Space Motion Sickness and Vestibular Adaptation to Weightlessness
Emesis, or vomiting is a debasing and debilitating act, especially for those with claims to the “right stuff.” It is bad enough to have to reach for the airsick bag in the rear seat of a gyrating fighter jet, but to fill a spacecraft’s motionless flight- or middeck with floating globules of half digested food and noxious odors is worse. Yet this often happened, usually in the first few hours of spaceflight, even to commanders, and often to those who were resistant to sickness in aircraft and other vehicles. Vomiting during spaceflight usually happens without warning and often too suddenly to get a bag up to one’s mouth in time. Emesis is only the beginning of what is known as space motion sickness (SMS). It is followed by increasing malaise, loss of appetite, lethargy, loss of interest and drive, with somnolence and variable headache. Body and head motions, especially pitching motions, are unpleasant and, if persisted in, can produce nausea, prolonged vomiting and other symptoms of motion sickness (MS). Motivated and trained crewmembers can work effectively during this period, albeit with varying amounts of discomfort. All of these symptoms typically dissipate within 2 days, and do not recur in flight. It is not surprising that early astronauts were not eager to report SMS, especially since nothing could be done about it except make it a part of their personal records. It was referred to only half jokingly as the “dreaded space motion sickness.” Somewhat less than half of first time space flyers will experience SMS until vestibular adaptation removes the cause.
Return to Earth in a spacecraft.
Predominant portion of nervous system that functions automatically and unconsciously.
Ejection of material in stomach/bowel through mouth.
Collection of nerve cells in brain stem that coordinates, controls vomiting.
Three collections of interconnected cells (emesis center, nausea center and chemical trigger zone, or CTZ) in brain stem that receive a variety of inputs whose outputs control gastrointestinal (GI) sensations, nausea and vomiting.
A system mode that protects a system from further damage in event of component or subsystem failure.
Valve in throat normally open to air for lungs that closes against liquids or solids going into or out of the esophagus.
Magnitude and direction of gravitational force of attraction of the Earth’s mass on or near its surface.
Spontaneous motion, in this case of the GI tract that normally propels food through the tract.
It is under neurological and hormonal control.
Also known as kinetosis, a more or less common set of GI autonomic and unpleasant sensations triggered by the vestibular system in response to motions or simulated motions outside the subject’s usual experience.
It is used here in that context, but MS in weightlessness is produced by abnormal sensitivity to motion from failure of the otolith sensors that continues until reprogramming occurs.
In this context a collection of nerve cells, often in a nodule, usually interconnected and with a system function. Multiple inputs from sensors and other cells may be input, processed, integrated and used to produce outputs.
As used here, it is spatial orientation, usually the relation of body axis to g vector.
Related to the vestibular sensors that detect gravitational orientation by weight of dense crystals once called otoliths (Gk.: ear stones).
Exit from spacecraft on Earth.
GI autonomic signs and symptoms produced by a intrinsic conflict in the vestibular otolith sensors produced by weightlessness. It is resolved by reprogramming in the vestibular system in 1–3 days. The conflict is independent of motion, and a better term is needed; however, SMS is reluctantly used here since it is in universal use.
Name derived from the convoluted spaces in bone housing the vestibular organs that comprise the inner ears, but it now applies to the ventricular system.
Consist of three sensory systems in each inner ear, which are cochlear for hearing, otolith for orientation to the g vector and for sensing linear and angular motions, and semicircular canals for sensing angular motion.
Consists of the vestibular organs, bilateral vestibular nuclei in the brain stem and numerous areas in the upper brain.
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