The Physiology and The Physiology and psychology of painpsychology of pain

Chapter 2Chapter 2

PainPain

Of all the components of the injury response, Of all the components of the injury response, none is less consistent or less understood than none is less consistent or less understood than an individuals response to painan individuals response to pain

The sensation of pain is a diffuse entity inherent The sensation of pain is a diffuse entity inherent to the nervous system and basic to all peopleto the nervous system and basic to all people

It is a personal experience that all humans It is a personal experience that all humans endureendure

Acute pain is the primary reason why people Acute pain is the primary reason why people seek medical attention and the major complaint seek medical attention and the major complaint that they describe on initial evaluation.that they describe on initial evaluation.

Chronic pain may be more debilitating than the Chronic pain may be more debilitating than the trauma itself and, in many instances, is so trauma itself and, in many instances, is so emotionally and physically debilitating that it is a emotionally and physically debilitating that it is a leading cause of suicide.leading cause of suicide.

Pain serves as one of the body’s defense Pain serves as one of the body’s defense mechanisms by warning the brain that its tissues mechanisms by warning the brain that its tissues may be in jeopardy, yet pain may be triggered may be in jeopardy, yet pain may be triggered without any physical damage to tissues.without any physical damage to tissues.

The pain response itself is a complex The pain response itself is a complex phenomenon involving sensory, behavioral phenomenon involving sensory, behavioral (motor), emotional, and cultural components.(motor), emotional, and cultural components.

Once the painful impulse has been initiated and Once the painful impulse has been initiated and received by the brain, the interpretation of pain received by the brain, the interpretation of pain itself is based on interrelated biological, itself is based on interrelated biological, psychological, and social factors.psychological, and social factors.

What are the nerve fibers that stimulate pain?What are the nerve fibers that stimulate pain? Nociceptors.Nociceptors.

Once these are stimulated, “pain” impulses are Once these are stimulated, “pain” impulses are sent to the brain as a warning that the body’s sent to the brain as a warning that the body’s integrity is at risk.integrity is at risk.

The emotional response may be expressed by The emotional response may be expressed by screaming, crying, fainting, or just thinking “#@screaming, crying, fainting, or just thinking “#@%&, that hurts!”%&, that hurts!”

When the pain is intense or unexpected, When the pain is intense or unexpected, an immediate reflex loop activates the an immediate reflex loop activates the behavioral response by sending behavioral response by sending instructions to motor nerves to remove the instructions to motor nerves to remove the body part from the stimulus.body part from the stimulus. Sticking your finger with a needleSticking your finger with a needle Placing your hand on a hot stovePlacing your hand on a hot stove

These stimuli’s activate specialized nerve These stimuli’s activate specialized nerve fibers to send signals through a peripheral fibers to send signals through a peripheral nerve networknerve network Routing the impulses up the spinal cord to the Routing the impulses up the spinal cord to the

brainbrain

When the afferent impulse reach the spinal cord, When the afferent impulse reach the spinal cord, a reflex loop is formed within the tract to activate a reflex loop is formed within the tract to activate the muscles necessary to remove your hand or the muscles necessary to remove your hand or finger from the stimulus.finger from the stimulus.

The remaining impulses of the reflex continue on The remaining impulses of the reflex continue on to the brain, where they are translated as pain, to the brain, where they are translated as pain, and you respond by saying “ouch!” or other and you respond by saying “ouch!” or other choice words.choice words.

If an individual has knowledge about a If an individual has knowledge about a potentially painful stimulus, such as receiving an potentially painful stimulus, such as receiving an injection, cognitive mechanisms can inhibit the injection, cognitive mechanisms can inhibit the reflex loop and block portions of the behavioral reflex loop and block portions of the behavioral response.response.

As a the painful stimulus increases, so does the As a the painful stimulus increases, so does the conscious effort required to keep from trying to conscious effort required to keep from trying to escape from the stimulus. escape from the stimulus.

The emotional component may still be in place The emotional component may still be in place as you grimace, make a fist, or think “what the as you grimace, make a fist, or think “what the @%^$ is this jerk doing to me.”@%^$ is this jerk doing to me.”

The cultural components of pain are almost too The cultural components of pain are almost too complex to define.complex to define. However, pain perception has been linked to ethnicity However, pain perception has been linked to ethnicity

and socioeconomic status.and socioeconomic status. ExampleExample

Italian patents are less inhibited in the expression of Italian patents are less inhibited in the expression of pain than are the Irish or Anglo-Saxon patientspain than are the Irish or Anglo-Saxon patients

Ultimately, cultural components can be viewed Ultimately, cultural components can be viewed as any variable that relates to the environment in as any variable that relates to the environment in which a person was raised and how that which a person was raised and how that environment deals with pain and responses to environment deals with pain and responses to pain.pain.

Pain ProcessPain Process

Noxious input or nociceptive stimulus causes the Noxious input or nociceptive stimulus causes the activation of pain fibers.activation of pain fibers.

