0
We're unable to sign you in at this time. Please try again in a few minutes.
Retry
We were able to sign you in, but your subscription(s) could not be found. Please try again in a few minutes.
Retry
There may be a problem with your account. Please contact the AMA Service Center to resolve this issue.
Contact the AMA Service Center:
Telephone: 1 (800) 262-2350 or 1 (312) 670-7827  *   Email: subscriptions@jamanetwork.com
Error Message ......
Neurological Review |

Space Exploration, Mars, and the Nervous System FREE

Robert Kalb, MD; David Solomon, MD, PhD
[+] Author Affiliations

Author Affiliations: Joseph Stokes Jr Research Institute, Children's Hospital of Philadelphia, Philadelphia, Pa, and Department of Neurology, University of Pennsylvania School of Medicine, Philadelphia (Dr Kalb); Kennedy Krieger Institute, and Departments of Neurology and Otolaryngology, The Johns Hopkins University School of Medicine, Baltimore, Md (Dr Solomon). Dr Solomon is now with Pathology at The Johns Hopkins University, Baltimore.


Section Editor: David E. Pleasure, MD

More Author Information
Arch Neurol. 2007;64(4):485-490. doi:10.1001/archneur.64.4.485.
Text Size: A A A
Published online

When human beings venture back to the moon and then on to Mars in the coming decade or so, we will be riding on the accumulated data and experience from approximately 50 years of manned space exploration. Virtually every organ system functions differently in the absence of gravity, and some of these changes are maladaptive. From a biologic perspective, long duration spaceflight beyond low Earth orbit presents many unique challenges. Astronauts traveling to Mars will live in the absence of gravity for more than 1 year en route and will have to transition between weightlessness and planetary gravitational forces at the beginning, middle, and end of the mission. We discuss some of what is known about the effects of spaceflight on nervous system function, with emphasis on the neuromuscular and vestibular systems because success of a Mars mission will depend on their proper functioning.

Figures in this Article

When the first human beings in the Rift Valley gazed up into the night sky 6 million years ago,1 they must have wondered, “What the heck are all those bright spots?” In the absence of any substantive knowledge of the nature of the universe—or perhaps because of this ignorance—great meaning was assigned to the stars and the heavens. The breadth of connotations was, and is, as vast as the diversity of humanity. Pioneers such as Tycho Brahe, Nicolaus Copernicus, and Galileo Galilei took us from the province of superstition and the supernatural to a world of reason and science. The march of research and technology during the past few centuries has made it possible for us to begin to comprehend and appreciate the universe. However vast, complex, fascinating, and beautiful the universe was to our early predecessors, our evolving understanding of the true nature of our cosmic home only adds to our awe and similar need to contemplate the space above us.

Human beings have had a nearly continuous presence in space for decades, and we are at the threshold of manned exploration of planets in our solar system, beginning with Mars.2 Within 2 generations, we could have a permanent presence on Mars, and colonization of the planet is a realistic possibility. To achieve these goals, technologic advances in material science, robotics, and power generation will be essential. There is every reason to believe that, with adequate monetary support, these targets can be reached.

It is reasonable to ask, “Are we up to the task?” We have learned a tremendous amount of extraterrestrial biology during the past 5 decades, though only about 400 of our fellow human beings have had any substantial experience in the space environment. The documented effects of spaceflight on the nervous system, in particular, has important implications for prolonged existence off Earth and specifically for the exploration of Mars.

In this article, we overview research on 2 aspects of nervous tissue function that undergo important spaceflight-induced alterations: the neuromuscular and vestibular systems. Effects of changes in circadian rhythm, cerebrovascular hemodynamics, and radiation exposure, to name a few, also have profound effects on the nervous system (Figure 1); however, advances in these and other areas are beyond the scope of this article.

Place holder to copy figure label and caption
Figure 1

Overview of physiologic responses to spaceflight.

Graphic Jump Location

Motor function is required for purposeful interaction of an extraplanetary explorer with that environment. A decay in motor function that interferes substantially with the human-human and human-machine interaction can impair or even prevent the success of the mission. From the perspective of the motor system, a manned mission to Mars and back includes a series of events during which motor operations are affected. The sequence can be divided as follows: alterations that occur in the days and weeks after first exposure to microgravity and then during the approximately 6 months required to reach Mars, alterations that occur on reexposure to the planetary gravitational field (the force of gravity on Mars is 38% of that experienced on Earth), alterations that occur during the second exposure approximately 6 months in microgravity during the return trip from Mars to Earth, and alterations that occur with extended existence at 1g. Some alterations in nervous tissue function are transient; some are long lasting. Some alterations are behaviorally useful adaptations to new environmental demands; some degrade motor performance. The latter can be anticipated to substantially impair function at distinct points along the described time line.

