Pain
Pain is both a
sensory and
emotional
experience, generally associated
tissue damage, or
inflammation. Pain is ultimately a
perception, and not an objective bodily state.Despite its
unpleasantness, pain is a critical component of the body's defense system. It
is part of a rapid warning and defence relay instructing the
motor
neurons of the central nervous system to minimize detected physical harm.
The
gate control theory of pain, offers insight into how
cognitive
and emotional
factors might dramatically influence painful sensations. Developed by Ronald
Melzak and Pat Wall, it focuses on different pain states at the brain, rather
than at the perceived site of injury.
Nociception
Nociception, is the physiological
sense for
perception of physiological pain. Nociception does not
describe
psychological pain.
Nociceptors are the free nerve endings of neurons that have their cell
bodies outside the
spinal column in the
dorsal root ganglion and are named according to their point of
termination.
The interpretation of pain occurs when the
nociceptors are stimulated and subsequently transmit signals through
sensory nuerons in the spinal cord, which releases glutamate, a major
exicitory
neurotransmitter that relays signals from one neuron to another and
ultimately to the
thalamus,
in which pain perception occurs. From the thalumus, the signal travels to the
cerebrum,
at which point the individual becomes fully aware of the pain.
Interestingly, the brain itself is devoid of nociceptive tissue, and hence
cannot experience pain (thus a
headache
is not pain in the brain itself). Some evolutionary biologists have speculated
that this lack of nociceptive tissue might be due to the fact that any injury
of sufficient magnitude to cause pain in the brain will incapacitate the
organism and prevent it from taking appropriate action, which is the actual
purpose of pain.
If pain is defined as a signal of present or impending tissue damage
effected by a harmful stimulus then the ability to experience pain or
irritation is observable in most multi-cellular
organisms.
Even some plants
have the ability to retract from a
noxious stimulus. Whether this sensation of pain is equivalent to the
human experience is debatable.
Interpretation of pain
The unpleasantness of pain encourages organisms to use any means at its
disposal to disengage from the noxious stimuli that it assumes cause the pain.
It may, of course, have incorrectly determined the cause. Preliminary pain can
serve to indicate that an injury is imminent, such as the ache from a
"soon-to-be-broken"
bone. After an initial insult to an organism, pain can prevent further
damage from occurring. Pain may also promote the healing process as most
organisms will protect an injured region from further damage in order to avoid
further pain. However, there is also evidence that pain may retard healing.
Despite its unpleasantness, pain remains an important part of human
existence.
Types of pain
Acute pain is roughly defined as short-term pain or pain
with an easily identifiable cause. Acute pain is the body's warning of present
damage to tissue or disease. It is often fast and sharp followed by aching
pain. Acute pain is centralized in one area before becoming somewhat spread
out. This type of pain responds well to medications.
Chronic pain is roughly defined as long-term pain. This
constant or intermittent pain has often outlived its purpose, as it does not
help the body to prevent injury. It is often more difficult to treat with
medication. Expert care is generally necessary to treat any pain that has
become chronic. When
opioid analgesics are used indiscriminately for prolonged periods,
tolerance,
dependence and even addiction may occur.
The experience of physiological pain can be grouped into four categories
according to the source and related nociceptors (pain detecting nerves).
Cutaneous pain is caused by injury to the
skin or
superficial tissues. Cutaneous nociceptors terminate just below the skin, and
due to the high concentration of nerve endings, produce a well-defined,
localised pain of short duration. Example injuries that produce cutaneous pain
include paper cuts, minor (first degree) burns and lacerations.
Somatic pain originates from
ligaments,
tendons,
bones,
blood
vessels, and even
nerves
themselves, and are detected with somatic nociceptors. The scarcity of pain
receptors in these areas produces a dull, poorly-localised pain of longer
duration than cutaneous pain; examples include
sprained
ankle and
broken bones.
Visceral pain originates from body organs visceral
nociceptors are located within body organs and internal cavities. The even
greater scarcity of nociceptors in these areas produces a pain usually more
aching and of a longer duration than somatic pain. Visceral pain is extremely
difficult to localise, and several injuries to visceral tissue exhibit
"referred" pain, where the sensation is localised to an area completely
unrelated to the site of injury.
Myocardial ischaemia (the loss of blood flow to a part of the
heart muscle
tissue) is possibly the best known example of referred pain; the sensation can
occur in the upper chest as a restricted feeling, or as an ache in the left
shoulder, arm or even hand.
Phantom limb pain is the sensation of pain from a limb that one no longer
has or no longer gets physical signals from - an experience almost universally
reported by
amputees and
quadriplegics.
Finally neuropathic pain ("neuralgia") can occur as a
result of injury or disease to the nerve tissue itself. This can disrupt the
ability of the sensory nerves to transmit correct information to the thalamus,
and hence the brain interprets painful stimuli even though there is no obvious
or documented physiologic cause for the pain.
Chronic pain treatment
In modern societies,
medical care
is highly effective at treating most causes of pain. The inability to provide
adequate relief for the remaining group causes dissatisfaction for both
professionals and patients. The small group of people that suffer from
chronic pain, have, by definition, been poorly served by the biomedical
model and often seek alternative therapy to assist their
pain
control.
Recently, scientific findings show the first evidence that
sunlight
can affect the perception of pain.
Pain and alternative medicine
A recent
survey (http://nccam.nih.gov/news/2004/052704.htm)
by
NCCAM found pain was the most common reason to use
complementary and alternative medicine (CAM) and that 38.7% of adult
Americans used CAM for pain in 2002 ([1]
(http://nccam.nih.gov/news/report.pdf)
p 9). The most common indication was
back pain
(16.8%), followed by
neck pain (6.6%),
arthritis
(4.9%), joint pain (4.9%),
headache
(3.1%), and recurring pain (2.4%).
One such alternative,
traditional Chinese medicine views pain as a
qi "blockage"
equivalent to
electrical resistance, or as "stagnation of blood" – theorized as
dehydration inhibiting metabolism. Traditional Chinese treatments such as
acupuncture are relatively more effective for nontraumatic
pain than with traumatic pain.
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