13 - Pain Flashcards
Example of a definition of pain
An unpleasant sensory and emotional experience associated with actual or potential tissue damage or described in terms of such damage
Different types of pain 1 2 3
1) Nociceptive pain 2) Inflammatory pain 3) Neuropathic pain
Chronic pain
Pain for three of the past six months. A large proportion of people with chronic pain don’t respond to treatment.
Relationship between pain and nociception.
Not synonymous. Nociception is nerve detection of noxious stimulus. Pain is cortical recognition thereof.
Stages of nociception 1 2 3 4
1) Transduction (receptor detection of H+. heat. noxious cold, pressure, chemicals, etc) 2) Transmission (peripheral and central) 3) Perception (sensory/discriminative, emotional) 4) Modulation
Sensory/discriminative pain
How intense pain is, where it is. Carried through lateral spinothalamic tract to the lateral thalamus.
Spinal tract through which nociceptive information travels to brain
Spino-parabrachial tract, lateral spinothalamic tract. Travel to the lateral thalamus, limbic centres.
Emotional/aversive pain
Emotional perception of pain. Travels through spinoparabrachial tract to limbic centres.
Responses to nociceptive pain 1 2 3
1) Pain 2) Autonomic reflexes 3) Withdrawal reflex
Nociceptor nerve endings
C-fibres, A-delta fibres.
Location of nociceptive neuron cell bodies
In dorsal root ganglia, trigeminal ganglia (for pain of head and face)
C-fibre morphology
Unmyelinated. Thin (under 1.5 micromete) Slow transmission (under 3m/s)
A-delta fibre morphology
Myelinated. Thin (1.5 - 4 micrometes) Medium-fast transmission (3-30m/s)
Temperature around which a heat nociceptor will start being stimulated
~42 degrees. High-threshold.
Difference in type of pain from C-fibres and A-delta fibres
C-fibres give slow, burning pain. A-delta give sharp pain.
*First and second pain
FIRSTSECONDPAIN
*Projection of second-order neurons to brain via anterolateral tract
Nociceptor afferents synapse ipsilaterally with a spinal interneuron, which crosses contralaterally and ascends to brain in anterolateral system.
Inflammatory pain
Similar to nociceptive pain, but system is modulated by inflammatory mediators released by immune cells (hyperalgesia). System evolved to protect damaged tissues (eg: with behaviour).
‘Inflammatory soup’
Inflamed or damaged tissues release nociceptor sensitisers.
*TRP channel
Transient receptor potential channel. TRPV1 is a nociceptive transducer.
Stimuli that TRPV1 often responds to
Noxious heat, acid, reactive chemicals.
TRP channel responsible for detecting environmental cold
TRVM8 (EG activated by menthol)
What causes secondary allodynia to come about?
Central sensitisation by inflammation. An innocuous stimulus of a low-threshold neuron leads to stimulation of sensitised central pathway, leading to secondary allodynia.
Difference between hyperalgesia and allodynia
Hyperalgesia is an increased response to a normally painful stimulus. Allodynia is a painful response to a normally innocuous stimulus.
