Final answer:
The second-order neurons of both specific and nonspecific ascending pathways terminate in the thalamus, where they synapse with third-order neurons, leading to the processing of sensory information in the somatosensory cortex.
Step-by-step explanation:
The second-order neurons of both the specific and nonspecific ascending pathways terminate in the thalamus. The axons from these neurons in the spinal cord and other parts of the nervous system ascend and enter the thalamus, where they synapse with the third neuron in their respective pathway.
Sensory information, such as touch, proprioception, pain, and temperature sensations, pass through these ascending tracts, namely the dorsal column-medial lemniscus system and the spinothalamic tract. These systems are crucial for the conscious perception of somatosensory stimuli that ultimately reach the somatosensory cortex after the third neurons project their axons to the postcentral gyrus.