Download - Pain pathway
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Pain pathway
Presented by SAMITH MOHANAN
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CONTENTS
•Introduction
•Characteristics of pain
•Types of pain sensation
•Gate control Hypothesis
•Difference b/w sometic & visceral sensory function
•Visceral pain & referred pain
•Receptors & Sensations
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•Pathway of sensory impulses
•Tooth pulp pain
•Applied physiology
•Management
•Conclusion
•References
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INTRODUCTION
Unpleasant sensory & emotional experience associated with actual or potential tissue damage.
Its imp: , symptoms of many diseases & when pt experiences pain he/she consults a physician.
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Characteristics
• specific with specific receptors & afferent fibers.
•Less adaptation & continues as long as pain causing agent persists.
•Chronic pain- psychological effects.
•Tolerance level varies from individuals.
•Cerebral cortex – localization, discrimination & interpretation.
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Types of pain sensation
1) Fast pain- short & sharp conducted by Aδ fibers localization of pain is better
2) Slow pain- more prolonged & severe conducted by C fibers dull, diffused & localization is poor
3) Deep pain- contraction of skeletal muscles when pain is severe, causes sweating, nausea &
vomiting, fall in B.P
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Aδ – fast, sensitive to mechanical noxious stimuli. small, myelinated. High conductance speed
C – slow, sensitive to many noxious stimuli (chemical, etc.) – small, unmyelinated. Slow conductance speed
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Receptors
They are specialized afferent nerve endings designed to respond appropriate & adequate stimulus.
Function
Converts various forms of energy into action potential in nerve fibersAct as transducersSituated at various parts of body- skin, eye, ear, nose, muscle etc
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Properties
Excitability – specificity receptive response
Adaptation
Effect of extend of stimulus
Localization & projection
Effect of strength of stimulus
Quality or modality of sensation
Intensity of sensation
Fatigue
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Classification
•Exteroreceptors- responds to change in external enviornment a) cutaneous receptors- touch, pain, temp: b) chemical receptors- taste & smell c) teleceptors- vision & hearing
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•Interoceptors – exited by stimuli within the body a) Stretch receptors- alvoeli of lungs
b) Chemoreceptors- aortic & carotid bodies
c) baroreceptors- carotid sinus & aortic arch
d) Osmoreceptors- hypothalamus
e) Volumereceptors- right atrium
f) Proprioreceptors- muscle spindle, tendon
g) Visceroreceptors- present in visera
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Nociceptors are special receptors that respond only to noxious stimuli and generate nerve impulses which the brain interprets as
“pain”.
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1. Prevents serious damage.
2. Teaches one what to avoid
3. If pain is in joints, pain limits the activity, so no permanent damage can occur.
but pain can become the problem, and cause people to want to die.
Purpose of pain
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Differences btw Somatic & Visceral sensory function.
Somatic :- seen on skin & subcutaneous tissues subserve sensory function of touch, temp,sensation, pressure & pain
Visceral:- have no proprioreceptors & sparesly distributed subserve osmorecptors, barorecptors
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PAIN STIMULI
3 types- thermal, mechanical & chemical.
Nociceptive stimuli- stimuli which threatens the welfare of tissues & causes pain.
Chemical substances that can induce pain intrinsic- bradykinin, histamine, prostaglandins extrinsic- irritant acid, alkali, plant & animal stings & venoms
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1. gray matter2. white matter3. gray commissure4. central canalDorsal and ventral nerve roots
Internal Anatomy
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Tracts of the Spinal Cord
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Cross section of spinal cord , showing ascending tracts & descending tracts
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Three major pathways carry sensory information
Posterior column pathway (gracile & cuneate fasciculi)
Anterolateral pathway (spinothalamic)
Spinocerebellar pathway
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THREE neurons from the receptor to the cerebral cortex
First order neuron:
Cell body located in the dorsal root ganglion. The Axon passes to the spinal cord through the dorsal root of spinal nerve, runs ipsilaterally and synapses with second-order neurons in the cord and medulla oblongata
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Second order neuron:Has cell body in the spinal cord or medulla oblongata &Terminate on 3rd order neuron
Third order neuron:Has cell body in thalamusAxon terminates on cerebral cortex ipsilaterally
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PAIN IMPULSE PATHWAY
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PAIN IMPULSE PATHWAY
Ventral spinocerebellar
Dorsal spinocerebellar
(1st order neuron)
(2nd order neuron)
(3rd order neuron)
Lateral corticospinal
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Pain
Free nerve ending
Posterior nerve root ganglion
Fibers from lateral spinothalamic tract
Ventral posterolateral nucleus of thalamus, reticular formation & midbrain.
Sensory cortex
Receptor
First order neuron
Second order neuron
Third order neuron
center
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Tissue ischemia
Blood flow is blocked for few min- pain
Results in anaerobic metabolism & release of bradykinin & proteolytic enzymes- cell damage
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Muscle spasm
Indirect effect muscle spasm to compress the blood vessels & cause ischemia
Results – release of chemicals and increase in metabolism in muscle tissue.