The painful impulse is triggered by the initial The painful impulse is triggered by the initial mechanical force of the injury (whether sudden mechanical force of the injury (whether sudden or gradual onset) and is continued by chemical or gradual onset) and is continued by chemical irritation resulting from the inflammatory processirritation resulting from the inflammatory process

In subacute and chronic conditions, pain may be In subacute and chronic conditions, pain may be continued by reflex muscle spasm in a positive continued by reflex muscle spasm in a positive feedback loop or through the continued feedback loop or through the continued presence of chemical irritationpresence of chemical irritation

The pain response is initiated by stimulation of The pain response is initiated by stimulation of nociceptorsnociceptors NociceptorsNociceptors- specialized nerve endings that - specialized nerve endings that

respond to painful stimulirespond to painful stimuli Mechanical stress or damage to the tissues Mechanical stress or damage to the tissues

excite mechanosensitive nociceptorsexcite mechanosensitive nociceptors Chemosensitive nociceptors are excited by Chemosensitive nociceptors are excited by

various chemical substances released during the various chemical substances released during the inflammatory responseinflammatory response

Chemical irritation of nerve endings may Chemical irritation of nerve endings may produce a severe pain response without true produce a severe pain response without true tissue distructiontissue distruction

Unlike other types of nerve receptors, Unlike other types of nerve receptors, nociceptors display a sensitization to nociceptors display a sensitization to repeated or prolonged stimulationrepeated or prolonged stimulation

During the inflammatory process, the During the inflammatory process, the threshold required to initiate an action threshold required to initiate an action potential is lowered, and the continued potential is lowered, and the continued stimulation of the chemosensitve receptors stimulation of the chemosensitve receptors perpetuates the cycleperpetuates the cycle

To understand the complexity of pain, To understand the complexity of pain, comprehension of the various comprehension of the various neurophysiological pathways involved in neurophysiological pathways involved in transmission, perception, and inhibition of pain is transmission, perception, and inhibition of pain is critical.critical.

The nervous systemThe nervous system Forms a complex network of Forms a complex network of afferentafferent and and efferentefferent

pathways.pathways.• Transmitting and reacting to impulses that the brain Transmitting and reacting to impulses that the brain

perceives as being painfulperceives as being painful

All noxious impulses are transmitted afferently to All noxious impulses are transmitted afferently to the thalmusthe thalmus This produces the “painful” stimulus which triggers the This produces the “painful” stimulus which triggers the

physiological and psychological process described physiological and psychological process described earlierearlier

Modulation of PainModulation of Pain

Acute pain response begins with a noxious Acute pain response begins with a noxious stimulus.stimulus. IE. A burn or cut externally or internally a IE. A burn or cut externally or internally a

muscle strain or ligament sprainmuscle strain or ligament sprain After trauma chemicals are released in After trauma chemicals are released in

and around the surrounding tissues.and around the surrounding tissues. Immediately after the trauma, primary Immediately after the trauma, primary

hyperalgesia occurshyperalgesia occurs Lowers the nerve’s threshold to noxious Lowers the nerve’s threshold to noxious

stimuli and magnifying the pain responsestimuli and magnifying the pain response

Within hours, secondary hyperalgesia occursWithin hours, secondary hyperalgesia occurs ↑ ↑ the size of the painful area as the chemicals the size of the painful area as the chemicals

diffuse into the surrounding tissuesdiffuse into the surrounding tissues• Causes hypersensitivityCauses hypersensitivity

The initiation of the pain process always The initiation of the pain process always begins with a chemical stimulus.begins with a chemical stimulus. Review chemical precursorsReview chemical precursors

During acute traumaDuring acute trauma Cell walls become damagedCell walls become damaged Causes dopamine and norepinephrine (NE) to be Causes dopamine and norepinephrine (NE) to be

released from precursors in the cell membranereleased from precursors in the cell membrane Causes the activation of phospholipasCauses the activation of phospholipas

• Allowing the cell membrane to release arachidonic acidAllowing the cell membrane to release arachidonic acid• When released in the presence of cyclooxygenase, it When released in the presence of cyclooxygenase, it

converts to prostaglandinconverts to prostaglandin

Prostaglandins have many roles in inflammation, Prostaglandins have many roles in inflammation, but they also sensitize the nerve endings to but they also sensitize the nerve endings to other chemicalsother chemicals IE bradykininIE bradykinin

• Which in turn initiate nociceptionWhich in turn initiate nociception Bradykinin, found in plasma and released during Bradykinin, found in plasma and released during

coagulation that follows injury, are direct activators of coagulation that follows injury, are direct activators of nociception.nociception.

• Powerful vasodilators, Powerful vasodilators, ↑ vascular permeability during ↑ vascular permeability during the inflammatory responsethe inflammatory response

NSAID’s play and important role in the tx NSAID’s play and important role in the tx of acute pain in that they block the of acute pain in that they block the formation cyclooxygenase and prevent the formation cyclooxygenase and prevent the synthesis of prostaglandins.synthesis of prostaglandins. Therefore, NSAID’s are important as an early Therefore, NSAID’s are important as an early

mediator for the interruption of the pain and mediator for the interruption of the pain and inflammation cycleinflammation cycle

Pain fibersPain fibers

A-delta fibers- a type of nerve that A-delta fibers- a type of nerve that transmits painful information that is often transmits painful information that is often interpreted by the brain as burning or interpreted by the brain as burning or stinging painstinging pain

C-fibers- a type of nerve that transmits C-fibers- a type of nerve that transmits painful information that is often interpreted painful information that is often interpreted by the brain as throbbing or achingby the brain as throbbing or aching

After an injury, A-delta and C fibers carry After an injury, A-delta and C fibers carry noxious stimuli from the periphery noxious stimuli from the periphery (using which (using which

pathway?) pathway?) to theto the dorsal horn of the spinal cord.dorsal horn of the spinal cord. The noxious stimuli activates 10-20% of the A-The noxious stimuli activates 10-20% of the A-

delta fibers and 50-80% of the C-fibers.delta fibers and 50-80% of the C-fibers. Triggered by strong mechanical pressure or Triggered by strong mechanical pressure or

intense heat, A-delta fibers produce a fast, intense heat, A-delta fibers produce a fast, bright, localized pain sensation.bright, localized pain sensation.

