The spinothalmic pain pathway involves a three neuron sequence (like most conscious pathways to the cerebral cortex):
1]. Primary afferent neurons (cell bodies in spinal ganglia) have nociceptors at the peripheral ends of their axons and pre-synaptic endings at the central ends of their axons.
2.] Spinal projection neurons (cell bodies in the dorsal horn of the spinal cord) receive synaptic input from primary afferent neurons and project their axons to the thalamus (ventral posterior lateral nucleus).
3.] Thalamic projection neurons (cell bodies in thalamic nuclei) receive synaptic input from spinal projection neurons and project their axons to the cerebral cortex (somatosensory cortical area).
In addition to the spinothalamic pain pathway, the spino-cervico-thalamic pathway is a significant pain pathway in carnivores The spino-cervico-thalmic pathway is a four neuron pathway.
The following animation illustrates traffic in the three neuron spinothalmic pathway following noxious stimulation (click Start to begin the animation & stop to halt it):