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.


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.


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.


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 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 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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