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Pain is crucial for our survival. It serves as a protective
warning when we are faced with tissue injury or conditions leading to
physical damage. It is only when it becomes excessive and persistent
that it ceases to be a warning mechanism and becomes a source of misery.
Pain is a complex and personal sensation that involves not only the physical
but also the psychological, cultural, and other facets that makes up
a person. This personal makeup translates to an emotional filter for
how an individual experiences pain. There is no reliable measurement
for pain due to its subjective nature. It is believed that the pain threshold
is about the same for everyone but pain tolerance can greatly vary between
individuals. That being the case, one person's debilitating pain experience
can be another person's mild irritation.
Gate Control Theory
Despite the countless advances in science through the ages, pain is still a
big mystery to the health community. One of the most accepted theories behind
the mechanism of pain transmission in the human body is the gate control theory
put forth by Melzach and Wall in 1965. According to this theory there is a
gate mechanism in the spinal segment of the central nervous system where all
sensory neurons enter the spinal cord. This gate mechanism modifies the pain
sensation in accordance to what other impulses are being transmitted along
the pathway within the spinal segment. For example, kissing an area where a
child feels hurt makes it feel better. The pain sensation is influenced by
small nerve cells called interneurons that sit across the first synapse of
the nerve pathway. The interneurons release naturally occurring analgesic called
endorphins that helps in inhibiting pain.
The mechanics of pain sensation
A pain sensation stimulates receptors called nociceptors. Nociceptors are free
nerve endings found in every tissue of the body except the brain.
Nociceptors can be activated by intense thermal, mechanical, or chemical stimuli.
Tissue irritation or injury releases chemicals, such as prostaglandins, kinins,
and even potassium ions that stimulate nociceptors. Pain may persist even after
a pain-producing stimulus is removed because pain-mediating chemicals linger,
and because nociceptors adapt only slightly or not at all. Conditions that
elicit pain include excessive distension or dilation of a structure, prolonged
muscular contractions, muscle spasms, or inadequate blood flow to an organ.
1
From the nociceptors, the pain sensation travels to the spinal cord. The two
types of nerve fibres that carry the impulses are fast and slow. Our awareness
of fast pain occurs instantaneously because the nerve impulses conduct along
medium-diameter, myelinated axons called A-delta fibres. A-delta fibres carry
impulses at 5-30m per second. Fast pain is associated with acute, sharp or
pricking sensation that can occur when an individual prick his finger. Fast
pain is not felt in deeper tissues of the body. The second type of pain is
called slow pain because it travels through slow nerve fibres called C fibres.
C fibres are small-diameter, unmyelinated axons that carry impulses at .5-2m
per second. Slow pain gradually increases in intensity over a period of several
seconds or minutes. This type of pain is also referred to as dull, chronic,
burning, aching, or throbbing pain. Slow pain can occur both in the skin and
in deeper tissues or internal organs. An example is chronic backache.
According to the gate control theory, the pain impulses travel along the nerve
fibres and enter the dorsal horn of the spinal cord. The balance of activity
between the fast and slow fibres may stimulate the next cells in the dorsal
horn and so open or close the gate to transmission of impulse higher up the
nervous system. The communication within the segment is responsible for the
withdrawal reflex that draws the body away from the damaging stimulus. Pain
impulse can be modified in accordance to the preexisting levels of activity
within the spinal cord. Some branches ascend and communicate with the reticular
activating system and hypothalamus, which trigger arousal and other accompanying
autonomic changes. Activation of the sympathetic nervous system can inhibit
or amplify the sensation of pain. Some reach the thalamus after crossing to
the opposite side soon after they enter the segment. From the thalamus the
impulses are projected to the cerebral cortex. This helps the body localize
the stimulus and also link it to past experiences. Communication also occurs
with the limbic system relating pain to emotions. Higher central nervous system
activity exert considerable influence on the gate, both by descending nerve
impulses and by the release of analgesic chemicals such as endorphins.
Pain Control
When tissue is damaged, a flood of chemicals including a peptide called bradykinin
is released. Bradykinin makes pain nerves more sensitive and creates tiny leaks
in the blood vessels in the area of the injury. The injury site is soon flooded
with fluid and infection fighting white blood cells, which in turn attracts
a group of chemical called prostaglandins. Prostaglandins initiate the healing
process in the inflamed tissue but create an ongoing pain nerve impulse. The
main treatment to combat inflammation pain is to take an anti-inflammatory
drug that will reduce the production of an enzyme called cyclooxygenase, which
is a key ingredient in the production of prostaglandins. The best-known anti-inflammatory
drug is Aspirin. Taking drugs to combat inflammation is a short-term treatment
strategy since over the long term it compromises the individual's immune system.
For more severe chronic pain condition, the use of opioids is the primary treatment
choice. Opioids are natural or synthetic drugs that act like drugs made from
opium. Morphine is the most famous synthetic opioid and endorphin is the body's
natural painkiller. For best results opioids are injected directly to locally
affected area. Doctors treat pain through the use of ganglion or plexus blocks
when the source of pain cannot be localized. Such treatment works in inhibiting
pain in the areas served by the central pathways. This form of treatment is
normally used in debilitating pain.
