NERVE(as in compression) or multiple peripheral
nerves, either in a pattern (as in RAYNAUD’S SYN-
DROME or shingles) or diffusely throughout the
body (as in neuropathy of DIABETES). Neurologists
classify the more than 100 forms of neuropathy
into broad categories according to the type of
nerve affected—motor, sensory, mixed, and auto-
nomic.
The symptoms of neuropathy vary widely with
the nerves affected and extent of the condition
causing the neuropathy. PAIN, MUSCLEweakness or
loss of muscle function, disturbances of sensory
perception, and dysfunction of autonomic
processes such as digestion are among the myriad
symptoms that can occur with neuropathy. The
diagnostic path typically seeks to identify the
underlying cause of the damage, which then
becomes the target for treatment methods. Some
neuropathies resolve (go away) with appropriate
treatment, though often there is some residual
damage as the nerves are delicate and the body
cannot replace neurons that die.
Because pain is a common symptom of neu-
ropathy, treatment often includes medications
such as analgesics, tricyclic antidepressants, cer-
tain antiseizure medications, injected anesthetics
and corticosteroids, and topical anesthetics or
analgesics (lidocaine or capsaicin). Surgery may be
appropriate to relieve compression against a nerve
or to sever the nerve when other treatments fail
to relieve incapacitating pain. Noninvasive
approaches to pain management that are some-
times effective include BIOFEEDBACKand ACUPUNC-
TURE.
CONDITIONS THAT CAN CAUSE NEUROPATHYchronic CIRRHOSIS CYTOMEGALOVIRUS(CMV)
DIABETES EPSTEIN-BARR VIRUS
GENETIC DISORDERS GUILLAIN-BARRÉ SYNDROME
Hansen’s disease HEAVY-METAL POISONING
HIV/AIDS HYPOTHYROIDISM
long-term ALCOHOLISM LYME DISEASE
MULTIPLE SCLEROSIS NEUROFIBROMATOSIS
PERIPHERAL VASCULAR DISEASE(PVD)RAYNAUD’S SYNDROME
RENAL FAILURE REPETITIVEmotion INJURIES
SCIATICA shingles
SYSTEMIC LUPUS ERYTHEMATOSUS(SLE) traumatic injury
VASCULITIS vitamin B 12 deficiency
See also ALTERNATIVE METHODS FOR PAIN RELIEF;
CRANIAL NERVES; NEURALGIA; NEURITIS; RETROBULBAR
NEURITIS; RHIZOTOMY; SPINAL NERVES.neuroreceptor A molecular structure on the
surface of a cell membrane that accepts (binds
with) a NEUROTRANSMITTER(chemical messenger).
Nearly always a neuroreceptor is specific for only
one neurotransmitter. The common analogy is
that a neuroreceptor functions like a lock and a
neurotransmitter functions like a key; only the
correct key can open the lock. Neuroreceptors
tend to align along the cell membrane such that
they match across cells, facilitating communica-
tion between cells. Most cells contain numerous
and different neuroreceptors. Drugs may also bind
with neuroreceptors, causing an effect (partial or
complete) that emulates that of the matching neu-
rotransmitter (agonist) or that blocks the neurore-
ceptor from accepting the neurotransmitter
(antagonist). Some neuroreceptors have multiple
binding sites that accept different chemicals (such
as neurotransmitters, drugs, and ions).
For further discussion of neuroreceptors within
the context of the structures and functions of the
nervous system, please see the overview section
“The Nervous System.”
See also ADDICTION; PARKINSON’S DISEASE.neurotransmitter A chemical that facilitates the
passage of NERVEimpulses among neurons. A neu-
rotransmitter may allow or block the travel of a
nerve impulse. Neurons store the chemical com-
ponents of their neurotransmitters in microscopic
structures called the synaptic vesicles, synthesizing
the appropriate neurotransmitter when conduct-
ing a nerve impulse. The sending NEURON’s axon
releases the neurotransmitter into the synapse
(space between neurons). The neurotransmitter
crosses the synapse to bind with the appropriate
NEURORECEPTORon the dendrites of the receivingNEUROTRANSMITTERS
acetylcholine aspartate
DOPAMINE EPINEPHRINE
gamma-aminobutyric acid (GABA) glutamate
monoamine oxidase (MAO) NOREPINEPHRINE
serotoninneurotransmitter 271