The vestibular system in the inner ear provides information to the central nervous system to enable four functions: general body orientation with respect to gravity, balanced locomotion, maintaining body position, and adjusting autonomic functions after reorientation. It processes rotational and translational motion along six degrees of freedom through the semicircular canals and macula. This information is used for gaze stabilization, maintaining an upright posture, spatial orientation, and automatic adjustments, though other factors like learning and environment can influence its processing.

1. VESTIBULAR
SYSTEM

2. To generate information for the central nervous system with
a four-fold purpose:
1. provide general orientation of the body with respect to
gravity
2. enable balanced locomotion and body position
3. readjust autonomic functions after body reorientation
ROLE OF THE VESTIBULAR SYSTEM

4. • Central processing of all this information in the brain leads to specific outcomes:
• vestibuloocular reflex (VOR) to ensure gaze stabilization;
• the vestibulospinal reflex (VSR) and the vestibulocollic reflex (VCR) to ensure
maintenance of
an upright position of the body and trunk and head stabilization in space orientation
-- in higher species, navigation and the perception of self-position with respect to the
surroundings and gravity, mediated by the vestibular cortex;
autonomic function adjustments after alterations of body orientation.

5. Although somatosensory, visual and vestibular inputs are constantly processed by the
brain, this information is heavily weighted by other factors, such as learning, memory,
drugs, ageing, as well as environmental conditions.
Additionally, the weight of the different inputs is constantly adjusted depending on the
circumstances.
It is obvious that, for example, walking in darkness, balance can not rely so heavily on
vision and so reliance on the somatosensory and vestibular senses is increased.
For optimal functioning in daily life, all systems are needed.

6. Motion decomposition and orientation in the head
Every motion in space can be broken down into three rotational degrees of freedom
(yaw, pitch and roll) and three translational degrees of freedom (left–right, up–down,
for–aft).
No event in one degree of freedom can be described by the others, hence every
movement is uniquely and appropriately described by a combination of all six degrees of
freedom.
The anatomical design of the motion sensors in the peripheral vestibular system in the
inner ear reflects these six degrees of freedom. The semicircular canals measure
predominantly rotations, whereas the macules of the utricle and saccule detect mainly
translations.

7. Nystagmus
The eye response to a head rotation consists of a combination of a slow phase or drift until the eye
reaches the edge of the outer canthus, and a fast phase to reset the eye in its initial position.
This saw-tooth pattern is called nystagmus.
The direction of the nystagmus is defined by the fast reset phase, since this is the most easy for the
clinician to identify.
The slow phase, however, represents the actual vestibular output and is quantified.