JD - Pain

Question 1

What are the main functions of pain? (3)

Answer 1

Respond to harmful stimuli and adapt behavior.

• Withdrawal reflex to avoid further damage.
• Immobilization to promote wound healing.
• Affective responses to influence future behavior (avoid similar situations)

Question 2

How can pain be categorized based on duration?

Answer 2

• Acute pain: Short-term response to a specific injury.
• Chronic pain: Long-lasting pain that persists even after healing (e.g., arthritis, phantom limb pain)

Question 3

What is neuropathic pain, and how does it differ from other types of pain?

Answer 3

Chronic pain arising from nerve damage (central or peripheral nervous system)

• Not protective, originates from within the nervous system.

Examples: Post-herpetic neuralgia (shingles), diabetic neuropathy

Question 4

What are the main analgesics for neuropathic pain?

Answer 4

NSAIDs and Opioids (morphine-like analgesics)

Question 5

How does pain perception differ from nociception?

Answer 5

• Nociception: The physiological process of detecting a harmful stimulus and tissue damage.
• Pain: The subjective experience of pain, influenced by emotional and psychological factors.

Question 6

What are the main types of nociceptive fibers?

Answer 6

• A-delta fibers: Myelinated, large diameter, transmit fast, sharp pain (first pain).
• C-fibers: Unmyelinated, small diameter, transmit slow, burning pain (second pain)

Question 7

Briefly describe the two main pain pathways in the spinal cord

Answer 7

Spinothalamic tract → discriminative/recognition/where/type (neospinothalamic)

Spinoreticulothalamic tract→ (limbic) affective-motivational aspect (paleospinothalamic)

Question 8

What is hyperalgesia, and how does it develop?

Answer 8

Increased sensitivity to pain, where a weaker stimulus can produce a more intense pain response

• Caused by various chemicals released from damaged tissues, sensitizing nerve terminals.

Question 9

How can pain signals be modulated at the periphery?

Answer 9

Peripheral sensitization: Chemicals released from damaged tissues increase excitability of nociceptors (e.g., 5-HT, bradykinin, prostaglandins)

Question 10

What is SP, CGRP and NGF?

Answer 10

SP = neuropeptide, Tachykinin. Preprotachykinin
CGRP = neuropeptide (37AA). Calcitonin family
Produced in the DRG

NGF = neurotrophin, axonal growth during development & nociception pathway

• Regulation of gene expression (eg. Substance P and CGRP)
• NGF is released following tissue damage
• NGF acts on the C-fibre to increased synthesis of SubP and CGRP

Question 11

How can pain signals be modulated at the spinal cord level?

Answer 11

Descending inhibitory pathways from the brainstem can suppress pain transmission in the dorsal horn

• Opioid drugs act at this level to inhibit pain signals

Question 12

How do nociceptors detect different stimuli?

Answer 12

Nociceptors express various receptors for different stimuli, including:

• Ionotropic receptors (direct ion channel activation)
• Metabotropic receptors (indirect signaling pathways)
• Voltage-gated ion channels

Question 13

Give 2 examples of chemicals that activate nociceptors

Answer 13

Bradykinin acts to increase sensitivity
BK2 → PLC → removes PIP2 →

• Increased VR1 activity

Prosaglandins
EP → PKA → Lowers VGSC threshold so increases sensitivity