1. ﴿و ما أوتيتم من العلم إلا قليلا﴾
بسم الله الرحمن الرحيم
﴿و ما أوتيتم من العلم إلا قليلا﴾
صدق الله العظيم الاسراء اية 58

2. Assist. Prof. of Medical Physiology
Sensory System By
Dr. Abdel Aziz M. Hussein
Assist. Prof. of Medical Physiology
Member of American Society of Physiology

3. Reaction to pain includes all the following, except :-
a- increased heart rate
b- depression
c- withdrawal reflexes
d- depressed transmission of pain impulses along sensory pain fibers

4. Pain receptors :-
a- become more sensitive with prolonged stimulation
b- are stimulated by prostaglandins
c- are more numerous in viscera than other tissues
d- include different morphological types

5. Pain Control System

8. Pain Control System 1) Def,
System which control pain transmission in CNS or inhibit pain transmission i.e. endogenous analgesia system
N.B
The activity of this system differs from one person to another and from time to time in the same person.

9. 2) Components : 1. Periventricular hypothalamic area
2. Periaqueductal area (PAG)
3. Nucleus reticularis paragigantocellularis (NRPG)
3. Nucleus raphe magnus (NRM)
4. Pain Inhibitory Complex (PIC)

10. Mechanism of action of Pain Control System

11. Posterior horn of spinal cord
Ascending pathway
1st order neuron of pain
Glutamate Substance P
Posterior horn of spinal cord

12. Posterior horn of spinal cord
Limbic system RF
Hypothalamus
Cerebral cortex
PAG
Severe stress
Strong emotions
Encephalin ++
NRM
NRPGC
Serotonin ++
Noradrenaline ++
Ascending pathway
1st order neuron of pain
Encephalins --
Glutamate Substance P
Posterior horn of spinal cord

13. Action of encephalins at PIC

14. Endogenous Opioid Peptides

15. Endogenous opioid peptides
Natural peptide substances produced inside the body and have the ability to bind the opioids receptors (morphine receptors) and produce analgesia.
Types: are 3 groups;
Enkephalins:
Derived from proenkephalins
Present in high conc. in brain stem and spinal cord
Are 2 main types: leu-enkephalin and met enkephalin.
2. Endorphins:
Derived from pre-opio-melanocortin “POMC”
Present mainly in anterior pituitary and hypothalamus.
Most common type is -endorphins.
3. Dynorphins: same sites of encephalins

17. Opiate Receptors
Are receptors which respond to opiates and endogenous opioids
Types: are 4 subtypes;
Delta receptors () respond to enkephalins.
Kappa receptors (K) respond to dynorphins
Mu receptors (µ) respond to endorphins.
Sigma receptors () respond to (4-phenyl-1-(4-phenylbutyl) piperidine) (4-PPBP)
N.B.
Neurons in PAG and Raphi nuclei contain opioids receptors which stimulated by exogenous or endogenous opioids→ pain suppression

19. Stimulation of thick myelinated N.F (Abeta) Stimulation of A delta NF.
Other Mechanisms for Pain Control and inhibition
Stimulation of thick myelinated N.F (Abeta)
Stimulation of A delta NF.
Acupuncture
Rubbing method

20. Pain Control by Rubbing
Interneuron
Rubbing of the skin
A beta fibers
Pain C fiber
Painful stimuli

21. Acupuncture Interneuron A delta fibers Pain C fiber Painful stimuli

22. Acupuncture Mechanism:
Acupuncture has been practiced in China for more than years as a method for pain relief.
Mechanism:
1- Needles in appropriate body regions are thought to excite certain sensory neural pathways which feed into the brain stem centers (such as the PAG) involved in the pain control system, with release of endogenous opioid peptides.
2- Simultaneous suppression of pain transmission at the spinal pain-gate by acupuncture

25. Gate Control Theory

27. Gate Theory of Pain Sites:
The sites of synapses along the pain pathway are considered as gates through which pain transmission can be;
Facilitated (if the gate is open) or
Blocked (if the gate is closed).
Sites:
The main pain gates are:
1- Spinal gate: at the SGR.
2- Brain stem gate: at the nuclei of reticular formation.
3- Thalamic gate: At neurons of PVLNT & intalaminar thalamic nuclei.

