NEUROPSYCHIATRY
NIACIN
N
Diagnostic tests such as
blood tests,
MRI
scans, and nerve or muscle
biopsy
may also be required. When possible,
treatment is aimed at the underlying
cause. If the cell bodies of the damaged
nerve cells have not been destroyed, full
recovery from neuropathy is possible.
neuropsychiatry
The branch of medic-
ine dealing with the relationship between
psychiatric symptoms and neurological
disorder. This may include the effects of
head injury and alcohol on the brain, or
disorders such as brain tumours, infec-
tions, inherited illnesses, and disorders
causing brain damage in childhood.
neurosis
An old term for a range of psy-
chiatric disorders excluding
psychosis
.
neurosurgery
The specialty concerned
with the surgical treatment of disorders
of the
brain, spinal cord
, or other parts of
the
nervous system.
Conditions treated by neurosurgery
include tumours of the brain, spinal cord,
or meninges (membranes surrounding
the brain and spinal cord);
brain abscess;
abnormalities of the blood vessels sup-
plying the brain, such as an
aneurysm
(balloon-like swelling at a weak point in
an artery); bleeding inside the skull (see
extradural haemorrhage,
intracerebral
haemorrhage
, and
subdural haemorrh-
age
); some birth defects (such as
neural
tube defects
and
hydrocephalus
); certain
types of
epilepsy
; and nerve damage
caused by illness or accidents. Neuro-
surgery may also be performed to relieve
pain
that is otherwise untreatable.
neurosyphilis
Infection of the brain or
spinal cord that occurs in untreated
syphilis many years after initial infection.
Damage to the spinal cord due to
neurosyphilis may cause tabes dorsalis,
characterized by poor coordination of
leg movements, urinary incontinence,
and pains in the abdomen and limbs.
Damage to the brain may cause
demen-
tia,
muscle weakness, and, in rare cases,
total paralysis of the limbs.
neurotoxin
A chemical that damages
nervous tissue. The principal effects of
neurotoxic nerve damage are numbness,
weakness, or paralysis of the part of the
body supplied by the affected nerve.
Neurotoxins are present in the venom
of certain snakes (see
snake bites
), and
are released by some types of bacteria
(such as those that cause
tetanus
and
diphtheria
). Some chemical poisons, such
as arsenic and lead, are also neurotoxic.
neurotransmitter
A chemical released
from a nerve ending that transmits
impulses from one
neuron
(nerve cell)
to another neuron, or to a muscle cell.
When a nerve impulse reaches a nerve
ending, neurotransmitters are released
from synaptic vesicles and cross a tiny
gap (synapse) to reach the target cell.
Here, they cause channels in the target
cell to open, letting through charged
particles that stimulate an impulse in
the cell. Alternatively, neurotransmitters
may inhibit nerve impulses.
Scores of different chemicals fulfil this
function in different parts of the
nervous
system
.
Many neurotransmitters act as
both neurotransmitters and hormones,
being released into the bloodstream to
act on distant target cells.
One of the most important neuro-
transmitters
is
acetylcholine
,
which
causes skeletal muscles to contract
when it is released by neurons connect-
ed to the muscles. Acetylcholine is also
released by neurons that control the
sweat glands and the heartbeat, and
transmits messages between neurons
in the brain and spinal cord.
Another chemical,
noradrenaline
(nor-
epinephrine), aids the nervous control of
heartbeat, blood flow, and the body's
response to stress.
Dopamine
plays an
important role in parts of the brain that
control movement.
Serotonin
is one of
the main neurotransmitters found in
parts of the brain concerned with con-
scious processes.
Another group of neurotransmitters is
called the neuropeptides. This group
includes the
endorphins
, which are used
by the brain to control sensitivity to pain.
neutrophil
A type of phagocyte, or white
blood cell
.
They are an important part of
the
immune system
, and their role is to
engulf and destroy invading bacteria.
newborn
An infant at birth and during
the
1
st few weeks of life (see also
pre-
maturity; postmaturity
).
NGU
An abbreviation for
nongonococcal
urethritis.
niacin
See
vitamin B complex
.
400
previous page 398 BMA Illustrated Medical Dictionary read online next page 400 BMA Illustrated Medical Dictionary read online Home Toggle text on/off