Definition: a band of white fibers originating from the gracile and cuneate nuclei and decussating in the lower medulla; thence it passes upward through the center of the medulla oblongata, close to the median raphe; on entering the pons it spreads out laterally to form a flat band ascending over the superior border of the pontine nuclei; in the mesencephalon it passes over the superior border of the substantia nigra and is displaced laterally by the red nucleus; passing medial to the medial geniculate body, the bundle enters and terminates in the ventral posterior nucleus of the thalamus. Throughout their course, the fibers retain a somatotopic order such that those originating from the gracile nucleus and representing the lower extremity lie lateral to those originating in the cuneate nucleus and representing the arm. The medial lemniscus conveys somatic-sensory information involved in tactile discrimination (2-point discrimination), position sense, and vibration sense.
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