Month: August 2019

Interstellar Spaceflight Is It Possible

first_imgWith current space travel limited to just a few robotic probes visiting nearby planets, how realistic is it to think about reaching the nearest stars? For the short term, not very – especially when we speak of manned missions. But the long term – 50 or even 100 years – chances are good mankind will have missions, unmanned to start with, traveling to stars in our galactic neighborhood. Image from: This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only. Citation: Interstellar Spaceflight: Is It Possible? (2005, December 7) retrieved 18 August 2019 from The sail material could be some form of Mylar – both thin and strong. Steering the sail and aiming the huge lasers, however, are not trivial problems. By huge lasers, think 10 gigawatts shining on a 1 kilometer in diameter sail just to send a 16 gram payload to the closest star. The laser must be precisely aimed on target for as long as possible to get the desired velocities. According to its inventor, this light-powered ship could make it to the next star in only ten years.This technology also scales up to allow for larger payloads but laser power levels quickly become gargantuan. To send a 1,000 ton ship with a crew to the same destination would require a 1,000 kilometer sail driven by a 10 million gigawatt laser – ten thousand times more than the power used on all the Earth today.These sails have been tested: On August 9, 2004 Japanese ISAS successfully deployed two prototype solar sails in low Earth orbit. A clover type sail was deployed at 122 km altitude and a fan type sail was deployed at 169 km altitude. Both sails used 7.5 micrometer thick film. They used the force of the sun’s photons as propulsion rather than a large laser.Faster speed could be achieved by fusion motors. Unfortunately, unlike light sails, fusion has yet to be sufficiently well understood to use as a propulsion device. Not for want of billions of dollars in funding to study it, however. Someday soon we may have the ability to control the same reaction that drives our sun. Fusion liberates tremendous energy from a given mass making it ideal for long voyages when fuel weight becomes the critical factor.One interesting idea is the Bussard ramjet first proposed in 1960 by the American physicist RW Bussard. Rather than bring fuel, why not get it from space? Explore further Actually, we already have space craft venturing into interstellar space. Pioneer and Voyager probes, 2 each, have reached the sun’s escape velocity and are now forever outward bound. The fastest, Voyager 1, is traveling at 62,000 kilometers per hour (39,000 mph). Even at that tremendous speed it’s painfully slow when interstellar distances are involved. Voyager 1 would take over 17,000 years to get Proxima Centuari, our nearest neighbor at 4.22 light years distance. With a theoretical speed limit imposed by Einstein’s Theory of Relativity at 1,079,252,848.8 km/h, or the speed of light, even the closest stars are very far away indeed. But if you take in to consideration the rapid pace of technological advancement, things look brighter. The Wright brothers’ first feeble flights advanced to a man on the moon in just 50 years. In less than 100 years, we can travel 1,000 times faster. If this rule holds true for the next hundred years, we will be able to travel to the nearest stars with relative ease.Predicting this future, however, is not easy. We simply lack even the basic theories to travel at above light speed making the engineering of an interstellar drive even further away. There are however, some interesting ideas on the drawing board that are within current theoretical limits.A study by NASA in 1998 identified 3 potential propulsion technologies that might enable exploration beyond our solar system. Antimatter, fusion and light sails.Light sails currently are the most technologically viable of the three. Robert L. Forward, scientist and science fiction writer first proposed them in 1984. The basic idea is to use huge lasers to push an object out of the solar system. Although it sounds strange to think of light pushing an object, photons do exert a very small force over objects they hit. Since the force it small, the object needs to be both large and lightweight – like a sail. It also needs to be reflective as only photons bouncing off an object impart velocity – absorbed photons generate heat. To prevent the heat from