C-fibers are triggered by thermal, mechanical, C-fibers are triggered by thermal, mechanical, and chemical stimuli and generate a more and chemical stimuli and generate a more diffuse, nagging sensationdiffuse, nagging sensation

After an injury, such as a sprained ankle, you After an injury, such as a sprained ankle, you athlete feelsathlete feels Sharp, well-localized, stinging or burning sensation Sharp, well-localized, stinging or burning sensation

coming from which fibers??coming from which fibers??• A-delta fibersA-delta fibers

This initial reaction allows an indiviual to realized that This initial reaction allows an indiviual to realized that trauma has occurred and to recognize the response trauma has occurred and to recognize the response as painas pain

Very quickly, the stinging or burning sensation Very quickly, the stinging or burning sensation becomes an aching or throbbing sensation, becomes an aching or throbbing sensation, which indicates activation of which fiberwhich indicates activation of which fiber C-fibersC-fibers

A third type of peripheral afferent nerve fiber A third type of peripheral afferent nerve fiber warrants mention. A-beta fibers, respond to light warrants mention. A-beta fibers, respond to light touch and low intensity mechanical information.touch and low intensity mechanical information. Rubbing and injured areaRubbing and injured area These interrupt nociception to the dorsal hornThese interrupt nociception to the dorsal horn

Ascending PathwaysAscending Pathways First-order neurons-First-order neurons- A-beta, A-delta, and C A-beta, A-delta, and C

nerve fibers.nerve fibers. Because they all originate in the periphery and Because they all originate in the periphery and

terminate in different areas of the dorsal hornterminate in different areas of the dorsal horn The gray matter of the spinal cord is divided into The gray matter of the spinal cord is divided into

10 layers of cell bodies called 10 layers of cell bodies called LaminaeLaminae Before synapsing in the laminae the peripheral Before synapsing in the laminae the peripheral

afferent nerves course into the tract of Lissauerafferent nerves course into the tract of Lissauer Where A-delta and C fibers divide and send impulses Where A-delta and C fibers divide and send impulses

up and down one to two segments of the spinal up and down one to two segments of the spinal column.column.

Once in the dorsal horn of the spinal cord, the Once in the dorsal horn of the spinal cord, the small A-delta and C fibers synapse with neurons small A-delta and C fibers synapse with neurons and terminate in the various laminaeand terminate in the various laminae

Lamina I contains several types of Lamina I contains several types of neuronsneurons The 2 of interest to us areThe 2 of interest to us are

• Wide-dynamic-range (WDR) neuronsWide-dynamic-range (WDR) neurons• Nociceptive-specific (NS) neuronsNociceptive-specific (NS) neurons

WDR- respond to both noxious and non-WDR- respond to both noxious and non-noxious stimulinoxious stimuli

NS- respond only to noxious stimuliNS- respond only to noxious stimuli These neurons in lamina I are part of the These neurons in lamina I are part of the

cells that make up the Long spinothalamic cells that make up the Long spinothalamic tract (STT)tract (STT)

The The Substantia Gelatinosa (SG)Substantia Gelatinosa (SG), found , found partially within lamina II, contain small partially within lamina II, contain small internuncial neuronsinternuncial neurons These neurons can excite (stalked cells) or These neurons can excite (stalked cells) or

inhibit (islet cells) the transmission of noxious inhibit (islet cells) the transmission of noxious stimulistimuli

These neurons in the SG send axons to lamina These neurons in the SG send axons to lamina I and release enkephalin and gamma-I and release enkephalin and gamma-aminobutyric acid.aminobutyric acid.• Both which inhibit the transmission of noxious Both which inhibit the transmission of noxious

stimulistimuli EnkephalinEnkephalin- a substance released by the body that - a substance released by the body that

reduces the perception of pain by bonding to pain reduces the perception of pain by bonding to pain receptors sitesreceptors sites

Lamina III and IV- composed of WDR neuron Lamina III and IV- composed of WDR neuron cells and low-threshold mechanoreceptors.cells and low-threshold mechanoreceptors. The mechanoreceptors play a limited role in the The mechanoreceptors play a limited role in the

modulation and transmission of painmodulation and transmission of pain Lamina V- is a major synapse of A-delta and C Lamina V- is a major synapse of A-delta and C

fibers in the dorsal horn.fibers in the dorsal horn. It also has a large # of WDR cells that respond to a It also has a large # of WDR cells that respond to a

spectrum of stimuli from light touch to mechanical spectrum of stimuli from light touch to mechanical pressure and heatpressure and heat

