Pain, temperature, and gross touch sense information from most of the body, except the face and a few other parts of the head, travels along axons from the periphery to the spinal cord, where they synapse in the ipsilateral posterior gray horn. Axons from these posterior horn neurons decussate at or near the level where the peripheral axons entered the spinal cord.
Abnormalities of these functions will be ipsilateral if a lesion occurs before the decussation of this pathway, or contralateral with lesions after it. These axons then ascend the spinal cord in a tract called the spinothalamic tract, which is anterolateral, on the border of the anterior and lateral columns.
The axons of this tract continue ascending up the brainstem, and then synapse in the thalamus. Axons of the third neuron in the chain, called the somatosensory thalamocortical tract, travel from the thalamus to the primary somatosensory cortex, from which neurons project to association somatosensory cortices.
Level 3 Unit 2 Part 11: Position, vibration, and fine touch perception of the face