building up, the backside of the sail needs to be an effective radiator. Although commonly perceived to be empty, interstellar space has a minuscule amount of hydrogen gas – at a density of about one or two atoms per cubic centimeter. Bussard’s idea is to scoop this gas up using electromagnetic force fields that extend outwards in front of the spacecraft. This field would need to be absolutely gigantic – upwards of 50,000 kilometers in diameter. Shipboard superconducting coils would steer interstellar gas towards the ship compressing it until the density was enough to produce usable fuel. In order to start this collection process the ship would already need substantial velocity – on the order of 3 to 4% light speed.A Bussard ramjet could conceivably achieve a constant 1g acceleration that would allow the pilot to make very long journeys. To an Earthbound observer, such a ship would take hundreds of thousands of years to reach the center of the galaxy. But because of relativistic time dilation, only 20 years would pass for the crew on the ship. Imagine – just 20 years to the center of the galaxy! Of course, technical problems remain such as force field drag, shielding the crew from interstellar radiation and the ability to control fusion reactions.Even farther off technically is the antimatter drive. When matter and antimatter come in to proximity, they annihilate each other releasing even more energy than fusion. A fusion based propulsion unit could generate 100 trillion joules per kilo of fuel – respectable when considering that it would be 10 million times more efficient than chemical rockets. Matter-antimatter reactions, however, dwarf all other reactions. Imagine a drive could generate 20 quadrillion joules per kilo of reaction mass. That’s enough power form one kilo to supply the world’s needs for about 25 minutes.Technical problems include lack of fuel – the world supply is a few dozen nanograms a year, fuel handling – you can easily predict the catastrophic results of an antimatter fuel accident – and reaction control. All these technologies are as far away now as the atomic bomb was to Alfred Nobel – the inventor of TNT. That is to say, not very. We may see the beginnings of an interstellar spaceflight program before the end of the millennium. We will simply need a compelling reason.To contemplate seriously reaching the nearest stars, we need to understand the hurdles involved. First, there is the enormous cost involved in deploying any of the understood technologies. Second, despite UFO enthusiast’s beliefs, there is no hard evidence that we have ever been visited by alien spacefarers. Third, we know we can send radio waves to these destinations without problems.With this in mind, it may simply be too expensive and technically difficult to travel in interstellar space. A better solution has been proposed: why not create an intergalactic Internet? Send small, self-replicating research probes to other stars. Once there, they build copies of themselves and continue to explore outwards, relaying a steady stream of information back to Earth.These self-replicating probes, also known as Von Neumann machines, are named after their inventor, mathematician John Von Neumann (1903-1957). The beauty of this idea is once you manage to construct the first self-replicating machine, the rest is automatic. The probes would expand into space geometrically, spreading rapidly to fill the whole galaxy. Once established, this network could be used for communication and localization of new Earthlike planets to colonize.As of now, building machines that work well unassisted remain a problematic task for even the best scientists if recent unmanned mission failures are any indication. A self-repairing and self-replicating robotic probe seems distant indeed.Travel in interstellar space represents a huge challenge to humankind. For now, it remains in the realm of science fiction – but soon, who knows? We may yet live to see the first missions to nearby stars – that is if the last 100 years of history is any Chuck Rahls, Copyright 2005 Image from: Because photons exert a tiny force even over a large area, the sail must be large indeed. However, since space is virtually empty, there is very little drag. This means any imparted velocity is incremental – a tiny push over a long period equals one big push. Experimental cosmologist group launches its first iterations of space-traveling ‘wafercraft’last_img read more

