Vertigo (cont.)
Motion sickness
Whereas vertigo, lightheadedness, and dizziness are symptoms of diseases,
motion sickness is a normal response to an abnormal situation. It is a general
term that includes such conditions as seasickness, airsickness, carsickness, and
even space sickness. Motion sickness is caused by a real or perceived motion
stimulus to which a person has not yet adapted. It occurs when conflicting
information is fed into the vestibular and other sensory systems.
Individual thresholds (the amount of motion it takes) to trigger motion
sickness differ. Eventually, however, anyone will develop motion sickness if
placed in a situation that provides enough motion. The symptoms of motion
sickness include nausea, vomiting, spinning, sweating, and headache. In fact,
motion sickness has ruined many a vacation, and has limited the activities or
even incapacitated those who are prone to it. (Motion sickness is discussed in
more detail below.)
What problems cause balance disorders?
The cause of a balance disorder may be a well-defined anatomical condition,
or simply a psychological reaction to an unpleasant life event. In some
situations, the underlying condition is of only minor significance, while at
other times it may be life threatening. Unfortunately, finding the cause of a
balance problem can at times be frustrating and exhausting. For example, almost
any problem in any system of the body can lead to the symptom of dizziness or to
a balance disorder.
Our orientation in space and, therefore, our balance or equilibrium, is
primarily measured by three sensory systems:
- The eye (visual) system
- The balance (vestibular) system of the inner ear
- The general sensory system including motion, pressure, and position
(proprioception) sensors in joints, muscles, and skin.
These three systems continuously feed information to the brainstem and brain
about our position in space relative to gravity. (The brainstem is the part of
the brain that connects to the spinal cord.) The brain, in turn, processes these
data and subsequently uses the information to make minute adjustments of our
head, body, joints, and eyes. When all three sensory systems and the brain are
properly functioning, the final result is a healthy balance system.
By the same token, when the balance system is not functioning, one can
usually trace the problem back to a disorder of one of the three sensory systems
or the data processor (brain). The problems in each of the following areas
correspond to one of these sensory systems or the brain.
Visual
Visual input provides essential clues about our spatial orientation. That is,
visual input tells the brain where the body is "in space:" what
direction it is pointing, what direction it is moving, and if it is turning or
standing still. Also, something as simple as walking a straight line is much
easier if we can see our surroundings. Feeling seasick is a problem resulting
from a miscommunication between a healthy visual system and a healthy inner ear
(vestibular) system. In this circumstance, the ears are telling the brain that
there is movement, while the eyes may be seeing the fixed surroundings of the
cabin. Simple eye refraction errors, glaucoma, and cataracts are examples of
visual problems that in some individuals may be enough to give them a balance
disorder.
Inner ear (vestibular)
Just where is the inner ear? Also known as the labyrinth, the inner ear is
located deep to the outer ear and middle ear, and is encased within the
so-called petrous portion of the temporal bone of the skull. The figure below is a
diagram showing the parts of the ear.
Figure 1. Diagram of outer, middle, and inner ear. The outer ear is labeled
in the figure and includes the ear canal. The middle ear includes the eardrum
(tympanic membrane) and three tiny bones for hearing. The bones are called the
hammer (malleus), anvil (incus), and stirrup (stapes) to reflect their shapes.
The middle ear connects to the back of the throat by the Eustachian tube. The
inner ear (labyrinth) contains the semicircular canals and vestibule for
balance, and the cochlea for hearing.
The vestibular structures of the inner ear are the vestibule (which is made
up of the utricle and saccule) and the three semicircular canals. These
structures work somewhat like a carpenter's level (a tool used to show how "level"
a horizontal or vertical surface is). That is, they work by way of the
vestibulocochlear nerve with the vestibular center in the brain to deal with
body balance and position. (The rest of the inner ear, that is, the cochlea, is
concerned with hearing.) Thus, the vestibular system includes the vestibule, the
semicircular canals, the vestibular branch of the vestibulocochlear nerve, and
the vestibular center in the brain.
The vestibular system measures linear and rotational movement. A number of
disorders can cause this system to stop working or provide inappropriate
information. These disorders include Meniere syndrome, labyrinthitis, benign
paroxysmal positional vertigo, ear infections, tumors, or trauma. Each of these
conditions is discussed below.
General sensory system
The general sensory system consists of motion, position, and pressure sensors
in the skin, muscles, and joints. These sensors provide important touch
(tactile) and position information to keep us balanced. For example, if someone
pushes you from behind, a slight increase will occur in the activity of the
pressure sensors in the ball of the feet. As these sensors note the increased
pressure, the brain is notified, and it knows from experience that the body is
being pushed forward. The brain then uses this information to tell the body to
shift a small amount of weight backward to prevent the body from toppling
forward. So, disorders involving the general sensory system can result in
balance problems.
Brain
As mentioned, the brain processes the information from the three sensory
systems. Any problem that interferes with the proper functioning of the central
nervous system (CNS), therefore, can lead to a balance disorder. (The CNS is
made up of the brain and spinal cord.) Unlike the problems associated with the
three sensory input systems discussed above, however, with CNS problems, it is
unusual to have vertigo as the only symptom.
Examples of processor problems include brain infections or abscesses, strokes
(vascular insufficiency), migraine
headaches, brain tumors, head trauma,
degeneration syndromes (due, for example, to alcoholism), and multiple
sclerosis. Furthermore, any disease that interferes with the proper functioning
of the CNS can also cause balance problems. Examples of these diseases include
heart conditions (e.g., abnormal heart rhythms or congestive heart failure),
anemia, metabolic or hormonal conditions (diabetes, dehydration, or thyroid
disorders), and psychological problems, such as anxiety or heavy breathing
(hyperventilation).
A common cause of this type of balance problem is insufficient blood flow to
the brain. In elderly individuals, there is often narrowing of the blood vessels
to the brain (hardening of the arteries or arteriosclerosis) or decreased blood
flow from the heart (e.g., with heart failure). In these situations, because of
decreased blood flow to the brain, the affected individual will become dizzy
when getting up from a sitting or reclining position.
Since the balance system has so many components with interdependent
functions, it is not surprising to find literally hundreds of different causes
of balance problems. Although it may not be possible to diagnose the exact cause
of imbalance in every patient, a patient's symptoms often can be classified into
a well-defined clinical disorder.
Next: How are patients with balance disorders evaluated? »
- promethazine, Phenergan - Explains the medication promethazine (Phenergan), a drug used to prevent motion sickness, nausea or vomiting, itching associated with allergies or for sedation.
- CT Scan (Computerized Axial Tomography) - CT Scan (Computerized Axial Tomography, CAT scan) is a procedure that assists in diagnosing tumors, fractures, bony structures, and infections in the organs and tissues of the body.
- Migraine - Learn about migraine headache including symptoms such as intense throbbing pain in the temple area of head. Migraine triggers vary from person to person.
Latest Medical News
Neurology RSS