Bma Illustrated Medical Dictionary

Treatment is of the underlying condition.

A low-sodium diet may be recommen-

ded, and diuretic drugsmay be given to

reduce oedema. If the concentration of

protein in the blood is very low, protein

may need to be given intravenously.

nerveA 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).

The most obvious nerves in the body

are the peripheral nerves, which extend

from the central nervous system(con-

sisting of the brainand spinal cord). Of

these, 12 pairs of cranial nerveslink

directly to the brain, and 31 pairs of

spinal nervesjoin 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 blockThe 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 studiesTests 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 NERVE CONDUCTION STUDIES

N

NERVE

NERVE CONDUCTION STUDIES

Nerve

fascicle

(bundle

of nerve

fibres)

Blood vessels

Axon (nerve fibre)

Myelin (fatty

insulating sheath)

Nerve

STRUCTURE OF A NERVE

Control panel Monitor displays

speed of nerve

response

Technician

Nerve

stimulator

Recording

electrode