Acute Pain + Analgesia 1 Flashcards
(27 cards)
What is the definition of pain?
Unpleasant sensory + emotional experience associated with actual or potential tissue damage
What is activity induced by noxious stimuli?
- NOT pain = always a psychological stage
- Pain in absence of tissue damage should be accepted pan
Describe the classification of pain
Duration (acute + chronic)
Nature:
1. Noiceptive - somatic + visceral
2. Non-noiceptive - neuropathic + sympathetic
Describe acute pain
- recent onset, limited duration
- activation of nociceptive sensory neutrons
- transient
- specific injury produces tissue damage
Describe chronic pain
- persists after expected healing time or absence of injury
- lasting 3+ months
- no identified cause
Describe nociceptive pain
- obvious tissue injury/illness
a. k.a physiological or inflam pain - protective function
- sharp/dull
- well localised
Describe neuropathic pain
- tissue injury not obvious
- NS damage/abnormality
- does not have protective function
- burning, shooting/numbness, pins and needles
- well localised
Explain plasticity in peripheral and central pain systems
Plasticity = response to activity, inflam + neural injury which can lead to…
- Central sensitisation = increases membrane excitability + synaptic efficacy + reduces inhibition
- Hypersensitivity to stimuli
- Chronic stimulation of nociceptors
What is the difference between nociception and pain?
Nociception = process through which potentially damaging stimuli detected Pain = how we feel
Describe the process of nociception
- Thermal, chemical + mechanical stimuli capable of causing tissue damage activate nociceptors to transmit signals via glutamate -> CNS
- Activation modulated by inflam influences in local EC enviro (prostaglandins, histamine + bradykinin)
What are the 4 main phases of nociception?
- Transduction - exposure to noxious stimuli = AP
- Transmission - travels along fibres to dorsal horn -> brain -> thalamus = translates nociception to pain
- Perception - experience discomfort…
- Modulation - response to pain
What are the 3 types of afferent nerve fibres?
- A-delta
- C fibres
- A-beta fibres
What is the role of A-delta fibres?
- fast
- myelinated
- respond to heat, pressure + 1st sharp pain sensation
What is the role of C fibres?
- slow
- unmyelinated
- respond to thermal, mechanical + chemical stimuli
- 2nd throbbing pain sensation
What is the role of A-beta fibres?
- respond to non-noxious stimuli
- detect light touch, vibrations
Describe the ascending pain pathways
- Enter CNS at substantial gelatinosa of dorsal horn
= receives input from A delta or C fibres which synapse with 2nd nerve - Also receives inputs from A-beta
- 2nd nerve travels up opposite side of spinal cord
- Ascends in contralateral spinothalamic tract
Where does pain perception occur?
Cortex
Thalamus = second relay structure
Describe the descending pain pathway
- Brain -> dorsal horn
- Usually decrease pain signal
Where does chronic noxious stimulation occur?
- Peripherally - misfiring by neural stimulus, amplifying signal to brain
- Centrally - firing of neutrons in spinal cord or brain in absence of stimulus
What is hyperalgesia?
- Peripheral sensitisation
- Localised inflam = hyper-excitability of peripheral nociceptors
What is allodynia?
- Central sensitisation
- Pain to normally painless stimulus: enables non-noiciceptive A-beta fibres to evoke pain
Explain the Gate control theory
- Excitation along A-delta + C-fibres opens gate
- Excitation alone A-beta fibres closes gate
On what principle does TENS work?
Mild mechanical stim. (rubbing) can activate inhibitory A-beta fibres = inhibiting nociceptive signals along spinothalamic interneuron
i.e. closes gate
What is the neuromatrix theory?
Pain arises from neural network with sensory, affective + cognitive components
Sensory = basic sensory info (location, qualities) Affective = emotional + motivation reactions to pain (fight+flight) Cognitive = meaning of sensory experience
