Brain

That portion of the central nervous system that is located within the skull. It functions as a primary receiver, organizer and distributor of information for the body. It has two (right and left) halves called "hemispheres."

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

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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

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n.

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.

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(brān) [A.S. braegen] that part of the central nervous system contained within the cranium, comprising the prosencephalon (forebrain: telencephalon plus diencephalon), mesencephalon (midbrain), and rhombencephalon (hindbrain: metencephalon plus myelencephalon). It is derived (developed) from the anterior part of the embryonic neural tube. Functions include muscle control and coordination, sensory reception and integration, speech production, memory storage, and the elaboration of thought and emotion. Called also encephalon [TA]. See Plates 9 and 10 and see also cerebrum.

PLATE 9 VARIOUS ASPECTS OF THE BRAIN AND SPINAL CORD

PLATE 10 HEMISECTION OF THE HEAD AND NECK, SHOWING VARIOUS PARTS OF THE BRAIN IN RELATION TO OTHER STRUCTURES