Exposure to microgravity causes muscle atrophy, increased muscle fatigue, and reduction in peak force and power.35 Decrement in muscle function is first detectable within days of existence in microgravity and progresses over the duration of the mission. Some evidence indicates that a stable state is reached at about 3 months,6 although this idea is complicated by several factors, including the few individuals studied and the lack of prescribed exercise programs. There is also substantial between-individual variability. Soon after the recognition of this myopathic problem, both the US and Russian space programs instituted in-flight exercise programs as countermeasures. Nevertheless, virtually all individuals who spend weeks or months in microgravity will experience loss of muscle bulk and strength. Optimal exercise programs have not been established.

Skeletal muscles can be differentiated on the basis of their fiber type composition, such as those required for upright stance at 1g (ie, so-called antigravity muscles such as the soleus, quadriceps, and short paraspinal muscles), fatigability, and so on. Considering this variability, it is not surprising that the effects of microgravity differ as a function of the muscle examined. Calf muscles (in particular, the soleus as opposed to the gastrocnemius) are affected by microgravity rapidly and undergo atrophy before all other studied muscles in human beings.5,7 As the duration of the mission lengthens, both flexor and extensor muscles are weakened, as demonstrated by studies undertaken during 6 months on Mir, the Russian space vehicle.6 While studies in rats suggest that type I fibers (slow and resistant to fatigue) atrophy preferentially in microgravity,8 limited studies in human beings suggest that type II fibers (IIa, fast and resistant to fatigue; IIb, fast and fatigue rapidly) are not spared.7,9

Research using human and animal (eg, rat) models defined 3 sets of factors that underlie the observed decrease in strength.4,5 The first important factor is the removal of the antigravity load, most apparent in antigravity muscles such as the soleus. Unloading leads to reduction in muscle gene transcription and protein translation. Proteins that participate in contractility (ie, actin and myosin) as opposed to energy metabolism (ie, oxidative and glycolytic enzymes) are preferentially affected. One approach to modeling this process on Earth involves studies of prolonged bed rest.10,11 Studies in rodents implicate activation of the ubiquitin-proteosomal pathway in myosin heavy-chain degradation.12 The second factor contributing to decreased soleus function is reduction in neural drive to muscle. There is a greater loss of leg muscle power than can be accounted for by a reduction in muscle mass, indicative of microgravity-induced change in motor control and coordination.13 Electromyographic study of the dynamics of leg muscle activation in monkeys at 1g and in microgravity confirm the existence of altered neuronal recruitment patterns.14 Anatomical alterations in the spinal cord circuitry subserving recruitment order are likely and microgravity-induced alterations in motor neuron dendritic architecture have been demonstrated.15 The third set of contributors to motor dysfunction are systemic factors including hormonal alterations and changes in metabolism.16,17 In sum, we know that substantial weakness occurs during exposure to microgravity, it is a progressive affliction, and we have some insight into its molecular pathogenesis. Effective countermeasures are likely to be multimodal, including exercise and hormonal, nutritional, and perhaps even pharmacologic interventions. Until proper resources are devoted to study the effectiveness of specific interventions (perhaps even controlled trials), microgravity-induced weakness will no doubt plague space explorers.

The reacquaintance of human beings with Earth's gravity is commonly associated with weakness and delayed-onset muscle soreness. Such symptoms probably indicate muscle damage, and a variety of studies in rats confirm that return to 1g leads to myopathology. The absence of demonstrable damage to muscles during microgravity and its development in the days after landing suggest that spaceflight induces vulnerability to damage in muscle fibers that is realized on postflight stress.18 It is believed the inciting insults are loading of previously unloaded muscles, and motor unit recruitment patterns not previously used in microgravity but now are appropriate to terrestrial needs. Myopathology (including extensive fiber necrosis, activated macrophages, and interstitial edema) is observable several days after landing.19 Extrapolating from rodents to human beings, we can anticipate that landing on Mars, after 6 months in microgravity, will incur substantial muscle damage. It is impossible to predict how much motor dysfunction will occur after the 6-month return voyage to Earth and reintroduction to 1g except to say it has the potential to be enormously disabling.

