Physiology of Pain 05/10/18 Flashcards
Why is pain difficult to assess?
It is very subjective
What is the time period for pain to be termed chronic?
Over 3 months
What age group is chronic pain highest in?
Over 65s
What is pain?
An unpleasant sensory and emotional experience, associated with actual tissue damage or described in terms of such damage
What are the 4 processes in the physiology of pain?
Transduction
Transmission
Modulation
Perception
What is transduction?
Translation of noxious stimulus into electrical activity at the peripheral nociceptor
What is transmission?
Propagation of pain signal as nerve impulses through the nervous system
What is modulation?
Modification/hindering of pain transmission in the nervous system e.e. by inhibitory neurotransmitters like endogenous opioids
What is perception?
Conscious experience of pain
Causes physiological and behavioural responses
What are Nociceptors?
Type of free nerve ending
Outgoing sensory neurones
How are nociceptors activated?
Intense noxious stimuli
What order of neurone is a nociceptor and what does it relay information to?
First order neurones
relays to second order neurones in the CNS
How do 1st order neurones transfer information to 2nd order neurones?
Chemical synaptic transmission
What is the nociceptive pathway?
Noxious stimuli acts on the free nerve ending
Creating an action potential along the 1st order neurone
Synapses with the second order neurone in the dorsal horn of the spinal cord
Axon is projected out
What are the neurotransmitters in the N pathway?
Glutamate and peptides
Substance P
Neurokinin A
Whwere do 2nd order neurones ascend?
In the anterolateral systen and terminate in the thalamus
What are the 2 main components of the anterolateral system?
Spinothalmic tract
Spinoreticular tract
What is the spinothalmic tract involved in?
Perception of pain
What is the spinoreticular tract involved in?
Autonomic responses to pain, arousal, emotional responnses and fear of pain
What are the two types of nociceptor?
A delta fibres
C fibres
What do A-delta fibres respond to?
noxious mechanical and thermal stimuli
Mediate fast pain
What do the C fibres respond to?
Poly modal
All noxious stimuli
Mediate slow pain
What are four ways of classifying pain and some examples?
Mechanisms - nociceptive, inflammatory, pathological
Time course - acute, chronic
Severity - mild, moderate, severe
Source of origin - somatic or visceral
What does nociceptive pain represent?
Normal response to injury of tissues by noxious (damaging) stimuli
What provokes nociceptive pain?
Intense stimulation by noxious stimuli
Is nociceptive pain adaptive?
Yes
What is the function of nociceptive pain?
Early warning physiological protective system to detect and avoid noxious stimuli
What causes inflammatory pain?
Activation of the immune system by tissue injury or infection
What is inflammatory pain activated by?
Variety of mediators released at the sit of inflammation by leucocytes, vascular endothelium and tissue resident mast cells
What does inflammatory pain cause?
Heightened pain sensitivity to noxious stimuli (hyperalgesisa) and pain sensitivity ti innocuous stimuli (allodynia)
What does inflammatory pain discourage?
Physical contact
Discourages movement
of inflammed part
Is inflammatory pain adaptive?
Yes
What are two types of pathological pain?
Neuropathic or Dysfunction
What is neuropathic pain caused by?
Damage to neural tissue
What are examples of neuropathic pain?
Compression neuropathies Peripheral neuropathies Central pain Postherpetic neuralgia Trigeminal neuralgia Phantom limg
What can neuropathic pain be percieved as?
Burning
shooting
Numbness
Pins and needles
What is dysfunctional pain?
No identifyable damage or inflammation
What are examples of dysfunctional pain?
Fibromyalgia IBS Tension headache Temporomadibular joint disease Interstitial cystitis
Are simple analgesics effective in pathological pain?
No
What can sometimes treat pathological pain?
Anti-depressants
Anti-epileptics
Opioids
Is pathological pain protective?
No
It is maladaptive
What is referred pain?
Pain developed in one part of the body is felt by another
What types of pain can be felt as referred pain?
Deep
Visceral
What is referred pain caused by?
Convergence of nociceptive visceral and skin afferents upon the same spinothalmic neurons at the same spinal level
What are some examples of referred pain?
Liver pain felt in shoulder
Heart pain felt in arm and jaw
Appendix pain felt in central stomach/umbilical region