Google Releases Chrome 20 Alpha

first_img( — With the full release of Chrome 1.0 in December, Google has just released Chrome 2.0 alpha that brings many noticeable improvements over Chrome 1.0. With this new alpha release of Chrome 2.0, the browser has been overhauled in which it handles HTTP. LG Launches Versatile LG-KF700 Google Chrome 2.0 alpha Explore further Chrome 2.0 browser also includes the addition of auto-complete in text fields, full page zoom, improvements in spell checker, and auto scroll. Google also states that the 2.0 alpha is more reliable and faster browsing is achieved by accessing your hard drive less often.Now you can even import bookmarks from Google Bookmarks, a feature that was not found in Chrome 1.0. You also have the ability to drag a tab to certain positions on your monitor and have a docking icon appear. One interesting feature, worth mention, is the “Profiles” feature in this new release. The “Profiles” feature lets users separate their browser settings, including bookmarks, history, and cookies into different categories. For example if you use your work computer for personal use, you can set up a work profile and a personal profile so that your bookmarks, history and home pages are kept separate.A new version of WebKit rendering engine has also been implemented in Chrome 2.0 that’s the same as the one used in Apple’s Safari 3.1 web browser. The new rendering engine enables some CSS coding features such as reflections, masks, gradients, and canvas drawing. To get the new version of Chrome 2.0 you will need to have Chrome 1.0 installed on your PC. You will also need to subscribe to Google’s Developer Preview Channel. Keep in mind that Chrome 2.0 is an alpha release and expect it to crash quite often.On the web:Chrome Release Notes: … s/releasenotes201561© 2009 Citation: Google Releases Chrome 2.0 Alpha (2009, January 14) retrieved 18 August 2019 from This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only.last_img read more

