Pain Pathway/physiology Flashcards
Define acute pain
Pain that occurs with acute tissue damage and subsides after tissue healing.
Define chronic pain
Pain that persists beyond the normal time of healing. Often cited as pain for >3 months.
What are nociceptors?
Free nerve endings of primary sensory (afferent) neurons.
What are the different types of nerve fibre involved in pain?
A-delta = acute pain (rapid, stabbing pain), myelinated
C-fibres = slower (0.5m/sec), higher activation thresholds (i.e. only higher temps elicit a response), non-myelinated. Repeated input from C-fibres contributes to central sensitisation in the dorsal horn.
What are A-beta nerve fibres?
Touch sensation rather than pain, myelinated
Which lamina in the dorsal horn do A-delta and C-fibres synapse at?
A-delta with lamina I & V
C-fibres with lamina II mostly
What is the route taken for afferent sensory neurons?
The first order nerve fibres synapse with the second order fibres within the lamina. The second order fibres travel up the spinal cord to the thalamus via the spinothalmic tract, where it then synapses with the third order fibre.
What are lamina?
Divisions or layer of the grey matter of the dorsal horn. Lamina I-VI
Define paresthesia and dysasthesia
An odd sensation and an unpleasant sensation
Define primary hyperalgesia
Exaggerated pain sensation to a painful stimulation. It occurs at the site of injury (peripheral sensitisation)
Define secondary hyperalgesia
It occurs in areas remote from the site of injury (central sensitisation) - lowered pain threshold. An example is reduced tolerance of having claws clipped on the hind limb with chronic hip arthritis.
Define allodynia
It describes altered perception where non painful stimuli are painful (like normal touch)
What is the spinothalmic tract?
It transmits nociceptive information from the dorsal horn of the spinal cord to the brain
What is the periaqueductal grey (PAG)?
A structure in the midbrain. Primarily responsible for descending modulation of pain perception
What is the Helsinki chronic pain index?
It is a pain scoring tool for dogs with chronic pain (particularly OA). Designed for owners to recognise and monitor pain.