Part 1: History / Introduction
Part 2: Pain Perception and Signal Reception (Please scroll down)
Part 6: Pain in the Avian Species
Part 8: Quality-of-Life Issues
What happens when you’re cutting up vegetables and you suddenly feel a sharp pain? The cut you just gave yourself is very painful immediately, but it soon becomes a longer-lasting dull ache. Eventually both will go away, but how does the pain happen in the first place? What will make it less painful? What is pain, and how can it be managed?
Let’s look at what pain actually is. It’s not an easy concept to define or explain because it’s such a subjective sensation; what one person considers painful another barely feels. It is defined as an “unpleasant sensory and emotional experience associated with tissue damage.” Your brain is telling you that a stimulus is causing damage, and you should do something about it.
Nociception, or pain perception, is the process by which a painful stimulus is relayed from the site of stimulation (injury) to the CNS (Center Nervous System). This process occurs in several steps:
First, Contact. The body makes contact with a stimulus. This stimulus can be
- Mechanical (pressure, punctures, and cuts)
- Chemical (burns)
- Thermal (heat, cold)
- Electrical (burns from lightning strikes, faulty wiring, shocks)
The nerve sends the signal to the CNS. The relay of information usually involves several neurons (nerve cells) within the CNS.
Fourth, Pain Center Reception.
The brain receives the information from the nerves for further processing and action.
Nociception uses different neural pathways than normal perception, like light touch, pressure and temperature. When these do not cause pain, the first group of neurons to fire is normal somatic (sensory) receptors. When something causes pain, nociceptors go into action first.
Freudenrich C. How Pain Works.
Both normal sensory neurons and nociceptor neurons connect to peripheral sensory nerves. The stimulus travels along these nerves to the spinal cord. Normal nerve endings specialize in responding to ordinary levels of pressure, touch, and heat. These normal sensory nerve endings are myelinated; they are covered with a protein coat which insulates them and causes them to conduct normal stimuli quickly.
Nociceptors sense pain through nerve endings that are not myelinated; these are slower to conduct stimuli. Lightly myelinated nerve fibers conduct mechanical and thermal stimuli, while others contain C-fibers which conduct stimuli slowly and respond to many different types of stimuli.
The initial pain felt when the hand is cut is sudden and intense at the moment of injury. The signal for this pain is conducted rapidly by the myelinated nerve fibers. The less-intense pain produces a slower, prolonged, dull ache. This is conducted by the slower, non-myelinated C-fibers. Anesthetists can block the neurons and separate the two types of pain. After that, analgesia can control the on-going pain.
Depending on the type of fiber, the neural impulse, or action potential, travels at speed ranging from two miles per hour in some unmyelinated fibers, to 200 or more miles per hour in myelinated fibers. Some actions must occur in a split second, such as withdrawing the hand from fire. In order for the nerve pathways to relay information that fast, there must be large, myelinated nerve fibers conducting them; on these, the impulses can travel as high as 0.6 miles per second. Some signals, such as those that originate in muscle position, travel at nearly 400 feet per second. This is how you know where each part of your body is as it moves. But some types of nociceptors travel more slowly. You will feel the pressure immediately if you hurt yourself because touch signals travel at 250 feet per second. But you won’t feel the pain for two or three more seconds because pain signals generally travel at only two feet per second.
Freudenrich C. How Pain Works.