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One of the more important functions of the vestibular system is its participation, along with vision and the somatosensory system, in postural control. While all parts of the nervous system, including the cerebral cortex, contribute to the construction of postural commands, of necessity these have to be executed by way of the spinal cord (and brain stem). This chapter considers the contribution of the vestibular system to these processes. It begins with a discussion of the relative roles of reflexes and multisensory strategies in postural control.

This study involves a kinematic analysis based on the examination of trajectories, velocities, and accelerations of all markers. The two questions pursued in this study are: (1) would it be possible to distinguish responses from subjects when normal humans walked under three different conditions of vertical head posture? (2) how could results fit into recent observations on the linkage between gaze position, otolith influences, and neck muscles as the uppermost part of the truncal/skeletal muscles? The results showed that the otolith input appears to dominate particularly neck prioceptive and gaze motor influences during normal gait. Thus, postural control depends on the integration of vestibular, somatosensory, and visual orientation signals.

This chapter's objective is to answer the question about the coordination of head and trunk movements as to whether head movements follow those of the trunk, as a passive mass-spring-dashpot system would. Three important factors of postural control must be analyzed, including the definition of head stabilization, the fact that the displacement of body segments set in motion may be greater than the muscles' available contractile forces, and the possibility that the presence of rapid adaptation of neck extensor responses to successive platform rotations may represent switching to a head stabilization regulation mode. The purpose of this study is to clarify these issues and determine the degree to which the passive biomechanical properties may dominate the head movements on the trunk.

This chapter studies the properties and the functional coupling of four sensory-motor subsystems that contribute to the head and eye stabilization during linear motion in the vertical plane. The problems investigated in this chapter include the way the reflexes interact and are functionally coupled and the solutions relating to the central nervous system (CNS) when the there is an impaired eye-head coordination. The dynamics of the vestibulocollic reflex, oculocollic coupling, and the compensatory eye movements are discussed here. It is concluded that tight coupling between the visual and vestibular systems in head postural control and gaze stabilization also operates during linear motion in the vertical plane.