2/6/25, 1:45 AM NEU physio-Pain analgesia system
Pain analgesia system
• Referred to as descending analgesia system or corticofugal fibers.
• it blocks the synaptic transmission of pain sensation in spinal cord
and thus attenuates the experience of pain.
• analgesic drugs such as opioids act by activation of this system and
provide a controlled pain relief.
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 posterior 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.
56
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, 2/6/25, 1:45 AM NEU physio-Pain analgesia system
5. At synaptic level, analgesic fibers release neurotransmitters and
inhibit the pain transmission before being relayed to brain.
57
about:blank 2/5
Pain analgesia system
• Referred to as descending analgesia system or corticofugal fibers.
• it blocks the synaptic transmission of pain sensation in spinal cord
and thus attenuates the experience of pain.
• analgesic drugs such as opioids act by activation of this system and
provide a controlled pain relief.
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 posterior 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.
56
about:blank 1/5
, 2/6/25, 1:45 AM NEU physio-Pain analgesia system
5. At synaptic level, analgesic fibers release neurotransmitters and
inhibit the pain transmission before being relayed to brain.
57
about:blank 2/5
