- Education and Science»
- Life Sciences
What Causes Dizziness
As children, we all had endless fun with playground games that made us dizzy. Many carnival and theme park rides are designed with dizziness in mind, leaving riders pleasantly (or unpleasantly) off-balance at the end of the ride. Producers of action and adventure movies have also become particularly skilled at rendering audiences dizzy and disoriented with visual effects alone.
However, dizziness is not always a laughing matter. Dizziness is one of the most commonly-reported medical complaints, with 20-30% of the population reporting experiencing dizziness in the past year according to some surveys. Dizziness is the primary reported symptom in 5-6% of physician visits and 3% of emergency room visits. Recurrent vertigo - a perceived sense of rotary movement or being pulled off-balance - can cause severe impairments to daily occupational, transportation, and leisure activities. In rare cases, chronic dizziness and vertigo can be a sign of a serious medical condition.
Dizziness itself is not a medical term. It is a general lay term describing symptoms such as light-headedness, imbalance, and faintness resulting from a malfunction of the vestibular system. This is the sensory system in our body that measures balance and motion. Before we can understand how this system malfunctions, it is important to understand how the system works to maintain our sense of equilibrioception.
What is Equilibrioception?
Although we're usually taught in grade school that there are five senses: sight, sound, touch, taste, and smell, in reality there are quite a few additional ones that we take for granted. Equilibrioception is one of these additional senses, and it refers to our sense of gravity.
The primary sensory organ for equilibrioception is the semicircular canal structure of the inner ear. the organ consists of three fluid-filled loops oriented roughly in the x, y, and z directions. At the base of each loop is a floating gumdrop-shaped structure called the cupula, which is connected to the nervous system by a number of hair-like nerve fibers.
When the head is turned, moved side-to-side, or pitched up or down, the fluid in the loop moves, shifting the cupula and triggering a signal from the nerve fibers. This is then interpreted in the brain as a change in orientation, and we are able to perceive the direction of gravity. A second pair of structures in the vestibule of the inner ear known as the utricule and saccule measure acceleration in much the same way. It is because of these sensory organs of equilibrioception that we are able to ride a roller coaster with our eyes closed and still know when we're going over the loop-de-loop (well, apart from the screams of our fellow passengers).
However, the semicircular canals are only one source of input for the vestibular system. This system also works in tandem with the visual system and our sense of proprioception - the positioning of the parts of our body to provide additional input. When all of these parts are working correctly, our brains can construct a full understanding of how we're oriented and how we're moving.
When the different components of this system are providing conflicting information, the brain struggles to reconcile the conflict. Dizziness is one of the usual results of this conflict.
Hitchcock's Masterpiece: Vertigo (1958)
Medical Causes of Dizziness
The feeling described by patients under the general term "dizziness" usually refers to one of three specific medical symptoms:
- vertigo - a sensation of spinning, often accompanied by motion sickness and nausea;
- disequlibrium - a sensation of being off-balance, occasionally causing repeated falls in a particular direction
- pre-syncope - a feeling of light-headedness, almost to the point of fainting.
The underlying medical conditions causing these symptoms range from the relatively benign to quite serious, and anyone experiencing chronic vertigo, disequilibrium, or light-headedness should seek medical attention.
On the benign end of the list are temporary disruptions to the flow of fluid in the inner ear. This is why the spinning games we played as children cause us to feel dizzy - repeated spinning changes the inertia of the fluid in one or more semicircular canals, causing the cupula to send signals to the brain that we are still in motion long after we've stopped. The flow of fluid can also be affected by colds, sinus infections, migrane headaches, prescription medications, and excessive alcohol consumption (a condition colloquially referred to as "the spins.")
Benign paroxysmal positional vertigo (BPPV) is a more chronic cause of dizziness, caused when some of the calcium deposits that help the utricle measure acceleration come loose and become lodged in the semicircular canals. Patients with BPPV will often have a feeling of dizziness triggered by turning their heads, looking up or down, or getting up from a lying position.
Another condition, known as Ménière's disease, occurs when an excess of fluid in the inner ear causes damage to the sensitive structures that measure balance and acceleration. Often prompted by an inner ear infection or injury to the head, the recurring dizziness of this condition can also be accompanied by tinnitus and temporary hearing loss.
On the more serious side, dizziness can also be caused by drops in blood pressure, anemia, tumors, thyroid disorders, hemmorhage or infection in the brain, and psychiatric conditions such as depression or anxiety. While these serious causes only account for about 5% of reported cases of dizziness, they are a good reason to treat chronic dizziness with care.
Sources and More Information
- Dizziness: A Diagnostic Approach
American Family Physician - Volume 82, Issue 4 (August 2010)
- Dizziness and Vertigo: Approach to the Patient With Ear Problems: Merck Manual Professional
- Vertigo: Epidemiologic Aspects
Hannelore K. Neuhauser, Thomas Lempert. Semin Neurol 2009; 29(5): 473-481
- Web of Life - NASA's Fundamental Space Biology Outreach Program
How does the human body maintain a sense of body position and balance on Earth, while flying in an airplane, or traveling through space?