Answer
The prefix "contra-" means "opposite" or "on the other side" This combining form is used in the term contralateral.
Work Step by Step
Nerve fibers of the lateral corticospinal tract convey impulses from upper motor neurons to lower motor neurons and neurons in the spinal cord. The nerve fibers in the lateral part of this tract start in in the sensory-motor cortex on one side of the cerebral cortex but cross over (decussate) to the other side ( contralateral side) when they reach the medulla oblongata. Anterior fibers continue ipsilaterally beyond the medulla.
Sensory fibers of the ascending columns also decussate. The fibers of the fasciculus gracilis ( and fasciculus cuneatus) carry proprioceptive information up the spinal cord to the medulla where they decussate ( cross over to the contralateral side of the brain/body). They travel in the posterior-medial lemniscal pathway to the thalamus, and thence to the primary somatosensory.
cerebral cortex to the contralateral side.
