Dictionary

bronchiole The tiny branch of air tubes within the lungs that is a continuation of the bronchus. The bronchioles connect to the alveoli (air sacs).

brain malleability See brain plasticity.

brain plasticity The phenomenon of change and learning in the adult brain. Also known as brain malleability.

brain stem The stem-like part of the base of the brain that is connected to the spinal cord. The brain stem controls the flow of messages between the brain and the rest of the body, and it also controls basic body functions such as breathing, swallowing, heart rate, blood pressure, consciousness, and whether one is…

brain stem glioma A type of brain tumor that involves the glial cells.

brain tumor A benign or malignant growth in the brain. Primary brain tumors initially form in brain tissue. Secondary brain tumors are cancers that have spread (metastasized) to the brain tissue from tissue elsewhere in the body. Brain tumors can occur in people of any age.

brain ventricle One of the communicating cavities within the brain. There are four ventricles: two lateral ventricles, the third ventricle, and the fourth ventricle. The lateral ventricles are in the cerebral hemispheres. Each lateral ventricle consists of a triangular central body and four horns. The lateral ventricles communicate with the third ventricle through the interventricular…

branchial cleft cyst A cavity that is a remnant from embryologic development and is still present at birth in one side of the neck, just in front of the large angulated muscle on either side (the sternocleidomastoid muscle). The cyst may not be recognized until adolescence, when it enlarges its oval shape. Sometimes a branchial…

branchial cyst See branchial cleft cyst.

Braxton Hicks contraction An irregular contraction of the womb (uterus) that occurs toward the middle of a woman’s first pregnancy and earlier, and more intensely, in her subsequent pregnancies. Braxton Hicks contractions tend to occur during physical activity. The uterus tightens for 30 to 60 seconds, beginning at the top of the uterus, and the…

BRCA1 A tumor suppressor gene that normally acts to restrain the growth of cells. Mutated forms of BRCA1 and BRCA2 are responsible for about half the cases of inherited breast cancer, especially those that occur in relatively young women. From the words breast and cancer. See also breast cancer susceptibility gene.

BRCA2 A tumor suppressor gene that normally acts to restrain the growth of cells. Mutations of BRCA2, like those of BRCA1, are responsible mainly for hereditary breast cancer. They seldom appear to be involved in sporadic, noninherited breast cancer—the 95 percent of breast cancer that does not run in families. Both BRCA1 and BRCA2 are…