Neural basis of pain. Flashcards
What is pain?
An unpleasant sensation and emotional experience with actual or potential tissue damage
It has visceral and somatic origin
Elicits sensation with autonomic, somatic, endocrine and emotional responses
(So it is both sensory - discriminative - and subjective - affective, behavioural processes)
Define nociception
Non-conscious neural traffic originating with trauma or potential trauma tissue
What is the difference between threshold for pain and tolerance to pain?
Stimulus threshold
- Is the same in each of us
Tolerance
- Is our variable reaction to a painful stimulus
(environment, situation, psychological/emotional factors, increases with age, ongoing pain, placebo effect)
What tracts are used for pain?
Anterolateral system
- Spinothalamic tract is the only conscious pain pathway
- Lateral spinothalamic tract is pain
There is also the routes to the Cerebellum that transmit pain, but that is unconscious
What are the two different type of pain sensations in terms of time cale?
Direct (fast) lateral STT
- Discriminative pain (quality, intensity, location)
- Somatotopic organization
- Contralateral
- No sub-cortical target
- Cortical locatin - Parietal lobe
- Other functions of temperature and crude touch
- Dorsal horn origin of lamina I, IV, V
Indirect (slow) Lateral STT
- Affective - arousal
- Bilateral
- Synapses in brain
- Sub-cortical targets - hypothalamus, RF, limbic
structures, autonomic centres.
- Dorsal horn origin - Lamina I, IV and V (VII,VIII)
Name the indirect pathways of pain sensation.
What sensations are they responsible for?
Spinoreticular fibres - Arousal, wakefulness Spinomesencephalic fibres - Contributes to activation of descending pain inhibition - Emotion Spinotectal fibres - Reflex eye, upper body and head turning Spinoghypothalamic fibres - Autonomic and reflex responses
What are the stages of nociception?
Transduction
- Activation of nociceptors by a stimulus
Transmission
- Relay of action potentials along nociceptive fibres to
CNS
Modulation
- By other peripheral nerves or CNS mechanisms
Perception (where pain is felt)
- The interpretation by the brain of the sensation as
painful
What are the two different types of nociceptors?
A-delta - Mechanical C - Mechanical - Thermal - Chemical
What are some analgesics acting at site of injury?
NSAID
Steroids
What are some of the things that happen in transduction of a pain stimulus?
A lesion of the skin would then:
- Cause increases of K+, prostaglandin, serotonin and
bradykinin levels, thus activating nociceptor.
- Substance P is the released from nerve endings,
increasing capillary permeability and contributing to
inflammation.
- Substance P also causes mast cells to release
histamine, which in turn activates nociceptor endings
Tell me about the two types of nociceptive fibres.
A-delta Sharp, stabbing pain Well localized First pain / phase 1 Lower threshold Initiates withdrawal reflex
C Dull, throbbing pain Poorly localised Second pain / phase 2 Higher threshold Tissue damage occurring
How do local anaesthetics work? (Very simple)
They inhibit voltage dependant sodium channel activity, thereby stopping the propagation of an action potential along a nociceptive fibre
Where do nociceptive afferents terminate in the spinal cord?
A-delta fibres to I and V
C fibres to I, II(substantia gelatinosa) and V
(A-beta branches to II, IV and V)
STT origin in I, IV to VII
How does visceral and referred pain work?
Visceral fibres converge on the same second order neurones shared by somatic nociceptive fibres (lamina V)
What is analgesia?
Inability to perceive pain when tissue damage is occurring
Can be caused by: Hypnosis Morphine TENS Natural childbirth techniques Placebos