12/08/2025
THE PHYSIOLOGY OF PAIN BY DR. BRIGHT MWANSA
We all go through and perceive pain but do you know how it occur! Follow through Dr. Bright Mwansa here on medical talks
1. Definition
Pain is an unpleasant sensory and emotional experience associated with actual or potential tissue damage.
It serves as a protective mechanism — warning the body about harmful stimuli.
2. Types of Pain
Nociceptive pain – from activation of pain receptors (nociceptors) by harmful stimuli.
Somatic pain: from skin, muscles, bones, joints (sharp, localized).
Visceral pain: from internal organs (dull, poorly localized).
Neuropathic pain – from nerve damage (burning, shooting).
Psychogenic pain – influenced by psychological factors.
3. Physiological Pathway
Pain transmission involves four main processes:
A. Transduction
What happens: Nociceptors in skin, muscle, joints, or viscera convert noxious stimuli (mechanical, thermal, or chemical) into electrical impulses.
Mediators involved: Bradykinin, prostaglandins, histamine, serotonin, substance P, hydrogen ions (H⁺), potassium (K⁺).
Nerve fibers involved:
A-delta fibers – myelinated, fast, sharp pain.
C fibers – unmyelinated, slow, dull, burning pain.
B. Transmission
Pathway:
1. Peripheral nerve → dorsal root ganglion → dorsal horn of spinal cord.
2. Synapse in dorsal horn: Neurotransmitters like glutamate & substance P are released.
3. Ascend via:
Spinothalamic tract → thalamus → somatosensory cortex (localization & intensity).
Spinoreticular tract → reticular formation (arousal & emotional aspects).
Key relay points: Spinal cord → brainstem → thalamus → cortex.
C. Perception
What happens: Brain becomes aware of pain.
Structures involved: Thalamus, somatosensory cortex, limbic system.
Influenced by mood, attention, past experience, and cultural factors.
D. Modulation
What happens: Pain signal can be amplified or suppressed.
Descending inhibitory pathways from the brainstem release:
Endogenous opioids (endorphins, enkephalins, dynorphins)
Monoamines (serotonin, norepinephrine)
These act on opioid receptors in the dorsal horn to inhibit neurotransmitter release.
4. Gate Control Theory of Pain
Proposed by Melzack & Wall.
Pain transmission is “gated” at the spinal cord level.
Non-painful input (e.g., rubbing the skin) activates A-beta fibers, which inhibit pain transmission from C fibers.
Explains why rubbing a bumped area can reduce pain
5. Key Neurotransmitters
Excitatory (increase pain): Glutamate, Substance P, Calcitonin Gene-Related Peptide (CGRP).
Inhibitory (reduce pain): Endorphins, enkephalins, serotonin, norepinephrine, GABA.
6. Clinical Relevance
NSAIDs: Block prostaglandin synthesis → reduce transduction.
Local anesthetics: Block sodium channels → stop transmission.
Opioids: Activate descending inhibitory pathways → suppress pain perception.
Antidepressants (SNRIs, TCAs): Enhance serotonin & norepinephrine in descending pathways.
Follow https://youtube.com/?si=ldsztzGG6DQSxpSo to watch the videos.
@ DR. BRIGHT MWANSA
