L1 - Neuroanatomy of Pain Systems Flashcards
Pain
Defn:
Unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage
NOCICEPTORS
- what are they
- where do their cell bodies lie
Damage sensing neurons that detect noxious stimuli
Specialised free nerve endings are in skin, muscle and viscera, cell bodies lie **dorsal root ganglia **(DRG)
Receptors:
what do they do
convert stimuli into electrical activity
larger the change in the voltage at the terminal, due to the influx of Na+ and Ca2+ through receptors forming ion channels, the greater the number of Action Potentials generated.
Að - A delta
Mechano nociceptors
Tissue damaging stimuli,
pressure
extreme heat & cold
C fibres
Thermal nociceptors - 45 degrees
Chemically sensitive - algogens, pH irritants
Polymodal nociceptors (most abundant) - thermal, mechanical, chemical
Ascending pathways
Spinothalamic:-
- Discriminative aspect of nociception; FAST PAIN
Spinoreticular:-
- Responsible for arousal and affective (unpleasantness) aspects; DULL PAIN
Gate Control theory of pain
Small interneurons in the dorsal horn acting as a gate which controls the amount of excitation of the transmission cells.
Gate closed - low pain
Gate open - high pain
Factors regulating gate
1) amount of activity in pain fibres
2~) amount of activity in other peripheral fibres ( activation of mechanoreceptors Aß fibres)
3)Messages descending from brain e.g. emotions and mental conditions
THUS: psychological factors influence pain perception by regulating the gate mechanism.
PAG - periaqueducta gray
rich in opioid receptors and enkephalins
electrical stimulation of PAG produces analgesia
PAG neurons’ axons end on serotoninergic neurons in the medulla
RVM - rostrol ventromedial medulla
important area for both **inhibition **and **facilitation **of nociceptive processing,
bi directional central control of nociception
Pain - subjective experience
3 components
1) sensory-discriminative
- sense of intensity, loaction and duration
2)affective-motivational
- unpleasantness and desire to escape it
3)cognitive component
- invovling judgements, beliefs, memories, perception of environment and patient’s own history
Pain pathways are not rigidly hard-wired
Neural substances that mediate pain are plastic, i.e. modifiable depending on use or modulatory influences.
Central role of the dorsal horn which integrates peripheral, local and descending input. Change in excitability at this level will control output to the brain.
what is catastrophizing in pain?
it is the process of adding negative emotion to pain signal resulting in a pain/panic reaction.
when present pain is much harder to control and may be triggered by memory of the inciting incident that produced the pain originally.
What are the types of pain?
Main are adaptive and maladaptive
Adaptive include:-
- Nociceptive
- Inflammatory
Maladaptive:-
- Neuropathic
- Dsyfunctional
Pathological pain occurs in maladaptive
PAIN HYPERSENITIVITY
Pain systems- have to be sensitive enough to detect potentially harmful stimuli
Too sensitive - pain that causes no benefit
Hypersenisitivity arises because our pain pathways actually increase in sensitivity when they relay pain messages.