Reversals of Earths Magnetic Field Explained by Small Core Fluctuations

first_img Explore further Although volcanic basalt reveals when reversals occurred, it’s much more difficult to find evidence for why or how the Earth’s magnetic field reverses. In a recent study, scientists from the Ecole Normale Supérieure and the Institut de Physique du Globe de Paris, both in Paris, have proposed a general mechanism that provides a simple explanation for field reversals. In their model, small fluctuations in convective flow in Earth’s core can push the planet’s sensitive magnetic system away from one pole toward an intermediate state, where the system becomes attracted to the opposite pole. “We have found a mechanism that gives simple explanations of many features of the reversals of Earth’s magnetic field,” François Pétrélis of Ecole Normale Supérieure told “In particular, it explains the existence and the shape (slow phase followed by fast phase) of reversals, the existence and the shape of aborted reversals (‘excursions’), the statistical properties of reversals, and the possibility for very long durations without reversals (‘superchrons’).”At present times, the Earth’s magnetic field can be described as a magnetic dipole, with the magnetic south pole currently located near the Earth’s geographic north pole, and the magnetic north pole near the geographic south pole (both magnetic poles are misaligned along the Earth’s rotational axis by about 11.3 degrees). The existence of such a long-lived magnetic field can be explained by dynamo theory, which describes how a convective, electrically conducting fluid that rotates can maintain a magnetic field. As the scientists suggest, the reversal mechanism relies on the existence of a second magnetic mode, in addition to the dipolar field. The presence of a second mode, such as a quadrupolar field, can have significant effects on how the magnetic system reacts to changes in equatorial symmetry. As the researchers explain, the equator can be thought of as a plane of symmetry, and the convective flow in the Earth’s outer core is usually north-south symmetric. Previous studies on paleomagnetic data have proposed that reversals involve an interaction between the dipolar and quadrupolar modes, which would correlate with changes in equatorial symmetry. In support of this idea, some recent numerical simulations have shown that reversals do not occur when the convective flow remains equatorially symmetric. ( — Based on studies of old volcanic basalt, scientists know that the Earth’s magnetic field reverses at irregular intervals, ranging from tens of thousands to millions of years. Volcanic basalt rock contains magnetite, and when the rock cools, its magnetic properties are frozen, recording the Earth’s magnetic field of the time. With this data, scientists estimate that the last magnetic field reversal occurred about 780,000 years ago. According to a new model, small fluctuations in convective flow in Earth’s core can explain how the Earth’s magnetic field reverses. Image credit: Wikimedia Commons. “The quadrupolar field (it is likely to be a quadrupole but another structure could be possible) is also generated by the flow of the liquid core of the Earth, exactly like the dipolar field,” explained the researchers. “Most of the time, we observe a dipolar field because it is more easily generated by the flow, but in other conditions a quadrupolar field could be maintained, and this occurs in a temporary manner during a reversal.”To further explain the dipole-quadrupole interaction, the scientists invoked a model that was recently used to describe the dynamics of a magnetic field generated in a very different system: a lab experiment involving a von Karman swirling flow of liquid sodium (which, like the Earth’s magnetic field, is generated by the dynamo effect). The scientists suggest that a general mechanism could explain both magnetic fields, independent of the different symmetries and velocities of the two systems.“We have shown that if the dipolar field of Earth is coupled to another magnetic mode (a quadrupolar field, for instance), this coupling provides a path to flip the dipole to its opposite,” the scientists said. “If this coupling is strong enough, the magnetic field will spontaneously oscillate between the two modes and their opposite polarities. We will then observe periodic reversals of the magnetic field (this is the case of the solar magnetic field, for which the period is 22 years). In the case of Earth, the coupling is not strong enough, and oscillations are not observed. Velocity fluctuations in the liquid core are then needed to trigger a reversal.”In the model, small fluctuations in convective flow can push the system away from one pole toward the intermediate quadrupolar state, where it becomes attracted to the opposite pole. A reversal occurs in two phases: a slow phase where the fluctuations are the motor of the evolution, and a fast phase during which the dynamics does not rely on the fluctuations. The first phase, during which the dipole amplitude decreases slowly, seems to last around 50 kiloyears (30,000-70,000 years). The second phase, which starts when the dipolar mode vanishes, is quite faster: 10,000 years are required for the dipole to recover with the opposite polarity. Sometimes, at the end of the first phase, the system may simply return to the initial pole, which is called an “excursion” when it occurs on Earth. However, if the system does reverse, the behavior happens relatively abruptly. In addition, the system usually overshoots immediately after reaching the opposite pole. The scientists noted that the amplitude of the fluctuations does not need to be large: “Fluctuations of the flow do not switch off the magnetic field and then regenerate it with the opposite polarity,” they said. “In contrast, the dipolar field continuously changes shape during a reversal because the amplitude of the other mode (the quadrupole, for instance) continuously increases, whereas the dipole decreases. When the dipolar component vanishes, it can increase again with the opposite polarity whereas the amplitude of the other mode decreases.”The model shows that the duration of the magnetic field in one state depends on the intensity of the convection fluctuations and also on the efficiency of the coupling between the two modes. Even a moderate change in convection can greatly affect the magnetic field polarity duration, which could account for “superchrons” – very long periods without geomagnetic reversals. Although little is known about the actual flow inside the Earth’s core, recent observations have shown that the ends of superchrons are often followed by major flood basalt eruptions, which are likely to produce equatorial symmetry breaking of convection at the core-mantle boundary, in support of the scientists’ model. More information: Pétrélis, François; Fauve, Stéphan; Dormy, Emmanuel; and Valet, Jean-Pierre. “Simple Mechanism for Reversals of Earth’s Magnetic Field.” Physical Review Letters, 102, 144503 (2009).Copyright 2009 All rights reserved. This material may not be published, broadcast, rewritten or redistributed in whole or part without the express written permission of Simulations shed light on Earth’s history of magnetic field reversals Citation: Reversals of Earth’s Magnetic Field Explained by Small Core Fluctuations (2009, April 23) retrieved 18 August 2019 from This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only.last_img read more

