NASA 2 is the name of the second long-duration stay of an American astronaut on board the Russian Space Station Mir. The NASA 2 increment started with the docking of the American Space Shuttle with the Mir station during STS-76 on March 22, 1996 and ended with the docking of the Shuttle Atlantis with Mir during the STS-79 mission, on September 18, 1996.
NASA 3 is the name of the third long-duration mission of an American astronaut on board the Russian Space Station Mir. The NASA 3 increment started with the docking of the American Space Shuttle with the Mir during the STS-79 mission, on September 18, 1996, and will end with the docking of STS-81 early in 1997.
Natriuresis is the excretion of abnormal amounts of sodium in the urine.
Natriuretic factors are hormone-like substances present in the two atrial walls of the heart (especially numerous in the right atria). Natriuretic factors can cause a three to ten times increase in renal (kidney) excretion of sodium. Consequent to the loss of sodium is a slight decrease in the extracellular fluid volume and blood volume. Although the exact mechanism of action is unclear, it is believed that these factors play a role in the regulation of blood volume.
Natural killer cell (NK cell)
A natural killer cell is a specific type of lymphocyte (white blood cell) which kills "target" (tumor or virus-infected) cells without involving antibodies. The mechanism of their killing activity is not yet clear, but interferon seems to play a role.
Necrosis is the death of cells in an organ or tissue, which can be caused by a variety of chemicals and toxic substances.
Negative energy balance
A negative energy balance occurs when the body expends more energy (measured as calories) than it receives through the consumption of food.
Nematodes are invertebrates comprising the parasitic roundworms. They are characterized by a smooth narrow cylindrical unsegmented body tapered at both ends. They shed their tough outer cuticle four times during life to allow growth. The microscopic free-living forms are found in all parts of the world, where they play an important role in the destruction and recycling of organic matter. The parasitic nematodes are much larger and some of them can cause serious diseases in man.
Nephrotic syndrome is characterized by generalized edema, albumin in the urine and low serum albumin. This condition is caused by increased permeability of the glomerular capillary basement membranes.
The nervous system is the vast network of cells specialized to carry information (in the form of nerve impulses) to and from all parts of the body in order to bring about bodily activity. In vertebrates, the brain and spinal cord together form the central nervous system; the remaining nervous tissue is known as the peripheral nervous system and includes the autonomic nervous system, which is itself divided into the sympathetic and parasympathetic nervous systems. The basic functional unit of the nervous system is the neuron (nerve cell).
Neural means pertaining to the nervous system.
The system of dual control of certain activities of the body by means of both nerves (neuro-) and circulating hormones (endocrine).
Neuroglia refers to glial cells or glia cells of the nervous system that support the neurons (nerve cells). They form insulating sheets of tissue around the neurons (called myelin), preventing impulses from traveling between adjacent neurons. Other functions include providing nutrition and controlling the fluids surrounding the neurons.
Neurological means of or relating to the nerves.
Neurology is the branch of medical science concerned with the nervous system and its disorders.
Neuromuscular means of or relating to nerves and the muscles they stimulate.
The neuromuscular junction is the point where a muscle fiber comes into contact with motor neurons carrying nerve impulses from the central nervous system. The impulses travel from the neurons to the muscle fiber by means of a neurotransmitter to overcome the small gap between the two nerve cells.
Neuromuscular physiology is the research area that focuses on studying the nerves and the muscles they stimulate.
The neuromuscular system consists of the nerves and the muscles they stimulate.
A neuron is a nerve cell, one of the basic functional units of the nervous system; it is specialized to transmit electrical nerve impulses and so carry information from one part of the body to another.
Neuropharmacological means relating to drugs that exert effects on nerve tissue or the transmission of nerve impulses.
Neurophysiology is the science related to the neurovestibular organ. The vestibular organ is located in the inner ear, is responsible for our sense of gravity and plays an important role in our ability to orient ourselves. The neurovestibular organ has two components: 1) the otolith receptors that sense the intensity of acceleration and the field of gravity; and 2) the semicircular canal receptors that sense the direction of acceleration.
The neuropil is the complex, feltlike net of axonal, dendritic and glial arborizations that forms the bulk of the central nervous system's gray matter, and in which the nerve cell bodies lie embedded.
Neuroscience is any one of the various branches of science concerned with growth, development and function of the nervous system.
Neurosensory means relating to the sensory aspects of the nerves and nervous system, i.e., the ability of the nerves to sense stimuli from the body itself or from the external environment.
Neurospora is a fungus. It was made famous in 1941 by G. Beadle and E. Tatum who succeeded in isolating a number of genetically different forms (mutants) of Neurospora. This Nobel prize-winning discovery opened the way to analysis of the consequences of permanent genetic change (mutations) in biochemical terms.
Neurovestibular relates to the interaction between the brain and the vestibular organ, located in the inner ear. The vestibular apparatus is responsible for balance. It consists of three semicircular canals, which detect movements of the head, and the utriculus and sacculus, which detect the position of the head.
A neutrophil is a phagocytic, short-lived granulocytic cell that is recruited to sites of infection, tissue damage, and cell death to aid in clean-up. Neutrophils are part of the innate immune system that protects individuals before other components of the immune system can be recruited or activated.
Neutrophilia is an increase in the number of neutrophils (a type of white blood cell) in the blood.
Nickel is a silver-white hard malleable ductile metallic element capable of a high polish and resistant to corrosion. It is used chiefly in alloys and as a catalyst.
Nitrogen is a gaseous element that occurs in air (78% of air volume). It is an essential component of proteins and nucleic acids in living organisms.
Nitrogen balance is the measure of the difference between nitrogen absorption and nitrogen release in the body.
Nitrogen tetroxide is a poisonous volatile liquid which gives off a brownish irritant fume.
The term non-antigravity refers to muscles (or bones) that are not affected by the absence (or pressure) of gravity, such as the respiratory diaphragm muscle.
Noninvasive describes diagnostic procedures which do not involve the insertion of devices into the body or require penetration of the skin. Common noninvasive techniques are ultrasound or EKG.
Nonspasmodic means not having the character of a spasm or convulsion.
Nonvascularity is used to describe a region where blood vessels are absent and blood perfusion does not occur. The vascular system is another name for the blood circulation system of the human body. Nonvascularity describes the absence of the vascular system.
Norepinephrine, also known as noradrenaline, is a hormone produced by the adrenal glands and also secreted from nerve endings in the sympathetic nervous system as a chemical transmitter of nerve impulses. Many of its general actions are similar to those of adrenalin, but it is more concerned with maintaining normal body activity than with preparing the body for emergencies.
Normoxia is a state in which the partial pressure of oxygen in the inspired gas is equal to that of air at sea level, about 150 mm Hg.
Normoxic is a state in which the partial pressure of oxygen in the inspired gas is equal to that of air at sea level, about 150 mmHg.
Noxious injurious or harmful to health.
Nucleation is the coalescence of molecules or small particles that is the beginning of a crystal or similar small deposit. For metals, nucleation is the beginning of the solid state structure of the alloy (mixture of metal elements), the forming of a pattern when the rest of metals are in the molten-liquid state. Around a "nucleus," the melted alloy solidifies more rapidly, possibly changing its structure (with less favorable characteristics), or forming bubbles, etc. As a basic rule investigators like to avoid nucleation during solidification. In microgravity, the occurrence of nucleation is reduced and the structure of the resolidified metal is more even.
Nucleic acid is either of two organic acids, DNA or RNA, present in the nucleus and in some cases the cytoplasm of all living cells. Their main functions are in heredity and protein synthesis.
In neuroanatomy, the nucleus is a group of nerve cells in the brain or spinal cord that can be demarcated from neighboring groups on the basis of either differences in cell type or the presence of a surrounding zone of nerve fibers or cell poor neuropil.
Nullify means to neutralize or to equalize a given stimuli which results in a neutralization of the impulse (thereby the sum of the given stimuli and the reaction must be zero).
A nutrient is a nourishing substance, especially a nourishing ingredient in a food.
Nutrition is the process of nourishing, by which organisms obtain energy (in the form of food) for growth, maintenance, and repair.
Nystagmus is a rhythmical oscillation of the eyeball, either pendulum-like or jerky. A variety of causes for nystagmus are known. In space-related research, the caloric nystagmus (caused by hot or cold water in the ear), the optokinetic nystagmus (triggered by looking at a rotating dome), and the vestibular nystagmus (when a rotation of the body stops abruptly) are of special interest.
Nystagmus dumping is a phenomenon associated with postrotational nystagmus, which occurs after rotation about the vertical axis. The "dumping" effect results from tilting the head during postrotational nystagmus and is characterized by a decrease in the gain of the response and a shortening of the nystagmus decay time constant.