734
Glossary
muscle tone
degree of resistance of muscle to
passive stretch due to ongoing contractile
activity;
see also
smooth muscle tone
muscularis externa
two layers of muscle in the
gastrointestinal tract consisting of circular and
longitudinal muscle
mutagen
(MUTE-uh-jen) factor in the
environment that increases mutation rate
mutation
(mu-TAY-shun) any change in base
sequence of DNA that changes genetic
information
myelin
(MY-uh-lin) insulating material covering
axons of many neurons; consists of layers of
myelin-forming cell plasma membrane wrapped
around axon
myenteric plexus
(my-en-TER-ik PLEX-us)
nerve cell network between circular and
longitudinal muscle layers in esophagus,
stomach, and intestinal walls
myo-
(MY-oh) pertaining to muscle
myoblast
(MY-oh-blast) embryological cell that
gives rise to muscle fi bers
myocardium
(my-oh-KARD-ee-um) cardiac
muscle, which forms heart walls
myoepithelial cell
(my-oh-ep-ih-THEE-lee-al)
specialized contractile cell in certain exocrine
glands; contraction forces gland’s secretion
through ducts
myofi
bril
(my-oh-FY-bril) bundle of thick and
thin contractile fi laments in cytoplasm of
striated muscle; myofi brils exhibit a repeating
sarcomere pattern along longitudinal axis of
muscle
myogenic response
(my-oh-JEN-ik) response
originating in muscle
myoglobin
(my-oh-GLOH-bin) muscle fi ber
protein that binds oxygen
myometrium
(my-oh-MEE-tree-um) uterine
smooth muscle
myosin
(MY-oh-sin) contractile protein that forms
thick fi laments in muscle fi bers
myosin ATPase
enzymatic site on globular head
of myosin that catalyzes ATP breakdown to
ADP and P
i
, releasing the chemical energy used
to produce force of muscle contraction
myosin light-chain kinase
smooth-muscle protein
kinase; when activated by Ca-calmodulin,
phosphorylates myosin light chain
myosin light-chain phosphatase
enzyme that
removes high-energy phosphate from myosin;
important in the relaxation of smooth muscle
cells
N
Na
+
/K
+
-ATPase pump
primary active transport
protein that splits ATP and releases energy
used to transport sodium out of cell and
potassium in
NAD
+
see
nicotinamide adenine dinucleotide
natural killer (NK) cell
type of lymphocyte that
binds to virus-infected and cancer cells without
specifi c recognition and kills them directly;
participates in antibody-dependent cellular
cytotoxicity
necrosis
death of a cell or population of cells
within a tissue or organ, usually due to oxygen
and nutrient deprivation
negative balance
loss of substance from body
exceeds gain, and total amount in body
decreases, also used for physical parameters
such as body temperature and energy;
compare
positive balance
negative feedback
characteristic of control systems
in which system’s response opposes the original
change in the system;
compare
positive feedback
nephron
(NEF-ron) functional unit of kidney; has
vascular and tubular components
Nernst equation
calculation for electrochemical
equilibrium across a membrane for any single
ion
nerve
group of many nerve fi bers traveling
together in peripheral nervous system
nerve cell
cell in nervous system specialized to
initiate, integrate, and conduct electrical signals;
also called
neuron
nerve fi
ber
axon of a neuron
nerve tissue
one of the four major tissue types in
the body, responsible for coordinated control of
muscle activity, refl exes, and conscious thought
net
amount remaining after deductions have been
made; fi nal amount
net fi
ltration pressure
algebraic sum of inward-
and outward-directed forces that determine the
direction and magnitude of fl uid fl ow across a
capillary wall
net fl
ux
difference between two one-way fl uxes
net glomerular fi
ltration pressure
sum of
the relevant forces resulting in glomerular
fi ltration; it is the hydrostatic pressure within the
glomerular capillary (
P
GC
) minus the hydrostatic
pressure in Bowman’s space (
P
BS
) and minus the
osmotic force in the glomerular capillary (
π
GC
)
neuroeffector junction
“synapse” between a