Space cannon to shoot payloads into orbit w Video

first_imgSpace gun. Image credit: John Hunter The rocket that thinks it’s a jet ( — A physicist has proposed using a 1.1 km (3,600 ft) cannon to deliver cargo into orbit, and says the cost would be around $250 per pound, a massive saving on the $5,000 per pound ($11,000 per kg) it currently costs to make deliveries using a rocket. This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only. Citation: Space cannon to shoot payloads into orbit (w/ Video) (2010, January 18) retrieved 18 August 2019 from John Hunter, from the company Quicklaunch, which was set up by himself and two other scientists, bases its plans on previous work they carried out at the Lawrence Livermore National Laboratory in California. In 1992 Hunter and his colleagues fired a 130 m (425 ft) cannon built to test launch hypersonic engines. Its piston, driven by methane, compressed hydrogen gas that expanded up the barrel of the over-sized gun to shoot the projectile. The Quicklaunch design has replaced the methane piston with a combustion system burning natural gas in a heat exchanger inside a chamber of hydrogen gas. The combustion system heats the hydrogen to 1,430˚C (2,600˚F), which increases the gas pressure by 500%. An operator then opens a valve to allow the hot, pressurized hydrogen into the 1100-meter-long barrel of the gun, where it instantly expands, shooting the projectile out and into space. As soon as the payload has left, an iris at the end of the barrel closes to capture the hydrogen for re-use. Once the projectile is launched, a small rocket engine then boosts the payload into a low-Earth orbit.Hunter calculates the pressure would be sufficient to launch a 450 kg payload at six kilometers per second (13,000 mph). The process would produce 5,000 Gs, and so would only be suitable for rugged payloads such as strengthened satellites and rocket fuel. Hunter said the system could not be used as a people-launcher because a person shot out of the cannon “would probably get compressed to half their size,” causing instant death.Hunter said the heat generated would be short-lived, with the projectile clearing the atmosphere in under 100 seconds. He also said the projectiles may need to be designed so that outer layers could burn off.Hunter’s proposal is to operate the “Quicklauncher” from the ocean near the equator, where the Earth’s faster rotation will help launch payloads into space. The cannon would float, with 490 m (1,600 ft) of it below the surface, where it would be stabilized by ballast. Operators would be able to swivel it as required to deliver the payload into different orbits.Hunter plans to test a 3 meter prototype in a water tank in February, and a full-size cannon could be built within seven years, if Quicklaunch can raise the required $500 million. While this is a sizeable upfront cost, the potential savings in the long term are substantial, because the cannon is reusable. Its use would significantly reduce the cost of keeping the International Space Station in orbit.The proposal was outlined in October in Boston, U.S., at the Space Investment Summit. More information: — Space Investment Summit: Explore further © 2010 PhysOrg.comlast_img read more

Japanese researchers using particle accelerator to breed salt resistant rice

first_img RIKEN ion beam technology used to create brewing yeast ( — Japanese researchers at the Riken Nishina Centre for Accelerator-Based Science have been using their particle accelerator to cause mutations in rice for over two decades with the aim of breeding rice that is more resistant to saltwater. Up to now their results have been limited; just one new salt resistant rice variety has been created and it faced mixed reactions regarding taste. But now, because of the tsunami in that country last year that contaminated a lot of farmland with seawater, efforts there have picked up and researchers are reportedly coming close to developing a whole host of new saltwater resistant strains. Explore further Cambodia, Kratie: A worker is removing the rice seedlings. Image: Wikipedia Citation: Japanese researchers using particle accelerator to breed salt resistant rice (2012, May 11) retrieved 18 August 2019 from The idea isn’t all that novel, breeding new varieties of plants has been done for centuries. What the researchers at the accelerator facility are doing is speeding up the process. All breeding is based on mutations that occur in plant cells. Those mutations that create positive results in plants are favored over those that don’t. Over time successive generations result in plants that are ever closer to what is desired. With the particle accelerator, the research team at Riken, led by Tomoko Abe, fire an ion beam at grains of rice, creating a huge variety of mutations in their genes; afterwards the grains are planted and tested to see which are more resistant to saltwater. Those that are go through testing and are sometimes bred with other varieties with the hope of finding the perfect mix of salt resistance and good taste. In so doing the team is able to create new strains of rice in just a few years that normally would take decades using natural mutation methods.Developing strains of rice that are resistant to the salt in seawater is important, not just for Japan, which saw yields drop by over half in areas where the sea inundated farmland, but for many other countries in the world as well. With both rising populations and ocean levels, land that is occasionally flooded by the sea could be made useable if strains of rice can be developed that are able to grow there.The researchers at Riken have already developed strains that see yields drop by just twenty percent when inundated with seawater, and are hoping to improve that number as more research continues. They expect to see fully resistant rice strains as soon as four years from now. © 2012 Phys.Org This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only.last_img read more

