G-16
Glossary
Nucleotide
(nu
9
kle-o-tīd) Building block of nucleic acids; consists of a
sugar, a nitrogen-containing base, and a phosphate group.
Nucleus
(nu
9
kle-is) (1) Control center of a cell; contains genetic mate-
rial; (2) clusters of nerve cell bodies in the CNS.
Nutrients
Chemical substances taken in via the diet that are used for
energy and cell building.
Oblique section
A cut made diagonally between the horizontal and ver-
tical plane of the body or an organ.
Occlusion
(ah-kloo
9
zhun) Closure or obstruction.
Octet rule (rule of eights)
(ok-tet
9
) Te tendency of atoms to interact in
such a way that they have eight electrons in their valence shell.
Olfaction
(ol-fak
9
shun) Smell.
Oligodendrocyte
(ol
0
ĭ-go-den
9
dro-sīt) A type of CNS supporting cell
that composes myelin sheaths.
Oocyte
(o
9
o-sīt) Immature female gamete.
Oogenesis
(o
0
o-jen
9
ĕ-sis) Process of ovum (female gamete) formation.
Ophthalmic
(of-thal
9
mik) Pertaining to the eye.
Optic
(op
9
tik) Pertaining to the eye or vision.
Optic chiasma
(op
9
tik ki-az
9
muh) Te partial crossover of fibers of the
optic nerves.
Organ
A part of the body formed of two or more tissues and adapted to
carry out a specific function; e.g., the stomach.
Organ system
A group of organs that work together to perform a vital
body function; e.g., the nervous system.
Organelles
(or
0
gah-nelz
9
) Small cellular structures (ribosomes, mito-
chondria, and others) that perform specific metabolic functions for the
cell as a whole.
Organic compound
Any compound composed of atoms (some of which
are carbon) held together by covalent (shared electron) bonds.
Organic
Pertaining to carbon-containing molecules, such as proteins,
fats, and carbohydrates.
Organism
Te living animal (or plant), which represents the sum total of
all its organ systems working together to maintain life.
Origin
Attachment of a muscle that remains relatively fixed during mus-
cular contraction.
Osmolality
Te number of solute particles dissolved in 1 kilogram
(1000 g) of water; reflects the solution’s ability to cause osmosis.
Osmolarity
(oz
0
mo-lar
9
ĭ-te) Te number of solute particles present in
1 liter of a solution.
Osmoreceptor
(oz
0
mo-re-sep
9
tor) Structure sensitive to osmotic pres-
sure or concentration of a solution.
Osmosis
(oz-mo
9
sis) Diffusion of a solvent through a membrane from a
dilute solution into a more concentrated one.
Osmotic pressure
A measure of the tendency of water to move into a
more concentrated solution.
Ossicles
See
Auditory ossicles.
Ossification
(os
0
ĭ-fi-ka
9
shun)
See
Osteogenesis.
Osteoblasts
(os
9
te-o-blasts) Bone-forming cells.
Osteoclasts
(os
9
te-o-klasts) Large cells that resorb or break down bone
matrix.
Osteocyte
(os
9
te-o-sīt) Mature bone cell.
Osteogenesis
(os
0
te-o-jen
9
e-sis) Te process of bone formation; also
called ossification.
Neural tube
Fetal structure that gives rise to the brain, spinal cord, and
associated neural structures; formed from ectoderm by day 23 of embry-
onic development.
Neuroglia
(nu-rog
9
le-ah) Nonexcitable cells of neural tissue that sup-
port, protect, and insulate the neurons; glial cells.
Neurohypophysis
(nu
0
ro-hi-pof
9
ĭ-sis) Posterior pituitary plus infun-
dibulum; portion of the pituitary gland derived from the brain.
Neuromuscular junction
Region where a motor neuron comes into
close contact with a skeletal muscle cell.
Neuron (nerve cell)
(nu
9
ron) Cell of the nervous system specialized to
generate and transmit electrical signals (action potentials and graded
potentials).
Neuron cell body
Te biosynthetic center of a neuron; also called the
perikaryon, or soma.
Neuronal pools
Functional groups of neurons that process and integrate
information.
Neuropeptides
(nu
0
ro-pep
9
tīds) A class of neurotransmitters including
beta endorphins and enkephalins (which act as euphorics and reduce
perception of pain) and gut-brain peptides.
Neurotransmitter
Chemical messenger released by neurons that may,
upon binding to receptors of neurons or effector cells, stimulate or in-
hibit those neurons or effector cells.
Neutral fats
Consist of fatty acid chains and glycerol; also called triglyc-
erides or triacylglycerols. Commonly known as oils when liquid.
Neutralization reaction
Displacement reaction in which mixing an acid
and a base forms water and a salt.
Neutron
(nu
9
tron) Uncharged subatomic particle; found in the atomic
nucleus.
Neutrophil
(nu
9
tro-fil) Most abundant type of white blood cell.
Nicotinic receptors
(nik
0
o-tin
9
ik) Acetylcholine-binding receptors of all
autonomic ganglionic neurons and skeletal muscle neuromuscular junc-
tions; named for activation by nicotine.
Nitric oxide (NO)
A gaseous chemical messenger; diverse functions
include participation in memory formation in the brain, and causing va-
sodilation throughout the body.
Nociceptor
(no
0
se-sep
9
tor) Receptor sensitive to potentially damaging
stimuli that result in pain.
Nondisjunction
Failure of sister chromatids to separate during mitosis
or failure of homologous pairs to separate during meiosis; results in ab-
normal numbers of chromosomes in the resulting daughter cells.
Nonmyelinated fibers
(non-mi
9
ĕ-lĭ-nāt
0
ed) Axons lacking a myelin
sheath and therefore conducting impulses quite slowly.
Nonpolar molecules
Electrically balanced molecules.
Nonvolatile (fixed) acid
Acid generated by cellular metabolism that
must be eliminated by the kidneys.
Norepinephrine (NE)
(nor
0
ep-ĭ-nef
9
rin) A catecholamine neurotrans-
mitter and adrenal medullary hormone, associated with sympathetic
nervous system activation.
Nuclear envelope
Te double membrane barrier of a cell nucleus.
Nucleic acid
(nu-kle
9
ik) Class of organic molecules that includes DNA
and RNA.
Nucleoli
(nu-kle
9
o-li) Dense spherical bodies in the cell nucleus involved
with ribosomal RNA (rRNA) synthesis and ribosomal subunit assembly.
Nucleosome
(nu
9
kle-o-sōm) Fundamental unit of chromatin; consists of
a strand of DNA wound around a cluster of eight histone proteins.
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