Final answer:
The path for touch and internal motion information to the brain crosses over in the brain stem, specifically within the medulla oblongata. Sensory information from the body below the neck travels via the spinal cord, through the dorsal column and spinothalamic pathways, forming the medial lemniscus, to reach the thalamus. The face and head sensations are transmitted by the trigeminal system, with information processed in different nuclei within the brain stem.
Step-by-step explanation:
The pathways that carry touch and proprioceptive information (related to body position and movement) from the body to the brain are termed ascending pathways, or ascending tracts. For the body below the neck, this information travels via the spinal cord and brain stem. Sensory information from the skin, muscles, tendons, and joints is processed through two main spinal cord systems: the dorsal column pathway and the spinothalamic pathway. As these pathways enter the brain stem, they form a structure known as the medial lemniscus, which carries the sensory data to the thalamus. It is here in the medulla oblongata, within the brain stem, that most of the axons from these pathways cross over to the opposite side, a process called decussation. This crossing over ensures that the right side of the brain processes sensory and motor signals from the left side of the body, and vice versa. In comparison, the sensation from the face and head travels through the trigeminal system via cranial nerves into the brain stem, passing through structures such as the mesencephalic, chief, and spinal trigeminal nuclei. The final destination for all these sensory signals is the postcentral gyrus of the parietal lobe in the cerebral cortex, which is responsible for the conscious perception of touch and proprioceptive stimuli.