Lecture 16 - Opioids Flashcards
What is the definition of Pain?
An unpleasant sensory and emotional experience associated with or resembling actual or potential tissue damage
What are some endogenous opioids?
B-endorphins
Endomorphins
Dynorphins
Enkephalins
What are the 2 types of pain fibres?
A delta fibres
C fibres
What type of pain do A delta fibres transmit?
Fast sharp pain
What type of pain do C fibres transmit?
Slow burning pain
What sensory pathway transmits pain?
Spinothalamic pathway
Which pain fibres are myelinated and which pain fibres are not myelinated?
A delta fibres = myelinated (fast sharp pain)
C fibre = unmyelinated (slow burning pain)
Where do the primary sensory neurones (A delta fibres or C fibres ) synapse to the second order neurone?
Synapse to second order neurone in the Ipsilateral dorsal horn
What is considered the pain gate?
The point where the primary sensory pain neurones (A delta and C fibres) synapse to the 2nd order neurone in the dorsal horn on the Ipsilateral side of the cord
Once the pain fibre has synapsed to the 2nd order neurone on the Ipsilateral cord what happens next?
2nd order neurone decussates and ascends to the thalamus where it synapses to a 3rd order neurone going to the cortex
A 2nd order neurone also goes to the limbic system (emotional response to pain)
What is the function of the limbic system in the pain pathway?
Emotional control
What carries the sensory dimension in the pain pathway?
What carries the affective/emotional dimension of pain?
Sensory = 3rd order neurone to cortex
Affective = 2nd order neurone to limbic system
Go to the first slide and label the spinothalamic pain pathway on the left hand side:
What effect does rubbing an area with pain have?
Relieves the pain
How does rubbing a painful area help relieve the pain?
Stimulating mechanoreceptors leads to their primary sensory neurone Stimualting inhibitory encephinergic neurones that lead to the secondary sensory neurone in the dorsal horn prevention pain reaching the cortex
What are the neurotransmitters from inhibitory interneurones that synapse onto the 2nd Order sensory neuorne in the dorsal horn?
GABA
Enkephalins
What class of molecule arer enkephalins?
Endorphins
What receptors do endorphins/enkephalins act on?
What do they do?
Mu opioid receptors
Inhibit pain transmission
What neurotransmitters are produced by descending fibres that inhibit the activation of the 2nd order sensory neurone prevntinig pain?
Noradrenaline
5-HT (serotonin)
Go to the first slide and label the right side pain pathway:
What part of the CNS have high levels of Mu opioid receptors so are important in pain?
High. Levels in Brain
Periqueductal grey matter in midbrain
Reticular formation (grey matter in medulla)
What is the pathway for altering pain threshold during stress?
Amygdala to periaqueductal grey matter then travels to reticular formation in medulla then to the dorsal horn in the cord
What is the pathway for altering pain threshold during the menstrual cycle?
Hypothalamus sends axons to periaqueductal grey matter in the midbrain
Then axons sent from here to the reticular formation in the in the medulla
Then axons sent from here to the spinal cord