Webster's New World Medical Dictionary

trichotillomania
Compulsive hair pulling. An
impulse control disorder characterized by the
repeated urge to pull out scalp hair, eyelashes, eye-
brows, or other body hair. Treatment may include
cognitive-behavior therapy and medications.
tricuspid
Having three flaps or cusps. For exam-
ple, the aortic valve and the tricuspid valve in the
heart each have three cusps.
tricuspid valve
One of the four heart valves, the
first one that blood encounters as it enters the heart.
The tricuspid valve stands between the right atrium
and the right ventricle, and it allows blood to flow
only from the atrium into the ventricle.
tricyclic antidepressant
One of a family of med-
ications that affect the neurotransmitters norepi-
nephrine, serotonin, and acetylcholine. The tricyclic
antidepressants are used to treat clinical depression,
fibromyalgia, and other pain conditions.
trigeminal nerve
The chief nerve of sensation
for the face, which is also the motor nerve that con-
trols the muscles used for chewing. Problems with
the sensory part of the trigeminal nerve result in
pain or loss of sensation in the face. Problems with
the motor root of the trigeminal nerve result in devi-
ation of the jaw toward the affected side and trouble
chewing. The trigeminal nerve is the fifth cranial
nerve.
trigeminal neuralgia
Inflammation of the
trigeminal nerve (the fifth cranial nerve) that most
commonly causes paroxysms of very intense light-
ning pain in the areas of the face that the nerve sup-
plies—the lips, eye, nose, scalp, forehead, gums,
cheek, and chin—on the involved side of the face.
Triggers for attacks can include touching the face,
brushing the teeth, putting on makeup, and a soft
breeze. Medications that may be effective include
anticonvulsants and antidepressants. Neurosurgery
may be necessary to relieve pressure on the nerve
or to reduce nerve sensitivity. Also known as tic
douloureux.
triglyceride
The major form of fat, which con-
sists of three molecules of fatty acid combined with
one molecule of the alcohol glycerol. Triglycerides
serve as the backbone of many types of lipids (fats).
Triglycerides come from food and are also pro-
duced by the body. See also 
triglyceride test.