Vestibular control of muscular tone and posture.

The vestibulospinal system helps to maintain upright posture and head stability. The semicircular canals and their short latency connections to the neck motoneurons, largely via the medial vestibulospinal tract, respond to angular accelerations so as to stabilize the head in space. The paired otolith organs, the utricles placed approximately horizontally, and the saccules vertically, respond to linear acceleration including gravity. Their influence leads, via the lateral vestibulospinal tract, to excitation of ipsilateral extensor motoneurons of the limbs and trunk, and to inhibition of reciprocal flexor motoneurons. Linear displacement of the otoliths leads to bracing of the limbs and body so as to maintain upright posture, and to extend the limbs so as to help in landing after sudden falls.