A balance disorder is a condition that makes you feel unsteady or dizzy, as if you
are moving, spinning, or floating, even though you are standing still or lying down.
Balance disorders can be caused by certain health conditions, medications, or a
problem in the inner ear or the brain.
Our sense of balance is primarily controlled by a maze-like structure in our inner
ear called the labyrinth, which is made of bone and soft tissue. At one end of the
labyrinth is an intricate system of loops and pouches called the semicircular canals
and the otolithic organs, which help us maintain our balance. At the other end is a
snailshaped organ called the cochlea, which enables us to hear. The medical term
for all of the parts of the inner ear involved with balance is the vestibular system
How does the vestibular system work?
Our vestibular system works with other sensorimotor systems in the body, such as
our visual system (eyes) and skeletal system (bones and joints), to check and
maintain the position of our body at rest or in motion. It also helps us maintain
a steady focus on objects even though the position of our body changes. The
vestibular system does this by detecting mechanical forces, including gravity,
that act upon our vestibular organs when we move. Two sections of the labyrinth
help us accomplish these tasks: the semicircular canals and the otolithic organs.
The semicircular canals are three fluid-filled loops arranged roughly at right
angles to each other. They tell the brain when our head moves in a rotating or
circular way, such as when we nod our head up and down or look from right to left.
Each semicircular canal has a plump base, which contains a raindrop-shaped
structure filled with a gel-like substance (see Figure 2). This structure, called
the cupula, sits on top of a cluster of sensory cells, called hair cells. The hair
cells have long threadlike extensions, called stereocilia, that extend into the
gel.
When the head moves, fluid inside the semicircular canal moves. This motion
causes the cupula to bend and the stereocilia within it to tilt to one side. The
tilting action creates a signal that travels to the brain to tell it the movement
and position of your head.
Between the semicircular canals and the cochlea lie the otolithic organs, which
are two fluid-filled pouches called the utricle and the saccule. These organs
tell the brain when our body is moving in a straight line, such as when we stand
up or ride in a car or on a bike. They also tell the brain the position of our head
with respect to gravity, such as whether we are sitting up, leaning back, or lying
down.
Like the semicircular canals, the utricle and the saccule have sensory hair cells.
These hair cells line the bottom of each pouch, and their stereocilia extend into
an overlying gel-like layer. On top of the gel are tiny grains made of calcium
carbonate called otoconia. When you tilt your head, gravity pulls on the grains,
which then move the stereocilia. As with the semicircular canals, this movement
creates a signal that tells the brain the head's position.
Our visual system works with our vestibular system to keep objects from blurring
when our head moves and to keep us aware of our position when we walk or when
we ride in a vehicle. Sensory receptors in our joints and muscles also help us
maintain our balance when we stand still or walk. The brain receives, interprets,
and processes the information from these systems to control our balance.
