neural tube defect Congenital defect of the brain or spinal cord from abnormal growth of their precursor, the neural tube (see embryology), usu-
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1348 I neuralgia ► Neuschwanstein Castle
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ally with spine or skull defects. The tube may fail to close properly, have parts missing, or have a blockage (see hydrocephalus). In spina bifida, ver¬ tebrae are open over the back of the spinal cord, usually at the base. This may not affect function if no further defects (local absence of skin or meninges, protrusion of tissue, defect opening into the spinal cord) exist. The more serious forms can cause paralysis and impair bladder and bowel function. In encephalocele, a meningeal sac containing brain tissue pro¬ trudes from the skull. The effects depend on the amount of tissue involved. Adequate folic-acid intake by women of childbearing age reduces the risk of neural tube defects. Early surgery can prevent or minimize disability.
neuralgia \nyu-'ral-jo\ Pain of unknown cause in the area covered by a peripheral sensory nerve. In trigeminal neuralgia (tic douloureux), brief attacks of severe shooting pain along a branch of the trigeminal nerve (in front of the ear) usually begin after middle age, more often in women. Initially weeks or months apart, they become more frequent and easily triggered by touching the affected area, talking, eating, or cold. Analge¬ sics help, but permanent cure requires surgery. Glossopharyngeal neural¬ gia causes recurring severe pain, most often in men over 40. Excruciating pains begin in the throat and radiate to the ears or down the neck, with or without a trigger (e.g., sneezing, yawning, chewing). Usually separated by long intervals, attacks subside before analgesics take effect. Surgery may help in extreme cases. See also neuritis.
Neurath Vnoi-ratA, Konstantin, baron von (b. Feb. 2, 1873, Klein-Glattbach, Ger.—d. Aug. 14, 1956, Enzweihingen, W.Ger.) German diplomat. He entered the diplomatic service in 1903 and served as min¬ ister to Denmark (1919-22), ambassador to Italy (1922-30), and ambas¬ sador to Britain (1930-32). As Germany’s foreign minister (1932-38), he lent respectability to Adolf Hitler’s expansionist foreign policy. As “pro¬ tector” of Bohemia and Moravia (1939—41), he was accused of being too lenient and was replaced by Reinhard Heydrich. After World War II, he was tried and imprisoned for war crimes (1946-54).
neuritis \nyu-'ri-tos\ Inflammation of one or several nerves. The cause may be mechanical, vascular, allergic, toxic, metabolic, or viral. Symptoms—tingling, burning, or stabbing pains with sensory nerves and anything from muscle weakness to paralysis with motor nerves—are usu¬ ally confined to the part of the body served by the inflamed nerve. In Bell palsy, facial nerve inflammation causes a characteristic facial muscle dis¬ tortion. Analgesics can relieve the pain. Once the underlying cause is treated, recovery is usually rapid but may be incomplete in severe cases, with residual motor and sensory disturbances. See also neuralgia.
neurology Medical specialty concerned with nervous system function and disorders. Clinical neurology began in the mid-19th century, when mapping of the functional areas of the brain first began and understand¬ ing of the causes of conditions such as epilepsy improved. The develop¬ ment of electroencephalography in the 1920s aided in the diagnosis of neurological disease, as did the development of computed axial tomogra¬ phy in the 1970s and nuclear magnetic resonance imaging in the 1980s. In addition to dealing with physical disorders (e.g., tumours, trauma), neu¬ rology is unique among medical specialties in its intersection with psy¬ chiatry. Greater understanding of the brain chemistry of disorders such as schizophrenia and depression has led to a wide array of effective drugs that nevertheless work best in conjunction with psychotherapy. Side effects of drug or surgical therapy can be serious, and many nervous system disor¬ ders have no effective treatment.
neuron or nerve cell Any of the cells of the nervous system. Sensory neurons relay information from sense organs, motor neurons carry impulses to muscles and glands, and intemeurons transmit impulses between sensory and motor neurons. A typical neuron consists of den¬ drites (fibres that receive stimuli and conduct them inward), a cell body (a nucleated body that receives input from dendrites), and an axon (a fibre that conducts the nerve impulse from the cell body outward to the axon terminals). Both axons and dendrites may be referred to as nerve fibres. Impulses are relayed by neurotransmitter chemicals released by the axon terminals across the synapses (junctions between neurons or between a neuron and an effector cell, such as a muscle cell) or, in some cases, pass directly from one neuron to the next. Large axons are insulated by a mye¬ lin sheath formed by fatty cells called Schwann cells. Bundles of fibres from neurons held together by connective tissue form nerves. See illustra¬ tion opposite.
neuropathy \nu-'ra-po-the\ Disorder of the peripheral nervous system. It may be genetic or acquired, progress quickly or slowly, involve motor,
sensory, and/or autonomic (see autonomic nervous system) nerves, and affect only certain nerves or all of them. It can cause pain or loss of sen¬ sation, weakness, paralysis, loss of REFLEXes, muscle atrophy, or, in auto¬ nomic neuropathies, disturbances of blood pressure, heart rate, or bladder and bowel control; impotence; and inability to focus the eyes. Some types damage the neuron itself, others the myelin sheath that insulates it. Examples include carpal tunnel syndrome, amyotrophic lateral sclerosis, poliomyelitis, and shingles. Causes include diseases (e.g., diabetes melutus, leprosy, syphilis), injury, toxins, and vitamin deficiency (e.g., beriberi). See also neuralgia; neuritis.
neuropsychology Science concerned with the integration of psycho¬ logical observations on behaviour with neurological observations on the central nervous system (CNS), including the brain. The field emerged through the work of Paul Broca and Carl Wernicke (1848-1905), both of whom identified sites on the cerebral cortex involved in the production or comprehension of language. Great strides have since been made in describing neuroanatomical systems and their relation to higher mental processes. The related field of neuropsychiatry addresses itself to disor¬ ders such as aphasia, Korsakoff syndrome, Tourette syndrome, and other CNS abnormalities. See also laterality.
neurosis Mental and emotional disorder that affects only part of the per¬ sonality, is accompanied by a less distorted perception of reality than in a psychosis, and is characterized by various physiological and mental dis¬ turbances (such as visceral symptoms and impaired concentration). The neuroses include anxiety attacks, certain forms of depression, hypochondri¬ asis, hysterical reactions, obsessive-compulsive disorders, phobias, various sexual dysfunctions, and some tics. They have traditionally been thought to be based on emotional conflict in which a blocked impulse seeks expression in a disguised response or symptom. Behavioral psychologists regard them as learned, inappropriate responses to stress, which can be unlearned.