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Pain & Temperature
Ascending Pathway in the Spinal Cord
Spinothalamic Pathway
Aka
Anterolateral System
• Sensory info
From thermo-
Receptors &
nociceptors
Spinothalamic Tract
• 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• C fibers unmyelinated
•convey dull achy pain
• A delta: thinly myelinated •convey fast sharp pain
Types of Stimuli
• 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