neck. Just above the level of the larynx
(voice-box), each carotid artery divides to
form an external carotid artery and an in-
ternal carotid artery. The external arteries
have multiple branches that supply most
tissues in the face, scalp, mouth, and jaws;
the internal arteries enter the skull to
supply the brain and eyes. At the base of
the brain, branches of the 2 internal ca-
rotids and the basilar artery join to form
a ring of vessels called the circle of Willis.
Narrowing of these vessels may be as-
sociated with transient ischaemic attack
(TIA); obstruction of them causes a stroke.
carpal tunnel syndromeNumbness,
tingling, and pain in the thumb, index
finger, and middle fingers caused by
compression of the median nerveat the
wrist. Symptoms may be worse at night.
The condition results from pressure on
the nerve where it passes into the hand
via a gap (the “carpal tunnel’’) under a
ligament at the front of the wrist. It is
common among keyboard users. It also
occurs without obvious cause in middle-
aged women, and is associated with
pregnancy, initial use of oral contracep-
tives, premenstrual syndrome, rheumatoid
arthritis, myxoedema, and acromegaly.
The condition often disappears without
treatment. Persistent symptoms may be
treated with a corticosteroid druginjected
under the ligament, or the ligament may
be cut to relieve pressure on the nerve.
carpusThe 8 bones of the wrist.
carrierA person who is able to pass on
an infectious or inherited disease with-
out actually suffering from it.
car sickness See
motion sickness.
cartilage A type
of connective tissue
made up of varying
amounts of the gel-
like substance colla-
gen. Cartilage forms
an important struc-
tural component of
various parts of the
skeletal system, in-
cluding the joints.
There are 3 main
types. Hyaline car-
tilage is a tough,
smooth tissue thatlines the surfaces of joints. Fibrocarti-
lage is solid and strong and makes up
the intervertebral discs that are situated
between the bones of the spine and the
shock-absorbing pads in joints. Elastic
cartilage is soft and rubbery and found
in structures such as the outer ear and
the epiglottis.
castA rigid casing applied to a limb or
other part of the body to hold a broken
bone or dislocated joint in position as it
heals. Most casts are made of bandages,
impregnated with plaster of Paris, which
are applied wet and harden as they dry.
castor oilA colourless or yellow-tinged
oil obtained from the leaves of the cas-
tor oil plant. Given orally, castor oil has
a laxative action. Zinc and castor oil are
combined in a soothing ointment for
conditions such as nappy rash.
castrationThe removal of the testes
(see orchidectomy). The term is some-
times used for removal of the ovaries
(see oophorectomy). Castration is per-
formed when organs are diseased or to
reduce the level of testosterone or of
oestrogen in people who have certain
types of cancer that are stimlated by
these hormones.
catabolismA chemical process by
which constituents of food stored in the
body (for example, fats) are broken
down, releasing energy into body cells
(see biochemistry; metabolism).
catalepsyA physical state in which the
muscles of the face, body, and limbs are
maintained in a semi-rigid, statue-like
position for minutes, hours, or even days.
Catalepsy occurs in people with schizo-
phreniaor epilepsy,but may also be
caused by brain diseaseor some drugs.
cataplexyA sudden loss of muscle tone,
causing an involuntary collapse without
loss of consciousness. Cataplexy is trig-
gered by intense emotion, particularly
laughter, and occurs almost exclusively
in those suffering from narcolepsyand
other sleep disorders.
cataractLoss of transparency of the
crystalline lens of the eye, due to
changes in its delicate protein fibres. At
an advanced stage, the front part of the
lens becomes densely opaque, but the
cataract never causes total blindness.
Almost everyone over 65 has someCARPAL TUNNEL SYNDROME CATARACTC
CARTILAGEBoneSynovial
fluidSynovial
membraneHyaline
cartilageLigamentJOINT