Astronauts gain some 2 to 3 in (5.08-7.62 cm) in height during a mission, mostly during the first 10 days of flight.20 Although it has not been directly measured, it is likely that most of the change occurs in the thorax, and this might lead to traction on nerve roots. Another potential consequence of thorax elongation is alteration in the length-tension relationships of the antigravity axial paraspinous muscles. This, along with alterations in vestibulospinal extensor tonus (see “Vestibular System”), might contribute to postural changes so characteristic of human beings in microgravity.

The importance of understanding the effects of weightlessness on vestibular function was recognized early in the manned spaceflight program. In 1965, the National Aeronautics and Space Administration held the first symposium on the role of the vestibular organs in the exploration of space. In his forward to the proceedings, Graybiel explained why the aerospace agencies would be interested in such a topic:

The reasons for their interest are no mystery. Man, in breaking away from the Earth, is transported in vehicles which move in 3-dimensional space and generate inertial forces that create environmental factors to which he is not accustomed either by inheritance or experience.

The vestibular organs, the semicircular canals and otoliths, sense angular and linear accelerative forces, respectively. They are unique in that they transduce forces acting at a distance. Whether it is the gravitational force of Earth or angular rotation when walking around the corner, the inner ear labyrinth provides the central nervous system with information about the head's orientation and movement through space. The challenge in the weightless environment is to adapt to circumstances that never existed either during the evolution of life on Earth or during any individual's development.

Proper operation of vestibular reflexes is a prerequisite for stable gaze during movement and for postural stability. In space, one might argue that balance function is irrelevant because astronauts and cosmonauts are already free-falling. Ambulation is replaced by a more swimming type of locomotion, and one cannot fall down because there is no down. Most studies of the angular vestibular ocular reflex have found that gains are not different in microgravity compared with a 1g environment.22,23 Most of the controversy about vestibular ocular reflex function during spaceflight concerns the otolith-mediated linear vestibular ocular reflex.24 We discuss selected examples of changes that occur at the cellular and morphologic levels, effects on motor development and postural control, and spatial disorientation at the perceptual level.

Disturbances in vestibular function could arise from damage from vibration and g loads during launch, end-organ changes in response to microgravity, and peripheral or central synaptic changes. Damage to labyrinthine structures occurs when they are overloaded by accelerations out of the normal range, either from head trauma25 or aerobatic flying.26 During shuttle launch, hypergravitational forces are about 3g and are unlikely to cause any damage. The vibration occurring during launch, however, is sufficient to cause short-term cytoskeletal changes in other tissues.27 In the periphery, there are changes in the gravity-sensitive otolith organs, with an increase in the otoconial mass after spaceflight.28 Adult rats had statistically significant increases in total ribbon synapses and in spherelike ribbons in both type I and type II hair cells29 after spaceflight. In a later experiment on board Space Life Sciences-2, a doubling in the mean number of synapses in the utricular macula of adult rats was seen by flight day 13. Synapse deletion began within 8 hours after return to Earth.30 Central nervous system changes are observed in the cerebellar nodulus, which receives afferent otolith projections. Purkinje cells had stacked lamellar bodies and some enlarged mitochondria. Degeneration and synaptic reorganization were also observed in the molecular layer.31 Thus, synaptic plasticity is demonstrated in an adult mammalian system in response to changes in the inertial environment.

Vestibulospinal reflexes are important in maintaining upright posture by facilitating extensor tone in antigravity muscles (Figure 2). After 9 days in orbit, adult rats demonstrated abnormal resting posture and movement that resolved within 9 days after spaceflight.29 Although no long-lasting deficits in postural control have been noted in human space travelers, neonatal rats that spent formative weeks in low Earth orbit exhibited enduring changes in gravity-dependent surface righting responses.32,33 Rats flown aboard the space shuttle Columbia from postnatal days 14 through 30 exhibited immature righting responses postflight compared with controls. The animals reared in space used the same percentage of postural strategies as postnatal day 14 controls. When the flight animals were tested 4 months after landing, their behavior showed no change, still exhibiting the immature pattern of postural responses. Animals flown on a shorter flight from postnatal days 14 to 24; however, performed the same as controls by the second day after landing. The permanent effect of the longer flight is consistent with a critical period of development of the righting response.34 The absence of gravity during this important interval meant that the animals never acquired the normal repertoire of motor responses to gravity.

