include anti-inflammatory medications to relieve
swelling or ANTIVIRAL MEDICATIONS when a VIRUS
appears to be the culprit. It is important to protect
the eye when the paralysis affects the muscles
controlling the eyelid, as the eyelid may not blink
or close. The doctor may prescribe topical oph-
thalmic medications and protection for the eye
such as an eye shield. Other therapies are prima-
rily supportive, such as speech and swallowing
therapy. Some people benefit from MASSAGE THER-
APYof the face, PHYSICAL THERAPY, and ACUPUNCTURE
to relieve symptoms and maintain muscle tone
and health while the damage to the facial nerve
heals.
About 85 percent of people recover with mini-
mal or no residual effects. The remainder experi-
ence improvement though may have persistent
paralysis and loss of function, including hearing
impairment. Rarely, Bell’s palsy results in signifi-
cant, permanent loss of function and feeling. In
such circumstances doctors may recommend cor-
rective surgery to restore the protective capability
of the eyelid as well as function and appearance
of the mouth. The symptoms of Bell’s palsy may
take two weeks to six months or longer to fully
resolve.
Risk Factors and Preventive MeasuresPeople who have DIABETESand women who are in
the third trimester of PREGNANCYare significantly
more likely to develop Bell’s palsy. Bell’s palsy is
more common as well in people who have MULTI-
PLE SCLEROSIS or who are IMMUNOCOMPROMISED.
Researchers do not know why these circum-
stances increase vulnerability to Bell’s palsy. There
are no known preventive measures for Bell’s palsy.
See also CONJUNCTIVITIS; CRANIAL NERVES; LYME
DISEASE; SKELETON; SMELL AND TASTE DISORDERS.
blood–brain barrier A protective mechanism
that regulates the size of molecules that may pass
from the bloodstream to the BRAIN. A layer of cells
called the endothelium lines the inner channel of
the body’s tiniest BLOODvessels, the capillaries. The
endothelium functions somewhat like a net. In
parts of the body other than the brain, the cells of
the endothelium are wider apart, forming a looser
net that allows NUTRIENTS, chemicals, and other
substances to pass into the spaces between cells.
From these spaces the substances can enter the
cells that need them.
In the brain the capillary endothelium is com-
pact, its cells forming a tight net to restrict sub-
stances from crossing into the intracellular spaces.
Glial cells, cells within the brain that support neu-
rons, also participate in the blood–brain barrier,
although researchers do not fully understand the
mechanisms through which they do so. In some
areas of the brain the blood–brain barrier is looser,
allowing substances to more easily cross (though
not as easily as in the body). Among these areas
are the:- area postrema, commonly called the NAUSEA
center, which allows toxins in the bloodstream
to rapidly trigger the vomiting REFLEX - pineal region, the area surrounding the PINEAL
GLAND - pituitary region, the area surrounding the PITU-
ITARY GLAND
The blood–brain barrier permits the brain to
maintain balances of neurotransmitters, GLUCOSE,
electrolytes, fluid, and other substances that differ
from those of the body and are essential for
proper brain function. The blood–brain barrier
also prevents many PATHOGENS(notably BACTERIA
and viruses) from entering the brain, helping
reduce the likelihood of INFECTION. Many drugs
are unable to cross the blood–brain barrier,
though those that can include barbiturates.
The body must metabolize drugs that cannot
cross the blood–brain barrier, such as ANTIBIOTIC
MEDICATIONS to treat infection and levodopa (a
precursor of DOPAMINEtaken to treat PARKINSON’S
DISEASE), into substances small enough to cross the
capillary endothelium to enter the brain. Thus,
though it is primarily protective, the blood–brain
barrier sometimes impedes therapeutic efforts.
Conditions such as HYPERTENSION(high BLOOD PRES-
SURE, which can cause microscopic ruptures in the
capillaries), STROKE, and penetrating trauma to the
brain can disrupt the blood–brain barrier by allow-
ing blood to come in direct contact with brain
tissues.
See also BARBITURATES; CEREBROSPINAL FLUID;
CREUTZFELDT-JAKOB DISEASE(CJD); NEURON; NEURO-
TRANSMITTER; PATHOGEN; VIRUS.blood-brain barrier 229