Pain pathways Flashcards
Opioids activate descending pathways that inhibit pain transmission by acting on neurons in which region?
Periaquedactal grey matter (PAG)
Transmitters in pain control system(s) include which neurotransmitters
Dopamine
When/ what can activate then pain control system?
It can be activated by touch
What are Abeta fibres?
Myelinated fibres for transmission of low intensity stimuli (touch, brush)
What are Adelta fibres?
Myelinated fibres for transmission of sharp sensation/acute pain
What are C-fibres?
Unmyelinated fibred, conducts slow pains/aches
Tissue damaging stimulation from deeper tissue layers i.e. muscle
What is neuropathic pain and list some potential causes?
Neuropathic pain : induced by lesions of the somatosensory CNS
Potential causes: SCI Diabetic neuropathy Stroke Viral infections (Herpes virus, HIV)
List potential drug classes that could be used for neuropathic pain. Briefly explain the mechanism
Tricyclic antidepressants: Inhibit noradrenaline and serotonin re-uptake
Pregabalin & Gabapentin : Inhibit L type voltage gated Calcium channels (bind to alpha2subunit)
Give examples of different types of pain
Acute Pain Inflammatory pain Neuropathic pain Musculoskeletal pain Physiological pain (acute)
What is the difference between allodynia and hyperalgesia?
Allodynia is pain evoked by non-noxious stimuli
Hyperalgesia is pain evoked by noxious stimuli
Briefly explain transmission of pain to the brain
1- Peripheral nociceptors detect pain at nerve endings
2- Action potential is triggered
3-This is propagated to the dorsal horn of SC.(neurotransmitters are released)
4- Ascending neurons are activated
5- Pain info is transmitted to the brain (Thalamus –> sensory cortex)
What class of receptor type are opioid receptors?
GPCRs
What occurs at the dorsal horn of SC when an action potential is triggered?
2 neurotransmitters are releaased:
Substance P : activates tachykinin
Glutamate : acts on NMDS receptors
Sends pain info up to the brain
Which endogenous neurotransmitter inhibits the release of glutamate?
Endorphins
What do periphery sensory nerves respond to? (Stimulus)
Temperature: Heat/cold Mechanical stimulation Chemical stimulation (Capsaicin, acid)
Give 4 examples of mediators generated from tissue damage.
Bradykinin,
5HT
Nerve growth factor
Inflammatory mediators (cytokines, histamine)
List mechanoreceptor fibres
Abeta fibres
Adelta fibres
C fibres
List Nociceptor fibres
Adelta fibres
C fibres
List Thermoreceptor fibres
C fibres
What neurotransmitters/compounds inhibit the release of glutamate at the pre-synaptic receptors (in dorsal horn (Cfibres) )?
Opioids
GABA
Noradrenaline
Endorphins
What is the gate control theory of pain?
Non-painful input closes the nerve “gate” to painful input.
Preventing pain sensation from travelling to the CNS
What is TENS?
Transcutaneous electrical nerve stimulation
Briefly explain the descending control system.
Opioid excite the PAG & NRGP neurons –> this stimulates neurons in the Raphe nucleus (NRM)
5HT and enkephalin neurons of the NRM (go down to the dorsal horn) inhibit the pain transmission
Which endogenous neurotransmitters inhibit pain and how?
5HT and enkephalins in the NRM inhibit pain at the dorsal horn
Noradrenergic neurons (of locus coerulus) inhibit pain at the dorsal horn
