Physiology: pain (not relevant for finals) Flashcards
Define what is pain ?
An unpleasant sensory and emotional experience, associated with actual tissue damage or described in terms of such damage
What are the 3 main forms of pain ?
- Nociceptive pain - adaptive
- Inflammatory pain - adaptive
- Pathological pain - maladaptive
What are nociceptors?
Nociceptors are primary afferent neurones innervating peripheral tissues – activated only by mechanical, thermal, or chemical stimuli that are noxious. (only provoked by intense stimuli)
Why is pain essential to the protection of the organism ?
Pain motivates the individual to withdraw from damaging situations, to protect a damaged body part while it heals, and to avoid similar experiences in the future.
Describe nociceptive pain
- Is adaptive – serves as an early warning system to detect and minimise contact with damaging stimuli (noxious events)
- Is high threshold – provoked only by intense stimuli that activate nociceptors
Describe inflammatory pain
- Is adaptive and protective – caused by activation of the immune system in injury, or infection
- Causes pain hypersensitivity (heightened sensitivity to noxious stimuli) and allodynia (innocuous stimuli now elicit pain)
Describe what pathological pain is
Is maladaptive with no protective function - results from abnormal nervous system function
What are the 2 different types of nociceptors ?
- Ad(delta)-fibres
- C-fibres
Describe the action of Ad (delta) nociceptor fibres
- Ad-fibres are mechanical/thermal nociceptors that respond to noxious mechanical and thermal stimuli.
- Mediate ‘first’, or fast, pain
Describe the action of C-fibre nociceptors
- Ad-fibres are mechanical/thermal nociceptors that respond to noxious mechanical and thermal stimuli.
- Mediate ‘first’, or fast, pain
Which nociceptors detect first pain and which detect second pain ?
- Ad (delta) fibres detect first pain
- C-fibres detect second pain
Describe the nociceptive pathway from a peripheral site to the dorsal horn of the spinal cord
- Stimulus (mechanical, thermal or chemical) opens ion channels in nerve terminal to elicit depolarising receptor potential
- Amplitude of generator potential in proportion to intensity of stimulus
- Local current flow triggers ‘all or none’ AP’s at a frequency proportional to the amplitude of the receptor potential
Describe the the projection pathways from the spinal cord to the brain
Nociceptive C and Ad(delta) fibres terminate Nociceptive C- and Aδ-fibres mostly terminate superficially in laminae I and II
Second order neurones then ascend the spinal cord in the anterolateral system comprising mainly:
- The spinothalamic tract (STT)
- The spinoreticular tract (SRT)
Describe the spinothalmic tract (STT) and the nociceptors it follows on from
- Projection neurones originating from lamina I (fast fibre Aδ pain) terminate in posterior nucleus of the thalamus
- Projection neurones originating from lamina V (WDR neurones) terminate in posterior and ventroposterior nucleus of the thalamus
- Pain perception (location, intensity) requires simultaneous firing in both pathways
Describe the spinorecticular tract (SRT) and the nociceptors it follows on from
- Largely transmits slow C-fibre pain
- Makes extensive connections with reticular nuclei in the brainstem [e.g. periaqueductal grey (PAG) and parabrachial nucleus (PBN)]
- Involved in autonomic responses to pain, arousal, emotional responses, fear of pain
Outline the development of neurogenic inflammation
