R

reflex An involuntary response to a stimulus
that produces a limited and predictable action.
Some reflexes are present only in early infancy
and are survival-related, such as the rooting
reflex, which guides an infant to locate the nipple
for BREASTFEEDING, or the startle (Moro) reflex, in
which an infant makes a grasping motion with the
arms and legs in response to stimulation that sug-
gests falling. Other reflexes that represent normal
neurologic function in infancy may reappear later
in life as signs of neurologic damage, such as
Babinski’s reflex (a spreading of the toes with firm
stimulation of the sole of the foot). Reflexes that
remain throughout life generally protect the body
in some way, such as the gag reflex (which helps
prevent large objects from entering the throat)
and the corneal reflex (in which contact with the
CORNEAcauses the eyelid to close). The SPINAL CORD
manages most reflexes.
A reflex represents a complete circuit of stimu-
lus, sensory NERVE function, spinal cord (and
sometimes BRAIN) participation, and motor nerve
function. Neurologists call this circuit a reflex arc.
Abnormal reflex responses indicate interruption of
the arc and damage to the neurologic structures. A
number of reflexes become abnormal when there
is TRAUMATIC BRAIN INJURY (TBI) or SPINAL CORD
INJURY, for example, or in neurologic disorders that
damage brain and nerve tissue such as PARKINSON’S
DISEASEand MULTIPLE SCLEROSIS.
See also NEUROLOGIC EXAMINATION.

restless legs syndrome A chronic disturbance of
the PERIPHERAL NERVESin the legs that causes symp-
toms of burning, irritation, itching, crawling sen-
sations, and often PAIN. Accompanying these
discomforts is the urge to move the legs, which
diminishes the symptoms. Restless legs syndrome

is most problematic at night because it interferes

with sleep. Neurologists do not know what causes

restless legs syndrome, though many believe it is a

movement disorder arising from dysfunction of

the structures in the midbrain that regulate motor

function. Many people receive relief when taking

medications used to treat PARKINSON’S DISEASEsuch

as DOPAMINEagonists and levodopa, suggesting dis-

turbances of neurotransmitters such as dopamine

and acetylcholine create subtle disruptions of

motor response. Restless legs syndrome is also

common in people who have Parkinson’s disease.

The diagnostic path incorporates a comprehen-

sive NEUROLOGIC EXAMINATIONprimarily to rule out

other potential causes for the symptoms. The neu-

rologist may conduct electromyogram (EMG)

studies of the muscles in the legs to evaluate their

responses to NERVEimpulses. Sleep studies often

reveal the extent to which the symptoms interfere

with sleep. Treatment may include a combination

of medications, such as dopamine agonists, MUSCLE

relaxants, sleep aids, and ANALGESIC MEDICATIONSfor

pain relief. Some people experience relief from

symptoms and improved sleep with alternative

therapies such as ACUPUNCTUREand BIOFEEDBACK.

Restless legs syndrome affects 12 to 20 million

Americans. Many people who have restless legs

syndrome do not seek medical care because they

do not know there are treatments available to ease

their symptoms. Restless legs syndrome is chronic,

often developing in midlife or later. There are no

known measures to prevent restless legs syn-

drome.

See also APNEA; NEUROTRANSMITTER; SLEEP DISOR-

DERS.

Reye’s syndrome A rare complication of certain

viral infections in children, notably CHICKENPOX,

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