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Physio

1. Neurophysiology
By
Prof. AlaaEldinH. Yusuf

2. Pain
Pain is unpleasant sensation that may be associated
with
motor, autonomic and emotional manifestations.

3. Types of pain
I)Somatic pain : it includes,
A)Cutaneous pain, that involves 2 components:
a.Fast component
b.Slow component
B) Deep pain.
II) Visceral pain.
III) Referred pain.

5. Mechanism of cutaneous pain
Tissue damage results in release of chemical mediators for
pain that arecalled pain producing substances (PPS)
as histamine , bradykinin, substance -P that irritate
pain nerve endings .

6. Effect of cutaneous pain
1-Emotional effect ascrying.
2-Autonomic effects asheart rate changes, sweating and ABP
changes due to sympathetic stimulation.
3-Motor effectsas flexion withdrawal reflex.
4-Hyperalgesia

7. Hyperalgesia
It is a condition of cutaneous hypersensitivity that usually
accompanyinflammatoryconditions specially burns.

8. Types of hyperalgesia

9. Deep pain
It a pain that arising from the deeper structureto skin as
muscles, tendons, ligaments and bone.
Causes
of deep pain:
1-muscle cramp , ischemia.
2-torn ligaments.
3-fracture of bone.

10. Characters of deep pain:
1-poorly localized.
2-dull aching.
3-associated with parasympathetic autonomic effects.
4-associated with spasm of the overlying muscles.

11. Visceral pain
Causes of visceral pain:
1-spasm or distension of hollow organs.
2-visceral ischemia.
3-chemical irritationeg. leakage of acid.

12. Visceral pain receptors
Sites:
a. wall of GIT
b. wall of urogenital tract
c. parietal layer of visceral cavities .
d. meninges
e. liver capsule
f. periosteum

13. Novisceral pain receptors in:
a.alveoli
b.brain
c.liver
d.bone
e.visceral layer of P, P & P

14. Characters of visceral pain
1-poorly localized.
2-dull aching.
3-associated with parasympathetic effects as bradycardia,
hypotension, nausea and vomiting .
4-associated with spasm of the overlying muscles.
5-may referred to a somatic structure.

15. Pathway of visceral pain
I)True visceral pathway:
Autonomic nerve fibers ( sympathetic & parasympathetic)
serve as visceral pain afferents that then join the ascending
spinothalamicpain pathway.

16. II) Parietal pathway:
Parietal layers of visceral cavities ( P. P & P), have somatic
nerve supply the same like skin that, will serve to carry pain
discharge then join spinothalamicpain pathway.

17. Referred pain
It is a visceral pain that is felt far away from the true
affected viscus and mislocatedin a somatic structure .

18. Examples of referred pain
1-cardiac pain : referred to left shoulder, left arm.
2-gall bladder pain: referred to tip of right shoulder.
3-renal pain: referred to the external genital organs.
4-intestinal pain: referred to the area around the umbilicus.

19. Mechanism of referred pain
the visceral pain if referred to the somatic structure that had
been developed from the same embryonic origin
(dermatome).
( Dermatomaltheory)

20. Theories explaining referred pain
I) Dermatomaltheory.
II)Convergence--projection theory.
III)Facilitation theory.

21. Convergence –Projection theory
Both visceral and somatic pain afferents converge to
the same spinothalamicneuron.
The brain is used to receive paindischarge from
somatic structures.

22. So, brain will falselyprojectvisceral pain impulses as if
they came from somatic structure.
Both the visceral & somatic structures had been
developed from the same dermatome.

23. Facilitation theory
Each of the somatic and visceral pain afferents synapse
with a specificspinothalamicneuron (SGR).
A collateral arises from the visceral pain afferent &
convegeto SGRreceiving the somatic pain afferent
facilitating it(produce EPSP).

24. So,minor( subthreshold) painful stimulation to the
somatic structure that normally can’t produce pain will
result in somatic pain sensation.

26. Pain control
(Analgesia)
1.Pain control at the spinal cord level :
This is explained by the gate theory :
(Synapses along pain pathway may act as gates at
which pain impulses can be blocked).
Eg1: Rubbing of a painful area alleviates pain sensation
Eg2: Acupuncture

27. Gate theory

28. 2.Pain control system at the level of the brain
Opiate analgesia (OA)
1.The brain has a neuronal circuit and endogenous
opioid system (endorphins and enkephalins) to
modulate pain.
2. These substances act on opioid receptors
.

29. High densities of opiate receptors are found in:
a. periaqueductal grey (PAG)
b. raphe magnusnucleus
c. locus ceruluswhich secrete catecholamines

30. The most important areas comprising the
pain control system
1.Periventricular area of diencephalon.
2.The periaqueductal grey area (PAGA)around the
aqueduct of Sylviusin the midbrain and pons& SN
(mainly enkephalinergicneurons).
3. The raphe magnusnucleus located in the lower
region of the pons and the upper region of MO.
(mainly serotonergic neurons)
4. Pituitary gland

31. Supraspinalpain control
(descending pathway)
1.From PAGAarise a descending pathway which project
to the medulla to (+)raphe magnusnucleus.
2.Raphe magnussends descending pathways to the
dorsal horns of the spinal cord to secrete serotoninat
their endings.
3.Theserotonin(+) local cord neurons to secrete
enkephalin.

32. Descending pathway(cont.)
4. The enkephalincauses both presynapticand postsynaptic
inhibition of incoming pain fibers as they synapse in the dorsal
horns.
a. Presynaptically,it decrease Ca2+ conductance that results
in decreased painneurotransmitter release.
b. Postsynaptically, it activates opioid receptors causing an
increase in K+ conductance resulting in an IPSP that inhibits
postsynaptic neurons.

34. Prof. Alaa El din Yusuf