Pain pathway

Presented by SAMITH MOHANAN

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

•Pathway of sensory impulses

•Tooth pulp pain

•Applied physiology

•Management

•Conclusion

•References

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.

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.

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

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

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

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

Classification

•Exteroreceptors- responds to change in external enviornment a) cutaneous receptors- touch, pain, temp: b) chemical receptors- taste & smell c) teleceptors- vision & hearing

•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

Nociceptors are special receptors that respond only to noxious stimuli and generate nerve impulses which the brain interprets as

“pain”.

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

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

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

1. gray matter2. white matter3. gray commissure4. central canalDorsal and ventral nerve roots

Internal Anatomy

Tracts of the Spinal Cord

Cross section of spinal cord , showing ascending tracts & descending tracts

Three major pathways carry sensory information

Posterior column pathway (gracile & cuneate fasciculi)

Anterolateral pathway (spinothalamic)

Spinocerebellar pathway

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

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

PAIN IMPULSE PATHWAY

PAIN IMPULSE PATHWAY

Ventral spinocerebellar

Dorsal spinocerebellar

(1st order neuron)

(2nd order neuron)

(3rd order neuron)

Lateral corticospinal

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

Tissue ischemia

Blood flow is blocked for few min- pain

Results in anaerobic metabolism & release of bradykinin & proteolytic enzymes- cell damage

Muscle spasm

Indirect effect muscle spasm to compress the blood vessels & cause ischemia

Results – release of chemicals and increase in metabolism in muscle tissue.

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.

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.

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.

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.

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

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

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.

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

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)

Pain assessment visual analogue scale

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

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

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

Herpes zoster- viral infection affecting dorsal root ganglion. Results in severe pain which facilitates the pain towards the ganglion.

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

Brown-Sequard syndrome

All sensations are blocked at one side

Sensations like pain, heat & cold, vibrations are blocked

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

Management

NSAIDs – paracetamol, capsacin

L.A- reduces pain

Opoids-

Anticonvulsants- interferes with Na & Ca channel function

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.

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)