Motion sickness: causes

Scopolamine i Used in motion sickness, causes sedation and short-term memory block 1... 

This compound has antihistaminic activity and is usehil in the therapy of motion sickness. It may also be effective in the control of post-operative nausea and vomiting. It is classified as FDA Category B for Pregnancy, ie, no demonstrated risks shown in animal studies however, no controlled trials in pregnant women. Large doses may cause drowsiness and dry mouth owing to decreased secretion of saUva. 

Motion sickness arises in the vestibular apparatus. Stimulation of the semicircular canals or the utricles by unfamiliar accelerating movement may cause a mismatch between the sensory information reaching the brain centres controlling balance and posture, with that anticipated. Motion sickness may be avoided by reducing sensory conflict fixing vision on a stable reference point, such as the horizon may be effective. Cortical centres may also contribute memories of previous travel or the sight, and sounds of others being affected often increases susceptibility. 

Motion sickness is caused by stimulation of the vestibular system. This area contains many histaminic (Hj) and muscarinic cholinergic receptors. The higher brain (i.e., cerebral cortex) is affected by sensory input such as sights, smells, or emotions that can lead to vomiting. This area is involved in anticipatory nausea and vomiting associated with chemotherapy. 

The answer is e. (Hardmanr p 930.) All the drugs listed in the question are used as antiemetics. Chlorpromazine is a general antiemetic, used orally, rectally, or by injection for the control of nausea and vomiting that is caused by conditions that are not necessarily defined. Ondansetron is indicated in the oral or intravenous route for the prevention of nausea and vomiting caused by cancer chemotherapy Diphenhydramine and dimen-hydrinate are used orally for the active and prophylactic treatment of motion sickness. Scopolamine is a transdermal preparation used in the prevention of motion sickness. The drug is incorporated into a bandage-like... 

Chimpanzees daily eat termite mound clay. The habit may have started by ingesting dirt along with termites. Rats, after rotation that causes motion sickness (stomach upset and diarrhea), eat more clay than normal (Mitchell et al, 1977). Geophagy may be instrumental in the success of rats in habitats with unpredictable diets and the resistance of the species to poisoning by humans. Clay can be eaten prophylactically but also in response to toxic food already in the gastrointestinal tract. 

The anticholinergic agent scopolamine is available as a patch formulation. Its slow release causes a duration of action of 3 days. It is highly effective for motion sickness. 

The most popular use of scopolamine today is for the prevention of motion sickness via the Transderm-Scop patch. This device delivers about 0.5 mg of the drug over a three day period. Scopolamine and other drugs in this class can accumulate in significant quantities in the blood and some can cause CNS effects such as drowsiness, dry mouth and blurry vision. In rare cases amnesia and even psychosis can occur. The sedation and dry mouth are useful effects in that some of the compounds are used as tranquilizers and to dry up the mouth prior to anesthesia. 

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