Pain Flashcards
Definition of pain
An unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage
Nociception is:
The neural process of encoding noxious stimuli
What is a nociceptive stimulus?
An actual or potentially tissue damaging event transduced and encoded by nociceptors
What is a nociceptor?
A high-threshold sensory receptor of the peripheral somatosensory nervous system that is capable of transducing and encoding noxious stimuli
Describe the difference between nociception and pain.
Pain is felt, nociception occurs.
We often fear pain but we cannot fear nociception because it is neither seen nor felt.
A painful stimulus triggers pain, a nociceptive stimulus triggers nociceptors.
Pain can only occur in a live animal, nociception can occur in a removed neuron.
What are the three types of pain?
Nociceptive, neuropathic and neuroplastic.
Describe nociceptive pain.
Pain that arises from actual or threatened damage to non-neural tissue and is due to the activation of nociceptors
Describe neuropathic pain.
Pain caused by a lesion or disease of the somatosensory nervous system
Describe neuroplastic pain.
Pain that arises from altered nociception, despite no clear evidence of actual or threatened tissue damage causing the activation of peripheral nociceptors, or evidence for disease or lesion of the somatosensory system causing the pain
What is the gate control theory of pain? What are the limitations of this theory?
Pain is modulated (gated) in the spinal cord. Large fibre signals (A beta) reduce small fibre signals (C).
Doesn’t explain chronic pain or phantom pain. Doesn’t consider tissue inflammation or psychosocial factors.
What are the two processess of neuroplastic pain?
Peripheral (inflammation & nerve injury) and central (receptor changes & plasticity).
What happens during acute inflammation?
influx of inflammatory cells
histamine release –blood vessels release plasma –oedema
nerves can also release inflammatory chemicals
creates inflammatory soup
What does inflammatory soup do?
Creates an acidic environment around the injury site
Increases sensitivity of nociceptors (peripheral sensitisation):
- decrease in threshold for nociceptor activation
- increase in responsiveness at nerve endings
- activation of silent nociceptors
What are the two afferent nociceptor fibre types?
A-delta and C.
Describe A-delta fibres.
specific to: mechanical & thermal stimuli medium diameter fast conduction rate (5-30 m/s) first input to be received small receptive field myelinated
Describe C fibres.
specific to: mechanical, thermal & chemical stimuli unmyelinated small diameter slow conducting rate (0.5-2 m/s) 2nd input to be received large receptive field (non-specific)
may be silent nociceptors waiting for activation during sensitisation.