The brain stem is the subcortical region that contains all but 2 of the 12 cranial nerves. Associated with the cranial nerves are centers that control the heart, lung, and GI systems and control the muscles in the head and neck. We speak and move our eyes and all the muscles in the head due to the cranial nerves. All major ascending pathways from the spinal cord and cerebellum pass through the brain stem on their way to the thalamus. Major pathways originate from the many nuclei in the brain stem and terminate in the thalamus. Cerebral cortical control of the cranial nerves, corticonuclear fibers, descends from the cortex to the brain stem, and cortical fibers to the spinal cord, corticospinal, pass through the stem on their way to provide motor control of the limbs.