Net filtration pressure (NFP) Net pressure that promotes fluid
outflow at the arterial end of a capillary, and fluid inflow at the
venous end of a capillary; net pressure that promotes glomerular
filtration in the kidneys.
Neural plate (Noo-ral) A thickening of ectoderm, induced by the
notochord, that forms early in the third week of development
and represents the beginning of the development of the nervous
Neuralgia (noo-RAL-je-a) Attacks of pain along the entire course or
branch of a peripheral sensory nerve.
Neuritis (noo-Rf-tis) Inflammation of one or more nerves.
Neuroglia (noo-ROG-le-a) Cells of the nervous system that per-
form various supportive functions. The neuroglia of the central
nervous system are the astrocytes, oligodendrocytes, microglia,
and ependymal cells; neuroglia of the peripheral nervous system
include Schwann cells and satellite cells. Also called glial cells
Neurolemma (noo-ro-LEM-ma) The peripheral, nucleated cytoplas-
mic layer of the Schwann cell. Also called sheath of Schwann
Neurology (noo-ROL-o-je) The study of the normal functioning and
disorders of the nervous system.
Neuromuscular junction (noo-ro-MUS-ku-lar) A synapse between the
axon terminals of a somatic motor neuron and the sarcolemma of
a muscle fiber (cell).
Neuron (NOO-ron) A nerve cell, consisting of a cell body, dendrites,
and an axon.
Neurosecretory cell (noo-ro-SEC-re-to-re) A neuron that secretes
a hypothalamic releasing hormone or inhibiting hormone into
blood capillaries of the hypothalmus; a neuron that secretes
oxytocin or antidiuretic hormone into blood capillaries of the
Neurotransmitter (noo'-ro-TRANS-mit-er) One of a variety of mol-
ecules within axon terminals that are released into the synaptic
cleft in response to a nerve impulse, and that change the mem-
brane potential of the postsynaptic neuron.
Neurulation (noo-roo-LA-shun) The process by which the neural
plate, neural folds, and neural tube form.
Neutrophil (NOO-tro-fil) A type of white blood cell characterized by
granules that stain pale lilac with a combination of acidic and
Nipple A pigmented, wrinkled projection on the surface of the
breast that is the location of the openings of the lactiferous ducts
for milk release.
Nociceptor (no'-se-SEP-tor) A free (naked) nerve ending that detects
Node of Ranvier (ron-ve-A) A space, along a myelinated axon,
between the individual Schwann cells that form the myelin sheath
and the neurolemma. Also called a neurofibral node.
Norepinephrine (NE) (nor'-ep-e-NEF-rin) A hormone secreted by the
adrenal medulla that produces actions similar to those that result
from sympathetic stimulation. Also called noradrenaline (nor-a-
Notochord (NO-to-cord) A flexible rod of mesodermal tissue that
helps form part of the backbone and intervertebral discs.
Nuclear medicine The branch of medicine concerned with the use of
radioisotopes in the diagnosis and therapy of disease.
Nucleic acid (noo-KLE-ic) An organic compound that is a long poly-
mer of nucleotides, with each nucleotide containing a pentose
sugar, a phosphate group, and one of four possible nitrogenous
bases (adenine, cytosine, guanine, and thymine or uracil).
Nucleolus (noo-KLE-o-lus) Spherical body within a cell nucleus com-
posed of protein, DNA, and RNA that is the site of the assembly of
small and large ribosomal subunits.
Nucleus (NOO-kle-us) A spherical or oval organelle of a cell that
contains the hereditary factors of the cell, called genes. A cluster
of unmyelinated nerve cell bodies in the central nervous system.
The central part of an atom made up of protons and neutrons.
Nucleus pulposus (pul-PO-sus) A soft, pulpy, highly elastic sub-
stance in the center of an intervertebral disc; a remnant of the
Nutrient (NOO-tre-ent) A chemical substance in food that provides
energy, forms new body components, or assists in various body
Obesity (o-BES-i-te) Body weight more than 20% above a desirable
standard due to excessive accumulation of fat.
Oblique plane (o-BLEK) A plane that passes through the body or an
organ at an angle between the transverse plane and either the
midsagittal, parasagittal, or frontal plane.
Obstetrics (ob-STET-riks) The specialized branch of medicine that
deals with pregnancy, labor, and the period of time immediately
after delivery (about 6 weeks).
Olfactory (ol-FAK-to-re) Pertaining to smell.
Olfactory bulb A mass of gray matter containing cell bodies of neu-
rons that form synapses with neurons of the olfactory (I) nerve,
lying inferior to the frontal lobe of the cerebrum on either side of
the crista galli of the ethmoid bone.
Olfactory receptor A bipolar neuron with its cell body lying between
supporting cells located in the mucous membrane lining the
superior portion of each nasal cavity; transduces odors into
Olfactory tract A bundle of axons that extends from the olfactory
bulb posteriorly to olfactory regions of the cerebral cortex.
Oligodendrocyte (ol'-i-go-DEN-dro-sft) A neuroglial cell that supports
neurons and produces a myelin sheath around axons of neurons
of the central nervous system.
Oligospermia (ol'-i-go-SPER-me-a) A deficiency of sperm cells in the
Oncogenes (ONG-ko-jenz) Cancer-causing genes; they derive from
normal genes, termed proto-oncogenes, that encode proteins
involved in cell growth or cell regulation but have the ability
to transform a normal cell into a cancerous cell when they are
mutated or inappropriately activated. One example is
p 5 3 .
Oncology (ong-KOL-o-je) The study of tumors.