Bma Illustrated Medical Dictionary

in hairy areas, particularly the armpits,
pubic region, and around the anus.
The sweat glands are controlled by the
autonomic nervous system. The glands
are usually stimulated to keep the body
cool, but anxiety or fear can also cause
sweating. Sweat is odourless until bac-
teria act upon it, producing body odour.
A common disorder of the sweat
glands is prickly heat. Other disorders
include hyperhidrosisand hypohidrosis.
sweatingThe process by which the body
cools itself. (See also sweat glands.)
sweeteners, artificial See artificial
sweeteners.
swimmer’s earA common name for
otitis externa.
sycosis barbaeInflammation of the
beard area due to infection of the hair
follicles, usually with STAPHYLOCOCCUS
AUREUS bacteria contracted from in-
fected razors or towels. Pus-filled
blisters appear around the follicles. Treat-
ment is usually with antibiotic drugs.
Sydenham’s choreaA rare childhood
disorderof the central nervous system
that causes involuntary jerky movements
of the head, face, limbs, and fingers. Vol-
untarymovements are clumsy, and the
limbs become floppy. The disorder usu-
ally follows an attack of rheumatic fever.
Sydenham’s chorea usually clears up
after 2–3 months and has no long-term
adverse effects.

sympathectomyAn operation in which

the ganglia (nerve terminals) of sympa-

thetic nerves are destroyed to interrupt

the nerve pathway. This may be per-

formed to improve blood supply to a

limb (as a treatment for peripheral vas-

cular disease) or to relieve chronic pain,

for example causalgia.

sympathetic nervous systemOne of

the 2 divisions of the autonomic nervous

system. In conjunction with the other

division (the parasympathetic nervous

system), this system controls many of

the involuntary activities of the body’s

glands and organs.

symphysisA type of jointin which 2

bones are firmly joined by tough carti-

lage. Such joints occur between the

vertebrae; between the pubic bones at

the front of the pelvis; and between the

upper and middle parts of the sternum.

symptomAn indication of a disease or

disorder that is noticed by the sufferer.

By contrast, the indications that a doc-

tor notes are called signs.

symptothermal methodSee contra-

ception, natural methods of.

synaesthesiaA condition in which stim-

ulation of one of the senses (by a sound,

for example) produces an additional

response, such as the appearance of a

colour in addition to the normal per-

ception associated with that stimulus.

synapseA junction between 2 neurons

across which a signal can pass. At a

synapse, the 2 neurons do not come

directly into contact but are separated

by a gap called the synaptic cleft. When

an electrical signal passing along a neu-

ron reaches a synapse, it causes the

release of a chemical called a neuro-

transmitter. The neurotransmitter travels

across the synaptic cleft to the surface

membrane of the next neuron, where it

changes the electrical potential of the

membrane. Signals can be transmitted

across a synapse in one direction only.

Most drugs affecting the nervous sys-

tem work as a result of their effects on

synapses. Such drugs may affect the

release of neurotransmitters, or they

may modify their effects.

syncopeThe medical term for fainting.

syndactylyA congenitaldefect in which

2 or more fingers or toes are joined.

SYNDACTYLY

S

SWEAT GLANDS

Hair Sweat droplet

Sweat

gland

ECCRINE SWEAT GLAND IN SKIN

SWEATING