Anatomy and physiology of pain Flashcards
What is pain? (rote learning)
Pain is an unpleasant sensory experience associated with, or resembling that associated with, actual or potential tissue damage
What is the purpose of pain?
Immediate pain - warns of tissue damage to withdraw from the source of the injury
Persisting pain - to immobolose injured area, give damaged tissue chance to heal
Nociception - neural process involved in producing the sensation of pain
What is acute pain?
Pain less than 12 weeks duration
What is chronic pain?
continuous pain lasting >12 weeks, pains that persist beyond the tissue healing time
Can be thought of in terms of cancer pain and non-cancer pain
Different types of pain processes?
Nociceptive
Neuropathic
Nociplastic
What is nociceptive pain?
Pain that arises from actual or threatened damage to non-neural tissues and is due to the activation of nociceptors
What is neuropathic pain?
Pain caused by a lesion or disease of the somatosensory nervous system
What is nociplastic 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 pain
What i the basic overall pain pathway?
Peripheral receptor - detect relevant stimulus
1st order neuron - from periphery to ipsilateral spinal cord
2nd order neuron - CROSSES to the contralateral cord and ascends to the thalamus, ‘relay station’
3rd order neuron - from thalamus to midbrain and higher cortical centres
What are nociceptors?
transduces a physical stimulus to an action potential
Most are poly-modal (thermal/chemical/mechanical)
they are the free nerve endings of primary afferent neurons: A delta and C, detect more extreme measures than mechanical and thermal receptors
Where are nociceptors found?
Any area of the body that can sense pain, externally or internally
Cell bodies of these neurons based in either dorsal root ganglion (body)
trigeminal ganglion (face/head/neck)
Dorsal root ganglion
Types of nerve fibres
A-alpha - proprioception - largest diameter - highest conduction speed (in m/s)
A-beta - touch
A-delta - pain (mechanical and thermal)
C (non-myelinated) - pain, mechanical and thermal and chemical) - smallest diameter - slowest conduction speed by a while
What do Aδ fibres synapse with?
What do C fibres synapse with?
Aδ - synapse directly with secondary afferents that carry pain signal to thalamus
C - don’t synapse directly with secondary, connect with interneurons that then synapse with secondary afferents in laminae I or V
What is the spinothalmic tract?
Sensory pathway of the spinal cord
Carries pain, temperature and crude touch information from the body
Lateral -pain and temp - and ventral - light touch
2nd order neurones
