1. Definition of Pain
An unpleasant sensory that is associated with actual or potential tissue damaging stimuli

2. Pain sensation Pain is a protective mechanism Types of pain: Fast pain
Slow pain

3. Fast pain
It is felt within about 0.1 sec after a pain stimulus applied
Sharp pain
Acute pain
Pricking pain
Electric pain

4. Slow pain
Begins only after 1 sec or more and then increases over many seconds and sometimes minutes
Slow burning pain
Aching pain
Throbbing pain
Nauseous pain
Chronic pain

5. Pain receptors : free nerve endings
stimuli excite pain receptors:
Mechanical, Thermal ,Chemical
Fast pain is elicited by thermal and mechanical stimuli
Slow pain can be elicited by all tree types

6. Some chemicals excite pain: Bradykinin, serotonin, histamine, potassium, acids, Ach, proteolytic enzymes
Prostaglandins and substance p enhance sensitivity of pain endings
Bradykinin is the most responsible for pain followed tissue damage

8. Non adapting nature of pain receptors
Adaptation is very little and sometimes not at all
Hyperalgesia

9. Rate of tissue damage is a stimulus for pain
The intensity of pain is proportional to degree of damage
Bradykinin
Potassium ion
Proteolytic enzymes

10. Tissue ischemia as a cause of pain
Accumulation of lactic acid
Bradykinin
Proteolytic enzymes

11. Muscle spasm Direct effect on pain receptors
Compress the vessels and cause ischemia
Increase the rate of metabolism and relative ischemia

12. Peripheral pain fibers
Fast pain: Aδ 6-30 m/sec
Slow pain: C m/sec
On entering they terminate in dorsal horn
Both fiber groups end in the dorsal horn

13. Dual pain pathways in the spinal cord
Neospinothalamic
For fast pain
Glutamate is the probable neurotransmitter
Paleospinothalamic
For slow pain
Substance p is the probable neurotransmitter

14. Transmission of the neospinothalamic tract in the brain stem and thalamus
A few fibers terminate in reticular areas of brain stem
Most pass all way to thalamus and terminate in venterobasal complex
A few fibers terminate in posterior nuclear group of thalamus

15. Capability of nervous system to localize fast pain
Fast pain can be localized much more exactly than slow pain
When tactile receptors that excite dorsal column system are simultaneously stimulated the localization can be nearly exact

16. Transmission of the paleospinothalamic tract in the brainstem and thalamus
Only one tenth to one forth fibers pass to the thalamus
Most terminate in: reticular nuclei of medulla, tectal area, peraquiductal gray
These lower areas are important for feeling of the suffering types of pain

17. Subcortical Perception
Perception alone does not require the cortex The cortical receiving areas are apparently concerned with the discriminative, exact, and meaningful interpretation of pain and some of its emotional components

19. Pain suppression Analgesia system
1-The periaqueductal gray and periventricular areas of mesencephalon and upper pons areas surround the sylvius and portions of third and forth ventricle
2-Raphe magnus nucleus located in lower pons and upper medulla and paragigantocellularis nucleus
3-A pain inhibitory complex in spinal cord

21. Inhibition of pain transmission by simultaneous tactile signals
Stimulation of Aβ sensory fibers from peripheral tactile receptors can depress transmission of pain signals from the same body area
This results from lateral inhibition in spinal cord
Rubbing the skin near pain area is effective in relieving pain

22. Referred pain
Person feels the pain in a part of the body that is remote from the tissue causing the pain
Pain in visceral organs often is referred to an area on the body surface
It is usually to a structure that developed from the same embryonic segment or dermatome as the structure in which the pain originates (dermatomal rule )

23. Mechanism of referred pain
Visceral pain fibers synapse in the spinal cord on the same second order neurons that receive pain signals from the skin

25. Visceral pain Localized damage to viscera seldom cause severe pain
This is probably due to a relative deficiency of Aδ nerve fibers in deep structures, so there is little rapid, bright pain
Diffuse stimulation of pain nerve endings causes pain that can be severe

26. Visceral pain Poorly localized unpleasant
Associated with nausea and autonomic symptoms
It is referred to other areas.

27. Causes of true visceral pain
Ischemia
Chemical damage
Spasm of smooth muscle
Excess distention of hollow organs
Stretching of connective tissue surrounding or within the organs

28. Ischemia
Acidic metabolic end products
Bradykinin
Proteolytic enzymes

29. Spasm of smooth muscle of hollow organs
Mechanical stimulation of pain nerve endings
Diminished blood flow
The pain occurs in form of cramps
Pain increasing in high degree of severity and then subsiding
The intermittent cycles result from periods of contraction of smooth muscle

30. Excess distention of hollow organs
Overstretch of tissues
Collapse the vessels and promoting ischemia

31. Pain sensitive areas in cranial valut
The brain tissues are insensitive
Tugging on the venous sinuses around the brain
Stretch or damage to dura
Damage or stretching the blood vessels of meninges

32. Thermal sensation
Thermal gradations are discriminated by at least three types of sensory receptors: cold, warmth and pain receptors
Thermal receptors are located immediately under the skin
There are 3 to 10 times as many as cold receptors as warmth

33. Thermal receptors Warm: free nerve endings, the fiber is c
Cold: it is a special, small type, A delta fiber that branches a number of time and the tips of the protrude into the bottom surfaces of basal epidermal cells.
Some cold sensations are transmitted in the c fibers

34. Stimulation of thermal receptors
pain receptors stimulated by cold Cease at 10-15
Cold receptors stimulated by cold (Peak stimulation at 24)
Warmth receptors stimulated by heat (Above 30)
Pain receptors stimulated by heat (begin at 45)

35. Adaptation of thermal receptors
Thermal receptors adapts to a great extent but never 100 percent
When the temperature of skin is actively falling, a person feels much colder than when the temperature remain cold

36. Mechanism of stimulation of thermal receptors
Thermal detection results not from physical effects of cold or heat on thermal receptors
Change in metabolic rate
For each 10 ° c intracellular chemical reactions became two fold

37. Transmission of thermal signals
Parallel to pain signals
Terminate in
1- Reticular areas of brain stem
2- Ventrobasal complex
3- A few signals are relayed to somatosensory cortex

38. Removal of post central gyrus reduces but does not abolish the ability to distinguish gradations of temperature