What Is Pain?

Sharp versus dull?

Pain is the nervous system’s (NS) way of telling you that something’s wrong. Some may suspect that different types of pain transmitters mediate sharp and dull pain. The truth is, the same ones mediate both: the difference is in how fast the signal gets to you. At least that’s part of it. The quality of pain includes the speed of travel, intensity, and area of impact. The quality of pain is decided via nociceptive transmitters. Prolonged pain, as one would feel from burns or inflammation, is mediated through neuropathic transmitters.

Quality versus quantity

Nociceptive: Quality pain

Axons, or nerve fibers, are the threads of nerve cells through which the signal travels. The myelin sheath is the fatty substance covering the axons to keep the electrical signal on its path. A-delta and C nerve fibers are responsible for relaying pain signals to the brain. A-delta axons have a wider diameter, so there is less resistance for the electrical signal and thus it moves much more quickly. This speed that allows the pain to fade away shortly. Though it can transmit signals very quickly (5-35 meters per second, or 11-78 miles per hour), it cannot relay how intense the pain is.

C fibers have a smaller diameter and thus transmit signals more slowly (0.5-2 meters per second, or 1-4.5 miles per hour). These slow signals take more time to reach from source to receiver, so the pain lasts longer and gives a sore feeling. These fibers are unmyelinated, so the signal isn’t insulated. It does a poor job at sending the signal to a single receptor, so multiple receptors get the signal. In other words, the pain is felt by a local collection of receptors and a larger area experiences pain. The same signal is split between multiple sensors, so signal’s strength is spread across them. Unlike A-delta fibers, C fibers deliver a reading for the intensity of pain. These fibers account for about 70% of the nerve fibers in the body. Nociceptive pain is simpler to explain partly due to it being regulated in the central nervous system (CNS).

Neuropathic: Lots of pain

Neuropathic pain is both generated and sustained by the NS. It is much more complicated because it is regulated by both the CNS and peripheral nervous system (PNS). Either system can be dominant and both interact with each other, making it harder to treat. The same pathways in the CNS that are used to mediate and suppress pain can be reorganized to react differently. The nerves in the PNS can change their sensitivity to stimulus.

Sensation

Each nerve fiber has a different function:

  • A-alpha: Motor function and muscular sensation (proprioception)
  • A-beta: Proprioception, touch, pressure
  • A-delta: Pain, temperature, touch
  • C: Pain, temperature
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