The Neurophysiology of Pain and Pain Modulation: Modern Pain Neuroscience for Musculoskeletal Physiotherapists 1

INTRODUCTION

NEUROPHYSIOLOGY

• UNDERSTANDING HOW THE BRAIN CONTROLS BODY MOVEMENTS.

• HOW NEUROMUSCULAR CONTROL CAN BECOME POTENTIAL PART OF TREATMENT IN PATIENTS.

THE NEUROPHYSIOLOGY OF MUSCULOSKELETAL PAIN: FROM TISSUE NOCICEPTION TO THE PAIN NEUROMATRIX

TISSUE

• HOLD THE CAPACITY TO ALERT NERVOUS SYSTEM OF POTENTIAL DANGER, HENCE TO PRODUCE ACTION.

NOCICEPTORS

• CONNECTED TO AN ION CHANNEL

• TWO TYPES OF NERVES : A AND C FIBERS (PRIMARY SENSORY NERVE FIBERS)

  • A FIBERS

    • FAST PAIN TRANSMITTED FROM TISSUE TO CNS.

    • SMALL MYELINATED NERVE FIBERS

    • HIGH CONDUCTION SPEED

    • SHARP & LOCALIZED

  • C FIBERS

    • SLOW PAIN TRANSMITTED FROM TISSUE TO CNS.

    • DULLER AND MORE DIFFUSE

    • LASTS MUCH LONGER

    • SMALL UNMYELINATED NERVE FIBERS

    • LOW CONDUCTION SPEED.

ION CHANNEL

• OPENS ONCE THE NOCICEPTOR IS ACTIVATED BY A STIMULUS.

SENSORY INFORMATION

• ENTERS THE CENTRAL NERVOUS SYSTEM IN SPINAL CORD

PAIN MATRIX

• WILL DECIDE WHETER OR NOT THE SIGNAL SHOULD BE INTERPRETED AS THREATENING TO THE BODY HOMEOSTASIS OR NOT.

TEMPORAL SUMMATION AND WIND UP

WIND UP

• PROGRESSIVE INCREASE OF ELECTRICAL DISCHARGES FROM THE SECOND-ORDER NEURON IN THE SPINAL CORD IN RESPONSE TO REPETITIVE C-FIBRE STIMULATION.

• CENTRAL SENSITIZATION.

BOX 2-1

The Nervous System as Source of Nociception and Pain: Neuropathic Pain Highlights for Clinicians

MUSCULOSKELETAL SYSTEM

• CAN GENERATE NOCICEPTION.

NERVOUS SYSTEM

• CAN BE A SOURCE OF NOCICEPTION

NEUROPATHIC PAIN

• PAIN ARISING AS A DIRECT CONSEQUENCE OF A LESION OR DISEASE AFFECTING THE SOMATOSENSORY SYSTEM.

• CAN BE: PERIPHERAL OR CENTRAL

LESION

• AVAILABLE EVIDENCE FROM DIAGNOSTIC INVESTIGATIONS TO REVEAL ABNORMALITY OF THE NERVOUS SYSTEM.

• MAY REFER TO POSTTRAUMATIC OR POSTSURGICAL DAMAGE TO THE NERVOUS SYSTEM.

DISEASE

• UNDERLYING CAUSE OF THE LESION

SOMATOSENSORY

• INFORMATION ABOUT THE BODY PER SE INCLUDING VISCERAL ORGANS, RATHER THAN INFORMATION ABOUT EXTERNAL WORLD.

PATIENT WITH NEUROPATHIC PAIN EXPERIENCE

• BURNING

• SHOOTING

• PRICKING

SENSORY TESTING

• PRIME IMPORTANCE FOR DIAGNOSIS OF NEUROPATHIC PAIN

• INCLUDES TESTING OF THE FUNCTION OF SENSORY FIBERS.

  • TUNING FORK

    • VIBRATION

  • SOFT BRUSH

    • TOUCH

  • TEMPERATURE

    • COLD/WARM

SUGGESTIONS FOR NEUROPATHIC PAIN.

• HYPERAESTHESIA

• HYPOAESTHESIA

• HYPERAGLESIA

• HYPOALGESIA

• ALLODYNIA

• PARAESTHESIA

• DYSAESTHESIA

• AFTERSENSATIONS

DESCENDING NOCICEPTIVE FACILITATION

CATASTROPHIZING

• AVOIDANCE BEHAVIOR

• FACTORS TO PREVENT EFFECTIVE DESCENDING INHIBITION

• ACTIVATE DESCENDING FACILITATION

BOX 2-2

Translating the Neurophysiology of Temporal Summation and Wind-Up to Clinical Practice

HANDS ON TECHNIQUES

• MUSCULOSKELETAL THERAPISTS CAN APPLY

• DELIVER IDENTICAL NOCICEPTIVE STIMULI TO THE SKIN

• ONCE EVERY 3 SECONDS CAN ABLE TO TRIGGER PAIN AMPLIFICATION.