Place holder to copy figure label and caption
Figure 2

Astronaut Stephen N. Frick, the pilot on the STS-110, floats in the Unity node on the International Space Station (ISS 8A) in April 2002. Note the cephalad fluid shift still present after 4 days in microgravity and the flexed posture assumed in weightlessness. Inset, Preflight photograph without cephalad fluid. Image from the archives of the National Aeronautics and Space Administration.

Graphic Jump Location

Even in the absence of any structural or developmental abnormalities, vestibular stimulation can cause spatial disorientation, illusory postural and visual perceptions, and disabling motion sickness. The central nervous system already has a difficult time on Earth differentiating linear acceleration owing to translation from tilt with respect to gravity. Figure 3A-C shows the somatogravic illusion experienced by pilots during takeoff, in which the otolith response to the combination of gravity and forward acceleration (resultant gravitoinertial acceleration) is misinterpreted by the brain as tilt, sometimes with fatal consequences.35 In space, tilt is not defined because there is no vertical orientation defined by gravity. Translation of the head, as occurs when an astronaut or cosmonaut pushes off from the wall of a spacecraft, is the only source of linear acceleration, unless one brings up a centrifuge, which can deliver centripetal acceleration, or “artificial gravity.” A sensory misinterpretation hypothesis36 has been offered to explain some of the space motion sickness and spatial disorientation experienced in microgravity and on return to Earth. The idea is that the brain adapts to the novel force environment of space by considering all linear accelerations as the result of translation of the head. If an astronaut has adapted such that utricular signals are interpreted only as owing to head translation, then tilting the head when back on Earth causes the illusion of translation. When bending to the side to release an emergency brake, one astronaut involuntarily guarded against an impending collision with the roof of the car because the gravitational pull on the utricle was misinterpreted as an upward linear translation.

Place holder to copy figure label and caption
Figure 3

Origins of somatogravic illusions. Ambiguity in the interpretation of vestibular cues can lead to spatial disorientation and the somatogyral illusion. A-C, During forward acceleration, the otolith organs respond to both gravity and linear acceleration. If the brain uses this combined acceleration vector to define the “upward” direction, there will be an illusion of being pitched backward when, in fact, the head is aligned with the earth-vertical axis. D-F, A similar illusion of lateral tilt occurs during centrifugation. GIA indicates gravitoinertial acceleration.

Graphic Jump Location

Experiments conducted in 1998 on the STS-90 Neurolab Spacelab Mission addressed the following question:37 Is linear acceleration sensed by the otoliths always perceived as linear motion or will it result in a sensation of tilt? Using the centrifuge shown in Figure 4, astronauts were exposed to interaural linear acceleration. During preflight testing, this resulted in perceptions of tilt (Figure 3D-F). In space, even after 5 days of experiencing only linear acceleration caused by translation, astronauts reported the sensation of tilt during centrifugation and none experienced a sense of translation.37 This suggests that exposure to artificial gravity in a centrifuge during a 6-month mission to Mars might allow spacefarers to respond normally to the gravitational fields they will encounter at their destination.

Place holder to copy figure label and caption
Figure 4

The Neurolab flight centrifuge in the Spacelab module housed in Columbia's cargo bay. An astronaut is preparing for in-flight centrifugation. The only stimulus to the otoliths will be centripetal linear acceleration directed along the subject's interaural axis. Photograph courtesy of the National Aeronautics and Space Administration.

Graphic Jump Location

We have taken the first steps toward exploration by human beings of space. We can accomplish what countless generations before us could only dream of; we can visit and explore other worlds. The technical challenges are daunting and expensive but not insurmountable. There is a risk that limited resources will be largely devoted to solving the engineering problems required for long-term existence in space. Diverse biologic responses to spaceflight is one of the fundamental insights gained from the more than 40 years that human beings have traveled and lived in space. If insufficient weight is given to the biologic responses to prolonged existence in space, 2 consequences can be anticipated. First, to the extent that a successful mission requires human action, accomplishing mission goals will be jeopardized. Second, lives will be unnecessarily lost. These are consequences no one wants, and they can be avoided by recognizing that the effects of spaceflight on biologic systems are profound. Increased research into the responses and adaptations of life to prolonged spaceflight is essential if we are to successfully explore the heavens.

Correspondence: Robert Kalb, MD, Joseph Stokes Jr Research Institute, Children's Hospital of Philadelphia, 3615 Civic Center Blvd, Philadelphia, PA 19104 (kalb@email.chop.edu).

Accepted for Publication: May 18, 2006.

