Lecture 26 - Pleasure and Pain II Flashcards
Example of responses to a fearful stimulus
1)
2)
3)
1) Somatic nerves -> skeletal muscles. Freezing behaviour.
2) Autonomic nerve -> Smooth or cardiac muscle. Leads to increased heartrate, blood pressure, etc
3) Autonomic nerve, hormones from pituitary->endocrine gland. Hormonal release
Definition of an emotion (EG: pain)
An emotion constitutes an internal, central (as in central nervous system) state, which
is triggered by specific stimuli (extrinsic or intrinsic to the organism)
Descending pain modulation system 1) 2) 3) 4)
1) Starts in cortex, amygdala, hypothalamus
2) Projects down to rostral ventromedial medulla
3) Rostral ventromedial medulla (including nucleus raphae magnus 5HT neurons) projects to dorsal horn of spinal cord.
4) These modulate sensitivity of secondary neurons in spinal cord onto which nociceptors synapse
Serotonin system
1)
2)
3)
1) A diffuse transmitter system (few neurons, very large number of projections)
2) Neuron cell bodies are in Raphae magnus of medulla.
3) Neurons project down spinal cord, EG: to dorsal horn, where they work with the descending pain modulation system
Noradrenaline system
1)
2)
3)
1) A diffuse system
2) Neuron cell bodies are in locus coeruleus of pons
3) Can inhibit nociceptor signals in dorsal horn
Two natural products made in opium poppy
Opium, codeine
Chemical name for heroin
Diacetyl morphine
Pure opioid receptor agonists
Morphine, fentanyl
Opioid receptor partial agonist
Buprenorphine
Opioid receptor pure antagonist
Naxolone.
Drug used to reverse opioid overdose
Naxolone. An opioid receptor complete antagonist.
How do norepinephrine and serotonin systems reduce nociceptor stimulation of dorsal horn neurons?
1)
2)
1) Directly inhibit neuron to which nociceptor projects
2) Stimulate an enkephalin interneuron, which synapses with the same dorsal horn neuron as nociceptor does, and inhibits nociceptor signal
Major classes of centrally-acting analgesic drugs 1) 2) 3) 4) 5) 6) 7)
1) Opioids
2) NSAIDs
3) Anticonvulsants (EG: gabapentin)
4) Cannabinoids
5) Tricyclic antidepressants
6) Alpha2 adrenergic agonists (EG: clonidine)
7) Serotonin-noradrenaline reuptake inhibitors
Four major classes of endogenous opioid peptides 1) 2) 3) 4)
1) POMC propeptide->beta-endorphin, endomorphin 1 and 2
2) Proenkephalin propeptide-> Met-enkephalin, leu-enkephalin
3) Prodynorphin->Dynorphin A, B
4) Pro-orphanin FQ propeptide->Orphanin FQ
Opioid receptors that POMC-propeptide-derived opioids stimulate
Mu- and delta-opioid receptors
Opioid receptors that pro-enkephalin opioids stimulate
Delta
Opioid receptors that prodynorphin opioids stimulate
Kappa
Opioids that particularly affect ascending pain pathways
Enkephalins, dimorphins
Two broad sections of amygdala
1) Cortical amygdala - fear, learning. Necessary for learned fear responses.
2) Central amygdala - projects to the rest of brain. Coordinates fear response
Areas involved in the psychological modulation of pain 1) 2) 3) 4)
1) Anterior cingulate cortex, prefrontal cortex, insula cortex
2) These project to periaqueductal grey matter in midbrain
3) These project to rostral ventromedial medulla in the midbrain.
4) Interfere with pain transmission neurons in the spinal cord
Where do dopamine-secreting neurons reside?
Ventral tegmental area (substantia nigra)
Roles of dopamine
Motor function
Motivation
Dopamine relationship to reward.
‘Pulse’ of dopamine release from neurons when an activity occurs that warrants a reward, EG: food.
This pulse decreases in intensity the more often the events occurs (begin expecting event)
Where does the dopamine system project to?
1)
2)
3)
1) Basal ganglia
2) Prefrontal cortex
3) Amygdala
Can placebo stimulate genuine analgesia in the brain?
Yes. This can be blocked with naxolone.
There is overlap between places that release opioids in the brain and areas that are stimulated in placebo analgesia.
