Purpose

• Protective?
• Perception happens after reflex withdrawal from stimulus
• Learning experience
• Healing and recovery?

Pain

• Conscious experience arising from integrated activity in multiple sensory and emotional centres in the brain
• Not just a sensation
• Multidimensional
• Lack a physiology of consciousness

Nociception

• Neural process of encoding noxious stimuli
• Involved transduction, transmission and modulation of neural signals from periphery to CNS
• Does not require consciousness

Nociceptor

• Neuron that responds specifically to noxious stimuli: mechanical, thermal, chemical
• A$\delta$ and C-fibres
• A-B-C: decreasing myelination (decreasing transmission speed)
• $\alpha$-$\beta$-$\gamma$-$\delta$: decreasing axon diameter (Decreasing transmission speed)
• Unmyelinated small diameter nerve endings in skin sense tissue damage
• Nociceptors enter the superficial dorsal horn

Neural morphology

• Nociceptors are pseudounipolar neurones
• Dendrites terminate in spinal chord
• Synaptic terminals projects to skin or other organs/tissues

Segmental spinal sensory nerves

• Trigeminal ganglion (brain)
• Dorsal root ganglion (spine)
• Peripheral nociceptor (body)

Pain pathways

• Spatial information relays via thalamus to S1 (where pain is and the intensity)
  
• Homunculus - brain surface map
• Affective component to limbic cortex: unpleasant, concerning, arousing