28. 3 2 1

30. Spinal Gate
At spinal gate pain transmission is blocked by;
Supraspinal pathways through the pain control system activating enkephalin-secreting interneuron
Spinal inhibition: through;
Stimulation of A beta (A beta) by skin rubbing
Stimulation of A delta by acupuncture and counter irritants
3. Cortico-fugal fibers (as during thinking the pain is ).

31. Gate Theory of Pain

32. Applications of Gate Control Theory
This theory provides basis for various methods of pain relief
Massaging a painful area
Applying irritable substances to a painful area (counter-irritation)
Transcutaneous Electrical Nerve Stimulation (TENS)
Acupuncture

33. TENS

34. Itching and tickling

35. Itching and tickling Are examples for cutaneous pain.
Itching sense is the sense of desire to scratch the skin usually accompanying the allergic diseases.
Tickling sense is the sense of something crawling through the skin leading to itching sense (e.g.) in case of scabies.
The receptors of both belong to the free nerve endings.
Both senses are transmitted by type C-non-myelinated nerve fibers along the anterolateral system.

36. Somatic Sensations
from Head

37. Trigeminal Pathway A) 1st order neuron:
Afferents from face (ophthalmic N. from upper 1/3 of face, maxillary N. from middle 1/3 of face, mandibular from lower 1/3 of face) → to trunk of trigeminal N. → mother cell in Gasserian Ganglia → central branches divide into 2 branches
Ascending branch end in sensory nucleus (carry touch and proprioception) and mesencephalic nucleus (proprioception)
Descending branch end in spinal nucleus (carry pain and temperature)

39. Trigeminal Pathway B) 2nd order neuron:
From both sensory and spinal nuclei → cross to opposite side and ascend as trigeminal leminiscus
End in medial part of PVNT
C) 3rd order neuron:
From PVNT of thalamus → sensory radiations → primary somatic sensory area

40. Trigeminal leminiscus
Area 3,1,2
Sensory radiations
PVNMT
Trigeminal leminiscus

41. Trigeminal Pathway
It carries the cutaneous sensations from the face, forehead, and anterior part of the scalp, conjunctiva, cornea and nasal mucosa
Also, it carries the proprioceptive sensations from the mandibular ms

42. Headache

43. Headache Def: Pain felt in the head region
It is an example of referred pain from deep structures of head
Pain sensitive structures in the head
Extracranial structures
All structures in the scalp , covering skull including skin, fasciae, ms, arteries and nerves
Eyes
Paranasal sinuses
Teeth

44. Headache Pain sensitive structures in the head
B) Intracranial structures
Brain is insensitive to pain
Some structures are sensitive to pain e.g.
Arteries e.g. middle meninegial arteries
Venous sinuses
Parts of dura covering skull base
Cranial nerves carrying pain V,IX, X

45. Headache Site of referral of intracranial headache :
A) Frontal headache:
Due to stimulation of pain receptors above tentorium (referred by trigeminal nerve)
B) Occipital headache:
Due to stimulation of pain receptors below tentorium (referred by 2nd cervical nerve)

48. Headache
Mechanism:
Irritation of pain sensitive structures e.g. in case of meningitis
Pressure or traction on pain sensitive structures e.g. in brain tumors
Dilatation of pain sensitive structures e.g. arterial dilatation and brain tumors
Spasm of ms e.g. spasm of neck and head ms

49. Headache Causes of Extracranial headache:
Due to stimulation of pain receptors in extracranial structures by;
Spasm of head and neck ms due to emotional tension (psychogenic headache).
Sinusitis: inflammation of nasal sinuses
Eye diseases:
Glaucoma →increased intraocular pressure
Errors of refraction e.g. astigmatism and myopia
4. Oral causes: e.g. teeth caries.

50. Headache Causes of Intracranial headache:
Meningeal irritation e.g. meningitis, trauma, alcoholics and constipation (absorption of toxins from rectum which cause meningeal irritation)
Brain tumours cause pressure, traction, or dilatation of intracranial pain sensitive structures.
Changes in CSF pressure:
a) ↓ CSF pressure → compensatory dilatation of blood vessels

51. Headache Causes of intracranial headache: 3) Changes in CSF pressure:
b) ↑ CSF pressure → pressure and traction on pain sensitive structures e.g. in hydrocephalus
4) Dilatation of intracranial arteries → pulsation of arteries and severe headache as in migraine (due to release of histamine)
Hypertension also leads to dilatation of cerebral vessels and headache

53. THANKS