Final answer:
The second-order neurons of the spinothalamic tract carry pain and temperature information, synapsing in the spinal cord before crossing to the contralateral side and ascending to the thalamus, then relaying this information to the somatosensory cortex.
Step-by-step explanation:
The second-order neurons in the spinothalamic tract are crucial for conveying pain and temperature sensations from the peripheral nervous system to the brain. Starting from the dorsal root ganglion, these neurons extend their axons to the dorsal horn of the spinal cord, where they synapse with the second neuron. This second neuron, situated in the spinal cord gray matter, sends its axon to decussate or cross over to the opposite side of the spinal cord before ascending to the thalamus in the brain. Upon reaching the thalamus, these neurons synapse with a third neuron that projects their axons to the somatosensory cortex located in the postcentral gyrus of the cerebral cortex.
Similar pathways are observed with the dorsal column system, where the second neurons also decussate but do so in the medulla, different from the spinothalamic tract that decussates directly at the spinal level of entry. These two systems, while different in their specifics, share commonality in their three-neuron pathways and their relay of sensory information to the somatosensory cortex.