Bma Illustrated Medical Dictionary

neuroendocrinologyThe study of the

interactions between the nervous system

and the endocrine systemthat control

internal body functions and the body’s

response to the external environment.

neurofibromatosisAn uncommon dis-

order that is inherited.Also called von

Recklinghausen’s disease, neurofibro-

matosis is characterized by numerous

neurofibromas (soft, fibrous swellings,

varying significantly in size), which

grow from nerves, and by café au lait

spots(pale, coffee-coloured patches) on

the skin, usually on the trunk and pelvis.

If neurofibromas occur in the central

nervous system, they may cause epilepsy

and other complications. Neurofibro-

matosis can lead to bone deformities.

Rarely, neurofibromas become cancerous.

Surgical removal of neurofibromas is

necessary only if there are complications.

Anyone with this disorder, and parents

of an affected child, should seek genetic

counsellingif planning a pregnancy.

neurologyThe medical discipline con-

cerned with the study of the nervous

systemand its disorders (see also neu-

ropathology; neurosurgery).

neuromaA noncancerous tumour of

nervetissue. In most cases, the cause is

unknown; rarely, a neuroma develops as

a result of damage to a nerve.

A neuroma may affect any nerve in the

body. Symptoms vary, but there is often

intermittent pain and sometimes weak-

ness and numbness in the areas that

are supplied by the affected nerve.

If symptoms are troublesome, the

tumour may be surgically removed. (See

also acoustic neuroma.)

neuronThe term used to describe a

nerve cell. A typical neuron consists of a

cell body, several branching projections

called dendrites, and a filamentous pro-

jection called an axon (also known as a

nerve fibre). An axon branches at its

end to form terminals through which

electrical signals are transmitted to tar-

get cells. Most axons are coated with a

layered insulating myelinsheath, which

speeds the transmission of the signals.

The myelin sheath is punctuated along

its length by gaps called nodes of Ran-

vier, which help this process. Because

the myelin sheath is nonconductive, ion

exchange (depolarization) only occurs

at a node, and signals leap from node

to node along the length of the axon.

The nervous system contains billions

of neurons, of which there are 3 main

types: sensory neurons, which carry sig-

nals from sense receptors into the central

nervous system(CNS); motor neurons,

which carry signals from the CNS to

NEUROENDOCRINOLOGY NEURON

N

Myelin sheath

Node of

Ranvier

Dendrites

Axon

(nerve fibre) Neuron cell body

Axon branches

NEURON

Nucleus

Synapse

Axon terminal