WDR cells from laminae I & 5 make up the WDR cells from laminae I & 5 make up the majority of fiber in the STT.majority of fiber in the STT. Where first order neurons terminate and second order Where first order neurons terminate and second order

neurons originateneurons originate• Second order- A nerve that has its body located in the spinal Second order- A nerve that has its body located in the spinal

cord. It connects second and third order neuronscord. It connects second and third order neurons• Third order- a nerve that has its body in the thalamus and Third order- a nerve that has its body in the thalamus and

extending into the cerebral cortexextending into the cerebral cortex

11stst order neurons course from the periphery order neurons course from the periphery to synapse in the dorsal root ganglion and to synapse in the dorsal root ganglion and the laminae before crossing the spinal cord the laminae before crossing the spinal cord to the STTto the STT Once in the STT, noxious stimulus is then Once in the STT, noxious stimulus is then

transmitted to the brain via 2 different portions transmitted to the brain via 2 different portions of the STTof the STT• The neospinothalamic (lateral) tract (NSTT)The neospinothalamic (lateral) tract (NSTT)• Paleospinothalamic (ventral) tract (PSTT)Paleospinothalamic (ventral) tract (PSTT)

This dual-tract system of afferent pain This dual-tract system of afferent pain pathways enables the body to have immediate pathways enables the body to have immediate warning of the presence, location, and intensity warning of the presence, location, and intensity of an injury as well as the slow, aching of an injury as well as the slow, aching reminder that tissue damage has occurred.reminder that tissue damage has occurred.

NSTT receives input from A-delta fibers that synapse NSTT receives input from A-delta fibers that synapse with the nociceptive-specific neurons and the WDR with the nociceptive-specific neurons and the WDR neurons in Laminae I & V.neurons in Laminae I & V.

These neurons of the NSTT immediately cross the These neurons of the NSTT immediately cross the ventral white column of the spinal cord to the ventral white column of the spinal cord to the opposite antrolateral white column.opposite antrolateral white column.

Once in the ant horn, the fibers of the NSTT and a Once in the ant horn, the fibers of the NSTT and a portion of STT synapse with motor units or stimulate portion of STT synapse with motor units or stimulate preganglionic neurons of the sympathetic or preganglionic neurons of the sympathetic or parasympathetic system and then communicate with parasympathetic system and then communicate with the thalamus.the thalamus. This transmission is responsible for the motor and This transmission is responsible for the motor and

autonomic response associated with tissue damage and autonomic response associated with tissue damage and info pertinent to the siteinfo pertinent to the site

• IntensityIntensity• And duration of the painful stimulusAnd duration of the painful stimulus

The NSTT has been described as the sensory The NSTT has been described as the sensory discriminative pathway of pain.discriminative pathway of pain.

The PSTT is located more medially, but still is in The PSTT is located more medially, but still is in the anterolateral portion of the white matter of the anterolateral portion of the white matter of the spinal cord.the spinal cord. The PSTT receives input predominately from the C The PSTT receives input predominately from the C

fibers.fibers.• These synapse with the nociceptive-specific neurons and the These synapse with the nociceptive-specific neurons and the

WDR neurons in Laminae I & V WDR neurons in Laminae I & V 22ndnd order neurons of Laminae I & V cross over the order neurons of Laminae I & V cross over the

spinal cord and project to the reticular formation (RF)spinal cord and project to the reticular formation (RF)• A diffuse network of cells and fibers located in the brain A diffuse network of cells and fibers located in the brain

stem. Influences alertness, waking, sleeping, and certain stem. Influences alertness, waking, sleeping, and certain reflexes.reflexes.

The RF is located in the central portion of the brain The RF is located in the central portion of the brain stem, medulla oblongata, hypothalamus, thalamus, stem, medulla oblongata, hypothalamus, thalamus, limbic system, and periaqueductal gray (PAG).limbic system, and periaqueductal gray (PAG).

The RF is responsible for evoking motor, The RF is responsible for evoking motor, sensory, and autonomic responses to sensory, and autonomic responses to noxious stimuli.noxious stimuli. This allows the injured person to respond This allows the injured person to respond

rapidly to the stimuli.rapidly to the stimuli. The PSTT has multiple synapses with The PSTT has multiple synapses with

other areas of the central brain other areas of the central brain responsible for poorly localized, dull, responsible for poorly localized, dull, aching pain as well as for the behavioral, aching pain as well as for the behavioral, emotional, and affective aspects of pain.emotional, and affective aspects of pain.

The brains limbic system aids in integrating The brains limbic system aids in integrating higher brain function with motivational and higher brain function with motivational and emotional reactions.emotional reactions. Contains afferent nerves from the hypothalamus and Contains afferent nerves from the hypothalamus and

the brain stem.the brain stem. Receives descending influence from the cortex.Receives descending influence from the cortex. This communication is responsible for the emotional This communication is responsible for the emotional

response to painful experiences.response to painful experiences. When an injury occurs, the neural When an injury occurs, the neural

communication between the limbic system, communication between the limbic system, thalamus, RF, and cortex produces reactions thalamus, RF, and cortex produces reactions such as such as fearfear, , anxietyanxiety, or , or cryingcrying..

In short , the limbic system is responsible for the In short , the limbic system is responsible for the body’s affective qualities of reward, punishment, body’s affective qualities of reward, punishment, aversive drives, and fear reactions to painaversive drives, and fear reactions to pain

AKA: motivational-affective system.AKA: motivational-affective system.

The integration of the cortex is an important component The integration of the cortex is an important component in both the ascending and descending aspects of pain in both the ascending and descending aspects of pain modulation.modulation.

Via axons, ascending pain stimuli are transmitted from Via axons, ascending pain stimuli are transmitted from the thalamus to the central sulcus in the parietal lobe the thalamus to the central sulcus in the parietal lobe (somatosensory cortex), where the pain is discriminated (somatosensory cortex), where the pain is discriminated and localized.and localized.

