2 backup of pain and nerve conduction

PAIN

BYDr. Nelly Hammouda

Associate Professor of OMFSFaculty of DentistryFuture University

PainPain is a more terrible loed of mankind than even death itself Dr. Albert Schweitzer

Pain International Association for the Study of pain (IASP): An unpleasant sensory & emotional experience associated with actulal or potential tissue damage. This definition emphasizes that.... A) Pain is always unpleasant: Unlike other sensory input such as smell, which can be ( pleasant, neutral or unpleasant)

PAINB) Pain is both sensory & emotional experience: * Individual dosen’t recognize perception of noxious stimulus without emotional feeling as pain. * Pain differs from other sensations in that “ it is always referred to some part of the body with varying degrees of precision”. C) Pain is associated with actual or potential tissue damage:

THEORIES OF PAIN

1) Specificity theory... Origin: The theory was highlighted by Descartes in 1664 and modified by Von Frey 1895. * Descartes explain the pain system as being like the ( bell - ringing mechanism ) in the church; i.e when someone pulls the rope to ring the bell, the bell rings in the tower. - He conceived that, pain is a specific entity similar to the sense of sight or olfaction.

THEORIES OF PAIN

* Von Frey proposed that, specific cutaneous pain receptors project to a specific pain center in the brain in a hard - wired system. - He conceived the pain occurs as follow: Injury to body tissue ---> damage to nerve fiber--> stimulation for specific pain receptor & fibers to send direct message to the specific pain center in the brain--> pain feeling.

THEORIES OF PAIN

Suggestions... 1- there is strong link between pain & injury and the severity of the injury determines the amount of pain experienced by the person. 2- peripheral receptors are specialized in their response to stimuli.

THOERIES OF PAIN

Challenges... 1) this theory has defects on anatomical,psychological & physiological grounds, e.g.: Injuries causing sever tissue damage don’t always cause pain. 2) it doesn’t explain referred pain triggered off by stimulation of normal skin. 3) it doesn’t consider the individual deference in how pain is perceived by people.

THEORIES OF PAIN2)Pattern theory... This theory proposes that specific nerve fibers or receptors don’t exist but rather free nerve ending respond non-selectively to multiple stimuli & their responses took the form of different patterns of impulses. * Painful stimuli will be associated with increasing impulse frequencies. * Pain is not a separate entity but results from overstimulation for other primary sensations ( sound, touch....)

THEORIES OF PAIN

Challenges: not true.... 1) Pain has distinct nociceptive afferent pathway (A- delta & C fibers). 2) Pain intenisty can be reduced while other sensory modalities are maintained. 3) Intense electrical stimulation to non-nociceptive axons doesn’t produce pain.

THEORIES OF PAIN

3) Gate control theory... ( Melzack & Wall in 1965) Proposals: * A modulating ( gating) mechanism exists in the dorsal horn & involves central neural factors. * It explains how innocuous stimulation inhibits pain via a presynaptic inhibitory mechanism.

PATHWAY OF PAIN

According to the gate theory: 1) Noxious stimuli from the peripheral nociceptors are carried to the spinal cord through two types of fibers:- a- Large myelinated fibers with faster conduction velocity ( A-beta fibers) b- Small fibers with slower conduction velocity: * small myelinated ( A- delta fibers ) * Unmyelinated ( C- fibers )

PATHWAY OF PAIN2) Impulse gating: * the gating is a neural mechanism that acts like a modulating or regulating system that control the amount of nerve impulse transmission from the periphery to the transmission cells ( T cell)deep in the spinal cord. 3)The projection of pain to the brain: After the noxious stimuli are modulated in the gate, they are projected through various pathways to two diffrent brain areas to be processed.... a- Motivational affective system: it consists of the reticular formation, limbic system & hypothalamus.

b- Sensory- discriminative system: noxious stimuli--> spinothalamic & neospinothalamic projection system --> ventrobasal thalamus --> somatosensory cortex. From the IASP definition of pain & the gate control theory, it is clear that pain is a multidimensional experience with physical & psychological components.

Components of Pain

Melzack &Casey suggests three components comprising the nature of pain: 1) Sensory - Discriminative. 2) Affective - Emotional. 3) Cognitive - Evaluative.

Sensory... Discrimination of pain in perspective of: * Time ( days, weeks, months ) * Space ( jaw, head ) * Intensity ( not bad , so bad ) Affective... Affective responses of feeling: * Negative responses * Positive responses Cognitive... Significance of pain to the patient.

