biodex BioSway Operation Manual page 17

CONTENTS
components of balance
(See Figure 4.3.)
Postural balance involves special sensory receptors that provide information in regards to vari-
ous environmental and physiological conditions that may affect a person's ability to maintain
equilibrium. They are as follows:
Figure 4.3. Components of balance.
vestibular apparatus
The vestibular apparatus (VA) consists of three semicircular canals, and provides sensory infor-
mation in regards to head position and gravitational changes. This information is used in three
distinct ways.
1. Assists with maintaining upright posture, these organs are referred to as "sense organs of bal-
ance." As they provide a sense of space via gravitational stimuli. This is apparent when the
eyes are closed and the subject must rely on VA input.
2. Controlling the movement of the eye muscles via the vestibular-ocular reflex (VOR), which
allows the eyes to remain fixed during movement or perturbation. The VOR is important for
maintaining a frame of reference and providing spatial information regarding the environ-
ment around the person. When the VA is disturbed, the eyes will exhibit nystagmus in order
to fix a reference point, otherwise, the movement of the eyes is equal and in the opposite
direction of head movement.
3. Provides conscious awareness in regards to the body's position and acceleration. This infor-
mation is provided after stimuli have been relayed by the thalamus to the cerebral cortex (3).
visual Input
Visual input is important to integrate the stimuli of the VA with the subject's physical environ-
ment. The eyes function to detect a focal point on an object long enough for them to gain a clear
image of that point. When the head is moved, the endolymph in the semicircular canals specific
to that plane of movement bends the tiny hairs located in the semicircular canals and sends
messages to the 8th cranial nerve, assisting to elicit a vestibular-ocular reflex, in turn rotating the
eyes in an equal and opposite direction of the head. This movement allows for a fixed reference
point.
CLINICAL CONSIDERATIONS — 4-2 —