Because of the proliferation of nerve cells and the Because of the proliferation of nerve cells and the cortex’s functionscortex’s functions

ConsciousnessConsciousness SpeechSpeech Hearing Hearing MemoryMemory ThoughtThought

It is unlikely that the afferent synapses that occur during It is unlikely that the afferent synapses that occur during noxious stimulation affect only one efferent neuron.noxious stimulation affect only one efferent neuron.

Thus, many areas of the cortex can be stimulated during Thus, many areas of the cortex can be stimulated during a painful experience.a painful experience.

Descending PathwaysDescending Pathways The descending pain modulation mechanisms The descending pain modulation mechanisms

could influence both the input and the mediation could influence both the input and the mediation of the noxious stimuliof the noxious stimuli

One of the descending mechanisms originates in One of the descending mechanisms originates in the cortex’s corticospinal tract.the cortex’s corticospinal tract. The corticospinal tract descends from the cortex to The corticospinal tract descends from the cortex to

the medulla, where fibers cross over to the opposite the medulla, where fibers cross over to the opposite side of the medulla and to lower levels of the spinal side of the medulla and to lower levels of the spinal cord, where it terminates in laminae I-VII and cord, where it terminates in laminae I-VII and transends through the dorsolateral funiculus (large transends through the dorsolateral funiculus (large fiber tract)fiber tract)

This tract could act to exert postsynaptic (descending) This tract could act to exert postsynaptic (descending) control over the afferent transmission of thermal, control over the afferent transmission of thermal, mechanical, and C fiber input at laminae I & IImechanical, and C fiber input at laminae I & II

A second structure exerting descending control A second structure exerting descending control of noxious stimuli is the PAGof noxious stimuli is the PAG PAG receives input from the cortex, limbic system, PAG receives input from the cortex, limbic system,

hypothalamus, and PSTT.hypothalamus, and PSTT. The hypothalamus sends The hypothalamus sends ßß-endorphins via -endorphins via

neurons to the PAGneurons to the PAG Here they are routed to the nucleusmagnocellularies Here they are routed to the nucleusmagnocellularies

of the rostral medulla that descends laterally to the of the rostral medulla that descends laterally to the dorsal horn.dorsal horn.

Another descending control system arises form Another descending control system arises form the nucleus raphae magnus in the upper the nucleus raphae magnus in the upper medullamedulla Descending axons from this region of the brain track Descending axons from this region of the brain track

down to the lower medulla and the spinal cord, where down to the lower medulla and the spinal cord, where they release serotonin at their terminal end, producing they release serotonin at their terminal end, producing analgesia at laminae I, II, and V.analgesia at laminae I, II, and V.

The notion of central control and descending The notion of central control and descending inhibition of pain is based on the body’s ability to inhibition of pain is based on the body’s ability to use and produce various forms of endogenous use and produce various forms of endogenous opiates.opiates. Each having a distinct function and a specific receptor Each having a distinct function and a specific receptor

affinity.affinity. The enkephalins are found throughout the The enkephalins are found throughout the

central nervous system, but particularly in the central nervous system, but particularly in the dorsal horn.dorsal horn.

Thus, the aggregation of noxious stimuli may Thus, the aggregation of noxious stimuli may cause both presynaptic and postsynaptic control cause both presynaptic and postsynaptic control of nociception in the dorsal horn via enkephalin of nociception in the dorsal horn via enkephalin releaserelease

Dynorphins are primarily located in laminae I & Dynorphins are primarily located in laminae I & 5, making it feasible for them to inhibit pain.5, making it feasible for them to inhibit pain. Levels of dynorphin Levels of dynorphin ↑ in laminae I & 5 during ↑ in laminae I & 5 during

periods of hyperstimulation.periods of hyperstimulation. However, their rapid degradation limits their However, their rapid degradation limits their

role in long-term pain reduction.role in long-term pain reduction. During periods of intense noxious input, During periods of intense noxious input, ßß--

endorphins are released and provide temporary endorphins are released and provide temporary inhibition to noxious stimulation.inhibition to noxious stimulation.

This concept is based on their location in the This concept is based on their location in the PAG and the idea that their release would block PAG and the idea that their release would block interneuron interaction.interneuron interaction.

Review of the process of Pain Review of the process of Pain TransmissionTransmission

Much decision making in the tx of pain can Much decision making in the tx of pain can be based on the understanding of the be based on the understanding of the physiological and chemical interaction that physiological and chemical interaction that occurs after trauma.occurs after trauma.

In simple terms, pain transmission In simple terms, pain transmission appears to be fairly straightforward.appears to be fairly straightforward. The acute pain response is initiated when The acute pain response is initiated when

substances are released form injured tissues, substances are released form injured tissues, causing a noxious stimulus to be transmitted causing a noxious stimulus to be transmitted via A-delta and C fiber to the dorsal hornvia A-delta and C fiber to the dorsal horn

Once in the dorsal horn, the stimulus is Once in the dorsal horn, the stimulus is transmitted to the higher brain centers via the transmitted to the higher brain centers via the STT, which bifurcates into 2 tracts.STT, which bifurcates into 2 tracts. The impulse is propagated via the NSTT to the The impulse is propagated via the NSTT to the

thalamus and then to the cortex, where discrimination thalamus and then to the cortex, where discrimination and location of the stimulus are assessed.and location of the stimulus are assessed.

