The Spinothalamic Tract and Pain Control

I find this pathway quite interesting, because the sensations of pain and temperature can be down regulated by the brain and our emotions. This what allows Yogis to calmly walk barefoot in the snow

There are three levels to this pathway

 Level 1

The pathway starts with free nerve endings of the primary neurons. The Axons of these neurons enter the spinal cord through Lissauer’s fasciculus. They will travel up at least one segment of the spinal cord before synapsing on the secondary neurons in the ipsilateral posterior horn of the spinal cord.

 Level 2

There are two travel options for the secondary neurons. Most axons will mostly travel up on the contralateral side but some will travel up on the ipsilateral side.

• 1. Contralateral ascension

The secondary neurons send their axons across the midline before going up through the lateral spinothalamic tract until they reach and synapse on the ventral post lateral nucleus of the thalamus.

There is already a sort of “map” in the lateral spinothalamic tract in that axons from the lower parts of the body travel up more on the lateral side of the tract whereas axons from the upper body travel up more on the “inner” side of the tract (the side closer to the middle of the spinal cord).

This is important for surgeons when they need to severe some of the fibers to alleviate pain.

Along the way, some secondary neurons send out branches that synapse in the reticular formation or in the periaqueductal gray. It’s in these regions that pain sensations can be down-regulated by the brain.

• 2. Ipsilateral ascension

It is important to note that some secondary neurons’ axons travel up on the ipsilateral side (through the Lissauer’s fasciculus) and synapse in the thalamus.

Level 3

The tertiary neurons send their axons through the internal capsule, then through the corona radiata and eventually synapse on the postcentral gyrus  or in the secondary sensory cortex.

Things to remember:

• The Lateral Spinothalamic tract is involved in the transmission of protopathic pain and temperature.
• There are three synaptic levels:

1. Dorsal horn of the spinal cord
2. Thalamus (mostly the ventral  post lateral nucleus of the thalamus)
3. Postcentral gyrus.

• As the fibers ascend through the spinothalamic tract, they arrange themselves with fibers from the lower body being more on the “side”