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