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nucleus of Darkschewitsch

(dark-she′vich) [Liverij Osipovich Darkschewitsch, Russian neurologist, 1858–1925] A midbrain nucleus in the ventrolateral periaqueductal gray matter, dorsal to the interstitial nucleus of Cajal and rostral to the oculomotor nucleus. This nucleus is one of the accessory oculomotor (preoculomotor) nuclei, which are composed of interneurons concerned with eye movements and reflex gaze coordination and which receive axons from the medial longitudinal fasciculus.

nucleus-to-cytoplasm ratio, nuclear-to-cytoplasmic

ratio The proportion of a nucleated blood cell occupied by the nucleus. In white blood cells, the larger the nucleus (relative to the cytoplasm), the more immature the cell.


(nū′klīd) An atomic nucleus identified by its atomic number, mass, and energy state.


[L. nudus, naked] 1. Bare; naked; unclothed. 2. An unclothed body.

nude mouse

SEE: under mouse.


1. In psychiatry, a morbid desire to remove clothing. 2. The practice of living without clothing.


necrotizing ulcerative gingivitis.


Anything that causes inconvenience, annoyance, or disturbance of normal physiology.

null hypothesis

The assumption that the observed difference between two groups of subjects in a research study results from chance and not from the intervention that is being studied.


(nŭl″ĭ-grăv′ĭ-dă) A woman who has never conceived a child.


(nŭl-ĭp′ă-ră) [L. nullus, none, + parere, to bear] A woman who has never produced a viable offspring.


(nŭl″ĭ-păr′ĭ-tē) The condition of not having given birth to a child.

null responder, nullresponder



(nŭm) 1. Insensible; lacking in feeling. 2. Deadened or lacking in the power to move.

numb chin syndrome

Loss of sensation in the area from the lower lip to the chin, caused by a lesion of the third division of the trigeminal nerve (fifth cranial nerve).


(nŭm′bĕr) [L. numerus, number] 1. A total of units. 2. A symbol graphically representing an arithmetical sum.

atomic mass n. A number equal to the sum of all the neutrons and the protons in an atom’s nucleus. SEE: mass n.

atomic n. SYMB: Z. The number of negatively charged electrons in an uncharged atom, or the number of protons in the nucleus. This number determines the position of elements in the periodic table of elements. It is used to describe isotopes of an element, ...

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