Sensory pathways from the periphery to the cortex are separate for touch-position and pain-temperature sensations.
All sensory information is sent to specific nuclei in the thalamus.
Thalamic nuclei, in turn, send information to specific areas in the cerebral cortex.
Each pathway consists of three bundles of nerve fibers connected in series:
The secondary neurons in each pathway decussate (cross the spinal cord or brainstem), because the spinal cord develops in segments.
Decussated fibers later reach and connect these segments with the higher centers.
The optic chiasm is the primary cause of decussation; nasal fibers of the optic nerve cross (so each cerebral hemisphere receives contralateral—opposite—vision) to keep the interneuronal connections responsible for processing information short.
All sensory and motor pathways converge and diverge to the contralateral hemisphere.

Although sensory pathways are often depicted as chains of individual neurons connected in series, this is an oversimplification.
Sensory information is processed and modified at each level in the chain by interneurons and input from other areas of the nervous system.
For example, cells in the main trigeminal nucleus (Main V in the diagram below) receive input from the reticular formation and cerebral cortex.
This information contributes to the final output of the cells in Main V to the thalamus.

Touch-position information from the body is carried to the thalamus by the medial lemniscus, and from the face by the trigeminal lemniscus (both the anterior and posterior trigeminothalamic tracts).
Pain-temperature information from the body is carried to the thalamus by the spinothalamic tract, and from the face by the anterior division of the trigeminal lemniscus (also called the anterior trigeminothalamic tract).

Pathways for touch-position and pain-temperature sensations from the face and body merge in the brainstem, and touch-position and pain-temperature sensory maps of the entire body are projected onto the thalamus.
From the thalamus, touch-position and pain-temperature information is projected onto the cerebral cortex.
Sensory pathways from the periphery to the cortex are separate for touch-position and pain-temperature sensations. All sensory information is sent to specific nuclei in the thalamus. Thalamic nuclei, in turn, send information to specific areas in the cerebral cortex. Each pathway consists of three bundles of nerve fibers connected in series:
The secondary neurons in each pathway decussate (cross the spinal cord or brainstem), because the spinal cord develops in segments. Decussated fibers later reach and connect these segments with the higher centers. The optic chiasm is the primary cause of decussation; nasal fibers of the optic nerve cross (so each cerebral hemisphere receives contralateral—opposite—vision) to keep the interneuronal connections responsible for processing information short. All sensory and motor pathways converge and diverge to the contralateral hemisphere.
Although sensory pathways are often depicted as chains of individual neurons connected in series, this is an oversimplification. Sensory information is processed and modified at each level in the chain by interneurons and input from other areas of the nervous system. For example, cells in the main trigeminal nucleus (Main V in the diagram below) receive input from the reticular formation and cerebral cortex. This information contributes to the final output of the cells in Main V to the thalamus.
Touch-position information from the body is carried to the thalamus by the medial lemniscus, and from the face by the trigeminal lemniscus (both the anterior and posterior trigeminothalamic tracts). Pain-temperature information from the body is carried to the thalamus by the spinothalamic tract, and from the face by the anterior division of the trigeminal lemniscus (also called the anterior trigeminothalamic tract).
Pathways for touch-position and pain-temperature sensations from the face and body merge in the brainstem, and touch-position and pain-temperature sensory maps of the entire body are projected onto the thalamus. From the thalamus, touch-position and pain-temperature information is projected onto the cerebral cortex.
Trigeminal nerve