At the same time, noxious stimulation is projected At the same time, noxious stimulation is projected upward toward the RF, the PAG matter, the upward toward the RF, the PAG matter, the hypothalamus, and the thalamus via the PSTThypothalamus, and the thalamus via the PSTT

Neurons in the thalamus send axon projections to the Neurons in the thalamus send axon projections to the limbic system and the cortex.limbic system and the cortex.

Once the noxious stimuli have reached the higher Once the noxious stimuli have reached the higher centers of the brain, the descending control centers of the brain, the descending control mechanisms are activated, the incoming noxious mechanisms are activated, the incoming noxious stimuli can be inhibited at various levels, and stimuli can be inhibited at various levels, and endogenous opiates can be released. endogenous opiates can be released.

Pain Theory: Historical Pain Theory: Historical PerspectivesPerspectives

Theories regarding the cause, nature, and Theories regarding the cause, nature, and purpose of pain have been debated since purpose of pain have been debated since the dawn of humankind.the dawn of humankind.

Most early theories were based on the Most early theories were based on the assumptions that pain was related to a assumptions that pain was related to a form of punishment.form of punishment.

The word “pain” is derived from the Latin The word “pain” is derived from the Latin word “poena” meaning fine, penalty, or word “poena” meaning fine, penalty, or punishment.punishment.

The ancient Greek believed that pain was The ancient Greek believed that pain was associated with pleasure because the associated with pleasure because the relief of pain was both pleasurable and relief of pain was both pleasurable and emotional.emotional.

Aristotle reassessed the theory of pain and Aristotle reassessed the theory of pain and declared that the soul was the center of declared that the soul was the center of the sensory processes and that the pain the sensory processes and that the pain system was located in the heartsystem was located in the heart

The Romans, coming closer to contemporary The Romans, coming closer to contemporary thought, viewed pain as something that thought, viewed pain as something that accompanied inflammation.accompanied inflammation.

In the 2In the 2ndnd century, Galen offered the Romans his century, Galen offered the Romans his works on the concepts of the nervous system.works on the concepts of the nervous system. However, the views of Aristotle weathered the winds However, the views of Aristotle weathered the winds

of time.of time. In the 4In the 4thth century, successors of Aristotle century, successors of Aristotle

discovered anatomic proof that the brain was discovered anatomic proof that the brain was connected to nervous systemconnected to nervous system Despite this, Aristotle’s belief prevailed until the 19Despite this, Aristotle’s belief prevailed until the 19thth

century, when German scientist provided irrefutable century, when German scientist provided irrefutable evidence that the brain is involved with sensory and evidence that the brain is involved with sensory and motor functionmotor function

Specificity Theory of Pain Specificity Theory of Pain ModulationModulation

Modern concepts of pain theory continue Modern concepts of pain theory continue to advance from the ideas of Aristotle.to advance from the ideas of Aristotle. However, controversy still exists as to which However, controversy still exists as to which

theories are correct.theories are correct. The theories accepted at the turn of the The theories accepted at the turn of the

century were the specificity theory and the century were the specificity theory and the pattern theory, two completely different pattern theory, two completely different and seemingly contradictory viewsand seemingly contradictory views

The specificity theory suggests that there is a The specificity theory suggests that there is a direct pathway from peripheral pain receptors to direct pathway from peripheral pain receptors to the brain.the brain. The pain receptors are located in the skin and are The pain receptors are located in the skin and are

purported to carry pain impulses via a continuous purported to carry pain impulses via a continuous fiber directly to the brain’s pain centerfiber directly to the brain’s pain center

The pathway includes the peripheral nerves, the The pathway includes the peripheral nerves, the lateral STT in the spinal cord and the hypothalamus lateral STT in the spinal cord and the hypothalamus (the brain’s pain center)(the brain’s pain center)

This theory was examined and refuted using clinical, This theory was examined and refuted using clinical, psychological, and physiological evidence by Melzack psychological, and physiological evidence by Melzack and Wall in 1965.and Wall in 1965.

• They discussed clinical evidence describing pain sensations They discussed clinical evidence describing pain sensations in severe burn patients, amputee patients, and patients with in severe burn patients, amputee patients, and patients with degenerative nerve disease.degenerative nerve disease.

These syndromes do not occur in a fixed, direct These syndromes do not occur in a fixed, direct linear systemlinear system

Rather in the quality and quantity of the Rather in the quality and quantity of the perceived pain are directly related to a perceived pain are directly related to a psychological variable and sensory input.psychological variable and sensory input.

This theory had been previously addressed by This theory had been previously addressed by Pavlov, who inflicted dogs with a painful Pavlov, who inflicted dogs with a painful stimulus, then immediately gave them food.stimulus, then immediately gave them food.

The dogs eventually responded to the stimulus The dogs eventually responded to the stimulus as a signal for food and showed no responses to as a signal for food and showed no responses to the painthe pain

The psychological aspect of pain perception was later The psychological aspect of pain perception was later addressed by Beecher, who studied 215 soldiers addressed by Beecher, who studied 215 soldiers seriously wounded in the Battle of Anzio, finding that only seriously wounded in the Battle of Anzio, finding that only 27% requested pain-relieving medication (Morphine).27% requested pain-relieving medication (Morphine).

