the energy is used in plant respiration, so by subtract-
ing this from the gross primary production, the net pri-
mary productivity (NPP) is deduced, and this
represents the rate of production of biomass available
tobe consumed by animals and other organisms. The
most productive areas on the Earth are those that have
higher temperatures, abundant soil nitrogen, and water.
These ecosystems include the tropical rain forest,
swamps, marshes, estuaries, and deciduous forests.
neural crest The neural crest is formed only in verte-
brate embryos during the final stages of neurulation, a
process in vertebrates where the ectoderm of the future
brain and spinal cord—the neural plate—develops
folds (neural folds) and forms the neural tube. The neu-
ral crest consists of paired dorsal lateral streaks of cells
that migrate away from the neural tube and spread
throughout the organism to differentiate into many cell
types that contribute to the development of systems
such as skin, heart, endocrine, bones of the skull, teeth,
and even parts of the peripheral nervous system, to
name a few.
neuron The basic data processing unit of the nervous
system; a specialized cell that carries information elec-
trically from one part of the body to another by spe-
cialized processes or extensions called dendrites and
axons. Widely branched dendrites carry nerve impulses
toward the cell body, while axons carry them away and
speed up transmitting nerve impulses (conduction)
from one neuron to another. Each neuron has a nucleus
within a cell body.
Neuroptera An order of insects with 18 families
worldwide comprising dobsonflies, fishflies, alderflies,
spongillaflies, owlflies, snakeflies, ant lions, and
lacewings. They are characterized by having usually
similar membranous wings with many veins, held in a
rooflike position, and chewing or sucking mouthparts.
They undergo complete metamorphosis, and they are
insectivorous.
neurosecretory cells Modified nerve cells that
have endocrine functions. Nerve cells in the hypotha-
lamus that react to other nerve cells and that have
characteristics of both neurons and endocrine cells
and release hormones (neurohormones) directly into
body fluids or storage areas. There are two classes of
neurosecretory cells in the hypothalamus. They are
located in the median eminence near the adenohy-
pophysis, the anterior glandular lobe of the pituitary,
and in the neurohypophysis, the posterior lobe of the
gland.
The adenohypophysis arises from epithelial tissue
at the roof of the mouth and includes the pars distalis,
pars tuberalis, and pars intermedia.
The median eminence is an enlarged area of the
infundibulum, the part of the brain between the
brainstem and cerebrum. Here nerve cells secrete
their releasing and inhibitory hormones that get
absorbed into the blood capillaries in the median
eminence and carried on in the venous blood down
along the infundibulum to the anterior pituitary
gland.
The adenohypophysis secretes FSH (follicle-
stimulating hormone), LH (luteinizing hormone),
ACTH (adrenocorticotropic hormone), TSH (thyroid-
stimulating hormone), GH (growth hormone), and
prolactin.
The neurohypophysis, or the posterior lobe of the
pituitary, is connected to the hypothalamus by the
stalklike infundibulum and receives two hormones
released by the neurons in the hypothalamus, oxy-
tocin (OT) and vasopressin or ADH (antidiuretic hor-
mone). Oxytocin and ADH are stored in the posterior
pituitary. The neurohypophysis is an outgrowth of
nervous tissue from the floor of the brain in the region
of the hypothalamus. It is made up of the pars ner-
vosa and is connected to the brain by the infundibu-
lum. Oxytocin acts on myoepithelial cells in the
mammary glands and uterine muscles, causing both to
contract. ADH stimulates the kidneys to reabsorb
more water.
The hypothalamus contains mammillary bodies,
the median eminence, and infundibulum. It contains
nuclei that produce the neurohormones. In the
supraoptic region are cell bodies of neurons in the par-
aventricular nucleus that synthesize oxytocin, while
those in the supraoptic nucleus synthesize ADH.
Neurosecretorycells are also found in other ani-
mals such as mollusks, nematodes, and platy-
helminthes, to name a few.neurosecretory cells 243