Session 15 - Pain and Nociception

Define nociception

The neural processes of encoding and processing noxious stimuli (danger messages)

What is pain (defined by the International Association for the Study of Pain)?

An unpleasant sensory and emotional experience associated with, or resembling that associated with, actual or potential tissue damage

Define affect

Emotional feeling, tone, or mood attached to a thought elicited by conditions and circumstances of internal and external environments

Define motivation

State of need within us that arouses, maintains, and directs behavior toward a goal

What are nociceptors?

Free nerve endings; come in 2 fiber types: A delta fibers (mechanical and thermal), C fibers (chemical and polymodal)

What neurotransmitter is implicated in the nociceptive processing?

Glutamate - fast potentials in dorsal horn neurons

Neuropeptides (substance P) - elicit slow excitatory postsynaptic potentials in dorsal horn neurons

What neurotransmitter has no reuptake pathway? What does this mean?

Neuropeptides (substance P); they can influence many postsynaptic dorsal horn neurons and have increased levels in chronic pain conditions

What is the only human sense that becomes more sensitive with repeated exposure?

Nociception

What are the two components of the Spinothalamic Tract?

Neospinothalamic component, Paleospinothalamic component

Describe the neospinothalamic component of the Spinothalamic Tract

Uses A-delta fibers, mediates fast pain, temperature, and touch, has a localized discriminative nature (pin prick)

Describe the paleospinothalamic component of the Spinothalamic Tract

Uses C-fibers, mediates slow pain, has a more enduring, aching, intense pain with an affective nature (diffuse)

Where does the first STT synapse occur?

Substantia gelatinosa

Where are Wide, dynamic-range neuron cell bodies found?

Dorsal horn

What do wide, dynamic-range neurons do?

Respond to either nociceptive or non-nociceptive stimuli

What are the methods by which nociceptive signals are modulated?

Sensitization or Inhibition

Describe sensitization

Peripheral (primary hyperalgesia) or Central (secondary hyperalgesia and allodynia) where you have a heightened response to painful stimuli

Define allodynia

A condition where ordinarily painless tactile stimulus is experienced as being painful

Describe the Gate Control Theory

Activation of light touch A-beta fibers then activate inhibitory interneurons (Enhephalin) in the spinal cord that shut OFF the nociceptor fiber transmission

Describe Descending Analgesia

Aerobic exercises will cause activation of the locus coeruleus to release norepinephrine and the raphe nuclei to release serotonin, the neurotransmitters will go to the dorsal horn of the spinal cord and inhibits dorsal horn information from being transmitted

Describe acute pain

Occurs as a result of tissue damage, has a well-defined onset, is protective in nature

Describe chronic pain

Outlasts time expected for tissue healing (usually 3 months), may occur with or without detectable tissue damage, does not serve a protective function

Define Nociceptive Pain

Pain that arises from actual or threatened damage to a non-neural tissue due to activation of nociceptors, pain is localized to the area of injury or dysfunction

Define Neuropathic Pain

Caused by a lesion or disease of the somatosensory nervous system, pain is referred in a dermatomal or cutaneous nerve distribution

Define Nociplastic pain

Pain arises from altered nociception despite no clear evidence of actual or threatened tissue damage; disproportionate, non-mechanical, unpredictable pattern of pain provocation in response to multiple or non-specific aggravating factors

Define peripheral sensitization

Increased sensitivity of receptors and primary afferents to noxious stimuli

Describe central sensitization

An amplification of neural signaling within the CNS that elicits pain hypersensitivity

What are methods of pain management from the periphery?

Touch/massage/grade 1-2 joint mobilization, heat and cold therapy, transcutaneous electrical nerve stimulation (TENS)

List common drugs for pain management

Non-opioid analgesics (aspirin), Tricyclic antidepressants, anticonvulsants, Narcotic (opioid) analgesics (morphine, oxycodone)

Clinical connection: Phantom Limb Pain

Following amputation of a limb surgically or accidentally, or following extensive denervation of a still present limb, pain and paresthesias of the missing limb

Treatment of Phantom Limb Pain

Surgical ablation of nociceptive pathways, hypnosis, rehabilitation (mirror therapy)

Clinical Connection: Thalamic syndrome

Central post stroke pain, intractable as pain generation is above the major centers of pain modulation, severe/burning/spontaneous paroxysmal pain

Clinical Connection: Complex Regional Pain Syndrome

Post traumatic pain is disproportionate to the severity of the injury and accompanied by allodynia and autonomic changes,