VENTRAL SPINOTHALAMIC TRACT

This sensory tract is found within the ventral or anterior column of the white matter (shown below). Its primary responsibility is to conduct information to higher centers regarding the sense of light touch.

When light touch skin receptors are stimulated, the primary sensory neuron carries the information to the spinal cord via the spinal nerve and dorsal or posterior root into the dorsal horn of the cord. It synapses in the dorsal horn on the secondary sensory neuron which immediately crosses the midline of the central nervous system and enters the ventral white matter. From there, the nerve impulse is carried via the ventral spinothalamic tract up to the level of the thalamus. A second synapse in this pathway occurs in the thalamus and the tertiary sensory neuron then relays the information regarding light touch on to the cerebral cortex for perceptual purposes.

Centrally located in the brainstem is the reticular formation. This area of the brainstem is responsible for "wakefulness" or alertness of the organism. The reticular formation "arouses" or excites the cerebral cortex; oftentimes to prepare it to react to a harmful stimulus or situation. Note that the ventral spinothalamic tract has collateral fibers that "feed into" the reticular formation. The sensation of light touch is considered to be a "protective" stimulus (also referred to as protopathic). These sensations are designed to alert our system to possible danger. As such, these collateral fibers are important in arousing the reticular formation to "fire" and therefore arouse the cerebral cortex as a whole!

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