NERVE
NERVE CONDUCTION STUDIES
N
Treatment is of the underlying condition.
A low-sodium diet may be recommen-
ded, and
diuretic drugs
may be given to
reduce oedema. If the concentration of
protein in the blood is very low, protein
may need to be given intravenously.
nerve
A bundle of nerve fibres which
travel to a common location. Nerve
fibres, known as axons, are the filamen-
tous projections of many individual
neurons
(nerve cells).
NERVE
Nerve
— ■— ------ Axon (nerve fibre)
fascicle
(bundle
________Myelin (fatty
of nerve
insulating sheath)
fibres)
Blood vessels
a
m-
j
STRUCTURE OF A NERVE
Nerve
The most obvious nerves in the body
are the peripheral nerves, which extend
from the
central nervous system
(con-
sisting of the
brain
and
spinal cord
). Of
these,
12
pairs of
cranial nerves
link
directly to the brain, and 31 pairs of
spinal nerves
join the spinal cord. In the
shoulder and hip regions, the spinal
nerves join to form plexuses, from
which branch the main nerves to the
limbs. Most nerves divide at numerous
points to send branches to all parts of
the body, particularly to the sense
organs, the skin, skeletal muscles, inter-
nal organs, and glands.
Nerve fibres may have a sensory func-
tion, carrying information from a receptor
or sense organ towards the central ner-
vous system (CNS), or they may have a
motor function, carrying instructions
from the CNS to a muscle or a gland.
The messages are carried by electrical
impulses propagated along the fibres.
Some nerves carry only sensory or
motor fibres, but most carry both.
Nerve function is sensitive to cold, pres-
sure, and injury (see
nerve injury
). The
peripheral nerves can be damaged by a
wide variety of disorders,
including
infection, inflammation, and metabolic
disorders (see
neuropathy
).
nerve block
The injection of a local
anaesthetic around a nerve to produce
loss of sensation in a part of the body
supplied by that nerve. For example, the
palm of the hand may be anaesthetized
by giving injections at sites up the arm,
blocking the ulnar and median nerves.
A nerve may be blocked as it leaves
the spinal cord. This occurs in
epidural
anaesthesia
, used mainly in childbirth,
and in
spinal anaesthesia
, used mainly
for surgery of the lower abdomen and
limbs. In a caudal block an anaesthetic
is injected around nerves leaving the
lowest part of the spinal cord. It produces
anaesthesia in the buttock and genital
areas, and is occasionally used in child-
birth. A pudendal nerve block involves
the injection of an anaesthetic into
nerves passing under the pelvis into the
floor of the vagina. This type of nerve
block is sometimes used in a
forceps
delivery.
(See also
anaesthesia,
local.)
nerve conduction studies
Tests car-
ried out to assess the extent of nerve
damage caused by disorders of the
peripheral nervous system (see
neuro-
pathy).
In the test, an electrical stimulus
is applied to a nerve, and the speed at
which the nerve responds to the stimu-
lus and transmits a signal is recorded.
NERVE CONDUCTION STUDIES
Control panel
Monitor displays
speed of nerve
Recording
response
Nerve
stimulator
electrode
Technician
394
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