Author Contributions:Study concept and design: Solomon. Acquisition of data: Solomon. Analysis and interpretation of data: Kalb and Solomon. Drafting of the manuscript: Kalb and Solomon. Critical revision of the manuscript for important intellectual content: Kalb and Solomon. Obtained funding: Kalb. Administrative, technical, and material support: Solomon. Study supervision: Kalb.

Financial Disclosure: None reported.

Funding/Support: This study was supported by grants NS 29837 and NS 52325 from the US Public Health Service (Dr Kalb) and by the Institutional Development Fund of Children's Hospital of Philadelphia.

Acknowledgment: Dr Kalb thanks David Pleasure, MD, and Gihan Tennekoon, MD, for their consistent support. Dr Solomon thanks Bernard Cohen, MD, for bringing neurology from the space capsule to the clinic.

Leakey  R The Origin of Humankind.  New York, NY: BasicBooks, HarperCollins;1994
White  RJBassingthwaighte  JBCharles  JBKushmerick  MJNewman  DJ Issues of exploration: human health and wellbeing during a mission to Mars. Adv Space Res 2003;317- 16
PubMed Link to Article
Fitts  RHRiley  DRWidrick  JJ Functional and structural adaptations of skeletal muscle to microgravity. J Exp Biol 2001;2043201- 3208
PubMed
Adams  GRCaiozzo  VJBaldwin  KM Skeletal muscle unweighting: spaceflight and ground-based models. J Appl Physiol 2003;952185- 2201
PubMed
Fitts  RHRiley  DRWidrick  JJ Physiology of a microgravity environment invited review: microgravity and skeletal muscle. J Appl Physiol 2000;89823- 839
PubMed
Greenleaf  JEBulbulian  RBernauer  EMHaskell  WLMoore  T Exercise-training protocols for astronauts in microgravity. J Appl Physiol 1989;672191- 2204
PubMed
Widrick  JJKnuth  STNorenberg  KM  et al.  Effect of a 17 day spaceflight on contractile properties of human soleus muscle fibres. J Physiol 1999;516915- 930
PubMed Link to Article
Ohira  YJiang  BRoy  RR  et al.  Rat soleus muscle fiber responses to 14 days of spaceflight and hindlimb suspension. J Appl Physiol 1992;7351S- 57S
PubMed
Edgerton  VRZhou  MYOhira  Y  et al.  Human fiber size and enzymatic properties after 5 and 11 days of spaceflight. J Appl Physiol 1995;781733- 1739
PubMed
Jones  N Lie back and think of science. Nature 2005;435730- 731
PubMed Link to Article
Portero  PVanhoutte  CGoubel  F Surface electromyogram power spectrum changes in human leg muscles following 4 weeks of simulated microgravity. Eur J Appl Physiol Occup Physiol 1996;73340- 345
PubMed Link to Article
Ikemoto  MNikawa  TTakeda  S  et al.  Space shuttle flight (STS-90) enhances degradation of rat myosin heavy chain in association with activation of ubiquitin-proteasome pathway. FASEB J 2001;151279- 1281
PubMed
Antonutto  GBodem  FZamparo  Pdi Prampero  PE Maximal power and EMG of lower limbs after 21 days spaceflight in one astronaut. J Gravit Physiol 1998;5P63- P66
Recktenwald  MRHodgson  JARoy  RR  et al.  Effects of spaceflight on rhesus quadrupedal locomotion after return to 1G. J Neurophysiol 1999;812451- 2463
PubMed
Inglis  FMZuckerman  KEKalb  RG Experience-dependent development of spinal motor neurons. Neuron 2000;26299- 305
PubMed Link to Article
Maillet  ABeaufrere  BDi Nardo  PElia  MPichard  C Weightlessness as an accelerated model of nutritional disturbances. Curr Opin Clin Nutr Metab Care 2001;4301- 306
PubMed Link to Article
Leach  CSJohnson  PCRambaut  PC Metabolic and endocrine studies: the second manned Skylab mission. Aviat Space Environ Med 1976;47402- 410
PubMed
Riley  DAEllis  SGiometti  CS  et al.  Muscle sarcomere lesions and thrombosis after spaceflight and suspension unloading. J Appl Physiol 1992;7333S- 43S
PubMed
Riley  DAIlyina-Kakueva  EIEllis  SBain  JLSlocum  GRSedlak  FR Skeletal muscle fiber, nerve, and blood vessel breakdown in space-flown rats. FASEB J 1990;484- 91
PubMed
National Aeronautics and Space Administrationhttp://lsda.jsc.nasa.gov/scripts/datasets/dataset_detail_result.cfm?dataset_catalog=J0000974; 2005:Life Sciences Data Archive. Accessed April 15, 2006
Graybiel  A The Role of the Vestibular Organs in the Exploration of Space. NASA SP-77.  Pensacola, Fla: National Aeronautics and Space Administration; 1965
Benson  AJVieville  T European vestibular experiments on the Spacelab-1 mission, 6: yaw axis vestibulo-ocular reflex. Exp Brain Res 1986;64279- 283
PubMed
Oman  CMBalkwill  MD Horizontal angular VOR, nystagmus dumping and sensation duration in Spacelab SLS-1 crewmembers. J Vestib Res 1993;3315- 330
PubMed
Cohen  BYakushin  SBHolstein  GR  et al.  Vestibular experiments in space. Adv Space Biol Med 2005;10105- 164
PubMed
Gordon  CRLevite  RJoffe  VGadoth  N Is posttraumatic benign paroxysmal positional vertigo different from the idiopathic form? Arch Neurol 2004;611590- 1593
PubMed Link to Article
Muller  TU G-induced vestibular dysfunction (“the wobblies”) among aerobatic pilots: a case report and review. Ear Nose Throat J 2002;81269- 272
PubMed
Lewis  MLCubano  LAZhao  B  et al.  cDNA microarray reveals altered cytoskeletal gene expression in space-flown leukemic T lymphocytes (Jurkat). FASEB J 2001;151783- 1785
PubMed
Ross  MDDonovan  KChee  O Otoconial morphology in space-flown rats. Physiologist 1985;28S219- S220
PubMed
Ross  MD A spaceflight study of synaptic plasticity in adult rat vestibular maculas. Acta Otolaryngol Suppl 1994;5161- 14
PubMed
Ross  MD Changes in ribbon synapses and rough endoplasmic reticulum of rat utricular macular hair cells in weightlessness. Acta Otolaryngol 2000;120490- 499
PubMed Link to Article
Holstein  GRKukielka  EMartinelli  GP Anatomical observations of the rat cerebellar nodulus after 24 hr of spaceflight. J Gravit Physiol 1999;6P47- P50
Walton  KDHarding  SAnschel  DHarris  YTLlinas  R The effects of microgravity on the development of surface righting in rats. J Physiol 2005;565(pt 2)593- 608
PubMed Link to Article
Ross  MDTomko  DL Effect of gravity on vestibular neural development. Brain Res Rev 1998;2844- 51
PubMed Link to Article
Walton  KDLieberman  DLlinas  ABegin  MLlinas  RR Identification of a critical period for motor development in neonatal rats. Neuroscience 1992;51763- 767
PubMed Link to Article
Cheung  BMoney  KWright  HBateman  W Spatial disorientation-implicated accidents in Canadian forces, 1982-92. Aviat Space Environ Med 1995;66579- 585
PubMed
Young  LROman  CMWatt  DGMoney  KELichtenberg  BK Spatial orientation in weightlessness and readaptation to Earth's gravity. Science 1984;225205- 208
PubMed Link to Article
Clement  GMoore  STRaphan  TCohen  B Perception of tilt (somatogravic illusion) in response to sustained linear acceleration during space flight. Exp Brain Res 2001;138410- 418
PubMed Link to Article

