spasmAn involuntary contraction of a
muscle. Examples include hiccupsand
tics. Disorders characterized by spasm in-
clude trigeminal neuralgiaand tetanus.
spasticityIncreased rigidity in a group
of muscles, causing stiffness and restric-
tion of movement. Spasticity occurs in
Parkinson’s disease, multiple sclerosis,
cerebral palsy, and tetanus.
spastic paralysisInability to move a
part of the body, accompanied by rigidity
of the muscles. Causes of spastic para-
lysis include stroke, cerebral palsy, and
multiple sclerosis. (See also paralysis.)
specific gravityThe ratio of the dens-
ityof a substance to that of water.
specific learning disabilityDifficulty
in one or more areas of learning in a
child of average or above average intel-
ligence. Specific learning disabilities
include dyslexiaand dyscalculia, where
there is a problem with mathematics.
specimenA sample of tissue, body fluids,
waste products, or an infective organism
taken for analysis, identification, and/or
diagnosis. The sample may be prepared
for examination under a microscope.
SPECTThe abbreviation for single pho-
ton emission computed tomography, a
type of radionuclide scanning.
spectaclesSee glasses.
speculumA device for holding open a
body orifice to enable a doctor to per-
form an examination.
speechA system of sounds by which
humans communicate. Children learn
speech through listening to and imitat-
ing the speech of others.
Speech production originates in 2
regions of the cerebral cortex on each
side of the brain. These regions are linked
to the centre for language expression
(Broca’s area) in the dominant hemi-
sphere. They send signals down nerve
pathways to muscles controlling the lar-
ynx, tongue, and other parts involved in
speech. The cerebellum plays a part in
coordinating movements of these parts.
Air from the lungs is vibrated through
the vocal cords in the larynx. This pro-
duces a noise, which is amplified in the
cavities of the throat, nose, and sinuses.
The sound of the vibrated air is modified
by movements of the tongue, mouth,
and lips to produce speech sounds.speech disordersDefects or disturb-
ances in speechthat lead to an inability
to communicate effectively.
Damage to the language centres of the
brain (usually due to a stroke, head
injury, or brain tumour) leads to aphasia,
which may impair speech.
Disorders of articulation may be caused
by damage to nerves that go to muscles
in the larynx, mouth or lips, due to
stroke, head injury, multiple sclerosis,or
Parkinson’s disease. A structuralabnor-
mality of the mouth, such as a cleft lip
and palate, can also be a cause.
Disorders of voice production include
hoarseness and inappropriate pitch or
loudness. In many cases, the cause is a
disorder affecting closure of the vocal
cords (see larynx, disorders of). A voice
that is too high or low or too loud or soft
may be caused by a hormonal or psy-
chiatric disturbance or by hearing loss.
Disorders of fluency include stuttering,
which is marked by hesitant speech and
repetition of sounds.
Delayed speech development in a child
may be due to hearing loss (see deaf-
ness), slow maturation of the nervous
system, poor tongue and lip control,
lack of stimulation, or emotional distur-
bance (see developmental delay).
Many people with speech disorders
can be helped by speech therapy.
speech therapyA form of treatment
for people who have a speech disorder.
A speech therapist
tests speech and
hearingand devises
exercises toimprove
the deficient aspect
of speech.
spermThe male sex
cell, which is respon-
sible for fertilization
of the female ovum.
Inside the head of
the sperm is genetic
material, while the
acrosome that caps
the head contains
enzymes that enable
sperm to penetrate
the ovum’s outer
covering. The tail of
the sperm propels it.SPASM SPERMS
SPERM
AcrosomeHeadTail