When the soldiers were asked if they were experiencing When the soldiers were asked if they were experiencing pain, almost 60% indicated that they suffered no pain or pain, almost 60% indicated that they suffered no pain or only slight pain, and only 24% rated the pain as bad.only slight pain, and only 24% rated the pain as bad.

This was most surprising because 48% of the soldiers This was most surprising because 48% of the soldiers had received penetrating abdominal wounds.had received penetrating abdominal wounds.

Beecher also noted that none of the men were suffering Beecher also noted that none of the men were suffering from shock or were insensitive to pain because inept from shock or were insensitive to pain because inept intravenous insertions resulted in complaints of acute intravenous insertions resulted in complaints of acute pain.pain.

The conclusion was drawn that the pain experienced by The conclusion was drawn that the pain experienced by these men was blocked by emotional factors.these men was blocked by emotional factors.

The physical injuries that these men had received was The physical injuries that these men had received was an escape from the life-threatening environment of battle an escape from the life-threatening environment of battle to the safety of a hospital, or even release form the war.to the safety of a hospital, or even release form the war.

This relationship suggests that it is possible for the This relationship suggests that it is possible for the central nervous system to intervene between the central nervous system to intervene between the stimulus and the sensation in the presence of certain stimulus and the sensation in the presence of certain psychological variables.psychological variables.

No physiological evidence has been found to suggest No physiological evidence has been found to suggest that certain nerve cells are more important for pain that certain nerve cells are more important for pain perception and response than others; therefore, the perception and response than others; therefore, the specificity theory can be discounted.specificity theory can be discounted.

Contemporary Pain Control Contemporary Pain Control TheoriesTheories

Although both the specificity and pattern theories Although both the specificity and pattern theories of pain transmission were eventually refuted, of pain transmission were eventually refuted, they did provide some lasting principles that are they did provide some lasting principles that are still present in contemporary pain modulation still present in contemporary pain modulation theoriestheories The strengths of these 2 theories, plus findings The strengths of these 2 theories, plus findings

obtained through additional research, were factored obtained through additional research, were factored together to for the basis of the current perspective together to for the basis of the current perspective regarding pain transmission and pain modulation.regarding pain transmission and pain modulation.

Still, there is much to be learned and studied Still, there is much to be learned and studied before the exact mechanisms of pain before the exact mechanisms of pain transmission and perception are understood.transmission and perception are understood.

Next timeNext time Gate control theoryGate control theory Levels Theory of pain controlLevels Theory of pain control Assessment of painAssessment of pain

Visual analogue scaleVisual analogue scale McGill pain questionaireMcGill pain questionaire Submaximal effort tourniquet testSubmaximal effort tourniquet test

Placebo effectPlacebo effect Referred painReferred pain Chronic PainChronic Pain Pain management techniquesPain management techniques Chapter 3: Development and delivery of Chapter 3: Development and delivery of

treatment protocoltreatment protocol

Pattern Theory of PainPattern Theory of Pain

States that there are no specialized States that there are no specialized receptors in the skin.receptors in the skin.

Rather, a single “generic” nerve responds Rather, a single “generic” nerve responds differently to each type of sensation by differently to each type of sensation by creating a uniquely coded impulse formed creating a uniquely coded impulse formed by a spatiotemporal pattern involving the by a spatiotemporal pattern involving the frequency and pattern of nerve frequency and pattern of nerve transmission.transmission.

An analysis of the word’s elements An analysis of the word’s elements ““Spatio”- the distance between the nerves implusesSpatio”- the distance between the nerves impluses ““temporal”- the frequency of the transmissiontemporal”- the frequency of the transmission

An example of this type of coding can be found An example of this type of coding can be found with most institutional phone systems.with most institutional phone systems. A call from inside a university has a different ring from A call from inside a university has a different ring from

an outside call.an outside call. Although this theory was closer to being Although this theory was closer to being

neurological correct there were still neurological correct there were still shortcomingsshortcomings

Melzack and Wall refuted this theory as well, Melzack and Wall refuted this theory as well, based on the physical evidence of physiological based on the physical evidence of physiological specialization of receptor-fiber units.specialization of receptor-fiber units. Plus this theory failed to account for the brains role in Plus this theory failed to account for the brains role in

pain perception.pain perception.

Gate Control TheoryGate Control Theory

Implies a non-painful stimulus can block the Implies a non-painful stimulus can block the transmission of a noxious stimulus.transmission of a noxious stimulus.

Is based on the premise that the SG, located in Is based on the premise that the SG, located in the dorsal horn of the spinal cord, modulates the the dorsal horn of the spinal cord, modulates the afferent nerve impulses.afferent nerve impulses.

This then influences the first central transmission This then influences the first central transmission (T) cells, which corresponds with the NSTT or (T) cells, which corresponds with the NSTT or the PSTT and activate a central control the PSTT and activate a central control triggering the mechanisms responsible for the triggering the mechanisms responsible for the response and perception of pain.response and perception of pain.

The SG acts as a modulating gate or a control system The SG acts as a modulating gate or a control system between the peripheral nerve fibers and central cells that between the peripheral nerve fibers and central cells that permits only one type of never impulse (pain or no pain) permits only one type of never impulse (pain or no pain) to pass through.to pass through.

Serving in a capacity similar to that of a “switch operator” Serving in a capacity similar to that of a “switch operator” in a railroad yard, the SG monitors the amount of activity in a railroad yard, the SG monitors the amount of activity occuring on both incoming tracts in a convergent systemoccuring on both incoming tracts in a convergent system

Opening and closing the gate to allow the appropriate Opening and closing the gate to allow the appropriate information to be passed along to the T cell.information to be passed along to the T cell.

