{nasal cavity}{}{Space within nose.}

{negative feedback system}{}{Mechanism activated by an imbalance that corrects the imbalance.}

{nephron}{}{Functional unit of kidney, consisting of a renal corpuscle and a renal tubule.}

{nerve}{}{Bundle of nerve fibers.}

{nervous tissue}{}{Neurons and neuroglia.}

{neural plate}{}{Group of embryonic cells that will become the neural tube.}

{neural tube}{}{Forms the dorsal hollow nervous system characteristic of chordates.}

{neuroglia}{}{Cells in the nervous system other than the neurons; includes astrocytes, ependymal cells, microglia, oligodendrocytes, satellite cells, and Schwann cells.}

{neurohypophysis}{}{Portion of the hypophysis derived from the brain; commonly called the posterior pituitary. Major secretions include antidiuretic hormone and oxytocin.}

{neuromodulator}{}{Substance that influences the sensitivity of neurons to neurotransmitters but neither strongly stimulates nor strongly inhibits neurons by itself.}

{neuromuscular junction}{}{Specialized synapse between a motor neuron and a muscle fiber.}

{neuron}{}{Morphologic and functional unit of the nervous system, consisting of the nerve cell body, the dendrites, and the axon.}

{neurotransmitter}{}{Any specific chemical agent released by a presynaptic cell on excitation that crosses the synaptic cleft and stimulates or inhibits the postsynaptic cell.}

{neurulation}{}{The formation of the neural tube from neural plate cells.}

{neutron}{}{Electrically neutral particle in the nuclei of atoms [except hydrogen].}

{nose}{}{Anterior-most portion of the respiratory system; is the site of olfaction.}

{notochord}{}{Flexible rodlike structure characteristic of chordates; is used for stability.}

{nuclear envelope}{}{Double membrane structure surrounding and enclosing the nucleus.}

{nucleic acid}{}{Polymer of nucleotides, consisting of DNA and RNA; forms a family of substances that comprise the genetic material of cells and control protein synthesis.}

{nucleolus [nucleoli]}{}{Somewhat rounded, dense, well-defined nuclear body with no surrounding membrane; contains ribosomal RNA and protein.}

{nucleotide}{}{Basic building block of nucleic acids consisting of a sugar [either ribose or deoxyribose] and one of several types of organic bases.}

{nucleus [nuclei]}{}{Cell organelle containing most of the genetic material of the cell; collection of nerve cell bodies within the central nervous system; center of an atom consisting of protons and neutrons.}