Neurophysiology of Nociception: Perception Flashcards
What does perception refer to?
the final output of the nociceptive stimulus being transmitted through the pathways of the nervous system and the interpretation of the higher cortical regions
What are so diverse behaviors or reactions that occur with perception of pain?
- Protection withdrawal reflexes (i.e. flexor reflex)
- Grimacing, shouting, crying, or even fainting
- Some responses to ANS
What are some ANS responses to pain?
- Diaphoresis
- Increased muscle tone
- Increased respiration rate
- Increased heart rate
- Pupil dilation
Pain is a complex sensory and emotional experience which involves the activation of what?
the higher centers of the CNS
What are the 4 principle cortical regions that appear to play a role in the processing of nociceptive information?
- Primary somatosensory cortex (S1) in the postcentral gyrus of the parietal lobe
- Secondary somatosensory cortex (S2) in parietal lobe
- Anterior part of the cingulate gyrus/cortex (ACC)
- Insula/insular cortex (IC)
What are S1 & S2 implicated in?
the sensory-discriminative component of pain
What are the ACC & IC linked to?
the affective-emotional component of pain
Where does the spinothalamic tract from the thalamus send projections?
to S1 and S2
What happens when damage occurs to S1 & S2?
a loss of the ability to localize and perceive the intensity of nociceptive stimulation
Plasticity to the somatosensory regions example?
in patients who have undergone a hemispherectomy, stimulation of the leg contralateral to the removed hemisphere produces activation of the ipsilateral S1 cortex (as opposed to the contralateral activation seen in healthy subjects)
A number of studies have implicated the anterior region of the cingulate cortex (ACC) plays a part in what?
nociception processing
Injury or surgical lesions to the ACC have shown?
to produce an inhibitory effect for pain perception
What does injury to the insular cortex (IC) show?
an absence of emotional responses to nociceptive stimuli
ACC has connections to?
the limbic system and appears to play a dominant role in the affective-emotional component of pain
What does visceral pain associated with irritable bowel syndrome (IBS) show strong activation of?
ACC
What other cortical areas does the IC send projections to?
- S1, S2, and the cingulate cortices
- also contacts limbic structures: amygdala an perirhinal cortex of the hippocampus
What does stimulation of the IC produce?
intense emotional sensations of fear
With interpretation of pain there is often a discrepancy between what?
objective reality of nociceptive stimulus and the subjective response to it
Example of interpretation of pain discrepancies?
in WWII battlefield soldiers suffering from severe battle wounds often reported experiencing minimal or no pain
- evidence of Top down/psychological effects on pain interpretation
What is the “placebo effect”?
the psychological response following the administration of a pharmacologically inert “treatment”
Who discovered the placebo effect?
Henry Beecher while woking as a medic in WWII
How did Beecher utilize the placebo affect?
after running out of morphine in WWII, he replaced it with simple saline solution but continued telling the wounded soldiers it was morphine
- almost half of the soldiers reported that the solution actually reduced or eliminated their pain
