Question

how precise the lesion would need to be see the ipsilateral motor losses and the contralateral sensory loss?

Answer 1

Answer:

In each of the somatosensory pathways covered thus far, afferent axons decussate (cross the midline) once on their course to the thalamus. At the level of decussation, the neurons in a somatosensory pathway represent the contralateral (i.e., opposite) side of the body or face.

It is important to learn the decussation site, as it will aid in clinical diagnosis. When an afferent pathway is damaged somewhere below the site of decussation, the sensory loss will be on the side ipsilateral to the lesion (i.e., the loss is on the same side as the lesion or ipsilesional).

When an afferent pathway is damaged somewhere above the site of decussation, the sensory loss will be on the side contralateral to the lesion (i.e., the loss is on the side opposite the lesion or contralesional).