Webster's New World Medical Dictionary

extension
The process of straightening or the
state of being straight. The opposite of flexion or
the state of being bent.
external ear
See 
ear, outer.
external jugular vein
The more superficial of
the two jugular veins in the neck that drain blood
from the head, brain, face, and neck and convey
blood toward the heart. The external jugular vein
collects most of the blood from the outside of the
skull and the deep parts of the face. It lies outside
the sternocleidomastoid muscle, passes down the
neck, and joins the subclavian vein. See also 
inter-
nal jugular vein.
external radiation therapy
See 
radiation
therapy, external.
extracorporeal shock wave lithotripsy
See
lithotripsy, extracorporeal shock wave.
extrapyramidal side effects
Physical symp-
toms, including tremor, slurred speech, akathesia,
dystonia, anxiety, distress, paranoia, and bradyphre-
nia, that are primarily associated with improper
dosing of or unusual reactions to neuroleptic
(antipsychotic) medications.
extrapyramidal system
The part of the nervous
system that regulates muscle reflexes.
extrasystole
A premature contraction of the
heart that is independent of the normal rhythm of
the heart. An extrasystole begins in a part of the
heart other than the normal heartbeat origin, the
sinoatrial (SA) node. Extrasystoles are followed by a
pause, as the heart electrical system “resets” itself,
and the contraction following the pause is usually
more forceful than normal. These more forceful
contractions can be perceived as palpitations. See
also 
palpitations.
extrauterine pregnancy
See 
ectopic preg-
nancy.