Figures

Place holder to copy figure label and caption
Figure 1

Overview of physiologic responses to spaceflight.

Graphic Jump Location
Place holder to copy figure label and caption
Figure 2

Astronaut Stephen N. Frick, the pilot on the STS-110, floats in the Unity node on the International Space Station (ISS 8A) in April 2002. Note the cephalad fluid shift still present after 4 days in microgravity and the flexed posture assumed in weightlessness. Inset, Preflight photograph without cephalad fluid. Image from the archives of the National Aeronautics and Space Administration.

Graphic Jump Location
Place holder to copy figure label and caption
Figure 3

Origins of somatogravic illusions. Ambiguity in the interpretation of vestibular cues can lead to spatial disorientation and the somatogyral illusion. A-C, During forward acceleration, the otolith organs respond to both gravity and linear acceleration. If the brain uses this combined acceleration vector to define the “upward” direction, there will be an illusion of being pitched backward when, in fact, the head is aligned with the earth-vertical axis. D-F, A similar illusion of lateral tilt occurs during centrifugation. GIA indicates gravitoinertial acceleration.

Graphic Jump Location
Place holder to copy figure label and caption
Figure 4

The Neurolab flight centrifuge in the Spacelab module housed in Columbia's cargo bay. An astronaut is preparing for in-flight centrifugation. The only stimulus to the otoliths will be centripetal linear acceleration directed along the subject's interaural axis. Photograph courtesy of the National Aeronautics and Space Administration.

Graphic Jump Location

Tables

References

Leakey  R The Origin of Humankind.  New York, NY: BasicBooks, HarperCollins;1994
White  RJBassingthwaighte  JBCharles  JBKushmerick  MJNewman  DJ Issues of exploration: human health and wellbeing during a mission to Mars. Adv Space Res 2003;317- 16
PubMed Link to Article
Fitts  RHRiley  DRWidrick  JJ Functional and structural adaptations of skeletal muscle to microgravity. J Exp Biol 2001;2043201- 3208
PubMed
Adams  GRCaiozzo  VJBaldwin  KM Skeletal muscle unweighting: spaceflight and ground-based models. J Appl Physiol 2003;952185- 2201
PubMed
Fitts  RHRiley  DRWidrick  JJ Physiology of a microgravity environment invited review: microgravity and skeletal muscle. J Appl Physiol 2000;89823- 839
PubMed
Greenleaf  JEBulbulian  RBernauer  EMHaskell  WLMoore  T Exercise-training protocols for astronauts in microgravity. J Appl Physiol 1989;672191- 2204
PubMed
Widrick  JJKnuth  STNorenberg  KM  et al.  Effect of a 17 day spaceflight on contractile properties of human soleus muscle fibres. J Physiol 1999;516915- 930
PubMed Link to Article
Ohira  YJiang  BRoy  RR  et al.  Rat soleus muscle fiber responses to 14 days of spaceflight and hindlimb suspension. J Appl Physiol 1992;7351S- 57S
PubMed
Edgerton  VRZhou  MYOhira  Y  et al.  Human fiber size and enzymatic properties after 5 and 11 days of spaceflight. J Appl Physiol 1995;781733- 1739
PubMed
Jones  N Lie back and think of science. Nature 2005;435730- 731
PubMed Link to Article
Portero  PVanhoutte  CGoubel  F Surface electromyogram power spectrum changes in human leg muscles following 4 weeks of simulated microgravity. Eur J Appl Physiol Occup Physiol 1996;73340- 345
PubMed Link to Article
Ikemoto  MNikawa  TTakeda  S  et al.  Space shuttle flight (STS-90) enhances degradation of rat myosin heavy chain in association with activation of ubiquitin-proteasome pathway. FASEB J 2001;151279- 1281
PubMed
Antonutto  GBodem  FZamparo  Pdi Prampero  PE Maximal power and EMG of lower limbs after 21 days spaceflight in one astronaut. J Gravit Physiol 1998;5P63- P66
