Vestibular nuclei are located under the floor of the fourth ventricle. The nuclei receive input from continually active axons of the vestibular nerve. The nuclei gives rise to tracts that reflexly activate motor neurons that innervate eye muscles, neck muscles, limb extensor muscles. Directly, and via the reticular formation, vestibular nuclei contribute to muscle tone of extensor muscles. They regulate that muscle tone to maintain upright posture.