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Visceral pain
They are dull & diffuse, poorly localized, and associated with symptoms like nausea & referred to other areas
Stimuli for visceral pain ischemia, obstruction, spasm, chemical stimuli.
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REFERRED PAIN FROM VISCERAL ORGANS
Referred pain
Pain felt in a part of the body that is fairly remote from tissue causing pain.
Pain at diaphragm is felt over tip of shoulder
Pain at maxillary sinus felt at nearby teeth.
A tooth abscess can cause jaw bone pain.
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Convergence theory
both somatic & visceral afferent fibers converge upon 2nd order neuron
Somatic fibers conduct impulses more frequent.
Visceral pain is felt as somatic pain because brain is familiar with somatic regions.
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Facilitation theory
Visceral & somatic fiber join at adjoining spinothalamic neurons( 2nd order neurons)
When strong impulses conduct, activation of spinothalamic neurons, resulting in impulses passing through spinothalamic pathway
This results in misinterpretation in location of pain.
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Melzack & Waller- 1965
Pain impulses in spinal cord can be modified by other afferent impulses entering the spinal cord with posterior horn acting as gate
Gate control hypothesis/ gate theory of pain
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Gate open Gate closed
Physiological Aδ and C fibers active, Overuse, Fatigue , improper mechanics, tired
Aδ or Aα active, Relaxation, exercise, strengthening/ conditioning
Medical Extent of injury/pathological condition
Medication, cooling/heating
Congenitive Focusing on pain, anxiety , fear, depression, stress
Distraction, relaxation, happiness, positive attitude
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Tooth pulp pain
1) Exposure of dentinal tubules elicit toothache & other non noxious sensation.
2) Both Aδ & C fibers respond to stimuli in dentine
3) Transmission of stimuli across dentin, mediated by movement of fluid through odontoblast tubules.
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4) Fibers terminate at medullary dorsal horn & synapse and also at trigeminal sensory nucleus
5) From trigeminal nucleus send inf: thalamus & sensory cortex
6) Pulpal innervation are capable of regenerating & reinnervating
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Determinants of painful experience during dental treatment
Pain occurs due to invasive procedures like extractions & surgeries or non invasive procedures. With regard to children, studies have shown that dentists do not believe in pain referred by children & tend not to use available methods to control pain.
Conclusion: anxiety is determinant for pain during dental care & pain is related to local anesthetic procedures. There are evidences that dentists attitude are determinants for pain.
Ruth et al Rev.dor; 2012; 13(4)
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Pain assessment visual analogue scale
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The sensory functions are affected by lesions in sensory pathways or other nervous disorders.
1) Anesthesia – loss of sensation
2) Hyperesthesia- increase sensitivity to sensory stimuli
3) Hypoesthesia- decrease sensitivity to sensory stimuli
4) Hemiesthesia – loss of sensation to one part of body
5) Paresthesia- abnormal sensation
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6) Dissociated anesthesia- loss of some sensation with loss of consciousness produced by anesthetic agents
7) General anesthesia- loss of all sensation with loss of conciousness produced by anesthetic agents
8) Local anesthesia- loss of sensation restricted area of body
9) Tactile anesthesia- loss of tactile sensation
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10) Hyperaglasia-increase in sensitivity to pain
11) Paraglesia- abnormal pain sensation
12) Thermic anesthesia- loss of thermal sensation
13) Pallanesthesia- loss of sensation of vibration
14) Analgesia- loss of pain sensation
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Herpes zoster- viral infection affecting dorsal root ganglion. Results in severe pain which facilitates the pain towards the ganglion.
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Tic Doulourex
Pain felt at one side of the face
Felt like sudden electric shock, may last for secs or may be continous
Corrected by surgery at hypersensitive area
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Brown-Sequard syndrome
All sensations are blocked at one side
Sensations like pain, heat & cold, vibrations are blocked
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In a study by Pornachi et al- A case reported on a 63yr old woman with Brown-Sequard Syndrome due to spontaneous C5-C6 cervical disc herniation. Anterior discectomy was performed with favorable outcome.
Neurology Asia .2007;12;65-67
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Management
NSAIDs – paracetamol, capsacin
L.A- reduces pain
Opoids-
Anticonvulsants- interferes with Na & Ca channel function
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Conclusion
Pain can induce physiological & anatomical changes within the nervous system. The complexity of pain transmission means there are many pharmological targets & multimodel therapy is required to optimize pain control.
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References
Essential of oral physiology- Robert M BradleyTextbook of medical physiology- Guyton & Hall Essential of medical physiology- K.Sembulingam & Prema SembulingamTextbook of human physiology- S Chand
Articles•Determinants of painful experience during dental treatment- Ruth Suzanne et al Rev.Dor 2012;13(4)•Case report study on Brown sequard syndrome- Ponachi et al Neurology Asia 2007;12;65-67•Anatomy, physiology & pharmacology of pain- Ryan Moffat, Colin P.Rae anesthesia & intensive care medicine; 2010;12(1)