Mechanism of Pain

The classic description of mechanism of pain typically includes four processes... 1)TRANSDUCTION: * Definition: It is the conversion of energy from a noxious stimulus into electrical signals ( nerve impulse ) by nociceptors.

Mechanism of Pain

* Mechanism: noxious stimulus--> tissue injury--> cells breakdown & release of their byproducts & inflammatory mediators--> activation & sensitization of nociceptors. what is NOCICEPTORS ? Definition: Receptors that respond to noxious stimulus or to stimulus which would become noxious if prolonged.

Mechanism of PainLocation: Present in most body tissues but notably absent in the brain. Type: Respond to mechanical,thermal or chemical stimuli. Nature : They are primary afferent nerve fibers & their nociception travels along:

Mechanism of Pain1) C-fibers ( unmyelinated-slowly conducting)--> carry sensation ( dull, aching pain ). 2) A-delta fibers ( myelinated- rapidly conducting)--> carry sensation ( sharp, localized pain ). Activation: They are not spontaneously active , their activation requires a stimulus over the threshold.

Mechanism of Pain

Their activation results in Nociception, which is the activity that arises in the nerve fiber as a result of activation of nociceptors. **Transduction is as follow ( activation ): Noxious stimulus --> tissue injury --> cells breakdown --> and release of their byproducts & inflammatory mediators ( e.g. PG, bradykinin, histamine, & serotonin)--> these substance will result in:

* Activation of nociceptors ( generation of nerve impulse) * Sensitization of nociceptors: - increase excitability - increase discharge frequency ADAPTATION: They are adapted slightly or not at all to the presence of tissue byproducts & inflammatory mediators ) . - This explain why pain persists after initial trauma.

Mechanism of Pain

2)TRANSMISSION... * Definition: Transfer of the neural signals from the site of transduction ( periphery ) to the spinal cord and brain.

Mechanism: Nociception along the afferent nerve fibers

Dorsal horn cell Gate

Permission for impulse transmission inhibition for transmission Impulse transmission at synape from the primary afferent neuron to second order neuron under the influence of exitatory amino acids & neuropeptides.

Mechanism of Pain

From the dorsal horn cells the impulse are then transmitted as follow: * BY spinothalamic tract TO thalamus * BY spinoreticular tract TO reticular formation * BY spinomesencephalic tract TO mesencephalon * BY spinohypothalamic tract TO hypthalamus

Mechanical

Electrical

ThermalChemical

Polymodal

Non-adaptive

Pain

Pain Pathway

Pain

Pain Pathway

Spinal Trigeminal Nucleus

TACTILE SENSATION

PAIN & TEMPERATUR

E

BRAIN

Mesencephalic Nucleus

PROPRIOCEPTION

(Position & Move.)

PONS

MID BRAIN

Trigeminal Leminscus

(spinothalamic tract)

Somato sensory Posterior cortex

Mechanism of Pain 3)MODULATION: It is the descending inhibitory & facilitory input from the brain that influences or modulates nociceptive transmission at the level of the spinal cord. 4)PERCEPTION ( awareness of pain ): * Definition: It is integration & recognition of signals arriving in the higher structures as pain. This involve both cortical & limbic system structures.

mechanism of painPerception of different types of pain: Recognition of type & intensity of pain occurs primarily in the cerebral cortex & differ according to origin. 1) Somatic pain: The cerebral cortex projects the somatic pain back to the stimulated area. e.g.: if you burn your finger feel pain in your finger & not in the cortex.

Mechanism of Pain2)Visceral pain: The visceral pain doesn’t project back to the stimulated area but rather, the pain is felt in the skin overlying the stimulated organ or in a surface area far from the stimulated organ ( Referred Pain Phenomenon) The referred phenomenon occurs because the same segment of the spinal cord innervates the areas to which the pain is referred as well as the visceral organ involved.

Mechanism of Pain3) Phantom pain: Pain often experienced by the patients who have had a limb amputation. * The reason of this phenomenon is that : The remaining proximal portions of sensory nerves that previously received impulses from the limb are stimulated by the trauma of the amputation & stimuli of these nerves are interpreted by the brain as pain coming from the nonexistent limb.

