Akademik

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Walter Russell, Lord, English physician, 1895–1966. See B. reflex.

brain 'brān n

1) the portion of the vertebrate central nervous system enclosed in the skull and continuous with the spinal cord through the foramen magnum that is composed of neurons and supporting and nutritive structures (as glia) and that integrates sensory information from inside and outside the body in controlling autonomic function (as heartbeat and respiration), in coordinating and directing correlated motor responses, and in the process of learning see forebrain, hindbrain, midbrain

2) a nervous center in invertebrates comparable in position and function to the vertebrate brain

the enlarged and highly developed mass of nervous tissue that forms the upper end of the central nervous system. The average adult human brain weighs about 1400 g (approximately 2% of total body weight) and is continuous below with the spinal cord. It is invested by three connective tissue membranes, the meninges, and floats in cerebrospinal fluid within the rigid casing formed by the bones of the skull. The brain is divided into the hindbrain (rhombencephalon), consisting of the medulla oblongata, pons Varolii, and cerebellum; the midbrain (mesencephalon); and the forebrain (prosencephalon), subdivided into the cerebrum and the diencephalon (including the thalamus and hypothalamus). Anatomical name: encephalon.