Necrosis The death of a cell caused by a progressive failure of essential metabolic and structural cell components, usually in the cytoplasm.  Necrosis generally involves a group of contiguous cells or occurs at the tissue level. Neoplasia A new growth of tissue with abnormal and unregulated cellular proliferation.  There are two types of neoplasia, benign and malignant.  Same as a tumor. Neoplastic Conversion The second major step in the carcinogenesis process in which specific agents (referred to as promoters) enhance the further development of the initiated cells. Nervous System The organ system that coordinates activities of other organ systems and responds to sensations.  It is composed of the central nervous system and peripheral nervous system. Nervous Tissue One of the four body tissues that is specialized so as to be capable to conduct electrical impulses and convey information from one area of the body to another.  Most of the nervous tissue (98%) is located in the central nervous system, the brain, and spinal cord. Neural Synapse The junction between the axon of one neuron and the dendrite of another neuron or an axon and a connection with a muscle cell (neuromuscular junction). Neuroglia Cells of the nervous system that provide physical support for the nervous tissue, control tissue fluids around the neurons, and help defend the neurons from invading organisms and xenobiotics.  Same as glial cells. Neurons The functional nerve cells directly responsible for transmission of information to and from the CNS to other areas of the body. Neurotoxin A chemical that damages an area of function of the nervous system. Neurotransmitters These are chemicals that move information across a synapse by diffusing across the synaptic junction, binding to receptors on the postsynaptic membrane, and stimulating generation of an action potential. Nicotine A neurotoxin that binds to certain cholinergic receptors thus preventing normal neural function and stimulation. Norepinepharine A chemical neurotransmitter of adrenergic nerves of both the central and peripheral nervous systems. It is also produced by the adrenal medulla in response to stimulation.  It is the same as noradrenaline. Nucleic acids These are large organic compounds inside virtually all body cells (RBCs is an exception) that store and process information at the molecular level. Nucleolus This is a dense region of the nucleus, which contains the RNA and DNA.  It is the site for rRNA synthesis and assembly of the ribosome components. Nucleus A membrane-bound part of a cell that contains nucleotides, enzymes, and nucleoproteins.  The nucleus controls metabolism, protein synthesis, and the storage and processing of genetic information.