nightmares may be associated with
traumatic experiences.
Nightmares should not be confused
with hypnagogic hallucinations, which
occur while falling asleep, nor with
night terror, which occurs in NREM
(nonrapid eye movement) sleep and is
not remembered the next day.
night terrorA disorder, occurring mainly
in children, that consists of abrupt arous-
als from sleep in a terrified state. Night
terror (also called sleep terror) usually
starts between the ages of 4 and 7, grad-
ually disappearing in early adolescence.
Episodes occur during NREM (non-
rapid eye movement) sleep, usually half
an hour to 3 and a half hours after fall-
ing asleep. Sufferers wake up screaming
in a semiconscious state and remain
frightened for some minutes. They do
not recognize familiar faces or sur-
roundings, and usually cannot be
comforted. The sufferer gradually falls
back to sleep and has no memory of the
event the following day.
Night terror in children has no serious
significance, but, in adults, is likely to
be associated with an anxiety disorder.
nippleThe small prominence at the tip
of each breast. Women’s nipples con-
tain tiny openings through which milk
can pass. The nipple and the areola, a
surrounding area of dark skin, both
increase in size during pregnancy. Invol-
untary muscle in the nipple allows it to
become erect.
Structural defects of the nipple are
rare. An inverted nipple is usually a
harmless abnormality of development.
Nipple inversion that develops in older
women is mostly due to ageing, but
mammographymay be advisable to rule
out the possibility of cancer.
Cracked nipples, common in the last
months of pregnancy and during breast-
feeding, may lead to infective mastitis.
Washing, drying, and moisturizing the
nipple daily can help to prevent cracking.
Papilloma of the nipple is a noncancer-
ous swelling attached to the skin by a
stalk. Paget’s disease of the nipple
appears initially as persistent eczema of
the nipple and is due to a slow-growing
cancer arising in a milk duct. Surgical
treatment is required.Discharge from the nipple occurs for
various reasons. A clear, straw-coloured
discharge may develop in early preg-
nancy; a milky discharge may occur
after breast-feeding is over. Galactor-
rhoea (milk discharge in someone who
is not pregnant or breast-feeding) may
be caused by a hormone imbalance, or,
rarely, a galactocele (a cyst under the
areola). A discharge containing pus
indicates a breast abscess. A blood-
stained discharge may be due to a
noncancerous breast disorder or cancer.
nitrate drugsA group of vasodilator
drugsused to treat angina pectoris(chest
pain as a result of impaired blood sup-
ply) and severe heart failure(reduced
pumping efficiency of the heart). Two
commonly used nitrate drugs are glyc-
eryl trinitrateand isosorbide.
Possible side effects of nitrate drugs
include headache, flushing, and dizzi-
ness. Tolerance(the need for greater
amounts of a drug for it to have the
same effect) may develop when the
drug is taken regularly.
nitrazepamA benzodiazepinedrug used
in the short-term treatment of insomnia.
Nitrazepam is long-acting and may cause
a hangover, with drowsiness and light-
headedness, the following day. Regular
use can lead to reduced effectiveness.
Nitrazepam can lead to drug depen-
dence and to withdrawal symptoms,
such as nervousness and restlessness.
nitric oxide (NO)A gas that is produced
both outside the body as a pollutant
(for example, in car exhaust fumes), and
inside the body, where it takes the form
of a molecule that acts as a messenger
between cells. Nitric oxide causes blood
vessels to dilate, affecting the flow of
oxygenated blood and regulating blood
pressure. Overproduction of nitric oxide
is associated with various disorders, in-
cluding toxic shock, rheumatoid arthritis,
and diabetes mellitus; underproduction
may cause impotenceand angina. The
control of nitric oxide is an important
element of many drug treatments.
nitritesSalts of nitrous acid (a nitro-
gen-containing acid). Sodium nitrite is
used in meat preservation. In large
amounts, nitrites can cause dizziness,
nausea, and vomiting.NIGHT TERROR NITRITESN