Neural Basis of Pain Flashcards
What is pain?
Unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage
What is a nociceptor?
Free dendritic nerve ending which detects pain stimuli
Name the 3 types of nociceptor
Chemical
Thermal
Mechanical
Which channel is most important in detecting noxious stimuli?
TRPV1 receptor
What is the TRPV1 receptor activated by?
Protons (pH<6.0)
Temperature (>43 Celcius)
Which ascending tract do pain neurones travel in?
Spinothalamic tract
Where do pain fibres decussate the midline?
At their spinal level
Name the system which pain fibres from the face enter
Trigeminothalamic system
Name the 2 fibres that nociceptors normally associate with
C-fibres
A-delta fibres
Describe pain C-fibres
Small, unmyelinated, slow conduction velocity, dull, aching pain, polymodal
Describe A-delta pain fibres
Larger, myelinated, faster conduction, sharp pain, only activated by mechanical stress and heat
Where abouts in the dorsal horn do the pain ascending tracts lie?
Lamina I and V
Where can the substantia gelatinosa be found?
Lamina II
What is the substantia gelatinosa?
Inhibitory interneurons which run to lamina I and V to inhibit transmission between 1st order and 2nd order neurons
Describe the process of descending inhibition of pain
Neurones from the peri-aquaductal grey have an analgesic effect
The descending fibres synapse on the substantia gelatinosa and cause more inhibition to the connecting 1st and 2nd order neurons
Why can rubbing an area of pain cause pain relief?
A-beta mechanoreceptors are activated which synapse on the substantia gelatinosa. This increases inhibition of the 1st order afferent neuron which relieves pain
Name the nucleus in the medulla of the descending inhibition pathway
Nucleus raphe magnus
Explain how peripheral sensitisation can occur
When cells are damaged, their contents are released and there is an inflammatory response. The ECF is filled with histamine, 5 HT, substance P, bradykinin and prostaglandins.
These can activate nociceptive receptors to cause pain or can sensitise the receptors like TRPV1 so they are activated more readily. More pain is felt
What is wind up?
Receptive field expansion at the peripheries
Describe acute pain
Short term pain, >3 months
Describe chronic pain
Long term, >3 months
What is hyperalgesia?
Increased pain at normal stimulation
What is allodynia?
Pain from a stimuli that is not normally painful
What is referred pain?
Pain in a different area to where the tissue damage is located
What is neuropathic pain?
Pain of neuronal origin. Cannot be explained by a single disease process or specific location
What is phantom limb pain?
Patients who have lost limbs sometimes complain of feeling pain in the limb which is no longer present
The pain does not respond to morphine suggesting the pain arises centrally
Describe some symptoms of Complex Regional Pain Syndrome
Severe, continuous burning pain Hyperalgesia Allodynia Temperature asymmetry Oedema Sweating Motor dysfunction
What can cause Complex Regional Pain Syndrome?
Minor trauma Bone fractures Surgery Stroke MI
