The Vestibulospinal System

Abstract

Activation of the labyrinth leads to a variety of reflexes of the body and limb musculature. For example, when an animal is rotated to one side, the head turns in the opposite direction, accompanied by appropriate body and limb movement. If the animal is tilted nose down, the dorsal neck muscles contract, leading to restoration of the head’s position in space. This contraction is accompanied by changes in the tone of forelimb and hindlimb muscles. Briefly put, the reflexes result in stabilization of head position and of the visual field. The reflexes are evoked by afferent impulses originating in the maculae and the canal cristae; this activity is processed in the vestibular nuclei and relayed to the spinal cord. An important link between vestibular nuclei and spinal motor centers consists of the lateral and medial vestibulospinal tracts (LVST and MVST), although activity is also relayed by reticulospinal tracts (RST). In this chapter we first examine the anatomy and physiology of these tracts, then consider vestibulospinal reflexes and their role in behaving animals.