N

nail (nail) Horny plate at the distal end of a finger or toe. p. 178 nasal cavity (na'zal kav'i-te) Space within the nose. p. 780 nasal concha (na'zal kong'kah) Shell-like bone extending outward from the wall of the nasal cavity; a turbinate bone. p. 780 nasal septum (na'zal sep'tum) A wall of bone and cartilage that separates the nasal cavity into two portions. p. 780 nasopharynx (na"zo-far"ingks) Portion of the pharynx associated with the nasal cavity. p. 695

natural killer cell (nat'u-ral kil'er sel) Lymphocyte that causes an infected or cancerous cell to burst. p. 663 negative feedback (neg'ah-tiv fed'bak) A mechanism activated by an imbalance that corrects it. p. 8 neonatal (ne"o-na'tal) The first four weeks of life. p. 962

nephron (nef'ron) The functional unit of a kidney, consisting of a renal corpuscle and a renal tubule. p. 825 nerve (nerv) A bundle of nerve fibers in the

PNS. p. 363 nerve fiber (nerv fi'ber) A thin process of a neuron (i.e., axon, dendrite). p. 400 nerve impulse (nerv im'puls) The electrochemical process of depolarization and repolarization along a nerve fiber. p. 363 nerve tract (nerv trakt) A long bundle of nerve fibers within the CNS having the same origin, function, and termination. p. 402

nervous tissue (ner'vus tish'u) Cells composing the brain, spinal cord and nerves. p. 161 neurilemma (nur"I-lem'ah) Sheath on the outside of some nerve fibers formed from Schwann cells. p. 365 neurofibril (nu"ro-fi'bril) Fine cytoplasmic thread that extends from the cell body into the processes of neurons. p. 364 neuroglial cell (nu-ro'gle-ahl sel)

Specialized cell of the nervous system that produces myelin, communicates between cells, and maintains the ionic environment, as well as provides other functions. p. 161 neuromodulator (nu"ro-mod'u-la-tor) A

substance that alters a neuron's response to a neurotransmitter. p. 381 neuromuscular junction (nu"ro-mus'ku-lar jungk'shun) Point of contact between a nerve and muscle cell. p. 302 neuron (nu'ron) A nerve cell that consists of a cell body and its processes. p. 161 neuropeptide (nu"ro-pep'tId) A peptide in the brain that functions as a neurotransmitter or neuromodulator. p. 381 neurosecretory cell (nu"ro-se-kre'to-re sel) Cell in the hypothalamus that functions as a neuron at one end but like an endocrine cell at the other, by receiving messages and secreting the hormones ADH and oxytocin. p. 513

Shier-Butler-Lewis: I Back Matter I Glossary I I © The McGraw-Hill

Human Anatomy and Companies, 2001

Physiology, Ninth Edition neurotransmitter (nu"ro-trans-mit'er)

Chemical secreted by the end of an axon that stimulates a muscle fiber to contract or a neuron to fire an impulse. p. 302 neutral (nu'tral) Neither acid nor alkaline;

pH 7. p. 48 neutron (nu'tron) An electrically neutral particle in an atomic nucleus. p. 39 neutrophil (nu'tro-fil) A type of phagocytic leukocyte. p. 554 niacin (ni'ah-sin) A vitamin of the

B-complex group; nicotinic acid. p. 754 niacinamide (ni"ah-sin'ah-mld) The physiologically active form of niacin. p. 754

nicotinic acid (nik"o-tin'ik as'id) Niacin. p. 754

nitrogen balance (ni'tro-jen bal'ans) Condition in which the quantity of nitrogen ingested equals the quantity excreted. p. 744 node of Ranvier (nod of Ron'vee-ay) A short region of exposed (unmyelinated) axon between Schwann cells on neurons of the peripheral nervous system. p. 365 nodule (nod'ul) A small mass of tissue detected by touch. p. 656 nondisjunction (non"dis-jungk'shun) Failure of a pair of chromosomes to separate during meiosis. p. 991 nonheritable gene therapy (non-her'i-tah-bl jen ther'ah-pe) Manipulation of genes in somatic cells to correct the effects of a mutation. p. 994 nonprotein nitrogenous substance (non-pro'ten ni-troj'e-nus sub'stans) A substance, such as urea or uric acid, that contains nitrogen but is not a protein. p. 562

norepinephrine (nor"ep-i-nef'rin) A

neurotransmitter released from the axons of some nerve fibers. p. 525 normal range (nor'mal ranj) Measurements or values obtained from a statistical sample of the healthy population for reference or comparison. p. 8 nuclear envelope (nu'kle-ar en've-lop)

Membrane surrounding the cell nucleus and separating it from the cytoplasm. p. 81

nuclear pore (nu'kle-ar por) Opening in the nuclear envelope. p. 81 nuclease (nu'kle-as) An enzyme that catalyzes decomposition of nucleic acids. p. 707

nucleic acid (nu-kle'ik as'id) A substance composed of bonded nucleotides; RNA or DNA. p. 56 nucleolus (nu-kle'o-lus) A small structure within the nucleus of a cell that contains RNA and proteins (pl., nucleoli). p. 81 nucleoplasm (nu'kle-o-plazm") The contents of the nucleus of a cell. p. 81 nucleotide (nu'kle-o-tld") A building block of a nucleic acid molecule, consisting of a sugar, a nitrogenous base, and a phosphate group. p. 56

nucleus (nu'kle-us) A cellular organelle that is enclosed by a double-layered, porous membrane and contains DNA; the dense core of an atom that is composed of protons and neutrons (pl., nuclei). p. 39 nutrient (nu'tre-ent) A chemical substance that must be supplied to the body from the environment. p. 738 nutrition (nu-trish'un) The study of the sources, actions, and interactions of nutrients. p. 738

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