N–O

narcolepsy A sleep disorder in which a person
feels chronically tired and sleep deprived, and may
experience uncontrollable episodes of falling asleep
during the day. People who have narcolepsy have
disturbed sleep patterns while falling asleep, often
experiencing premature sleep PARALYSIS(an inabil-
ity to move which normally occurs in rapid eye
movement [REM] sleep as a protective mechanism
to keep the body from enacting dreams), hypna-
gogic hallucinations (inability to distinguish
between dreamlike images and reality when falling
asleep), and daytime cataplexy (sudden, brief
episodes of MUSCLEweakness or inability to move).
As well, the person experiences abnormal and very
short REM sleep periods (detected through diag-
nostic sleep studies) that prevent restful sleep.
Researchers believe narcolepsy is far more common
than diagnosis data suggest because many people
do not seek medical evaluation or treatment.
The diagnostic path includes a general medical
examination and basic NEUROLOGIC EXAMINATIONto
evaluate overall health and neurologic function.
Diagnostic sleep studies reveal the characteristic
traits of narcolepsy, distinguishing the disorder
from other SLEEP DISORDERS. Treatment is a combi-
nation of medications that may include

• AMPHETAMINES(STIMULANTS) to diminish daytime
  sleepiness


• modafinil, a nonamphetamine DRUGthat targets
  different BRAINfunctions from amphetamines to
  improve daytime alertness


• sleep medications such as flurazepam and other
  benzodiazepine drugs to encourage relaxation
  when falling asleep


• tricyclic antidepressants such as imipramine
  and desipramine to improve REM sleep

Some people also benefit from scheduled short

naps throughout the day, which may provide rest-

ful sleep as well as decrease feelings of sleepiness.

Researchers do not know what causes narcolepsy,

though there is some evidence that it may be an

Autoimmune disorder because there seems to be

involvement of HUMAN LEUKOCYTE ANTIGENS(HLAS),

which are fundamental to the IMMUNE RESPONSE.

There is also some evidence that people who have

narcolepsy have reduced levels of a neuroprotein

called hypocretin. However, researchers do not

know what these correlations mean or how they

cause narcolepsy. Narcolepsy is a lifelong condition.

See also APNEA; AUTOIMMUNE DISORDERS; RESTLESS

LEGS SYNDROME.

nerve An organization of connected neurons

that conducts electrical impulses, typically forming

the structure of a fiber. The nerve fibers may be

microscopic, such as the nerves that carry

impulses from the fingertips to the BRAIN, or

clearly visible to the EYE, such as the SPINAL CORD.

The PERIPHERAL NERVESoriginate in the brain, brain-

stem, and SPINAL CORDand extend to their destina-

tions in the body. A cluster or mass of nerves

located outside the CENTRAL NERVOUS SYSTEM(brain

and spinal cord) is a ganglion.

For further discussion of nerves within the con-

text of the structures and functions of the nervous

system, please see the overview section “The Ner-

vous System.”

See also DIABETES; NEURALGIA; NEURITIS; PERIPHERAL

VASCULAR DISEASE(PVD).

nerve cell See NEURON.

nervous system The BRAIN and network of

nerves that convey electrical impulses to and from

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