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pain control system
Transcript of pain control system
done by :
Adel Wagdi Abd-Elwahab
Atef Neural Connections and How This System Acts
The periventricular gray area in the hypothalamus send descending fibers to the periaqueductal gray area. These descending fibers may produce:
Inhibition of pain impulses transmission at this level through the release of enkephalins
stimulate the descending fibers from the periaqueductal gray area to the raphe magnus and NRPGC which by turn stimulate them and then send descending fiber
These descending fibers end on the local inhibitory complex in the dorsal horn, and stimulate its neurons through the release of serotonin.
The stimulated local inhibitory neurons in the dorsal horn by its turn inhibits the release of the neurotransmitters ( glutamate and substance- P ) from the terminals carrying pain impulses at SGR cells by closing the Ca channels, this effect is mediated by the enkephalins which open Cl channels hyperpolarization inhibiting the release of pain chemical transmitters from the central terminals of pain fibers. Also Enkephalins bind to opiate receptors in postsynaptic neurons in pain pathway opening of K channels hyperpolarization inhibition of the response to excitatory pain transmitter. Opiate Receptors
Delta receptors which respond mainly to Enkephalins
Kappa receptors which respond mainly to dynorphin & keto-cyclazocine ( analgesia, sedation , diuresis and miosis)
Muta receptors which respond mainly to Endorphins ( analgesia, euphoria, respiratory depression , miosis & constipation)
Omega receptors which respond mainly to Dynorphins
Sigma receptors which ombind with glazocune drugs ( hallucination) Neurochemistry of PCS ( Opioid Peptides)
Natural peptide substances produced inside the body and have the ability to bind the opiods receptors ( morphine receptors ) and produce pain analgesia. They are divided into 3 classes:Enkephalins, Endorphins & Dynorphins Other Mechanisms for Pain Control and Inhibition
Stimulation of large sensory fibers ( type- A alpha and type A beta ) in the area of pain produces pain relief , how?
The stimulation of the large sensory nerves carrying tactile and proprioceptive sensations during their ascent in the dorsal column, send collaterals that produce presynaptic inhibition of pain carrying nerve fibers at the SGR cells e.g; the relief of pain sense by rubbing the skin area around the site of pain
Apuncture: The insertion of certain needles by the Chinese at certain areas may stimulate the large sensory nerve mostly type A which by its turn:
Through collaterals can inhibit pain transmission at SGR presynaptic inhibition via enkephalins
Can stimulate PCS at the level of brain stem Components of PCS
The periaqueductal gray area (PAGA) around the aqueduct of sylvius in the midbrain & pons
Raphe magnus nucleus in lower pons and upper medulla
Nucleus reticularis paragigantocellularis (NRPGC) in medulla
Locus ceruleus in pons
A pain inhibitory complex in dorsal horn of spinal cord in substantia gelatinosa of Rolandi ( SGR ). Enkephalins
Derived from proenkephalins
Present in high concentration in brain stem , spinal cord and limbic system
Types: leuenkephalin & metenkephalin Endorphins
Derived from Pro-opi-melano-corten (POMC) in anterior pituitary & hypothalamus
Most common type is Beta – endorphin ( 30 amino acids )
They act as :
1-Neurotransmitters: stimulation of arcuate nucleus & some specific areas of hypothalamus of brain stem , secrete endorphins
2-Neurohormones: in stress conditions, Beta endorphins are secreted from hypothalamus & pituitary to general circulation to reach all the opiate receptors in the body causing analgesia. This explains stress analgesia in battles and accidents. They also increase secretion of growth hormone & prolactin from the pituitary. Dynorphins
Derived from prodynorphin
Present in the same sites as enkephalin
They are very potent analgesics
It is believed that they are responsible for addiction for opiates
Location of PCS:
The PCS consists of special areas in the brain & spinal cord , which when activated can reduce or even completely abolish pain sensation