Definition
- Pain (IASP) is an unpleasant sensory and emotional experience linked to actual or potential tissue damage.
- A nociceptive stimulus is one capable of damaging tissue; the sensation it evokes is nociception.
Nociceptors and Pain Fibres
- Nociceptors are free nerve endings, present throughout the body except the neural tissue of the brain; the meningeal coverings of the brain do contain nociceptors.
Aδ vs C fibre nociceptors
Feature
Fibre type
- Aδ (mechanical) nociceptors
- Myelinated, 1 to 5 µm diameter
- C fibre (polymodal) nociceptors
- Unmyelinated, 0.3 to 1.2 µm diameter
Conduction velocity
- Aδ (mechanical) nociceptors
- 10 to 30 m/s
- C fibre (polymodal) nociceptors
- 0.5 to 2 m/s
Stimuli
- Aδ (mechanical) nociceptors
- Intense mechanical only
- C fibre (polymodal) nociceptors
- Mechanical, thermal (45°C or higher) and chemical
Pain conveyed
- Aδ (mechanical) nociceptors
- Fast (first) pain
- C fibre (polymodal) nociceptors
- Slow (second) pain
Dorsal horn termination
- Aδ (mechanical) nociceptors
- Laminae I and V
- C fibre (polymodal) nociceptors
- Lamina II