Glossary

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G

GABA:

Gamma-aminobutyric acid, a brain chemical that causes sedation. Medicines such as Valium act on receptors for GABA to induce relaxation. GABA also refers to the receptors themselves.

Gait:

The style or manner of walking. Gait disturbances may be associated with certain neurologic or neuromuscular disorders, orthopedic conditions, inflammatory conditions of the joints (i.e., arthritic changes), or other abnormalities.

Gait apraxia:

Loss of the ability to consciously sequence and execute the movements required to coordinate walking. Gait apraxia may result in unsteady walking patterns; "toe-walking"; a widely based, jerky gait; and balance difficulties.

Gamma-aminobutyric acid (GABA):

An amino acid neurotransmitter that inhibits or decreases the electrical activities of nerve cells. GABA is the primary inhibitory neurotransmitter in the brain.

Gamma Knife Radiosurgery:

A highly specialized technique using a device that produces ionizing radiation to produce a lesion in the target tissue. This device focuses a beam of high intensity irradiation to a targeted area and is used as localized therapy to treat individuals with certain brain diseases (e.g., brain tumors, certain movement disorders, etc.).

Ganglion:

A cluster of nerve cells.

Gastroesophageal reflux:

Backflow of stomach contents into the esophagus. This condition may be chronic and cause weakness of the lower esophageal sphincter, the ring-shaped muscle located at the junction of the esophagus and stomach.

Gastrointestinal:

Gastrointestinal refers to the stomach and small and large intestines, as well as to the mouth, esophagus, anus, and related organs.

Gastrostomy:

The introduction of a feeding tube directly into the stomach through a small opening, for persons who have difficulty chewing, or are unable to chew or swallow.

Gastrostomy Tube:

A plastic tube inserted into the stomach through a surgical incision in the abdomen. A gastrostomy tube is used to deliver liquified food to the digestive system when swallowing becomes dangerous or difficult.

Gene:

The smallest units of heredity. The information from all the genes, taken together, makes up the blueprint or plan for the human body and its functions. A gene is a short segment of DNA, which is interpreted by the body as a plan or template for building a specific protein.

Genetic anticipation:

A phenomenon in which the onset of symptoms of a hereditary disease appears to occur at a progressively earlier age in successive generations. Genetic anticipation has been demonstrated in a number of hereditary disorders (such as Huntington's disease, dentatorubropallidoluysian atrophy, etc.) in which the gene mutation consists of abnormally long sequences or "repeats" of particular coded instructions (e.g., unstable expansion of CAG repeats). With other disorders in which genetic anticipation has previously been suggested (e.g., essential tremor), studies have indicated that increased awareness of the condition in affected families may be responsible for earlier recognition of symptom onset.

Genetic heterogeneity:

Manifestation of similar or the same observable characteristics or traits (i.e., phenotype) resulting from different genetic mechanisms, such as changes (mutations) of different genes or a combination of genes.

Germline mosaicism:

The presence of a gene mutation for a disease trait in some yet not all of an individual's sexual reproductive cells (germ cells) within the ovaries or testes (gonads). Germline mosaicism is sometimes suspected when parents have more than one child with a genetic disorder transmitted as a dominant trait yet neither parent appears to be affected by the condition.

Gland:

A structure or organ that makes a substance, such as a hormone or chemical, that is used elsewhere in the body. Some of these hormones and chemicals are insulin, bile, growth hormone, estrogen, and testosterone.

Glaucoma:

A sustained increase of pressure within the eyeball which can injure the optic nerve and cause impaired vision or blindness. Treatment with anticholinergics may exacerbate glaucoma.

Gliosis:

A proliferation of astrocytes in damaged areas of the central nervous system (CNS). Astrocytes are relatively large glial cells, which are the connective tissue cells of the CNS. Astrocytes have various functions, including accumulating in areas where nerve cells (neurons) have been damaged. Gliosis and neuronal loss in certain brain regions are findings seen in various neurodegenerative disorders.

Globus pallidus:

A major substructure of the basal ganglia deep within the brain. Specialized groups of nerve cells in the globus pallidus function as an "intermediate relay system." This system processes and transmits information from the basal ganglia by way of the thalamus to areas of the brain that regulate complex motor functions (e.g., motor cortex, premotor area of frontal lobe).

Glottis:

The slit-like opening between the vocal cords; the region of the voice box (larynx) consisting of the vocal cords and the opening between them.

Glucocorticoid:

Any steroidlike compound capable of significantly influencing some aspects of metabolism, such as the promotion of glycogen deposition in the liver, and having anti-inflammatory effeats. Cortisol is the most potent of the naturally occurring glucocorticoids, but some synthetic derivatives, such as prednisone, are more potent.

Glucose:

(1) A sugar found in foods, and the product of the digestion of starches. It is the primary compound metabolized for energy in the brain. (2) Blood sugar the body uses as a primary source of energy, and the end product of carbohydrate metabolism. Fluctuating levels of glucose can affect mood states and fat metabolism, and act as key triggers in the development of diabetes.

Glutamate:

An amino acid that is a primary excitatory neurotransmitter in the central nervous system. This chemical agent plays an essential role in initiating and transmitting nerve impulses, crossing synapses to stimulate postsynaptic neurons.

Glycerol:

A three-carbon substance that forms the backbone ot fatty acids in fats.

Gonad:

A testicle or ovary.

Gram staining:

A method used to classify bacteria. In the first step of the process bacteria are stained with gentian violet and then treated with Gram solution (named after Dr. Gram, the inventor of the technique). After the bacteria have been decolorized with alcohol and treated with safranine, a red organic dye, and washed in water, those bacteria that keep the gentian violet are gram-positive and those that do not are gram-negative.

Gray Matter:

(1)The darker-colored tissues of the central nervous system; in the brain, the gray matter includes the cerebral cortex, the thalamus, the basal ganglia, and the outer layers of the cerebellum. (2)Nerve tissue that primarily consists of nerve cell bodies, dendrites, and unmyelinated axons, thus having a gray appearance. In contrast, white matter predominantly contains myelinated nerve fibers.

Grievance:

A complaint filed with your Medicare health plan about the care you are receiving. For example, you may file a grievance if you are dissatisfied with the condition of a health care facility or if you have a complaint about staff behavior or the facility’s operating hours. An appeal, not a grievance, is the appropriate way to complain about a denial of care or coverage.

Growth Hormone:

Hormone produced by the pituitary gland that stimulates growth and development of muscle tissue, energy production, sexual function, skin resilience, bone density, and other important functions. A decline in growth hormone levels often accompanies the degenerative process associated with aging.

Guillain-Barré Syndrome:

A disorder in which the body's immune system attacks part of the nervous system.

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Document last modified:04/22/09 12:19:31 PM