Final answer:
The spinothalamic tract begins with neurons in the dorsal root ganglion, synapses with second neurons in the spinal cord, and then ascends to the thalamus. After decussation, the pathway ends at the postcentral gyrus of the cerebral cortex, chiefly responsible for pain and temperature sensation.
Step-by-step explanation:
The spinothalamic tract is a critical component of the sensory system, starting with neurons in a dorsal root ganglion. These neurons extend their axons to the dorsal horn, synapsing with the second neuron within the spinal cord's gray matter. The axons of these second neurons decussate, or cross over within the spinal cord, then ascend to the brain, entering the thalamus. Here, they synapse with the third neuron that ultimately projects to the postcentral gyrus of the cerebral cortex.
The spinothalamic pathway is primarily responsible for transmitting pain and temperature sensations, in contrast with the dorsal column system, which conveys touch sensations and proprioception. Both systems involve three successive neurons and exhibit a contralateral organization, where the second neuron projects across the midline. In the dorsal column system, the decussation occurs in the brain stem, while in the spinothalamic tract, it happens at the spinal level where the sensory information enters.
These pathways, along with the trigeminal pathway, which carries somatosensory information from the face, compose the major ascending pathways connecting the periphery with the brain. The second neurons in all these pathways synapse in the thalamus, and then the third neurons project to the somatosensory cortex, underscoring the fundamental architecture of the sensory pathways.