Nausea, << NAW shuh or NAW shee uh, >> is a disagreeable sensation in the area of the stomach. It is often followed by vomiting. In nausea, the muscles of the stomach wall slow or stop their movement. In turn, digestion of the contents of the stomach slows or stops. This action can help prevent the body from absorbing a poisonous substance that has been swallowed. If vomiting takes place, most of the substance will be expelled.
Nausea also may result from many other causes, both mental and physical. Mental causes of nausea include unpleasant sights, disgusting odors, and severe anxiety. Physical causes include severe pain, obstruction or irritation of the digestive tract, excessive physical exercise, and unnatural stimulation of the vestibular system, the organs of balance of the inner ear. Nausea that results from disturbances of the vestibular system is called motion sickness (see Motion sickness). Nausea often accompanies pregnancy, especially in the mornings of the first three months.
Some poisonous substances cause nausea by stimulating nerve endings in the lining of the stomach or intestine. Other poisons cause nausea after being absorbed into the blood. The blood carries the poison to special cells in the medulla, the lower part of the brain stem. These cells create nausea by sending impulses to higher parts of the brain, where sensations are received. Various drugs, including chlorpromazine and Dramamine, are used to control certain types of nausea (see Chlorpromazine; Dramamine).