Recktenwald  MRHodgson  JARoy  RR  et al.  Effects of spaceflight on rhesus quadrupedal locomotion after return to 1G. J Neurophysiol 1999;812451- 2463
PubMed
Inglis  FMZuckerman  KEKalb  RG Experience-dependent development of spinal motor neurons. Neuron 2000;26299- 305
PubMed Link to Article
Maillet  ABeaufrere  BDi Nardo  PElia  MPichard  C Weightlessness as an accelerated model of nutritional disturbances. Curr Opin Clin Nutr Metab Care 2001;4301- 306
PubMed Link to Article
Leach  CSJohnson  PCRambaut  PC Metabolic and endocrine studies: the second manned Skylab mission. Aviat Space Environ Med 1976;47402- 410
PubMed
Riley  DAEllis  SGiometti  CS  et al.  Muscle sarcomere lesions and thrombosis after spaceflight and suspension unloading. J Appl Physiol 1992;7333S- 43S
PubMed
Riley  DAIlyina-Kakueva  EIEllis  SBain  JLSlocum  GRSedlak  FR Skeletal muscle fiber, nerve, and blood vessel breakdown in space-flown rats. FASEB J 1990;484- 91
PubMed
National Aeronautics and Space Administrationhttp://lsda.jsc.nasa.gov/scripts/datasets/dataset_detail_result.cfm?dataset_catalog=J0000974; 2005:Life Sciences Data Archive. Accessed April 15, 2006
Graybiel  A The Role of the Vestibular Organs in the Exploration of Space. NASA SP-77.  Pensacola, Fla: National Aeronautics and Space Administration; 1965
Benson  AJVieville  T European vestibular experiments on the Spacelab-1 mission, 6: yaw axis vestibulo-ocular reflex. Exp Brain Res 1986;64279- 283
PubMed
Oman  CMBalkwill  MD Horizontal angular VOR, nystagmus dumping and sensation duration in Spacelab SLS-1 crewmembers. J Vestib Res 1993;3315- 330
PubMed
Cohen  BYakushin  SBHolstein  GR  et al.  Vestibular experiments in space. Adv Space Biol Med 2005;10105- 164
PubMed
Gordon  CRLevite  RJoffe  VGadoth  N Is posttraumatic benign paroxysmal positional vertigo different from the idiopathic form? Arch Neurol 2004;611590- 1593
PubMed Link to Article
Muller  TU G-induced vestibular dysfunction (“the wobblies”) among aerobatic pilots: a case report and review. Ear Nose Throat J 2002;81269- 272
PubMed
Lewis  MLCubano  LAZhao  B  et al.  cDNA microarray reveals altered cytoskeletal gene expression in space-flown leukemic T lymphocytes (Jurkat). FASEB J 2001;151783- 1785
PubMed
Ross  MDDonovan  KChee  O Otoconial morphology in space-flown rats. Physiologist 1985;28S219- S220
PubMed
Ross  MD A spaceflight study of synaptic plasticity in adult rat vestibular maculas. Acta Otolaryngol Suppl 1994;5161- 14
PubMed
Ross  MD Changes in ribbon synapses and rough endoplasmic reticulum of rat utricular macular hair cells in weightlessness. Acta Otolaryngol 2000;120490- 499
PubMed Link to Article
Holstein  GRKukielka  EMartinelli  GP Anatomical observations of the rat cerebellar nodulus after 24 hr of spaceflight. J Gravit Physiol 1999;6P47- P50
Walton  KDHarding  SAnschel  DHarris  YTLlinas  R The effects of microgravity on the development of surface righting in rats. J Physiol 2005;565(pt 2)593- 608
PubMed Link to Article
Ross  MDTomko  DL Effect of gravity on vestibular neural development. Brain Res Rev 1998;2844- 51
PubMed Link to Article
Walton  KDLieberman  DLlinas  ABegin  MLlinas  RR Identification of a critical period for motor development in neonatal rats. Neuroscience 1992;51763- 767
PubMed Link to Article
Cheung  BMoney  KWright  HBateman  W Spatial disorientation-implicated accidents in Canadian forces, 1982-92. Aviat Space Environ Med 1995;66579- 585
PubMed
Young  LROman  CMWatt  DGMoney  KELichtenberg  BK Spatial orientation in weightlessness and readaptation to Earth's gravity. Science 1984;225205- 208
PubMed Link to Article
Clement  GMoore  STRaphan  TCohen  B Perception of tilt (somatogravic illusion) in response to sustained linear acceleration during space flight. Exp Brain Res 2001;138410- 418
PubMed Link to Article

