Acute Somatic Pain:
Pathophysiology
Acute tissue damage, from three types of causes:
Mechanical (eg: sharp pin) Thermal (eg: hot stove) Chemical (eg: inflammation)
Nociceptors activated at site of injury (1st order sensory neurons)
Nociceptive fibres (A∂ and C) carry noxious sensory information to the ipsilateral dorsal horn of the spinal cord
Excitatory neurotransmitters are released and stimulate 2nd order sensory neurons
2nd order sensory neurons immediately cross the midline of the spinal cord, and ascend up the opposite side’s anterolateral (aka spinothalamic) tracts, terminating in various locations:
Authors: Lisa Murphy Yan Yu* Reviewers: Mackenzie Gault Melinda Davis* * MD at time of publication
Nociceptors: neurons that detect noxious or painful stimuli and carry this information to the spinal cord. There are two major types:
A∂ fibres: myelinated, initial “sharp, fast” feeling
C fibres: unmyelinated, delayed, “dull, burning” feeling
To hypothalamus
2nd order neuron synapses in the hypothalamus
Hypothalamic neurons coordinate the body’s visceral response to pain
2
nd
To thalamus
order neuron terminates in thalamus
To brainstem
2nd order neuron synapses in brainstem’s reticular formation
To midbrain
2nd order neuron synapses in periaqueductal gray area (PGA) in the midbrain
In the thalamus, 2nd order sensory neurons synapse with 3rd order sensory neurons, which carry the signal to the cerebral cortex
Stimulates descending pathways to modulate the incoming pain signal
Decreased or increased perception of pain
Pain localization and sensation
Emotional and behavioural response
↑ Heart Rate
Nausea
Legend:
Pathophysiology
Mechanism
Sign/Symptom/Lab Finding
Complications
Published April 25, 2019 on www.thecalgaryguide.com