Diencephalon Health Dictionary

A part of the diencephalon of the brain, it is a major actor in the limbic system. This is a functional, not anatomic, system in the brain that influences and is influenced by emotions. Call the limbic system an ad hoc committee that decides how things are going today, based on past, present, potential, and myriad informational inputs from the somatic body. The hypothalamus gathers the data and sets the levels of the pituitary thermostat. The pituitary does what the hypothalamus tells it to do, and our whole chemical nervous system responds to the pituitary, which responds to the hypothalamus, which, along with the rest of the limbic system, decides the kind of day we need to get ready for. And to think that some doctors used to (and still) scoff at a “psychosomatic disorder.”... hypothalamus

n. the enlarged and highly developed mass of nervous tissue that forms the upper end of the *central nervous system (see illustration). 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, and *cerebellum; the *midbrain (mesencephalon); and the forebrain (prosencephalon), subdivided into the *cerebrum and the *diencephalon (including the *thalamus and *hypothalamus). The brain is usually considered to be the site of the working of the mind, but to what extent the concepts of ‘brain’ and ‘mind’ are interchangeable is a matter of debate and of concern to anyone facing brain surgery. Anatomical name: encephalon.... brain

(telencephalon) n. the largest and most highly developed part of the brain, composed of the two cerebral hemispheres, separated from each other by the longitudinal fissure in the midline (see illustration). Each hemisphere has an outer layer of grey matter, the *cerebral cortex, below which lies white matter containing the *basal ganglia. Connecting the two hemispheres at the bottom of the longitudinal fissure is the corpus callosum, a massive bundle of nerve fibres. Within each hemisphere is a crescent-shaped fluid-filled cavity (lateral *ventricle), connected to the central third ventricle in the *diencephalon. The cerebrum is responsible for the initiation and coordination of all voluntary activity in the body and for governing the functioning of lower parts of the nervous system. The cortex is the seat of all intelligent behaviour. —cerebral adj.... cerebrum

n. the furthest forward division of the *brain, consisting of the *diencephalon and the two cerebral hemispheres.... forebrain