Movement of action potentials in C-fibers peripherally releasing vasoactive and inflammatory substances such substance P |
| C-fibers: Unmyelinated fibers responsive to a wide range of noxious stimuli including, mechanical, thermal, and pathophysiologic factors; these fibers are involved in a slow but long-lasting painful sensation of burning. Their conduction velocity of action potentials is 0.5–2.0 meters/second |
| Central sensitization: Increased responsiveness of second-order neurons to subthreshold inputs after a sustained noxious stimulus |
| Hyperalgesia: An increased painful sensation to a noxious stimulus |
| Hyperesthesia: Heightened sensitivity to painless and painful stimuli |
| Neurogenic inflammation: Inflammation caused by the release of inflammatory mediators from peripheral nerve fibers after stimulation by a noxious stimulus |
| Nociceptors: Receptors in the peripheral somatosensory nervous system involved in the detection and transduction of noxious stimuli |
| Noxious stimulus: A stimulus that could cause tissue damage; it can be mechanical, chemical, or thermal |
| Pain: An unpleasant sensory and emotional experience caused by injury or pathophysiology |
| Pain threshold: Lowest intensity of stimulus that evokes pain |
| Paresthesia: A sensation that is abnormal |
| Peripheral sensitization: Increased response to noxious stimuli at the site of injury resulting from the decreased threshold for depolarization in the peripheral nerve fiber nociceptors |
| Tolerance: Decreased response to a substance after long-term use, requiring a dosage increase to accomplish similar effects |