Lecture 4: Spinothalamic Pathway Flashcards
What types of fibers are associated with pain and temperature?
Delta-cooling, 1st pain crude touch, has thin myelin C- warming, 2nd pain, no myelin
Where do pain and temperature fibers first enter the spinal cord/
Lissauer’s tract in dorsal horn next to dorsal column
Where do pain and temperature fibers go after they enter Lissauer’s tract?
Up and down 2 spinal segments before crossing midline to ventral horn
How does the conduction velocity of delta fibers compare to C fibers?
Delta fibers transmit faster because they are lightly myelinated while C fibers have no myelin
Where do pain and temperature nerve fibers synapse?
Same level +/- 2 spinal levels in contralateral ALS
What will happen if you cut ALS?
Contralateral loss of pain and temperature 2 spinal levels below lesion
How are 2nd order axons arranged in the ALS?
Sacral is lateral, cervical is medial; neurons get pushed laterally as new ones come in; delta fibers are more dorsal than C fibers
Where do some visceral pain fibers run?
Fasciculus Gracillis
Why do animals lick a wound?
Rubbing a wound activates Ab fibers which activate inhibitory interneurons which turn off pain fibers
Why do people scratch an itch?
Pruriceptive C fibers stimulate inhibitory interneurons for the itch signal but not to threshold. Scratching activates C pain fibers which then puts interneuron over threshold
Hyperalgesia
Increased sensitivity to pain
Allodynia
Pain due to stimulus that usually doesn’t cause pain
Mechanisms of hyperalgesia and allydynia
Where do 2nd order delta fibers synapse?
Ventral posterior lateral nucleus, 3rd order goes to somatosensory cortex
Paleospinothalamic Pathway
C fibers bring info to thalamus, mostly contralateral but also bilateral, which then goes to emotional areas of brain
