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Glossary - N




"n" neuron




Two sensory neurons with ciliated endings in the head with elliptical closed processes near the cilium. The endings have no associated sheath and socket cells and are not directly attached to the hypodermis. The cell bodies are situated anterior to the nerve ring and send processes to the head.


Most studies of C. elegans use this reference strain isolated originally in Bristol, U.K. For more details on the population genetics of C. elegans see Barriere and Felix, 2005.

See Bergerac
See Bristol


The region bordering the head and the midbody in which bodywall muscle are dually innervated at both the nerve ring and at the ventral nerve cord. This portion of the body shows more flexible searching motions that depart from a strictly dorsal/ ventral orientation.

Necromenic Necromeny

A special version of commensal lifestyle where dauer stage animals associate with a live host, such as an insect or beetle, but do not harm it.  When the host dies, the necromenic nematode advances to adulthood while feeding on the corpse of the host (Baird, 1999; Hong and Sommer, 2006; Kiontke and Sudhaus, 2006).

See Commensal
See Phoretic


A common form of cell death caused by external insults to cellular integrity; in some cases, necrosis may spread from cell to cell to damage many neighboring cells. Necrotic cells show early swelling in cytoplasmic organelles and the nucleus, lytic activity in the cytoplasm, and late changes in chromatin, while the cell gradually swells in volume before dying (Hengartner, 1997).

Necrotic-like cell death in C. elegans has been carefully characterized in neurons undergoing degenerin-induced cell death (Hall et al., 1997).

See Apoptosis
See Phagocytosis


A characteristic, specialized pattern of fasciculation among neurites (generated during process outgrowth) that causes individual neurites to be surrounded by a standard set of neighbors along a nerve cord or within neuropil; the pattern surrounding any particular nerve process is called its “neighborhood” (White et al., 1983).

Nematicide Nematocide (S)  

Any agent that will destroy nematodes, especially those species that parasitize plants. This term is commonly used for any agent used to kill nematodes for agricultural purposes.

See Anthelminthic

Nematode Roundworm (S)
Worm (S)
Nema (S)

Any member of the phylum Nematoda, including the pinworm, hookworm and Trichinella; all of these are characterized as “roundworms”. C. elegans is a member of this phylum (De Ley, 2006).

Nerve Process bundle (S)
Nerve cord (S)
Nerve bundles (S)

A bundle of thin neuronal processes running in parallel, connecting different ganglia, sensory endings, synaptic neuropil, and/or regions of motor output. In the nematode there are generally no glial-like wrappings (no myelin) associated with a nerve, but virtually all nerves in the bodywall are closely associated with hypodermis and the hypodermal basal lamina. Nerves in the pharynx seem to run independent of any epithelia, often lying within a groove established by the muscles. Most major nerves in the nematode run longitudinally and are interconnected via circumferential commissures.

Named nerves:
Amphid (2) = Chemosensory
Dorsal cord
Labial (6) = Mechanosensory
Dorsal (pharynx)
Lateral (2)
Lumbar-preanal (2) [runs as a pair of commissures]
Pharyngeal (3) = Dorsal and Subventral (2)
Phasmid (2)
Ventral Cord (2)

See Fascicle

Nerve cord Nerve Chord (S)  

An organized bundle of nerve processes. The dorsal and ventral nerve cords run the length of the worm from head to tail.

See Cord/ Chord
See Dorsal Cord
See Nerve
See Ventral Cord

Nerve fiber Neurite (S)  

Part of a nerve cord. An individual neuronal process lying within a nerve; thus an axon, dendrite or neurite with mixed function. Can also refer to a neuronal process running independently away from an organized nerve cord.

Nerve ring  

The major zone of overlap, among approximately 200 overlapping axons in the head, which encircles the isthmus of the pharynx to form a tightly packed ring-like structure on the outside of the pharynx. The nerve ring lies directly over a cylindrical muscle plate formed by arms from the head muscles. The nerve ring is the most concentrated zone of synaptic interconnections among the neurons of the head, and most head neurons lie very close by, such that the nerve ring and its associated neurons could be considered one huge ganglion, acting as “the brain” of the nematode.

A much smaller ring of axons lies within the pharynx, formed by neurites extended from many pharyngeal neurons. Head neurons form almost no synapses away from the nerve ring or the longitudinal motor nerves.

See Pharyngeal nerve ring

Nervous system Neurons (S)
Nervous tissue (S)

The nervous system of C. elegans is formed from 302 neurons, each of which has unique properties, morphologies and connectivities. While C. elegans does not have a "brain" per se, most of the nervous system is situated in the head region which is where most of the sensing by the animal occurs. For more details see Hobert, 2005.

