An unpleasant sensory experience associated with tissue damage
It is not a stimulus, it is a final interpretation of nociception in the brain
What nerve fibres carry nociception?
Adelta - Small Myelinated - Fast Pain
C - Unmyelinated - Slow/delayed Pain
What are Rexed Layers?
Rexed divided the spinal cord into 10 layers based on their cytoarchitecture
What are the 3 types of neurons in the spinal cord and what rexed layer are they found?
Low Threshold Mechanoreceptive Neurons - Layer 3/4 - Abeta fibres
Nociceptive Specific Neurons - Layer 1/2 - Adelta/C fibres
Wide Dynamic Range (WDR) neurons - Layer 5 - respond to both noxious and non-noxious stimuli
What tracts do pain fibres travel up?
Spinothalamic Tract, divided in two:
- Lateral STT carries fast and slow pain + Temp
- Anterior STT Carries crude touch
The STT arises in Rexed LAmina 2 & 5
Where do the fibres in the Spinothalamic Tract go?
Ventral STT -> Medial Thalamic Nuclei -> Limbic System (emotional response to pain & desc. control)
Lateral STT -> Ventroposterior Thalamic Nuclei -> Primary Somatosensory cortex (spatial & intensity discrimation of pain)
Explain the descending pathways of pain?
Periacqueductal grey (PAG) matter activates a descending noradrenergic system to the dorsal horn where it gates pain using endogenous opioids
What are the categories of pain sensitization?
What are the types of peripheral pain sensitization?
- Hyperalgesia (Increased neuronal response to pain signals)
- Spontaneous Pain (Spontaneous activity in nociceptive nerve fibres)
What is Allodynia?
Sensitization of the nociceptors themselves
So the nociceptor threshold lowers causing it to trigger signals for stimuli that arnt normally considered noxious
What is hyperalgesia?
Exaggerated response of the neurons to already painful stimuli
I.e. the stimulus-response curve shifts left, your perception of pain increases
What are the types of Segmental Central Sensitization?
Wind up - Increased response through the 1-2nd order synapse
Classical - Opening up of new synapses
How does Wind up sensitization work?
Homosynaptic Activity-Dependant Progressive increase in Neuronal Response.
Over the course of the stimulus the active synapses become more responsive, this terminates with the stimulus
How does Classical Sensitization work?
If the stimulus is intense enough then it opens up new synapses, thus increases the active pain fibres.
Can outlast the stimuli as maintainable by a low intensity stimulus
How does longterm potentiation work?
We dont really know but it involved already activated synapses (unlike classical) and very intense stimuli
Pain conditions such as fibromyalgia and the painful symptoms of depression are caused by what?
Its believed the pain is sourced from supra-segmental pain sensitization in the thalamus & Cortex
Whats the difference between chronic and acute pain?
In acute pain theres usually obvious damage and the pain resolves with healing, Its serving a protective function. Nociceptive
In chronic pain it lasts beyond the period of healing, It has no protective function and actually degrades health and function. Nociceptive and/or Neuropathic
Whats the difference between Nociceptive & Neuropathic pain?
- Localised to site of injury
- Responds to conventional analgesics
- May be chronic e.g. osteoarthritis
- Causes by lesion or dysfunction of somatosensory nervous system
- E.g. Neuroma caused by nerve damage, stroke or MS
- Pain found at region supplied y nerve not necessarily region of injury
- Almost always chronic
What are the categories of pain management?
- Descending Modulation
Whats involved in pain management through Transduction?
What methods are there for pain management through transmission?
- Nerve blocks e.g. General Aneasthetics
- Drugs e.g. Opiods or Anticonvulsants
- Surgery e.g. Cordotomy
How do we manage perception of pain?
- Cognitive Behavioral Therapy
Also for people with missing limb pain we can use Graded Motor Imagery & Mirror Box Therapy
How do we control pain through descending modulation?
- Drugs e.g. Opiods and antidepressants
- Surgery e.g. Spinal Cord Stimulation