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Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Definition of Pain An unpleasant sensory that is associated with actual or potential.

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Presentation on theme: "Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Definition of Pain An unpleasant sensory that is associated with actual or potential."— Presentation transcript:

1 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Definition of Pain An unpleasant sensory that is associated with actual or potential tissue damaging stimuli

2 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Pain sensation Pain is a protective mechanism Types of pain: I. Fast pain II. Slow pain

3 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Fast pain It is felt within about 0.1 sec after a pain stimulus applied Sharp pain Acute pain Pricking pain Electric pain

4 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings 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 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Pain receptors : free nerve endings stimuli excite pain receptors: o Mechanical, Thermal,Chemical Fast pain is elicited by thermal and mechanical stimuli Slow pain can be elicited by all tree types

6 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings 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

7 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings

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

9 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings 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 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Tissue ischemia as a cause of pain Accumulation of lactic acid Bradykinin Proteolytic enzymes

11 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Muscle spasm Direct effect on pain receptors Compress the vessels and cause ischemia Increase the rate of metabolism and relative ischemia

12 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings 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 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings 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 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings 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 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings 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 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings 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 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings 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

18 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings

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

20 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings

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 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings 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 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings 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

24 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings

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 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Visceral pain Poorly localized unpleasant Associated with nausea and autonomic symptoms It is referred to other areas.

27 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings 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 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Ischemia Acidic metabolic end products Bradykinin Proteolytic enzymes

29 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings 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 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Excess distention of hollow organs Overstretch of tissues Collapse the vessels and promoting ischemia

31 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings 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 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings 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 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings 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 pain receptors stimulated by cold Cease at Cold receptors stimulated by cold (Peak stimulation at 24) Warmth receptors stimulated by heat (Above 30) Pain receptors stimulated by heat (begin at 45) Stimulation of thermal receptors

35 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings 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 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings 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 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings 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 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Removal of post central gyrus reduces but does not abolish the ability to distinguish gradations of temperature


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