Glossary 595
myocarditis (MIGH-oh-kahr-DIGH-tis) infl ammation of
the myocardium, the middle layer of the heart; the heart
muscle
myocardium (MIGH-oh-KAHR-dee-um) the middle layer
of the heart, which makes up about 2/3 of the heart
muscle
myometrium (migh-oh-MEE-tree-um) smooth muscle
that comprises the bulk of the uterine wall
myopia (migh-OH-pee-a) the condition that results from
an elongated eyeball shape; nearsightedness
myosin a widely distributed protein that is the major
component of thick fi laments in skeletal, cardiac, and
smooth muscle fi bers
myositis ossifi cans (migh-oh-SIGH-tis ah-SIF-i-kanz) a
condition in which a calcium mass forms within a muscle
over three to four weeks after a muscle injury
myxedema (MIKS-eh-DEE-ma) a condition in adults with
hyperthyroidism that causes weight gain; a swollen, puffy
face; low body temperature; dry skin; and decreased
mental acuity
N
nail bed a specialized region of the stratum basale under
each nail
nail matrix a thickened region of the nail that serves as
its growth zone
nares two openings in the nose through which air enters;
nostrils
nasal bones two bones forming the bridge of the nose
nasal cavity opening within the nose
nasal septum the bony and cartilaginous partition
dividing the nasal cavity into two passages
nasolacrimal duct (NAY-zoh-LAK-ri-mal) the channel into
which the lacrimal canaliculi drain
nasopharyngitis (NAY-zoh-FAIR-in-JIGH-tis)
infl ammation of the nasal passages and pharynx; the
common cold
nasopharynx (NAY-zoh-FAIR-ingks) the upper section of
the pharynx
natural killer (NK) cells lymphocytes that play an
important role in the nonspecifi c defense system of the
body by killing virus-infected cells and cancer cells
negative feedback mechanism that reverses a condition
that has exceeded the normal homeostatic range to
restore homeostasis
neonatal hypothyroidism hypothyroidism that occurs
in infants and children; may develop congenitally, or
following birth
nephron (NEH-frahn) the fundamental excretory unit of
each kidney
nephron loop the U-shaped part of the nephron that is
between the proximal convoluted tubule and the distal
convoluted tubule; has a descending limb and ascending
limb; loop of Henle
nerve impulse electrical charge that travels along a
nerve fi ber when stimulated
nerve tissue a type of tissue that conveys information by
electrical signaling
net force the single force resulting from the summation of
all forces acting on a structure at a given time
neural control type of endocrine control in which
nerve fi bers stimulate the endocrine organs to release
hormones
neurilemma (NOO-ri-LEHM-a) the thin, membranous
sheath enveloping a nerve fi ber
neuroglia (ner-ROHG-lee-a) non-neural tissue that forms
the interstitial or supporting elements of the CNS; glial
cells
neuromuscular junction the link between an axon
terminal and a muscle fi ber
neurons the cells that make up nerve tissue
neurotransmitters chemical messengers
neutrophils (NOO-troh-fi ls) the most common type
of white blood cell; can slip out of capillaries and into
surrounding tissues, where they destroy bacteria and
cellular debris
night blindness a condition that affects the rods in the
retina and makes it diffi cult to see well at night
nitrogenous waste waste substances in urine that
contain nitrogen; mainly urea
nocturnal emission the discharge of semen during sleep
nodes of Ranvier (rahn-vee-AY) the uninsulated gaps
in the myelin sheath of a nerve fi ber where the axon is
exposed
non-planar the term used to describe movements that do
not occur in the direction of one of the three imaginary
planes
noradrenalin a neurotransmitter involved in the body’s
fl ight or fi ght response; norepinephrine
norepinephrine (NOR-ehp-i-NEHF-rin) a
neurotransmitter released by postganglionic neurons in
the sympathetic nervous system; noradrenalin
normal contractility condition a normal sinus rhythm of
the heart
nuclear envelope a membrane that defi nes the boundary
of the cell’s nucleus
nuclear pore an opening in the nucleus through which
mRNA can leave
nucleic acids key information-carrying molecules in cells
nucleotides (NOO-klee-oh-tighdz) subunits that make up
nucleic acids
nucleus a rounded or oval mass of protoplasm within the
cytoplasm of a cell that contains the cell’s DNA and is
bounded by a membrane
nutrients chemicals that the body needs for energy,
growth, and maintenance
O
occipital bone (AHK-sip-i-tal) forms the base and lower
back portions of the skull
occipital lobes (AHK-sip-i-tal) sections of the brain
located behind the parietal lobes; responsible for vision
odor molecules tiny airborne particles from food that
trigger the sense of smell
olfactory bulb (ohl-FAK-toh-ree) the thickened end of
the olfactory nerve that sends sensory impulses to the
olfactory region of the brain
olfactory fi laments (ohl-FAK-toh-ree) fi bers in the
olfactory nerve that receive impulses from olfactory
receptor cells
olfactory hairs (ohl-FAK-toh-ree) threads that extend
from the olfactory receptor cells into the nasal cavity
olfactory nerve (ohl-FAK-toh-ree) sensory pathway from
the nasal cavity to the olfactory cortex of the brain
olfactory receptor cells (ohl-FAK-toh-ree) the sensors
responsible for smell
olfactory receptors (ohl-FAK-toh-ree) sensory cells in
the olfactory region that provide the sense of smell
olfactory region (ohl-FAK-toh-ree) a dime-sized area
along the mucous membrane on the roof of the nasal
cavity where olfactory epithelium and glands are found