Encyclopedia of Health and Medicine

P
pain An unpleasant perception in response to a
stimulus to the body. Multiple mechanisms contribute
to the perception of pain, which follows
specific and predictable pathways to the BRAIN. The
brain then interprets the nature of the pain and
directs the appropriate body response. Pain is one
of the body’s main defenses for protecting itself
from harm. The pain REFLEX is the unconscious
and immediate effort to remove the body part
from the source of the stimulus and protect it
from further damage, for example pulling the
hand from contact with a sharp object and grabbing
the wound (which applies pressure to stop
bleeding as well as the further release of
PROSTAGLANDINS and other substances that stimulate
INFLAMMATION and the pain response.
Pain can take the form of many and varied
characteristics: it can be sharp, dull, constant,
intermittent, stabbing, throbbing, burning, localized,
widespread. These characteristics help identify
possible causes for the pain. The presence of
health conditions such as DIABETES, PERIPHERAL VAS-
CULAR DISEASE (PVD), MULTIPLE SCLEROSIS, and SYS-
TEMIC LUPUS ERYTHEMATOSUS (SLE) also provide clues
as to the underlying reasons for pain.
Pain management methods target various intersections
along the pain pathway. Some approaches
and medications aim to reduce the production of
substances (such as prostaglandins) at the site of
injury, reducing the body’s biochemical call to
action that stimulates nociceptors. Others attempt
to block NERVE signals from entering the dorsal
root ganglia, and still others manipulate neurotransmitters
and neuroreceptors in the brain to
alter the brain’s interpretation and resulting perception
of pain signals that reach the thalamus
and the cerebral cortex. Numerous methods are
available to relieve pain, including ANALGESIC MED-
382
ICATIONS, NEURAL BLOCKADE (NERVE BLOCK), and
ACUPUNCTURE.
For further discussion of pain mechanisms and
pain management, please see the overview section
“Pain and Pain Management.”
See also ACUTE PAIN; ALTERNATIVE METHODS FOR
PAIN RELIEF; CHRONIC PAIN; EUDYNIA; MALDYNIA; NEU-
RORECEPTOR; NEUROTRANSMITTER; TERMINAL PAIN.
phantom pain The sensation of PAIN that feels as
though it came from an amputated limb or other
body part. Researchers believe phantom pain
results from continued activity, after the AMPUTA-
TION, among neurons in the BRAIN that interpret
NERVE signals. Severed nerve fibers near the site of
the amputation continue to send signals even
though the surgery has removed most of their
nociceptors (molecules that detect stimuli as pain).
The remaining portions of the nerves continue to
function, and the brain interprets their incomplete
messages as pain signals. The pain often feels of
the same nature as pain that might have been
present in the limb before the amputation.
Many people who have phantom pain also
have stump pain (pain in the remaining portion of
the limb). Stump pain generally results from the
damage to the nerves at the site of the amputation.
Doctors do not know the extent to which
stump pain contributes to phantom pain.
One therapeutic approach that may prevent
phantom pain is administration of CALCITONIN, a
HORMONE that prevents calcium from leaving the
BONE to enter the BLOOD circulation, after the OPER-
ATION. Doctors are uncertain why calcitonin has a
preventive affect in this way. Phantom pain seems
to respond better to medications used to treat NEU-
ROGENIC PAIN than to conventional ANALGESIC MED-
ICATIONS. Such medications include antiseizure