The Vestibular System
The vestibular system not only drives gaze and body stabilizing responses to head
motion in space, but also interacts in complex ways with other sensory systems to
generate spatial percepts and to guide reflexive and voluntary action.
Humans have the ability to control posture and movements of the body and eyes
relative to the external environment. The vestibular system mediates these motor
activities through a network of receptors and neural elements. This system
integrates peripheral sensory information from vestibular, somatosensory,
visceromotor, and visual receptors, as well as motor information from the
cerebellum and cerebral cortex. Central processing of these inputs occurs rapidly,
with the output of the vestibular system providing an appropriate signal to
coordinate relevant movement reflexes. Although the vestibular system is
considered to be a special sense, most vestibular activity is conducted at a
subconscious level. However, in situations producing unusual or novel vestibular
stimulation, such as rough air in a plane flight or wave motion on ships, vestibular
perception becomes acute, with dizziness, vertigo, or nausea often resulting.
The vestibular system is an essential component in the production of motor
responses that are crucial for daily function and survival. Throughout evolution,
the highly conserved nature of the vestibular system is revealed through striking
similarities in the anatomic organization of receptors and neuronal connections in
fish, reptiles, birds, and mammals.
For the present discussion, the vestibular system can be divided into five
components: (1) the peripheral receptor apparatus resides in the inner ear and is
responsible for transducing head motion and position into neural information. (2)
The central vestibular nuclei comprise a set of neurons in the brainstem that are
responsible for receiving, integrating, and distributing information that controls
motor activities such as eye and head movements, postural reflexes, and gravity-
dependent autonomic reflexes and spatial orientation. (3) The vestibulocular
network arises from the vestibular nuclei and is involved in the control of eye
movements. (4) The vestibulospinal network coordinates head movements, axial
musculature, and postural reflexes. (5) The vestibulothalamocortical network is
responsible for the conscious perception of movement and spatial orientation.