Medical Terminology
Glossary
nail matrix - the part of the nail beneath the body and root from which the nail is produced
narcosis - an unconscious state due to physical or chemical factors that depress neuronal excitability
nasal septum - vertical partition separating the nasal cavity into left and right sides; of bone (perpendicular plate of ethmoid and vomer) and cartilage, covered with a mucous membrane
nasolacrimal duct - a canal that transports the lacrimal secretion (tears) from the nasolacrimal sac into the nose
nasopharynx - the uppermost portion of the pharynx, lying posterior to the nose & extending down to the soft palate
nausea - discomfort characterized by loss of appetite and sensation of impending vomiting
nebulization - administration of medication to selected portions of the respiratory tract by droplets suspended in air
necrosis - death of a cell or group of cells as a result of disease or injury
neonatal - pertaining to the first 4 weeks after birth
neoplasm - a new growth that may be benign or malignant
nephritis - inflammation of the kidney
nephron - the functional LETTER of the kidney
nephrotic syndrome - a condition in which the endothelial-capsular membrane leaks, allowing large amounts of protein to escape into the urine
neuralgia - attacks of pain along the entire course or branch of a peripheral sensory nerve
neuritis - an inflammation of a single nerve, two or more nerves in separate areas, or many nerves simultaneously
neuroeffector junction - collective term for neuromuscular and neuroglandular junctions
neurofibral node - a space (along a myelinated nerve fiber) between the individual neurolemmocytes (Schwann cells) that form the myelin sheath; also called the node of Ranvier
neurofibril - one of the delicate threads that forms a complicated network in the cytoplasm of the cell body and processes of a neuron
neuroglandular junction - area of contact between a motor neuron and a gland
neuroglia - nervous system cells specialized to perform connective tissue functions; in the CNS, include astrocytes, oligodendrocytes, microglia, & ependyma; in the PNS, include neurolemmocytes (Schwann cells) & ganglion satellite cells; also called glial cells
neurohypophyseal bud - an outgrowth of ectoderm located on the floor of the embryonic hypothalamus; it gives rise to the neurohypophysis (posterior lobe) of the pituitary gland
neurohypophysis - the posterior lobe of the pituitary gland
neurolemma - the peripheral, nucleated cytoplasmic layer of the neurolemmocyte (Schwann cell); also called sheath of Schwann
neurology - the branch of science that deals with the normal functioning and disorders of the nervous system
neuromuscular junction - an area of contact between the axon terminal of a motor neuron and the underlying sarcolemma of a muscle fiber (cell); also called a myoneural junction
neuron - a nerve cell, consisting of a cell body, dendrites and axon(s)
neuropeptide - molecule of two to about 40 amino acids that occurs naturally in the brain and acts primarily to modulate responses associated with neurotransmitters; examples are enkephalins and endorphins
neurophysin - small protein that aids in transport, storage, and subsequent release of oxytocin (OT) and antidiuretic hormone (ADH)
neurosecretory cell - cell in the paraventricular or supraoptic nucleus of the hypothalamus that produces oxytocin (OT) or antidiuretic hormone (ADH) that will be released subsequently from axonal endings in the neurohypophysis
neurosyphilis - form of the tertiary stage of syphilis in which various types of nervous tissue are attacked by bacteria and degenerate
neutrophil - a type of white blood cell characterized by granular cytoplasm and staining equally readily with acid or basic dyes
nicotinic receptor - a receptor found on both parasympathetic and sympathetic postganglionic neurons; so named because actions of acetylcholine (ACh) in such receptors are similar to those produced by nicotine application
nociceptor - a free (naked) nerve ending that detects pain
Node of Ranvier - a space, along a myelinated nerve fiber, between the adjacent neurolemmocytes (Schwann cells) that form the myelin sheath and the neurolemma; also called neurofibral node
nondisjunction - failure of sister chromatids or homologous chromosomes to separate properly during anaphase of mitosis (or equatorial division of meiosis) or reductional division of meiosis; both pass to the same daughter cell
norepinephrine (NE) - hormone secreted in small amounts by the adrenal medulla; produces actions similar to those resulting from stimulation of the sympathetic nervous system, where it is the transmitter substance for the postganglionic neurons; also called noradrenaline
notochord - flexible rod of embyronic tissue that lies where the future vertebral column will develop
nuclease - enzyme that breaks nucleotides into pentoses and nitrogenous bases; examples are ribonuclease and deoxyribonuclease
nucleic acid - organic compound that is a long polymer of nucleotides, each containing a pentose sugar, a phosphate group and one of five possible nitrogenous bases (adenine, cytosine, guanine, thymine, or uracil)
nucleolus - a nonmembranous spherical body within the nucleus; composed of protein, DNA, and RNA; it functions in the synthesis and storage of ribosomal RNA
nucleosome - the elementary structural subLETTER of a chromosome; it consists of histones and DNA
nucleus - spherical or oval organelle of a cell that contains the hereditary factors called genes; a cluster of unmyelinated nerve cell bodies in the CNS; the central portion of an atom, made up of protons and neutrons
nucleus cuneatus - a group of nerve cells in the inferior portion of the medulla in which fibers of the fasciculus cuneatus terminate
nucleus gracilis - a group of nerve cells in the inferior portion of the medulla in which fibers of the fasciculus gracilis terminate
nucleus pulposus - a soft, pulpy, highly elastic substance in the center of an intervertebral disc, a remnant of the notochord
nystagmus - rapid, involuntary, rhythmic movement of the eye-balls; horizontal, rotary, or vertical