neuron and muscle or gland cell
neuroglia
see
glial cell
neurohormone
chemical messenger that is
released by a neuron and travels in bloodstream
to its target cell
neuromodulator
chemical messenger that acts
on neurons, usually by a second-messenger
system, to alter response to a neurotransmitter
neuromuscular junction
synapselike junction
between an axon terminal of an efferent nerve
fi ber and a skeletal muscle fi ber
neuron
(NUR-ahn)
see
nerve cell
neuropeptide
family of more than 50
neurotransmitters composed of 2 or more
amino acids; often also functions as chemical
messenger in nonneural tissues
neuropeptide Y
a peptide found in the brain
whose actions include control of reproduction,
appetite, and metabolism
neurotransmitter
chemical messenger used by
neurons to communicate with each other or
with effectors
neurotrophic factor
(neur-oh-TRO-fi c) protein
that stimulates growth and differentiation of
some neurons
neutral solution
a solution that is neither basic
nor acidic (pH 7.0)
neutron
noncharged component of the nucleus
of an atom
neutrophil
(NOO-troh-fi l) polymorphonuclear
granulocytic leukocyte whose granules show
preference for neither eosin nor basic dyes;
functions as phagocyte and releases chemicals
involved in infl ammation
nicotinamide adenine dinucleotide (NAD
+
)
coenzyme derived from the B vitamin niacin;
transfers hydrogen from one substrate to another
nicotinic receptor
(nik-oh-TIN-ik) acetylcholine
receptor that responds to nicotine; primarily,
receptors at motor end plate and on
postganglionic autonomic neurons
nitric oxide
a gas that functions as intercellular
messenger, including neurotransmitters; is
endothelium-derived relaxing factor; destroys
intracellular microbes
n-methyl-d-aspartate (NMDA) receptor
ionotropic glutamate receptor involved in
learning and memory
nociceptor
(NOH-sih-sep-tor) sensory receptor
whose stimulation causes pain
node of Ranvier
(RAHN-vee-ay) space between
adjacent myelin-forming cells along myelinated
axon where axonal plasma membrane is
exposed to extracellular fl uid; also called
neurofi
bril node
nonpenetrating solute
dissolved substance that
does not passively diffuse across a plasma
membrane
nonpolar
pertaining to molecule or region of
molecule containing predominantly chemical
bonds in which electrons are shared equally
between atoms; having few polar or ionized
groups
nonshivering thermogenesis
the creation of
bodily heat by processes other than shivering;
for example, certain hormones can stimulate
metabolism in brown adipose tissue, resulting
in heat production in infants (but this does not
occur to any signifi cant extent in adults)
nonspecifi
c ascending pathway
chain of
synaptically connected neurons in CNS that are
activated by sensory units of several different
types; signals general information;
compare
specifi c ascending pathway
nonspecifi
c immune defense
response that
nonselectively protects against foreign material
without having to recognize its specifi c identity
nonsteroidal anti-infl
ammatory drug
(NSAID)
inhibitor of enzymes within the
synthetic pathway leading from arachidonic
acid to leukotrienes and prostaglandins
nonvolatile acid
organic (e.g., lactic) or inorganic
(e.g., phosphoric and sulfuric) acid not derived
directly from carbon dioxide
noradrenergic
referring to neurons that release
norepinephrine as a neurotransmitter or
membrane receptors that bind norepinephrine
norepinephrine (NE)
(nor-ep-ih-NEF-rin)
biogenic amine (catecholamine)
neurotransmitter released at most sympathetic
postganglionic endings, from adrenal medulla,
and in many CNS regions
NREM sleep
sleep state associated with large,
slow EEG waves and considerable postural-
muscle tone but not dreaming; also called
slow-wave sleep
nuclear bag fi
ber
specialized stretch receptor in
skeletal muscle spindles that responds to both
the magnitude of muscle stretch and the speed
at which it is stretched
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