It is surprising to learn that even with the advances of biotechnology and
chemical engineering, the gold standard of pain relief is still the old-fashioned
opiates. The medical profession has long had opiates to induce senselessness,
and until the late nineteenth century there were few rivals in the realm of
painkillers. Mankind has known about the power of opium and its offspring for
thousand of years. Squeezed from bright blue-purple, white, or red poppies,
opium's potent mind-bending properties over the ages have been applied to a
procession of conditions - gallbladder pain, kidney stones, headaches, asthma,
congestive heart failure, colic, insomnia, toothaches, and more. 2
Opioids work systemically and circulate throughout our bodies to latch onto
specific receptors on the outside of cells in the brain and elsewhere. Cells
in our body contain special receptors that can only be activated by opioid
molecules, either natural occurring or synthetic. These molecules act like
a key that fits into a lock to open the door of the cell. It is this precise
fit that makes them so fast acting and potent. Once the cell door is open,
there are countless possibilities for any variety of effects, depending on
the cell, the receptor, the timing, and other reactions in other cells or parts
of the body. In the case of morphine, once the opioid has unlocked the receptor,
it may cause the nerve to fire more differently, and such change in cell action
ultimately produces pain relief as well as other sensations.
Emotional aspect of pain
The gate control theory proposes that input from other parts of the nervous
system especially the limbic system provides emotional characteristic to our
perception of pain. The influence of emotion in an individual's pain experience
could be the difference between a bearable and unbearable pain. Emotion such
as fear increases one's sensitivity to pain. Anxiety triggers the body's autonomic
responses that can in turn inhibit or magnify pain. Past emotional trauma may
trigger pain sensation such as in cases of phantom limb syndrome experienced
by amputees. In cases of referred pain, where pain is felt away from the affected
area, chronic pain sufferers could easily ride a vicious circle of pain escalation
created by the difficulty in diagnosis and non-corresponding nature of pain
and illness. Responses to pain are normally associated with emotional feelings
and given emotional descriptions by sufferers. Suffering is the unpleasant
emotional response generated in the higher nervous centres by pain and other
emotional situations. Suffering also occurs with anxiety, grief, stress, fear,
or depression. Most drugs used for depression are also used in the treatment
of pain. The close relationship between pain and emotion raises speculation
that severe pain trauma creates a "greased" pathway to a corresponding emotional
expression. This emotional expression could in the future travel the same pathway
to create a pain sensation even though the initial source of pain has healed.
As most condition of chronic pain create a symbiotic relationship between pain
and emotion, it is important to provide a holistic approach to its treatment.
In most cases, drug treatment alone is not enough to alleviate the condition.
The use of counselling and other complementary therapies is as relevant as
the strongest pain-inhibiting drug. At this stage pain becomes highly personal.
According to Dr. Fishman,
" Pain is like a symphony conducted by the brain with major input from various
instruments in the body and mind sections. The sound can be as varied as those
from an orchestra, and too often it's hard to know exactly which instruments
are playing, particularly when sweet healthy melodies turn into blaring nightmarish
noises. Have you ever listened to a stereo with the volume turned up so high
that the sound just breaks down and is uninterpretable? You know there is a song
playing but you just can't make out the words. And this is when I choose to embrace
the widest definition of what it might mean when someone says she hurts."
In order to fully understand one's chronic pain condition, it is important
to appreciate the interaction between the physical, emotional, and behavioural
aspects of the pain sufferer's life. At this point most sufferers have had
intensive treatment that encompassed the physical and behavioural aspects of
their condition. As the emotional aspect of our being is interwoven with our
physical surroundings it creates an environment where pain is the chief expression
of its current negative state. The sufferer must therefore explore his personal
beliefs, thoughts, memories, and attitudes, and try to understand how he had
organized his world around him. The underlying structure with most "psycho" therapy
discipline is the retrieval of memory of events, experiences, and ideas with
the associated painful emotion. Once retrieval is accomplished, then the person
can then "repackage" the memory with either a more positive perception or a
complete reconstruction. This memory is then put back into storage and hopefully
next time it is accessed it will be detached of the pain experience.
This is an arduous process and most people in our society would not put in
the time and effort unless they are in critical or disabled condition. The
sufferer in most cases endures the pain rather than reorganize his perception
of the world. This is lost opportunity for it is at this point of suffering
when the mind is most often open and receptive to change. According to traditional
Chinese medicine, illness contains the seeds of health. So in time of high
emotional pain and stress, the mind in its holistic wisdom causes the incapacitation
of the person through disease or accident. Only in this condition would most
people take time to reflect and try to understand their relationship with the
world of their own creation.
1. Principles of Anatomy and Physiology
2. The War on Pain
Bibliography
Fishman S, 2000. The War on Pain. Gill & Macmillan Ltd., Dublin
Lance J, 1998. Migraine and other Headaches. Simon & Schuster, Sydney
Premkumar K, 1997. The Massage Connection: Anatomy, Physiology & Pathology.
VanPub Books, Calgary
Totora GJ, Grabowski SR, 2000. Principles of Anatomy and
Physiology. 9th ed. John Wiley & Sons, Inc., New York
Walddell G, 1999. The Back Pain Revolution. Harcourt Publishers
Limited, London
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