SENSORY FUNCTION AND PAIN

1
SENSORY FUNCTION AND PAIN

• NEURAL MECHANISMS OF PAIN SENSATION
• NON-PHARMACOLOGICAL METHODS OF ANALGESIA
• ANALGESIC DRUGS

2
WHAT IS PAIN?

• A complex experience influenced by factors
  physiological
• psychological
• social
• cultural
• cognitive

3
PAIN MECHANISMS

• sensory nerve? spinal ? thalamus ? cortex ?
  reaction
• endings cord
• NOCICEPTION PAIN

4
PAIN PATHWAYS

• somatosensory
  limbic cortex
• cortex
  (emotion)
• thalamus
• sharp dull,
  aching
• pain
  pain
• painful ? A-delta fibre ? ? dorsal horn ?
  withdrawal
• stimuli ? C-fibre ? ? ? of spinal cord
  reflex

5
PAIN PERCEPTION AND MODULATION

• Gate control theory sensory stimulation near
  painful area ? long-lasting pain ?
• May be due to touch fibres and pain fibres
  synapsing on same association neurons - so a
  block (gate) may occur in spinal cord
• Pain receptors free nerve endings in skin, some
  organs, periosteum

6
PAIN PERCEPTION AND MODULATION

• Pain-producing substances at receptors and in
  nerve pathway
• bradykinin (from plasma)
• prostaglandins (from damaged tissue - enhance
  this effect)
• substance P (at synapse in spinal cord)

7
TYPES OF PAIN

• Sources - cutaneous
• - deep somatic (more diffuse)
• - visceral (little pain, except
  from
• ischemia or strong contraction)
• - visceral becomes referred pain
• - neuropathic pain
• Fast vs slow conduction by A-delta fibres
• vs
  C-fibres

8
TYPES OF PAIN

• Duration acute ? sympathetic responses
• (?HR, ?BP, anxiety)
  
• chronic ?withdrawal, depression
• (gt6 mths) (no useful function)
• Headache causes
• - intracranial vascular, meningeal,? CSF,
• vasospasm and dilation (migraine)
• - extracranial nasal, eyes, muscle tension

9
PAIN MODULATION IN CNS

• Endogenous analgesia centres in midbrain and
  brainstem
• Signals sent down spinal cord inhibit pain
  signals
• Opioid neurotransmitters (endorphins and
  enkephalins) act like morphine
• Action may be by inhibiting release of substance
  P from C-fibres
• Other modulators in ?path 5-HT and NA

10
TREATMENT OF PAIN

• Non-pharmacological
• - distraction imagery
• - heat and cold
• - TENS, acupuncture
• Pharmacological - analgesics
• a) Non-narcotic aspirin and NSAIDs
• Action ?PG synthesis in damaged tissue
• Side-effects ?bleeding, ?gastric irritation

11
TREATMENT OF PAIN

• b) Narcotic analgesics opioids
• 
  (morphine-like)
• Action mimic endogenous opioid peptides at
  receptors in brain and spinal cord (descending
  pathway)
• -more effective against dull pain
• c) Progressive approach to analgesia
• NSAIDs weak opioid ? ? strong opioid
• (eg codeine) (morphine)