Scotland lunarcalendar find sparks Stone Age rethink

first_img Explore further More information: Citation: Scotland lunar-calendar find sparks Stone Age rethink (2013, July 27) retrieved 18 August 2019 from The beginning of time? World’s oldest ‘calendar’ discovered Scientists are now calling this discovery in Scotland that seems to mimic the phases of the moon to track lunar months the world’s oldest known calendar.”What we are looking at here is a very important step in humanity’s earliest formal construction of time, even the start of history itself,” said Vincent Gaffney, professor of landscape archaeology at Birmingham University, who led the team who analyzed the pits and their functions.Also referred to as the “Warren Field calendar,” referring to the land area in Aberdeenshire where the calendar was found, the discovery consists of an array of 12 pits and arc. They appear to represent the phases of the moon, going from waxing and waning to central arc, corresponding to the lunar months of the year. However, said Prof. Gaffney, because the lunar year does not correspond to the natural year, the sequence had to be calibrated annually, and the site seems to align along the midwinter solstice, indicating that each year it was calibrated, and kept good time.The experts believe the site dates back to around 8000 BC. Gaffney and team in their paper on the subject observed that the site “also aligns on the south east horizon and a prominent topographic point associated with sunrise on the midwinter solstice. In doing so the monument anticipates problems associated with simple lunar calendars by providing an annual astronomic correction in order to maintain the link between the passage of time indicated by the Moon, the asynchronous solar year, and the associated seasons.”Although previously excavated back in 2005, geophysical survey teams from several universities have been working to map the sites again and to look for further features. The Warren Field site was first discovered as unusual crop marks spotted from the air by the Royal Commission on the Ancient and Historical Monuments of Scotland (RCAHMS).The pit-creators are identified as a Mesolithic group, referring to a group of cultures between Paleolithic and the Neolithic. The three “lithics” belong to the Stone Age, and the Mesolithic were a transition group who succeeded in adapting to a collecting and fishing as well as hunting economy The question remains, why did these hunter gatherers track the phases of the moon? For hunting purposes? To explore celestial bodies? One theory comes from project member, Dr Christopher Gaffney, Archeological Science at the University of Bradford: “For pre-historic hunter-gatherer communities, knowing what food resources were available at different times of the year was crucial to survival. These communities relied on hunting migrating animals and the consequences of missing these events were potential starvation. They needed to carefully note the seasons to be prepared for when that food resource passed through, so from this perspective, our interpretation of this site as a seasonal calendar makes sense.”center_img © 2013 This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only. Archeologists have discovered a lunar calendar in Aberdeenshire, Scotland, that is nearly ten thousand years old. Their findings show that the calendar makers (1) thought about time and (2) figured out a means to follow it at a period in history that was still in the Stone Age. The discovery is considered both surprising and important because it now places a calendar nearly five thousand years before what was previously considered as the first formal calendar, created in Mesopotamia 5,000 years ago. But here, a discovery has been made of a calendar construct appearing to track the phases of the moon nearly 10,000 years ago.last_img read more

