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.
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.
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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