Nucleus Health Dictionary

The central core, structure, or focal point of an object.

The nucleus of a living cell is a roughly spherical unit at the centre of the cell. It contains the chromosomes (composed mainly of nucleic acid), which are responsible for directing the cell’s activities, and is surrounded by a membrane. The membrane has small pores through which various substances can pass between the nucleus and the cytoplasm, a thick fluid that forms the bulk of the cell. Usually, the nucleus has 1 nucleolus, a smaller dense region with no membrane that is concerned with protein manufacture.

A nerve nucleus is a group of neurons (nerve cells) within the brain and spinal cord that work together to perform a particular function.

The nucleus of an atom, composed of protons and neutrons, accounts for almost the total mass of the atom but only a tiny proportion of its volume. Nuclear energy is produced through changes in atomic nuclei.

The central body in a cell, which controls the activities of the latter. (See CELLS.)

n. 1. the part of a *cell that contains the genetic material, *DNA. The DNA, which is combined with protein, is normally dispersed throughout the nucleus as *chromatin. During cell division the chromatin becomes visible as *chromosomes. The nucleus also contains *RNA, most of which is located in the *nucleolus. The nucleus is separated from the cytoplasm by a double membrane, the nuclear envelope. 2. an anatomically and functionally distinct mass of nerve cells within the brain or spinal cord. 3. the central part of the lens of the eye, which is harder than the outer cortex.