Researchers find Europes forests moving toward carbon sink saturation point

first_img Explore further More information: First signs of carbon sink saturation in European forest biomass, Nature Climate Change (2013) DOI: 10.1038/nclimate1853AbstractEuropean forests are seen as a clear example of vegetation rebound in the Northern Hemisphere; recovering in area and growing stock since the 1950s, after centuries of stock decline and deforestation. These regrowing forests have shown to be a persistent carbon sink, projected to continue for decades, however, there are early signs of saturation. Forest policies and management strategies need revision if we want to sustain the sink. Journal information: Nature Climate Change © 2013 The amount of carbon dioxide in the atmosphere can be reduced in two ways. The first and most obvious is for people to stop pumping so much of it into the air. The second is to take more out (i.e., create carbon sinks), which for now at least, means planting more trees. As many of us may recall from grade school, trees pull carbon dioxide out of the air and store it in new growth—in return, oxygen is released into the atmosphere. Absorbed carbon remains in the wood until it either rots or is burned. For that reason, those concerned with reducing the amount of carbon in the atmosphere and the associated rise in global temperatures promote the idea of planting more trees, while reducing deforestation.Europe is unique in that it’s one of the few places on the planet that has more trees now than it did a century ago. Replanting was initiated as part of rebuilding the continent after the ravages of two World Wars—particularly in France and Germany. Unfortunately, trees don’t live forever—those trees planted after the wars have grown so old that their ability to absorb carbon is slowing. The research team estimates these trees will reach a saturation point by 2030. The researchers also found that some parts of the continent have seen some deforestation as trees are cut to make room from expanding towns and cities. Cutting down trees and using the wood from them isn’t a problem of course, it’s when they are cut and not replaced that the problem occurs. For that reason, the research team suggests that old wood forests become part of harvesting programs to replace older trees with newer growth.The researchers also note that older forests are more at risk—fires, disease and insects all contribute to killing trees, allowing the carbon they hold to be released into the atmosphere. Cutting the trees and using the wood before they are killed, and then replacing them, the team notes, would make far more sense. Citation: Researchers find Europe’s forests moving toward carbon sink saturation point (2013, August 19) retrieved 18 August 2019 from read more

