Transcript Chapter 14 Part 2

Pain & Temperature
Ascending Pathway in the Spinal Cord
Spinothalamic Pathway
Aka
Anterolateral System
• Sensory info
From thermoReceptors &
nociceptors
Spinothalamic Tract
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DRGN enters dorsal horn at each spinal cord level
Ascend/descend in Lissaur’s 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.
•Two fiber types for
Temperature
•Two fiber types for
pain
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C fibers unmyelinated
•convey dull achy pain
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A delta: thinly myelinated
•convey fast sharp pain
Types of Stimuli
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Mechanical stimulation
Temperature extremes
Oxygen deprivation
Chemical exposure
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
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
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
Insert 12.26 and 27
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
Insert 12.24• Aspirin suppresses
synthesis of
prostaglandins
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
Insert 12.28 and 29