neurotransmitter Chemical released by neurons to stimulate neigh¬ bouring neurons, allowing impulses to be passed from one cell to the next throughout the nervous system. A nerve impulse arriving at the axon ter¬ minal of one neuron stimulates release of a neurotransmitter, which crosses the microscopic gap (see synapse) in milliseconds to the adjoin¬ ing neuron’s dendrite. Many chemicals are believed to act as neurotrans¬ mitters. The few that have been identified include acetylcholine, dopamine, and serotonin. Some neurotransmitters activate neurons; others inhibit them. Some mind-altering drugs act by changing synaptic activity.
Neuschwanstein Vnoi-'shvan-.shtlnV Castle Elaborate castle built on a rock ledge over the Pollat Gorge in the Bavarian Alps, near Fiissen, Ger. Begun in 1869 at the behest of Bavaria’s Louis II, this lavish stronghold is an eccentric romantic reconstruction of a medieval castle, complete with
Structure of a neuron. Dendrites, usually branching fibres, receive and conduct impulses to the cell body, where inputs arriving from various dendrites are inte¬ grated. Nerve impulses are conducted along the axon. When an impulse reaches the axon terminals, neurotransmitter chemicals are released into a gap (synapse) between the neuron and a neighbouring cell, and the impulse is transmitted to an adjacent neuron or effector cell (as of a muscle or gland). Schwann cells surround large axons, forming an insulating sheath. Spaces (nodes of Ranvier) between Schwann cells serve to conduct the nerve impulse quickly along the axon.
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Neusiedler Lake ► Neville I 1349
a walled courtyard, indoor garden, towers, and an artificial cave. Its two- story throne room is modeled after a Byzantine basilica. Wall paintings depict scenes from Richard Wagner’s operas.
Neusiedler Vnoi-.zed-lorV Lake Hungarian Ferto-to Vfer-tce-'toX Lake, eastern Austria and northwestern Hungary. The shallow lake was formerly entirely within Hungary, but in 1922 the northern two-thirds were transferred to Austria. Formed during the Pleistocene Epoch, it is Austria’s lowest point, 377 ft (115 m) above sea level. Heavy reed growth along its shores supports many species of birds, which are protected by an international sanctuary and a biological station.
Neustria \'nu-stre-o\ During the Merovingian period, the western part of the kingdom of the Franks after the 6th-century conquest by Clovis. The eastern kingdom was Austrasia. Neustria corresponded roughly to the area of present-day France west of the Meuse River and north of the Loire River. The name later denoted a much smaller area; by the 11th—12th cen¬ turies it was sometimes used synonymously with Normandy.
neutering See castration
Neutra Vnoi-tra,\ English Vnii-troX, Richard (Joseph) (b. April 8, 1892, Vienna, Austria—d. April 16, 1970, Wuppertal, W.Ger.) Austrian- born U.S. architect. Educated in Vienna and Zurich, Neutra moved to the U.S. in 1923. His most important early work was the Lovell House, Los Angeles (1927-29), which features glass expanses and cable-suspended balconies. Shortly after World War II, Neutra created his most memorable works: the Kaufmann Desert House, Palm Springs, Calif. (1946-47), and the Tremaine House, Santa Barbara, Calif. (1947—48). Elegant and pre¬ cise, these houses are considered exceptionally fine examples of the Inter¬ national Style, which Neutra helped introduce into the U.S. Carefully placed in the landscape, Neutra’s houses often have patios or porches that make the outdoors seem part of the house. He believed that architecture should be a means of bringing man back into harmony with nature and with himself and was particularly concerned that his houses reflect the way of life of the owner. His later works included office buildings, churches, housing projects, and cultural centres. His many writings include Survival Through Design (1954).
neutralism See nonaligned movement
neutrality Legal status of a country arising from its abstention from all participation in a war between other countries, the maintenance of an atti¬ tude of impartiality toward the belligerents, and the recognition by the belligerents of this abstention and impartiality. Historically, the rights of neutral countries typically included freedom from use or occupation of their territory by any warring party, maintenance of diplomatic relations with other neutrals and belligerents, freedom of their citizens to go about their business, and respect for their intent to be neutral. In both World War I and World War II, many of the basic concepts of neutrality ceased to be respected, and by the late 20th century the freedom of the neutral had been sharply reduced.
neutrino \nii-'tre-no\ Fundamental particle with no electric charge, little mass, and a spin value of Vi. Neutrinos belong to the lepton family of sub¬ atomic particles. There are three types of neutrino, each associated with a charged lepton: the electron, the muon, and the tau. Neutrinos are the most penetrating of subatomic particles because they react with matter only by the weak force. They do not cause ionization, because they are not elec¬ trically charged. All types of neutrino have masses much smaller than their charged partners.
neutrino \nu-'tre-no\ problem, solar Shortfall in the expected num¬ ber of neutrinos produced by the Sun that are detected on Earth. Long- running experiments begun in the 1960s found only one-third to two- thirds the number of neutrinos predicted by theory to arrive from the Sun, where they are emitted as a result of nuclear fusion in the solar core. The discrepancy implied either that the theory of solar energy production was wrong or that neutrinos transformed en route to Earth in a way that made some of them seem to vanish. By the early 2000s strong evidence had been gathered in support of the latter explanation—that neutrinos “oscil¬ late” in flight among their different types, not all of which could be detected in the experiments. For this to occur, neutrinos must have at least a tiny mass, though the specific values remained to be determined.
neutron One of the constituent particles of every atomic nucleus except ordinary hydrogen. Discovered in 1932 by James Chadwick (1891-1974), it has no electric charge and has nearly 1,840 times the mass of the elec¬
tron. Free neutrons undergo beta decay with a half-life of about 10 min¬ utes. Thus, they are not readily found in nature, except in cosmic rays. They are a penetrating form of radiation. When bombarded with neutrons, various elements undergo nuclear fission and release more free neutrons. If enough free neutrons are produced, a chain reaction can be sustained. This process led to the development of nuclear power as well as the atomic bomb. Neutron beams produced in cyclotrons and nuclear reactors are important probes of matter, revealing details of structure in both organic and inorganic susbtances.
neutron bomb or enhanced radiation warhead Small ther¬ monuclear weapon that produces minimal blast and heat but releases large amounts of lethal radiation. The blast and heat are confined to a radius of only a few hundred yards; within a somewhat larger area, the bomb throws off a massive wave of neutron and gamma radiation, which is extremely destructive to living tissue. Such a bomb could be used with deadly effi¬ ciency against tank and infantry formations on the battlefield without endangering towns or cities only a few miles away. It can be carried in a missile or delivered by a howitzer or even an attack aircraft.
neutron star Any of a class of extremely dense, compact stars thought to be composed mainly of neutrons with a thin outer atmosphere of pri¬ marily iron atoms and electrons and protons. Though typically about 12 mi (20 km) in diameter, they have a mass roughly twice the Sun’s and thus extremely high densities (about 100 trillion times that of water). Neutron stars have very strong magnetic fields. A solid surface differenti¬ ates them from black holes. Below the surface, the pressure is much too high for individual atoms to exist; protons and electrons are compacted together into neutrons. The discovery of pulsars in 1967 provided the first evidence of the existence of neutron stars, predicted in the early 1930s and believed by most investigators to be formed in supernova explosions. See also white dwarf star.