injuries poisoning
Motion Sickness
Etiology of Motion Sickness
Excessive stimulation of the vestibular apparatus by motion is the primary cause. Vestibular stimulation can result from angular motion (sensed by the semicircular canals) or linear acceleration or gravity (sensed by the otolithic organs [utricle and saccule]). Central nervous system (CNS) components that mediate motion sickness include the vestibular system and brain stem nuclei, the hypothalamus, the nodulus and uvula of the cerebellum, and emetic pathways (eg, medullary chemoreceptor trigger zone, vomiting center, and emetic efferents). The exact pathophysiology is undefined, but motion sickness occurs only when the 8th cranial nerve and cerebellar vestibular tracts are intact; those lacking a functional vestibulo-cochlear system are immune to motion sickness. Movement via any form of transportation, including ship, motor vehicle, train, plane, spacecraft, and playground or amusement park rides can cause excessive vestibular stimulation. The trigger may involve conflicting vestibular, visual, and proprioceptive inputs. For example, visual input that indicates being stationary may conflict with the sensation of movement (eg, looking at an apparently unmoving ship cabin wall while sensing the ship rolling). Alternatively, moving visual input may conflict with lack of perception of movement, eg, viewing a rapidly moving slide with a microscope or watching a virtual reality game while sitting still (also termed pseudomotion sickness or pseudokinetosis, given the lack of actual acceleration). When watching waves from a boat, a person may experience conflicting visual input (the movement of the waves in one direction) and vestibular input (the vertical motion of the boat itself). Another possible trigger is a conflict in inputs between angular motion and linear acceleration or gravity, as can occur in a zero-gravity environment when turning (angular acceleration). Also, a pattern of motion that differs from the expected pattern (eg, in a zero-gravity environment, floating instead of falling) can be a trigger. Factors that may increase the risk of developing motion sickness or increase the severity of symptoms include the following: Poor ventilation (eg, with exposure to fumes, smoke, or carbon monoxide) Emotional factors (eg, fear, Overview of Anxiety Disorders about travel or the possibility of developing motion sickness) Migraine None Vestibulopathy (such as Vestibular Neuronitis ) Hormonal factors (eg, from pregnancy or use of hormonal contraceptives) Genetic factors may also increase susceptibility to motion sickness ( General reference ). Inspace adaptation syndrome(motion sickness during space travel), weightlessness (zero gravity) is an etiologic factor. This syndrome reduces the efficiency of astronauts during the first few days of space flight, but adaptation occurs over several days. 1.Hromatka BS, Tung JY, Kiefer AK, et al: Genetic variants associated with motion sickness point to roles for inner ear development, neurological processes and glucose homeostasis.Hum Mol Genet24(9):2700-2708, 2015. doi: 10.1093/hmg/ddv028 