The origins of polarized nervous systems

first_imgComb Jelly from phylum Ctenophora. Credit: (—There is no mistaking the first action potential you ever fired. It was the one that blocked all the other sperm from stealing your egg. After that, your spikes only got more interesting. Waves of calcium flooding the jointly-forged cell stiffened its glycoprotein-enhanced walls against all other suitors and kicked off the developmental program ultimately responsible for constructing your brain. Unlike the nervous systems of the lower forms of life, our neurons have a clearly polarized form—a single output axon projecting far to parts unknown is charged by input dendrites feeding on the local metabolic soup de jour. The origins of this polarity in neurons, and therefore in nervous systems in general, are written in the primitive body plans of the mostly gelatinous organisms still hailing intact across deep time. Journal information: Journal of Experimental Biology This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only. Citation: The origins of polarized nervous systems (2015, March 3) retrieved 18 August 2019 from Complex nerve-cell signaling traced back to common ancestor of humans and sea anemones How a blunt multipurpose neuronal toolkit that originally evolved to nourish was morphed into the precise cellular utensils we now use to mince the world is the subject of a new special issue in the Journal of Experimental Biology (JEB). The story of the acquisition of polarity, or rather the loss of universality, in the flow of resource through crude nerve nets is the story of our brains. Last year,Tim Jegla from Penn State published work showing that the human Erg potassium channels that are tuned to repolarize the long action potentials underlying the strong muscular contractions of our hearts have their origins in the earliest nervous systems ever evolved. Since then he has been piecing our brains together by tracing the evolution of related channels like the EAG potassium channels, and the so-called Shaker potassium channels in various primitive organisms. The creatures that have been the most informative mostly fall into taxonomic groups of typically radially-symmetric animals named with a strange variation on the letter C. The ‘cnidarians’ are animals like hydras and the true jellyfish, while the ‘ctenophores’ are the comb jellies that swim with cilia. In an article on polarity written together with Melissa Rolls, Tim explores how the positioning of different kinds of channels by the cytoskeleton (at places like the axon initial segment, nodes, and dendrites) is crucial for establishing directional signalling in neurons. So I asked him point blank if he could nail down when polarity first evolved. He said it was likely in an ancestor of the parahoxozons, a group defined by their possession of at least one of the Hox/ParaHox genes associated with the the specification of the body axis. With genetic experiments now in progress in his lab Jegla is looking for indications that polar neurons exist, contrary to the current literature, even in the lowly sea anemone. As cnidarians, anemone are privy to the benefits of parahoxozoans, something the ctenophores cannot claim. More information: Journal of Experimental Biology, © 2015 In looking for larger developmental trends in which to anchor the idea of increased polarity, or loss of flexibility in neurons, ctenophores may have other secrets to tell. One author writing in the special issue of JEB suggests that recent whole genome data puts ctenophores as a sister group to all other animals, placing them at the earliest branching lineage—a move which would make them a more basal metazoan than even SpongeBob himself. Two factors which complicate such analysis are convergent evolution and the loss of genes and function. We might imagine that the possibility of having at least two independent origins for neural systems exists regardless of which lineage was prior.It has been known since the work of Chun in 1880 that when ctenophore blastomeres are separated at the two-cell stage each half-embryo develops exactly half of adult structures. It seems that this high degree of determinism at the organism level, which fades in the progression of species, contrasts with the aquisition of specification at the cell level. Among the important proteins known to exist in these primitive organisms are various kinds of G-protein coupled receptors and gap junctions. Originally it looks like these proteins played important roles in cell adhesion and communication, and therefore in early development and specification of the body plan. Enzymes to synthesize and transport neurotransmitters were also present early on. A trend in moving to more advanced body plans, and neurons, is the restriction of the expression of these transmitter systems to specific cells. On top of this there is an inexorable refinement of multipurpose symmetric synapses into asymmetric synaptic diodes, with concommitant exclusivity of transmitter profile in both dense core and clear vessicles. In creature like planarians, worms, or flies, the percentage of neurons we might call ‘polar’ becomes an increasingly important thing for us to take account of. In C. elegans for example, many neurons, with the exception of the elaborate and highly branched sensory neurons that span the whole body, are fairly simple with just a few processess containing synapses that can be both pre and post synaptic. The neurons of many insects, like drosophila, are conspicuous for their dense regions of idiosyncratic branching where the terms dendrite or axon would seem to have little meaning. While the neurons of higher and larger vertebrates are expected to in a sense ‘feel’ every spike they might pull off throughout the whole neuron, it paradoxically seems that tiny invertebrate neurons none-the-less are more likely to contain isolated domains of protected metabolic and electrical activity. The details of all this are to be found at the molecular level, which at this time in the history of neurobiology means the the directions of the ‘plus’ and ‘minus’ ends of various cytoskeletal proteins, and the preferences of the motors that ride them in either direction. Like vertebrates, drosophila have axons that exclusively use plus-end-out microtubules. However, although their dendrites similarly are distinguished by the presence minus-end-out microtubules, one surprise was that almost all of their dendrites were this way. The kicker is that they start out with a even mix like vertebrates do, but over time somehow weed them out. An important element in any potential theory of neurons would be the role of the cell body (the nucleus, centriole and primary cilium) in the ongoing specification of the larger tree of axons and dendrites. A cell body that stands largely aloof from them, whether transiently or permanently, would appear to lose some of the authority it might have if interposed instead between them.The unique geometry of the pseudounipolar neurons of our dorsal root ganglion has been known for a while, but only more recently has the frequent presence of axons sprouting from dendrites in our hippocampus and cortex been appreciated. In seeking explanations for the structure of such neurons the influences of mitochondria in various states of performance and lifecycle should not be underestimated. In fact, mitochondria figure importantly in the entire evolutionary curiosity we have tried to lay out here. The same article above which stirred up question surrounding the primitive phylogeny of sponges also explored newly identified trends that emerge in looking at the sizes and contents of the genomes of mitochondria across metazoans—but that is probably a topic sufficient for another post. 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