Impulses traveling on the fast, nonpain fibers Impulses traveling on the fast, nonpain fibers ↑ activity ↑ activity in the SG.in the SG.

Impulses on the slower pain fibers exert an Impulses on the slower pain fibers exert an inhibitory influence.inhibitory influence.

When the SG is active, the gate is in its “closed” When the SG is active, the gate is in its “closed” position and a nonpainful stimulus is allowed to position and a nonpainful stimulus is allowed to pass on to the T cell.pass on to the T cell.

Example:Example: Bumping the headBumping the head

• The initial trauma activates the A-delta and, The initial trauma activates the A-delta and, eventually, C fiberseventually, C fibers

• Rubbing the traumatized area stimulates the A-Rubbing the traumatized area stimulates the A-beta fibers, which activate the SG to close the beta fibers, which activate the SG to close the spinal gatespinal gate

• Thus inhibiting transmission of the painful stimulusThus inhibiting transmission of the painful stimulus

Assessment of pain Assessment of pain Visual analogue scaleVisual analogue scale

PicturePicture McGill pain questionnaireMcGill pain questionnaire

Part I: is used to localize the pain and identify whether the Part I: is used to localize the pain and identify whether the perceived source of the pain is superficial (external), internal, or perceived source of the pain is superficial (external), internal, or both.both.

Part II: incorporates the VAS that was described in the visual Part II: incorporates the VAS that was described in the visual analogue scale.analogue scale.

Part III: is the pain rating index, a collection of 76 words grouped Part III: is the pain rating index, a collection of 76 words grouped into 20 categories. Patients are to underline or circle the words into 20 categories. Patients are to underline or circle the words in each group that describes the sensation of pain being in each group that describes the sensation of pain being experienced.experienced.

• Groups 1-10= somatic in natureGroups 1-10= somatic in nature• Groups 11-15= affective Groups 11-15= affective • Group 16= evaluativeGroup 16= evaluative• Group 17-20= miscellaneous words that are used on in the scoring Group 17-20= miscellaneous words that are used on in the scoring

process. process.

ScoringScoring

Add up the total number of words chosen, up to Add up the total number of words chosen, up to the maximum of 20 words (one for each the maximum of 20 words (one for each category)category) The level of intensity of pain is determined by the The level of intensity of pain is determined by the

value assigned to each word.value assigned to each word.• 11stst word = 1 point word = 1 point• 22ndnd word = 2 point word = 2 point • And so onAnd so on

Pt could have a high score of 20, but have a low-Pt could have a high score of 20, but have a low-intensity score by selecting the 1intensity score by selecting the 1stst word in each word in each category.category.

Submaximal Effort Tourniquet TestSubmaximal Effort Tourniquet Test

In 1966, Smith et al described a method of matching a In 1966, Smith et al described a method of matching a patients pain using a SETT.patients pain using a SETT.

The SETT is performed by inflating a BP cuff to above The SETT is performed by inflating a BP cuff to above systolic pressure on the pt elevated arm.systolic pressure on the pt elevated arm.

Once the cuff is inflated, the pt is instructed to open and Once the cuff is inflated, the pt is instructed to open and close the hand or fist rhythmically.close the hand or fist rhythmically.

A handgrip dynamometer and a metronome can be used for A handgrip dynamometer and a metronome can be used for standardization.standardization.

The pt should continue opening and closing the hand or The pt should continue opening and closing the hand or fist until the cramping sensation that he or she feels fist until the cramping sensation that he or she feels “matches” the pain from the “original” pathology.“matches” the pain from the “original” pathology.

The amount of time that elapses form onset to fruition of The amount of time that elapses form onset to fruition of matched pain is the recorded objective measure.matched pain is the recorded objective measure.

The SETT can be repeated at every tx session to gauge The SETT can be repeated at every tx session to gauge tx progress and is effective in matching all types of paintx progress and is effective in matching all types of pain

Placebo EffectPlacebo Effect Placebo stems from the Latin word for “I Placebo stems from the Latin word for “I

shall please”shall please” Used to describe pain reduction obtained from Used to describe pain reduction obtained from

a mechanism other than those related to the a mechanism other than those related to the physiological effects of the tx.physiological effects of the tx.

Linked to psychological mechanismsLinked to psychological mechanisms All TM have some degree of placebo All TM have some degree of placebo

effecteffect Most studies involving TM involving the use of Most studies involving TM involving the use of

a sham TM (ultrasound set at the intensity of a sham TM (ultrasound set at the intensity of 0) and an actual treatment have shown 0) and an actual treatment have shown ↓ ↓ levels of pain in each group.levels of pain in each group.

Referred painReferred pain

Chronic PainChronic Pain

Characteristics ofCharacteristics of Symptoms last longer than 6 monthsSymptoms last longer than 6 months Few objective medical findingsFew objective medical findings Medication abuseMedication abuse Difficulty sleepingDifficulty sleeping DepressionDepression Manipulative behaviorManipulative behavior Somatic preoccupationSomatic preoccupation

Pain Management TechniquesPain Management Techniques

Physical measuresPhysical measures

Behavioral and cognitive measuresBehavioral and cognitive measures

On to Chapter 3On to Chapter 3

Development and Delivery of Development and Delivery of Treatment ProtocolTreatment Protocol