Week 7 Pain

Neurons and Pain Pathways

• Afferent neurons transmit information from peripheral tissues to the spinal cord.
• Aβ fibres are responsible for carrying non-painful stimuli such as touch and vibration, contributing to the sensation of pressure and proprioception.
• Sharp and localized pain is carried by Aδ fibres, which transmit signals rapidly due to their myelination.
• C fibres transmit dull, aching pain and are unmyelinated; they convey slower pain responses from tissues.
• Signals from nociceptors crossover to the contralateral side of the spinal cord at the level of the dorsal horn.

Neuron Functions

• Second-order neurons relay pain signals from the spinal cord to the brain, contributing to the pain perception process.
• Third-order neurons further transmit signals from the thalamus to the sensory cortex, allowing for pain localization and interpretation.
• Changes in ion channels can alter neuronal excitability, affecting pain thresholds and sensitivity.

Sensitization Processes

• Peripheral sensitization refers to an increased sensitivity of nociceptors to stimuli caused by inflammation or injury.
• Central sensitization is a heightened response of neurons in the central nervous system following stimuli.
• Peripheral sensitization impacts nociceptors, while central sensitization affects central pathways.
• Mechanisms explaining central sensitization include wind-up, altered neurotransmitter release, and receptor changes.
• Wind-up or temporal summation occurs when repeated stimuli lead to progressively stronger pain sensations.

Pain Types and Characteristics

• Hyperalgesia is an exaggerated response to a painful stimulus.
• Allodynia is pain due to a stimulus that normally does not provoke pain.
• Wind-up or temporal summation can be assessed through quantitative sensory testing.
• Pain is categorized primarily into nociceptive, neuropathic, and nociplastic.
• The main goal of physiotherapy for patients with pain is to reduce pain and improve functional outcomes.

Nociception and Pain Modulation

• Nociceptors are specialized sensory receptors that respond to potentially damaging stimuli.
• Nociception refers to the sensory process that encodes harmful stimuli, while pain is the subjective experience resulting from nociception.
• The 'spinal gate' mechanism filters pain signals in the spinal cord, influencing pain perception.
• Pain modulation involves both descending pathways from the brain that can enhance or inhibit pain signals.
• Two main types of neurotransmitters involved in pain perception are excitatory (e.g., glutamate) and inhibitory (e.g., GABA).

Pain Classification

• Acute pain is a normal, temporary response to inflammation or tissue injury; chronic pain persists beyond the expected healing time.
• Nociplastic pain arises from altered pain processing without clear nociceptive or neuropathic causes.
• Chronic pain has a duration exceeding three months and impacts daily functioning.
• Neuropathic pain results from nerve damage or dysfunction.

Recognizing and Managing Pain

• Nociceptive pain is characterized by sharp, localized sensations often resulting from injury.
• Nociplastic pain exhibits variable behaviors, often relating to psychological factors.
• Conditions like diabetic neuropathy, post-herpetic neuralgia, and fibromyalgia can cause neuropathic pain.
• Symptoms of diabetic sensory peripheral neuropathy include numbness, tingling, and pain, predominantly affecting the legs and feet.

Specific Conditions

• Diabetic sensory peripheral neuropathy damage is often bilateral and symmetric, primarily affecting distal nerve fibers.
• The main symptom of post-herpetic neuralgia is persistent pain following a shingles infection.
• Complex regional pain syndrome was previously known as reflex sympathetic dystrophy, marked by chronic pain and sympathetic nervous system dysregulation.
• Neuropathic pain can be associated with conditions like multiple sclerosis, phantom limb pain, and shingles.

Psychological Aspects

• The fear avoidance model describes how fear of pain can lead to avoidance of activities, perpetuating chronic pain cycles.
• Psychosocial factors, such as anxiety and depression, can significantly influence pain perception and management outcomes.
• Recognizing nociplastic pain involves assessing the patient's pain history, psychological state, and symptom patterns.

Test your knowledge on the brain's role in pain perception and localization with Davidson's 23rd Ed Building Blocks of Pain quiz. Discover the multiple brain structures responsible for the emotional and attentional aspects of pain and memory formation.