Spinothalamic Tract

Summary

The spinothalamic tract, also known as the anterolateral system or ALS, is a neural pathway that transmits sensory information from the body to the brain. The spinothalamic tract is actually further subdivided into anterior and lateral parts. The anterior tract carries the senses of crude touch and pressure, while the lateral tract carries the senses of pain and temperature.

The anatomical journey of the spinothalamic tract begins in the sensory nerve endings under the skin of the periphery. The sensory information travels up these nerves to bypass the pseudounipolar cell body of the dorsal root ganglion, which serves as the first order neuron of this pathway. The nerve fibers continue into the spinal cord, where they synapse with the dorsal horns on the same side.

The neurons of the dorsal horns are the second order neurons of this pathway. These neurons contain nerve fibers that then decussate or cross sides at the anterior white commissure of the spinal cord. After crossing over to the opposite side of the body, these fibers continue ascending in the spinal cord and brainstem as the anterior and lateral spinothalamic tracts.

Finally, these tracts end by synapsing with the ventral posterolateral or VPL nucleus of the thalamus. The VPL nucleus therefore serves as the third order neuron of this pathway, and nerve extensions from the VPL nucleus continue upwards to eventually reach the primary somatosensory cortex.

Key Points

• Spinothalamic Tract
  • Ascending sensory tract
    • Nerve tract carries sensory information from periphery to brain
  • Functions
    • Lateral: pain, temperature
    • Anterior: crude touch, pressure
  • Pathway
    • 1st order neuron: Pseudounipolar cell body in dorsal root ganglion
      • Sensory nerve ending (A-delta fibers + C fibers) → bypasses pseudounipolar cell body in dorsal root ganglion → enters spinal cord
      • Synapses in dorsal horn of spinal cord
    • 2nd order neuron: ipsilateral dorsal horn of spinal cord grey matter
      • Decussates in spinal cord as the anterior/ventral white commissure
      • Ascends in the contralateral lateral funiculus
      • Synapses in VPL nucleus of thalamus
    • 3rd order neuron: ventral posterolateral nucleus of thalamus
      • Run to primary somatosensory cortex