Pain

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Pain Temperature

• Ascending Pathway in the Spinal Cord
• Spinothalamic Pathway
• Aka
• Anterolateral System

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• Sensory info
• From thermo-
• Receptors
• nociceptors

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Spinothalamic Tract

• DRGN enters dorsal horn at each spinal cord level
• Ascend/descend in Lissaurs tract
• Synapse in Substantia Gelatinosa
• Decussate in ventral spinal cord
• Ascend ventrally in spinal cord as the
  Spinothalamic Tract
• Synapse in thalamus (Ventral Posterior and
  intralaminar Nuclei)
• Thalamic axons travel to S1 somatosensory cortex
  and synapse in layer 4.

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• Two fiber types for
• Temperature
• Two fiber types for
• pain
• C fibers unmyelinated
• convey dull achy pain
• A delta thinly myelinated
• convey fast sharp pain

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Types of Stimuli

• Mechanical stimulation
• Temperature extremes
• Oxygen deprivation
• Chemical exposure

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Nociception Pain

• Nociception is the sensory process that signals
  potential damage to body called nociceptors
• Sore, stinging, throbbing, achy, mildly
  irritating, searing unbearable
• Activation of nociceptors generate action
  potential that trigger the feeling of pain

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Nociceptive Ion Channels

• Ion channels that open when exposed to painful
  stimuli (extreme heat or cold, compression)
• Present in membrane of axons of nociceptor
  neurons
• Mechanically gated channels
• Temperature sensitive neurons called
  thermoreceptor neurons have temperature gated
  channels
• Sense cold or warm burning is sensed by
  different neurons called nociceptors which signal
  damaging temperature extremes

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Polymodal Nociceptors

• Respond best to one but some to all
• Thermal
• Mechanical
• Chemical
• NTs glutamate and Substance P
• Capsaicin causes release of Sub P from nociceptor
  axons
• Large amounts of capsaicin cause analgesia due to
  depletion of sub P from synapses

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Insert 12.26 and 27
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Hyperalgesia

• Increased sensitivity to pain after tissue injury
• Damaged tissue also releases molecules sa
  bradykinin that gate other channels/bind
  receptors
• Secretion of substances, substance P, bradykinin,
  prostaglandin that cause inflammation
• Can cause long lasting intracellular changes that
  increased sensitivity of nociceptive ion channels

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Insert 12.24

• Aspirin suppresses synthesis of prostaglandins

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Referred Pain

• Due to mixing of nociceptive axons from viscera
  with those from skin at the level of spinal cord.
• Perception of visceral information as coming from
  skin areas
• Angina low oxygen in heart is perceived as chest
  and arm pain

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Insert 12.28 and 29