Glossary
G
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.
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.
Gait apraxia:
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.).
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.
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.
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:
Genes are 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.
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.
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.
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.
Gram staining:
Gram staining is 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:
: 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.