Anatomy and Physiology of Pain Flashcards
Define transduction
Noxious stimuli translated into electrical activity at sensory nerve endings
Define transmission
Propagation of impulses along pain pathways
Define perception
Discrimination/affect/motivation
Our interpretation of a stimulus
Which primary afferent axon has the widest diameter? A. A alpha B. A beta C. A delta D. C
A alpha
Speed of conduction of stimuli is highest in which primary afferent axon? A. A alpha B. A beta C. A delta D. C
A alpha
What genetic defect/s is associated with loss of transduction/transmission?
Loss of NaV1. 7 (sodium channel subunit)
Results in congenital indifference to pain
trKA - NGF receptor mutation
results in congenital insensitivity to pain with anhydrous CIPA
What type of pain is mediated by A delta and some A beta fibres? What is the result of these fibres being activated?
Sharp pricking FAST PAIN
Allows precise localisation of stimulus
Results in reflex withdrawal
What type of pain is mediated by C fibres? What is the result of these fibres being activated?
SLOW burning pain
Peptidergic C fibres release peptides peripherally when activated resulting in vasoactive, pro-inflammatory responses
Peptide-poor C fibres have distinct receptors and projections (idk notes say it leads to mechanical nociception?)
Which lamina/e is innervated by C fibres?
Lamina I
and interneurones in lamina II (also innervate lamina V through these interneurones)
Which lamina/e is innervated by A-delta fibres?
Laminae I and V via projection neurones
Which primary afferent axon/s innervate anterior/neospinothalamic tract?*
Mostly A-delta fibres
Come input from C-fibres and A-Beta fibres
Which areas of the brain does the anterior/neo spinothalamic tract project to?
- Ventral posterior lateral and ventral posterior medial thalamus (somatosensory thalamus)
- Ventral posterior inferior
- Central lateral nuclei of the thalamus
What is the VPL/VPM responsible for, in terms of response to pain?*
Localisation and physical intensity of noxious stimulus
Where does the CL nucleus project to in the anterior/neo spinothalamic tract??
ACC (emotion)
PFC + striatum (cognitive function + strategy)
Which primary afferent axon/s innervate lateral/paleospinothalamic tract?*
Mainly C fibres
some A delta
Which areas of the brain the lateral/paleo spinothalamic tract?
- Mediodorsal nucleus (ventrocaudal) (MDvc)
- Posterior nucleus (medial subnucleus)
- Ventral medial nucleus (posterior)
some projections to VPL, VPM and CL
Which areas of the brain does the mediodorsal/ventrocaudal (MDvc) nucleus project to?*
Anterior cingulate cortex
Which areas of the brain does the posterior thalamus project to?*
Anterior or rostral insula
What are the collateral projections from the lateral spinothalamic tract?*
- Spinal circuitry (reflexes)
- Reticular formation + reticular thalamus (arousal + alerting cortex)
- Periaqueductal grey (descending pain modulation)
- Parabrachial nucleus –> limbic system (memory + autonomic integration)
State the 4 cardinal signs of inflammation.
- Calor (heat)
- Rubor (redness)
- Dolor (pain)
- Tumour (swelling)
What causes neurogenic inflammation?
Peptides released from C-fibres
Describe how prostaglandins are synthesised.
Phospholipase A2 releases arachidonic acid from cell membranes (due to inflammatory mediators)
Cyclooxygenase 1 and 2 enzymes use arachidonic acid as a substrate for prostaglandin synthesis
How do prostaglandins sensitise C-fibres?
By increasing the number of other receptors and increasing the number of OPEN sodium channels
How does central sensitisation occur?
nociceptor afferents release glutamate and peptides
this results in increased sensitivity of second order neurones in the dorsal horn
Define chronic pain.
Pain or more than 12 weeks, normally associated with an underlying condition
What kind of treatment is there for maladaptive pain?
treatments target abnormal neural activity/imbalance in modulatory systems regulating pain
Anticonvulsants and antidepressants can be effective
What kind of drugs target pain modulation in peripheral nociceptors?
Local anaesthetics
Anti-inflammatory drugs
What kind of drugs target pain modulation in peripheral nerves?
Local anaesthetics
What kind of drugs target pain modulation in dorsal horn?
local anaesthetics
opioids
alpha 2 agonists
What kind of drugs target pain modulation in cortex?
opioids
alpha 2 agonists
Explain how acupuncture is thought the alleviate pain?
Activate A-delta fibres and in doing so stimulates diffuse noxious inhibitory control (DNIC) of pain via the periaqueductal grey
Describe the basis of Transcutaneous Electrical Nerve Stimulation (TENS).
Non-noxious afferent are stimulated and this input stimulates lamina II interneurones
What part of the brain is sensitive to u opioid antagonists such as naloxone?
ACC-PFC-PAG path
- responsible for the unpleasantness of pain
Where does the VPI of the thalamus project to in the anterior/neo spinothalamic tract?
Secondary somatosensory cortex
What is/are the function(s) fo the anterior rostral insular?
- emotion
- quality (of pain)
- autonomic integration