Correspondence

CME
Also Meets CME requirements for:
Browse CME for all U.S. States
Accreditation Information
The American Medical Association is accredited by the Accreditation Council for Continuing Medical Education to provide continuing medical education for physicians. The AMA designates this journal-based CME activity for a maximum of 1 AMA PRA Category 1 CreditTM per course. Physicians should claim only the credit commensurate with the extent of their participation in the activity. Physicians who complete the CME course and score at least 80% correct on the quiz are eligible for AMA PRA Category 1 CreditTM.
Note: You must get at least of the answers correct to pass this quiz.
Please click the checkbox indicating that you have read the full article in order to submit your answers.
Your answers have been saved for later.
You have not filled in all the answers to complete this quiz
The following questions were not answered:
Sorry, you have unsuccessfully completed this CME quiz with a score of
The following questions were not answered correctly:
Commitment to Change (optional):
Indicate what change(s) you will implement in your practice, if any, based on this CME course.
Your quiz results:
The filled radio buttons indicate your responses. The preferred responses are highlighted
For CME Course: A Proposed Model for Initial Assessment and Management of Acute Heart Failure Syndromes
Indicate what changes(s) you will implement in your practice, if any, based on this CME course.

Multimedia

Some tools below are only available to our subscribers or users with an online account.

2,104 Views
12 Citations
×

Related Content

Customize your page view by dragging & repositioning the boxes below.

See Also...
Articles Related By Topic
Related Collections
PubMed Articles
Jobs