Glossary 573share a common function within the central nervous sys-
tem; a tract may be ascending (sensory) or descending
(motor) (Chapter 8).
Nervous system(NERV-us SIS-tem) The organ system
that regulates body functions by means of electrochemi-
cal impulses; consists of the brain, spinal cord, cranial
nerves, and spinal nerves (Chapter 8).
Neuralgia(new-RAL-jee-ah) Sharp, severe pain along the
course of a nerve (Chapter 8).
Neuritis(new-RYE-tis) Inflammation of a nerve (Chapter
8).
Neuroglia(new-ROG-lee-ah) The non-neuronal cells of
the central nervous system; produce the myelin sheath
and contribute to the blood–brain barrier, among other
functions (Chapter 4).
Neurohypophysis(NEW-roo-high-POFF-e-sis) The pos-
terior pituitary gland (Chapter 10).
Neurolemma(NEW-roh-LEM-ah) The sheath around
peripheral axons and dendrites, formed by the cytoplasm
and nuclei of Schwann cells; is essential for the regener-
ation of damaged peripheral neurons (Chapter 8).
Neuromuscular junction (NYOOR-oh-MUSS-kew-lar
JUNK-shun) The termination of a motor neuron on the
sarcolemma of a muscle fiber; the synapse is the micro-
scopic space between the two structures (Chapter 7).
Neuron(NYOOR-on) A nerve cell; consists of a cell body,
an axon, and dendrites (Chapter 4).
Neuropathy(new-RAH-puh-thee) Any disease or disorder
of the nerves; may be primary, such as shingles or rabies,
or secondary, such as diabetic neuropathy (Chapter 8).
Neurotoxin(NEW-roh-TOK-sin) A chemical that dis-
rupts an aspect of the functioning of the nervous system
(Chapter 7).
Neurotransmitter (NYOOR-oh-TRANS-mih-ter) A
chemical released by the axon of a neuron, which crosses
a synapse and affects the electrical activity of the postsy-
naptic membrane (neuron or muscle cell or gland)
(Chapter 4).
Neutron(NEW-trahn) A subatomic particle that has no
electrical charge; found in the nucleus of an atom
(Chapter 2).
Neutrophil(NEW-troh-fill) A type of granular white blood
cell; capable of phagocytosis of pathogens (Chapter 11).
Nevus(NEE-vus) A pigmented area of the skin; a mole
(Chapter 5).
Night blindness(NITE BLIND-ness) The inability to see
well in dim light or at night; may result from a vitamin A
deficiency (Chapter 9).
Nine areas(NYNE) The subdivision of the abdomen into
nine equal areas to facilitate the description of locations
(Chapter 1).
Non-communicable disease(NON-kuhm-YOO-ni-kah-
b’l) A disease that cannot be directly or indirectly trans-
mitted from host to host (Chapter 22).Non-essential amino acids(NON-e-SEN-shul ah-MEE-
noh ASS-ids) The amino acids that can be synthesized by
the liver (Chapter 16).
Norepinephrine (NOR-ep-i-NEFF-rin) A hormone
secreted by the adrenal medulla that causes vasoconstric-
tion throughout the body, which raises blood pressure in
stressful situations (Chapter 10).
Normal flora(NOR-muhl FLOOR-uh) 1. The population
of microorganisms that is usually present in certain parts
of the body. 2. In the colon, the bacteria that produce
vitamins and inhibit the growth of pathogens (Chapter
16).
Normoblast(NOR-mow-blast) A red blood cell with a
nucleus, an immature stage in red blood cell formation;
usually found in the red bone marrow and not in the
peripheral circulation (Chapter 11).
Nosocomial infection(no-zoh-KOH-mee-uhl) An infec-
tion acquired in a hospital or other healthcare institution
(Chapter 22).
Nuclear membrane (NEW-klee-er MEM-brayn) The
double-layer membrane that encloses the nucleus of a
cell (Chapter 3).
Nucleic acid(new-KLEE-ik ASS-id) An organic chemical
that is made of nucleotide subunits. Examples are DNA
and RNA (Chapter 2).
Nucleolus(new-KLEE-oh-lus) A small structure made of
DNA, RNA, and protein. Found in the nucleus of a cell;
produces ribosomal RNA (Chapter 3).
Nucleotide(NEW-klee-oh-tide) An organic compound
that consists of a pentose sugar, a phosphate group, and
one of five nitrogenous bases (adenine, guanine, cytosine,
thymine, or uracil); the subunits of DNA and RNA
(Chapter 2).
Nucleus(NEW-klee-us) 1. The membrane bound part of a
cell that contains the hereditary material in chromo-
somes. 2. The central part of an atom containing protons
and neutrons (Chapters 2, 3).—O—
Occipital bone(ok-SIP-i-tuhl) The flat bone that forms
the back of the skull (Chapter 6).
Occipital lobes(ok-SIP-i-tuhl LOWBS) The most poste-
rior part of the cerebrum; contain the visual areas
(Chapter 8).
Oculomotor nerves (OK-yoo-loh-MOH-tur) Cranial
nerve pair III; motor to the extrinsic muscles of the eye,
the ciliary body, and the iris (Chapter 8).
Olfactory nerves(ohl-FAK-tuh-ree) Cranial nerve pair I;
sensory for smell (Chapter 8).
Olfactory receptors(ohl-FAK-tuh-ree ree-SEP-ters) The
sensory receptors in the upper nasal cavities that detect
vaporized chemicals, providing a sense of smell (Chap-
ter 9).30Scanlon(p3) Glossary 8/17/06 11:08 AM Page 573