N - Glossary of Terms

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N - Glossary of Terms

nail	A hardened, keratinized plate that develops from the epidermis and forms a protective covering on the surface of the distal phalanges of fingers and toes.
nares	(na'rez) Openings of nasal passages; anterior nares are commonly called nostrils.
nasal cavity	(na´zal) A mucosa-lined space above the oral cavity, divided by a nasal septum. It is the first chamber of the respiratory system.
nasal concha	(na'zal kon´cha) A scroll-like bone extending medially from the lateral wall of the nasal cavity; also called a turbinate bone.
nasal septum	(sep´tum) A bony and cartilaginous partition that separates the nasal cavity into two portions.
nasion	(na'zi-on) Midpoint of frontonasal suture.
naso-	(na'zo-) Prefix denoting relation to nose; as nasofrontal, nasopharyngeal.
nasopharynx	(na´´zo-far´ingks) The first or uppermost chamber of the pharynx, positioned posterior to the nasal cavity and extending down to the soft palate.
nates	(na-tez) Buttocks.
natural	A zero dose of radiation exposure.
natural environmental radiation	Naturally occurring ionising radiation, including cosmic rays, terrestrial radiation, and internally deposited radionuclides.
natural magnet	A magnet that gets its magnetism from the Earth.
nausea	(naw'she-ah) Feeling of sickness at stomach, associated with desire to vomit.
navel	(na'vel) Cicatrix, or scar, in center of abdomen, marking point of attachment of umbilical cord; umbilicus.
neck	Two meanings:1.Any constricted portion, such as the neck of an organ. 2.The cervical region of the body between the head and thorax.
necrosis	(ne-kro´sis) Cellular death or tissue death due to disease or trauma.
necrotic	(ne-krot'ik) Affected with or pertaining to necrosis, or death of tissue.
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.
neo-	(ne'o) Prefix meaning new or recent; as neonates. a newborn infant.
neonatal	(ne´o-na´tal) Newborn, the stage of life from birth to the end of 4 weeks.
neoplasm	(ne´o-plasm) A new, abnormal growth of tissue, as in a tumor.
nephro-	(nef'ro-) Prefix denoting relation to kidney; as nephrolith, nephritis, nephrectomy.
nephrocalcinosis	Calcium deposits within the substance of the kidney.
nephrolithiasis	(nef'ro-li-thi'a-sis) Condition caused by accumulation of calculi in kidney.
nephron	(nef´ron) The functional unit of the kidney, consisting of a glomerulus, convoluted tubules, and a nephron loop.
nephroptosis	(nef'rop-to'sis) Abnormal dropping or downward movement of kidney.
nerve	A bundle of nerve fibers outside the central nervous system.
nervous tissue	Tisue that consists of neurons and is the avenue through which electrical impulses are transmitted throughout the body for control and response.
neural	(nu'ral) Pertaining to a nerve of nervous system.
neurilemma	(noor´´i-lem´a) A thin, membranous covering surrounding the myelin sheath of a nerve fiber.
neuro-	(nu-ro-) Prefix denoting relation to nerves, as in neurofibroma, neuralgia, neuritis.
neurofibril node	A gap in the myelin sheath of a nerve fiber; also called a node of Ranvier.
neurogenic	Originating in the nervous system.
neuroglia	(noo-rog´le-a) Specialized supportive cells of the central nervous system.
neurohypophysis	(noor´´o-hi-pof´i-sis) The posterior lobe of the pituitary gland derived from the brain. Its major secretions include antidiuretic hormone (ADH), also called vasopressin, and oxytocin, produced in the hypothalamus.
neurolemmocyte	(noor´´o-lem´o-s-it) A specialized neuroglia cell that surrounds an axon fiber of a peripheral nerve and forms the neurilemmal sheath; also called a Schwann cell.
neuron	(noor´on) The structural and functional unit of the nervous system, composed of a cell body, dendrites, and an axon; also called a nerve cell.
neutron	Uncharged elementary particle, with a mass slightly greater than that of the proton, found in the nucleus of every atom heavier than hydrogen and in the nucleus of an atom.
newton (N)	The unit of force in the SI system.
nexus	(nek´sus) A bond between members of a group; the type of bonds present in single-unit smooth muscles.
niche	(nich) Small recess or hollow space in a wall; abnormal saccular prominence on wall of stomach resulting from an ulcer crater.
nidus	Focal point, especially of a stone or inflammatory process.
nipple	(A dark pigmented, rounded projection at the tip of the breast.
node	One of many stations or terminals of a computer network.
node of Ranvier	(ran´ve-a) See neurofibril node.
nodular	(nod'u-lar) Pertaining to or having form of a node or nodule.
nodule	(nod-ul) Small, rounded prominence. In medical imaging: - Any pulmonary or pleural lesion represented in a radiograph by a discrete opacity 2-30 mm diameter, explicitly shown or presumed to be extended in all three dimensions. Should be qualified with regard to opacity (especially presence of calcification), homogeneity, border characteristics, location, and number.
noise	The grainy or uneven appearance of an image caused by an insufficient number of primary x-rays. A uniform signal produced by scattered x-rays.
nxxonfocused grid	A grid in which the lead strips are all perpendicular to the face of the grid; also called a parallel grid. See focused grid.
nonionising radiation	Radiation for which the mechanism of action in tissue does not directly ionise atomic or molecular systems through a single interaction.
nonlinear - nonthresh old	Referring to varied responses that are produced from varied doses, with any dose expected to produce a response.
nonlinear - threshold	Referring to varied responses that are produced from varied doses, with a particular level below which there is no response.
nonscheduled maintenance	Maintenance that becomes necessary because of a failure in the system that necessitates repair.
nonstochastic effects	Biologic effects of ionising radiation that demonstrate the existence of a threshold. The severity of the biologic damage increases with increased dose.
norm	(norm) Fixed or authoritive standard; a rule; a pattern or model; a type.
normal	(normal) Conforming to an established norm or principle; regular; natural; functioning properly.
normal salt solution.	A normal or, more correctly, a physiologic salt solution that is approximately isotonic with body fluids. It is a 0.9% solution of sodium chloride
north pole	A magnetic pole that has a positive electrostatic charge.
notochord	(no´to-kord) A flexible rod of tissue that extends the length of the back of an embryo.
nuclear energy	The energy contained in the nucleus of an atom.
nucleolus	A rounded structure that is often attached to the nuclear membrane and controls the passage of molecules, especially RNA, from the nucleus to the cytoplasm.
nucleon	A proton or a neutron.
nucleotide	The unit formed from a nitrogenous base, a five-carbon sugar molecule, and a phosphate molecule.
nucleus	(nu´kle-us) The centre of a living cell; a spherical mass of protoplasm containing the genetic material (DNA), which is stored in its molecular structure. The centre of an atom containing neutrons and protons.
nucleus pulposus	(pul-po´sus) Fibrocartilaginous soft core of an intervertebral disc (see annulus fibrosus)
nuclide	General term referring to all know isotopes, both stable and unstable, of chemical elements.
nullipara	(nu-lip'ar-ah) Woman who has never borne a child.
nystagmus	(ni-stag´mus) Involuntary oscillary movements of the eye.