spasm An involuntary contraction of a
Disorders characterized by spasm in-
spasticity Increased rigidity in a group
, causing stiffness and restric-
tion of movement. Spasticity occurs in
Parkinson's disease, multiple sclerosis,
spastic paralysis Inability to move a
part of the body, accompanied by rigidity
of the muscles. Causes of spastic para-
. (See also
specific gravity The ratio of the
of a substance to that of water.
specific learning disability Difficulty
in one or more areas of learning in a
child of average or above average intel-
ligence. Specific learning disabilities
and dyscalculia, where
there is a problem with mathematics.
specimen A 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
SPECT The abbreviation for single pho-
ton emission computed tomography, a
speculum A device for holding open a
body orifice to enable a doctor to per-
form an examination.
speech A system of sounds by which
humans communicate. Children learn
speech through listening to and imitat-
ing the speech of others.
Speech production originates in
regions of the cerebral cortex on each
side of the
. 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 disorders Defects or disturb-
that lead to an inability
to communicate effectively.
Damage to the language centres of the
brain (usually due to a
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,
. A structural abnor-
mality of the mouth, such as a
, 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
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
which is marked by hesitant speech and
repetition of sounds.
Delayed speech development in a child
may be due to hearing loss (see
), slow maturation of the nervous
system, poor tongue and lip control,
lack of stimulation, or emotional distur-
Many people with speech disorders
can be helped by
speech therapy A form of treatment
for people who have a
exercises to improve
the deficient aspect
sperm The male sex
cell, which is respon-
of the female ovum.
Inside the head of
the sperm is genetic
material, while the
acrosome that caps
enzymes that enable
sperm to penetrate
covering. The tail of
the sperm propels it.