Final answer:
The primary neuron of the spinothalamic pathway is found in the dorsal root ganglion and synapses with the second-order neuron in the dorsal horn of the spinal cord. This pathway is critical for conducting pain and temperature senses to the brain.
Step-by-step explanation:
Spinothalamic Pathway Primary Neuron The primary neuron of the spinothalamic pathway originates in the dorsal root ganglion. These neurons send axons to the spinal cord's dorsal horn, where they synapse with the pathway's second-order neuron. The spinothalamic pathway is responsible for transmitting pain and temperature sensations to the brain.
The axons of the second-order neurons cross over (decussate) to the opposite side of the spinal cord before ascending to the thalamus. Here, they synapse with third-order neurons that project to the postcentral gyrus of the cerebral cortex. The axons from the second neuron cross over to the other side of the spinal cord before ascending to the brain. In the thalamus, the second neuron synapses with the third neuron, which then projects its axon to the somatosensory cortex in the brain.