REFERRED PAIN
DEFINITION
Referred pain is the pain that is perceived at a site adjacent to or away from the site of origin. Deep pain and some visceral pain are referred to other areas. But, superficial pain is not referred.
EXAMPLES
OF REFERRED PAIN
1. Cardiac
pain is felt at inner part of left arm and left shoulder
2. Pain in
ovary is referred to umbilicus
3. Pain
from testis is felt in abdomen
4. Pain in
diaphragm is referred to shoulder
5. Pain in
gallbladder is referred to epigastric region
6. Renal
pain is referred to loin.
MECHANISM OF REFERRED
PAIN
Dermatomal Rule
According
to dermatomal rule, pain is referred to a structure, which is developed from
the same dermatome from which the pain
producing structure is developed.
A
dermatome includes all the structures or parts of the body, which are
innervated by afferent nerve fibers
of one
dorsal root. For example, the heart and inner aspect of left arm originate from
the same dermatome. So, the pain in heart is referred to left arm.
NEUROTRANSMITTERS INVOLVED IN PAIN
SENSATION
Glutamate
and substance P are the neurotransmitters secreted by pain nerve endings. Aδ
afferent fibers,
which
transmit impulses of fast pain secrete glutamate. The C type fibers, which
transmit impulses of slow pain secrete substance P.
ANALGESIA SYSTEM
Analgesia
system means the pain control system. Body has its own analgesia system in
brain, which
provides a
shortterm relief from pain. It is also called endogenous analgesic
system. Analgesia system
has got
its own pathway through which it blocks the synaptic transmission of pain
sensation in spinal
cord and
thus attenuates the experience of pain. In fact analgesic drugs such as opioids
act through this
system and
provide a controlled pain relief.
ANALGESIC PATHWAY
Analgesic
pathway that interferes with pain transmission is often considered as
descending pain pathway, the ascending pain pathway being the afferent fibers
that transmit pain sensation to the brain.
Role of Analgesic
Pathway in Inhibiting
Pain Transmission
1. Fibers
of analgesic pathway arise from frontal lobe of cerebral cortex and
hypothalamus
2. These
fibers terminate in the gray matter surrounding the third ventricle and aqueduct
of Sylvius (periaqueductal gray matter)
3. Fibers
from here descend down to brainstem and terminate on:
i. Nucleus
raphe magnus, situated in reticular formation of
lower pons and upper medulla
ii. Nucleus
reticularis, paragigantocellularis situated in
medulla
4. Fibers
from these reticular nuclei descend through lateral white column of spinal cord
and reach the
synapses
of the neurons in afferent pain pathway situated in anterior gray horn
Synapses of
the afferent pain pathway are between:
i. Aδ type
afferent fibers and neurons of marginal nucleus
ii. C type
afferent fibers and neurons of substantia gelatinosa of Rolando.
5. At
synaptic level, analgesic fibers release neurotransmitters and inhibit the pain
transmission
before
being relayed to brain.
Neurotransmitters of
Analgesic Pathway
Neurotransmitters
released by the fibers of analgesic pathway are serotonin and opiate receptor
substances namely enkephalin, dynorphin and endorphin.
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