Final answer:
The cell body of the third neuron in the medial lemniscus pathway is in the thalamus, projecting axons to the postcentral gyrus for processing somatosensory stimuli.
Step-by-step explanation:
The cell body of the third neuron within the medial lemniscus pathway is located in the thalamus. The axons from the second neurons in this system, which start in either the nucleus gracilis or nucleus cuneatus after the fibers in the dorsal columns synapse there, cross the midline in the medulla and ascend through the brain stem as the medial lemniscus. These axons eventually terminate in the thalamus, synapsing with third neurons. These third neurons then project their axons toward the cerebral cortex, specifically terminating in the postcentral gyrus, which is responsible for the initial processing and conscious perception of somatosensory stimuli.