MYOFASCIAL TRIGGER POINTS

• DIFFERS FROM NORMAL MUSCLE TISSUE BY ITS LOWER PH LEVELS

3 MONTHS

• TISSUE INJURY HEALING

• FOCAL PAIN RECOVERY

CHRONIC WIDESPREAD PAIN

• INJURIES TO DEEP TISSUES WHICH DO NOT HEAL WITHIN SEVERAL MONTHS.

DESCENDING NOCICEPTIVE INHIBITION

DESCENDING INHIBITORY PATHWAYS

• APPLY NEUROTRANSMITTERS

• SUCH AS: SEROTONIN AND NORADRENALINE

• FUNCTION IS TO FOCUS/TARGET THE EXCITATORY STATE OF DORSAL HORN NEURONS

• SUPRESSING SURROUNDING NEURONAL ACTIVITY

EXERCISE-INDUCED ENDOGENOUS ANALGESIA

• EXERCISE IS A PHYSICAL STRESSOR THAT ACTIVATES DESCENDING NOCICEPTIVE INHIBITION.

CHRONIC LOW BACK PAIN

• HAVE NORMAL ENDOGENOUS ANALGESIC RESPONSE TO EXERCISE

MANUAL JOINT MOBILIZATION

• HAVE BEEN SHOWN TO ACTIVATE DESCENDING NOCICEPTIVE INHIBITION.

PAIN NEUROMATRIX OR PAIN MATRIX

• BRAIN CO-WORK OR COMMUNICATE WHEN THERE IS A PAIN.

THE PAIN NEUROMATRIX

BRAIN

• CAN PRODUCE PAIN WITHOUT NOCICEPTION AND VICE VERSA.

CIRCUITRY

• A NUMBER OF REGIONS THAT BECOME ACTIVE ALL TOGETHER WHEN A PERSON IS IN PAIN.

PRIMARY SOMATOSENSORY CORTEX

• RESPONSIBLE FOR IDENTIFYING THE LOCATION OF PAIN IN THE BODY

• THE MORE ATTENTION, MORE ACTIVITY OBSERVED

AMYGDALA

• FEAR-MEMORY CENTRE OF THE BRAIN

• KEY ROLE IN NEGATIVE EMOTIONS

• PAIN RELATED MEMORIES

THALAMUS

• SENDING INCOMING MESSAGES TO OTHER BRAIN REGIONS.

• TARGET FOR DEEP BRAIN STIMULATION IN PATIENTS WITH NEUROPATHIC PAIN

BRAINSTEM

• TOP-DOWN PAIN INHIBITION

• KEY REGIONS FOR MAINTAINANCE OF CENTRAL SENSITIZATION PAIN IN HUMANS

BOX 2-3 Long-Term Pain Memories are often Apparent in Patients with Chronic Musculoskeletal Pain

KINESIOPHOBIA

• FEAR OF MOVEMENT

EXTINCTION TRAINING

• RESULTS INCREASED CONNECTIVITY BETWEEN PREFRONTAL CORTEX AND AMYGDALA

PREFRONTAL CORTEX

• INHIBITS THE EXPRESSION OF PAIN MEMORIES

• COMMUNICATES WITH AMYGDALA AND HIPPOCAMPUS

PAIN MEMORIES CIRCUITRY

• PREFRONTAL CORTEX

• AMYGDALA

• HIPPOCAMPUS

ON-CELLS

• PROMOTE NOCICEPTION

OFF-CELLS

• SUPRESS NOCICEPTION

ANTERIOR CINGULATE CORTEX

• IMPORTANT FOR AFFECTIVE-MOTIVATIONAL ASPECTS OF PAIN

• EMPATHY AND SOCIAL EXCLUSION

INSULA

• A BRAIN REGION THAT HAS A ROLE IN THE EMOTIONAL COMPONENT OF EVERY PAIN SENSATION.

• CONTRIBUTES TO SENSORY DISCRIMINATIVE ASPECT OF PAIN

CENTRAL SENSITIZATION

• AUGMENTATION OF RESPONSIVENESS OF CENTRAL PAIN SIGNALLING NEURONS TO INPUT FROM LOW THRESHOLD MECHANORECEPTORS.

PERIPHERAL SENSITIZATION

• LOCAL PHENOMENON

• IMPORTANT FOR PROTECTING DAMAGED TISSUE DURING THE EARLY PHASES POST INJURY.

GAMMA AMINOBUTYRIC ACID (GABA)

• SECOND MECHANISM CONTRIBUTING TO THE OVERACTIVE PAIN NEUROMATRIX.

• IMPORTANT INHIBITORY NEUROTRANSMITTER

• LESS GABA MEANS LONG TERM STRESS

BOX 2-5 Recognition of Central Sensitization Pain in Musculoskeletal Pain Patients

CHRONIC MUSCULOSKELETAL PAIN

• OSTEOARTHRITIS

• LOW BACK PAIN

• FIBROMYALGIA

• RHEUMATOID ARTHRITIS

• WHIPLASH

• PELVIC PAIN

• LATERAL EPICONDYLITIS

DOES THE AUTONOMIC NERVOUS SYSTEM INFLUENCE PAIN?

AUTONOMIC NERVOUS SYSTEM

• HYPOTHALAMUS

• PITUITARY

• ADRENAL

• STRESS RESPONSE SYSTEM

END OF LESSON 1(: