Note: Some words can have differing definitions depending on the context in which they are used. The definitions presented here are the ones that best apply to the words as they are used on the HOPES site.
NAD - Nicotinamide adenosine dinucleotide; an electron carrier involved in cellularmetabolism. It accepts and donates electrons to various enzymes involved in metabolism, ultimately providing the cell with energy.
N-terminus - The end of the amino acid chain that makes up a protein that is terminated by an amino group (-NH2).
necropsy - An examination of a body after death, more commonly called an autopsy when performed on humans instead of animals.
negative feedback - A mechanism in the body for maintaining a state of internal constancy, or homeostasis; effectors are activated by changes in the internal environment, and the actions of the effectors serve to counteract these changes and maintain a state of balance.
negative regulator - One molecule that controls the effects of another (or itself) by repressing or inactivating it.
neocortex - Part of the cerebral cortex; constitutes about 85% of the human brain’s total mass. The neocortex is thought to be responsible for higher level cognitive functions, such as language, learning, memory, and complex thought. Also referred to as the isocortex.
nerve cell - One of the major classes of cells in the nervous system. They are the fundamental signaling units of the nervous system. They are unique from other cells in that they have the ability to communicate rapidly with one another over great distances and with great precision. Also referred to as a neuron.
nerve cell body - The largest part of a cell, the cell body holds all of the general parts of a cell as well as the nucleus, which is the control center. The nucleus contains the cell's genetic material (DNA, located in the chromosomes). The cell body also contains many other unique structures responsible for making energy and getting rid of cellular wastes. Also referred to as the soma.
nerve growth factor - The first member of the NGF superfamily discovered, NGF has been shown to promote nerve growth and development. NGF has been shown to have an important role in Alzheimer’s disease.
nervous system - A regulatory system of the body that consists of neurons and neuroglial cells. The nervous system is divided into two parts, the central nervous system (CNS) and the peripheral nervous system (PNS).
neurodegeneration - The deterioration or loss of function of nerve cells. Neurodegenerative diseases include HD, Alzheimer’s, Parkinson’s and many more. Adj.neurodegenerative.
neurogenesis - Formation of the nervous system; the process through which neurons are produced.
neuroglia - The supporting tissue of the nervous system; made up of neuroglial cells. Astrocytes (spider cells) are a type of neuroglial cell. Also referred to as glia.
neuronal ceroid lipofuscinoses (NCLs) - A group of rare, inherited degenerative disorders of the nervous system; associated with the accumulation of an abnormal pigment in the brain called lipofuscin. These disorders can have severe diseases including blindness, mental retardation, and early death.
neuronal inclusions (NI) - Clumps of protein formed by aggregation of mutant proteins. These mutant proteins have abnormally expanded polyglutamine tracts in hereditary tri-nucleotide repeat disorders. Also referred to as neuronal intranuclear inclusions, nuclear inclusions, or inclusion bodies.
neuropathy - A group of symptoms caused by abnormalities in motor or sensory nerve cells. Symptoms include tingling or numbness in hands or feet followed by gradual, progressive muscular weakness. oxidative damage - Another term for oxidative stress.
neuroplasticity - The brain's natural ability to form new connections in order to compensate for injury or changes in the environment. The ability of the brain to reorganize pathways between neurons as a result of new experiences.
neuroprotectant drugs - Drugs that prevent harmful calcium ions from destroying the m\itochondria of the nerve cells, which leads to cell death. An example of a neuroprotectant drug is Cyclosporin A.
neuropsychiatrist - A physician who treats people with psychiatric symptoms that are caused by a brain disorder. For more information, click here.
neuropsychological tests - Tasks specifically designed to measure psychological function linked to a particular brain structure or pathway.
neuropsychology - A scientific area of study that combines psychology and neuroscience to relate behavior and psychological processes to anatomical aspects of the brain.
neurotoxic - Describes a substance that damages or destroys nerve tissue.
neurotransmitter - A chemical messenger produced in and released by one neuron. A neurotransmitter can excite or inhibit another neuron.
neurotrophic factor hypothesis - A hypothesis suggesting that any single neuron extending into a target organ must compete with its neighboring neurons for specific proteins, known as neurotrophic factors. The Neurotrophic factor hypothesis has been extended into non-neuronal biology—it is now believed that almost all cells depend on their interactions with neighboring cells for their survival.
neurotrophin-3 (NT-3) - Another member of the NGF superfamily, NT-4 acts upon both sensory neurons and neurons from the sympathetic nervous system. NT-4 has also been shown to promote the survival and development of certain neurons in the striatum.
neurotrophin-4 (NT-4) - Another member of the NGF superfamily, NT-4 acts upon both sensory neurons and neurons from the sympathetic nervous system. NT-4 has also been shown to promote the survival and development of certain neurons in the striatum.
neurturin - A member of the GNDF family, neurturin has been shown to regulate and protect neurons of the striatum and the sympathetic nervous system. In animal models, gene therapy using neuturin has been shown to improve motor function by protecting neurons in the striatum from death.
new indication studies - New phase II and III trials required when a drug seems promising as a new treatment for a different condition than it was originally approved for.
NF-kappa B (NF-KB) - A transcription factor that enhances the production of inflammatory mediators. Association with the GR complex inhibits the transcription of COX-2 genes.Abbr. NF-kB
nitric acid - A chemical that increases blood flow; also used to make organic compounds in the body.
nitric oxide (NO) - A gas where each molecule is made of one nitrogen atom and one oxygen atom; it is found in many brain and body tissues, and plays a part in many bodily functions.
nitric oxide synthase - a family of enzymes responsible for the synthesis of nitric oxide (NO). NO can become mutated in some neurodegenerative disorders like Alzheimer’s, causing oxidative stress and neurodegeneration.
nitrogenous base - One of the molecular components of a nucleotide; a class of ringed molecules with carbon, oxygen, hydrogen, and nitrogen.
NMDA receptor - One type of receptor that binds glutamate. It is selectively activated by the drug NMDA (N-methyl-D-aspartate).
non-coding region - A segment of DNA that does not comprise a gene and thus does not code for a protein. Non-coding regions are interspersed throughout DNA.
non-hd allele - A version of the Huntington gene that contains a normal number of CAG repeats and codes for the normally functioning form of the huntingtin protein. Individuals with the non-HD allele will not develop Huntington’s Disease, and they will not pass the disease on to their children. This allele is sometimes called the "normal Huntington allele." See Table A-1.
nonpolar - a nonpolar molecule does not have a separation of positive and negative electric charges within the molecule. Nonpolar molecules are pushed towards one another by polar molecules. For example, nonpolar compounds, like oil, can’t dissolve in water because of the water's polarity.
non-refined - refers to breads and cereals in which the whole grain (including its bran and germ) are included in the food product. Non-refined breads and cereals (such as whole wheat bread and oatmeal) are healthier than refined products because of the fiber they contain.
non-specific - Describes a type of response that is not specific to any particular body organ or location. Rather, the response occurs throughout the body.
nonsteroidal anti-inflammatory drugs (NSAIDs) - Compounds that significantly reduce the inflammatory response by interfering with the cyclooxygenase pathway, reducing the level of compounds that mediate inflammation.
nucleosome - A structure composed of histones that aids in the coiling up of DNA into compact chromosomes. It can be thought of as a spool that winds up the DNA "thread."
nucleotide - The molecular subunit that makes up DNA; consists of a sugar, phosphate group, and nitrogenous base; see Figure B-2. A molecule of DNA is made up of a long chain of nucleotides.
nucleus - 1. A spherical body within the cell that is enclosed by a double membrane. The nucleus contains the chromosomes and is the information center of the cell. 2. A collection of nerve cells in the brain that are anatomically discrete and which typically serve a particular function. (Plural form: nuclei.)
nullizygous - Missing both alleles of a particular gene.
nurse practitioner - A registered nurse who has also completed advanced training (usually a master's degree) and provides a broad range of services in management of common, as well as complex, medical conditions.
Last Modified: 07/31/2009
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