Mechanism of Pain

Factors affecting pain perception: 1) Pain threshold... The point at which the painful stimulus is perceived as painful, it is variable from one person to another. 2) Pain tolerance... The amount of pain which the one can endure.also vary from one to another. 3) Psychological & cultural factors.

• Pain Perception:

Transmission of an impulse to CNS.

• Pain Reaction:

Patient’s reaction (manifestation) to pain perception.

Pain

Pain Perception and Reaction

Pain


Pain Threshold

P A

I NN

O

P A

I N

Impulse of equal intensity (all or none)

Pain threshold is the least intensity of a stimulus that can be recognized as pain.

Reaction

Stim

ulus

Sev

erity

Pain


Pain

Pain Reaction

Definition:Patient’s reaction (manifestation) to pain

perception.

Hyporeactive high pain threshold

Hyperreactive low pain threshold

• Factors affecting pain reaction:

Pain

Pain Reaction

↓ PRT

PRT: Pain Reaction Threshold

• Factors affecting pain reaction:

Pain

Pain Reaction

PRT: Pain Reaction Threshold

Pain

Pain Reaction

Factors affecting pain reaction

Psychological and Educational Considerations

PainHypoalgesia

Hypoalgesia: Hypo – decreased

Algesia: pain

“Reduction or even diminishment of the intensity of pain that occurs in response to a stimulus that is

normally painful”

Pain

Hypoalgesia

Causes: 1. Chemically induced; e.g. due to

opioids. 2. Hereditary malfunction of

nociceptors. 3. Associated with some diseases,

e.g. Diabetes.

Pain

Hyperalgesia

S 1

S 2

100 1 2 3 4 5 6 7 8 9

Hyperalgesia: Hyper – increased, over.

Algesia: pain

“Increased response to a stimulus that is normally painful”.

Pain

Hyperalgesia

• Types:

Focal or diffuse

• Causes:

1. Damage of nociceptors. 2. Damage of peripheral nerves.

Types of PainA) According to the PAIN DURATION & THE CAUSE: a- Acute ( short time less than one month ) b- Chronic ( 3-6 months or more ) c-Subacute (daily pain for several weeks ) d- Recurrent acute ( several limited pain episodes over many months)

Types of PainB) According to the PATHOPHYSIOLOGY: a- Nociceptive pain: Normal pain due to normal stimuli in response to noxious stimuli. Type: - Physiologic : when acute - Pathologic : when chronic b- Neuropathic pain: Pain in nerve themselves ( neuralgia) caused by damage to peripheral or central nervous system.

Type of Pain

c- Psychological pain: Pain originates in the mind No noxious stimulus or abnormality in the nervous system.felt in many areas as there is no relation between the pain source & site of pain. d- Idiopathic pain: Pain without any identifiable organic lesion.

Type of Pain

ACCORDING TO THE ORIGION OF PAIN: 1) Visceral pain:body viscera or organ 2) Somatic pain: skin, mucous membrane & subcutaneous tissue)

Methods of Pain Control1)Removal of the cause 2) Blocking the way of painful stimuli : LA action 3) Elimination of pain by cortical depression: GA act 4) Pain control by drugs: Analgesics 5) Non pharmacological:Acupuncture, transcutaneous electrical nerve stimulation & hypnosis.

Methods of Pain Control

1. Removal of the Cause:

Inferior alveolar nerve


2. Blocking the pathway of painful impulses:

Inferior alveolar nerve

Methods of Pain Control2. Blocking the pathway of painful

impulses:

Anesthesia versus analgesia:

Anesthesia An – No, without

Esthesia – Sensation.

“Absence of all sensation”


2. Blocking the pathway of painful impulses:

Analgesia: An – No, without

Algesia: pain “Absence of pain in response to a

stimulation that would normally be painful”


3. Cortical depression:

Pain

Sensation


4. Pharmacological:

Pain Threshold


4. Pharmacological:

Pain Free

Pain Threshold

Analgesic

Methods of Pain ControlPoints to remember:

Stimulus is still present.

Stimulus: beyond threshold = below threshold.

Pain threshold can be raised to a limited degree only depending on

the drug used.


5. Non-Pharmacological:

• Acupuncture. • Hypnosis. • TENS (Transcutaneous Electric Nerve Stimulator).


Points to Remember

Pain is an alarm for a potential or actual tissue damage.

Every effort should be made to diagnose the source of the pain, and to treat

the pathologic condition rather than the discomfort alone

Thank You

2 backup of pain and nerve conduction

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