See Nerve ring

Neural plasticity    

Functional changes in the nervous system ranging from changes at the synapses during development (Jorgensen and Rankin, 1997; Hobert, 2005) to changes in behavior of the adult animal (Jorgensen and Rankin, 1997). Behavioral assays have been developed to test for neural plasticity by chemotaxis (Jensen, 2005 and Mori, 2005 in Hart, 2006).

Neurite Axon or dendrite (S)
Process or branch or Commissure (S)
Nerve fiber (S)

This term is often used preferentially to “dendrite” or “axon” to refer to neuronal processes with mixed functions (e.g. having some sensory role and also an important role in synaptic interactions), or to an unspecialized neuronal process which has not yet developed a specific function.

Neuroblast Blast cell (S)
Epidermoblast (S)

Precursor, or stem cell, to neurons. In C. elegans there are few true neuroblasts since most neuronal lineages are not pure; their precursors yield mixtures of neurons, structural cells and hypodermis.

Neurocratic control of locomotion  

A theory of behavioral control of nematode locomotion in which the primary role of the nervous system is to switch between alternate waveforms, where each waveform is chiefly generated by a “myogenic” control mechanism (Crofton, 1971; Croll, 1975), inherent to muscle-muscle interconnections.

See Myogenic control of locomotion


Intermediate filament (S)

Any type of filamentous protein lying within the cytoplasm, e.g. any filamentous cytoskeletal component within a neuron soma or process, especially those whose biochemical nature is not immediately known. However, the term is most often used to refer to an intermediate filament.


The formation and development of neurons. C. elegans adults have 302 neurons. For discussions on the specification and patterning of the nervous system in C. elegans see Ruvkun, 1997 and Hobert, 2005.


Tissue that originates from the nervous system or that is competent to produce neuronal cells.

See Myogenic control of locomotion
See Neurocratic control of locomotion


Non-neuronal cells that provide support and nutrition to neurons. A large class of these in C. elegans are the support cells of the neuronal sensilla.

See Glial cell


A secreted substance from a neuron, perhaps from the active zone, or from a synaptic vesicle, which has a direct chemical action at a distance from the release site, further away than the closest postsynaptic processes. Such chemical action at a distance may influence other neurons, muscles, and perhaps other tissues.



A substance released by a neuron that influences other neurons, but is not classified as a neurotransmitter. For example, in C. elegans neuromodulators are thought to influence dauer formation (Riddle and Albert, 1997) and egg laying (Schafer, 2006).

See Neurotransmitter

Neuromuscular junction


Neuromuscular synapse (S)
Myoneural junction (S)


This is a form of chemical synapse that connects a presynaptic motor axon to one or more postsynaptic muscle arms. A typical animal has about 2000 neuromuscular junctions. In many cases a single NMJ is dyadic, with one presynaptic axon contacting two separate muscle arms simultaneously (as in nerve ring NMJs), or contacting a muscle arm and a neuron dendrite simultaneously (as at most NMJs of the ventral nerve cord and dorsal nerve cord). NMJs exhibit virtually all the same features as other chemical synapses in C. elegans. There is rarely any evidence for a postsynaptic specialization on the muscle arm membrane.


Nerve cell (S)


A specialized cell that communicates with other neurons and muscles via chemical and/or electrical synapses, or by releasing neurohormones to direct the behavior of the animal, but which has no motor function of its own. Typical neurons are small cells with long nerve processes; they have primary roles as sensory neurons, interneurons or motor neurons. In C. elegans, in rare instances, neurons may have a principal role in development, guiding neurite outgrowth or maintaining nerve positions, rather than passing along intercellular signals via vesicle release at synapses. Nematode neurons generally do not utilize action potentials, but instead send graded electrical potentials along their axons and dendrites between their input and output zones.


Specialized peptidergic neurotransmitters encoded as preproproteins that are posttranslationally processed to yield bioactive neuropeptides. They modulate synaptic signaling through other, small-molecule, neurotransmitters and exert their function via seven-span transmembrane receptors. Thirty-two neuropeptide-like proteins have been identified in C. elegans (Nathoo et al., 2001).

See Neurotransmitter

Neuropil/ Neuropile  

The network of neuronal processes (axonal and dendritic) together without the cell bodies of the neurons. In higher animals the main neuropil is the gray matter of the brain and spinal cord. For C. elegans, this is the nerve ring, where many neurons come together and synapses are formed (Ware et al., 1975).

Neurosecretory ending

Neurohumoral transmission (S)

Synaptic ending without a clear postsynaptic target, suggesting that vesicle contents may diffuse via pseudocoelom to a distant target cell or tissue (e.g. NSM).


A chemical compound, packaged inside of a membrane-bound “synaptic vesicle” in the cytoplasm of a neuron. The neurotransmitter is released from the vesicle at a chemical synapse via exocytosis, where the vesicle fuses to the presynaptic membrane at the active zone.  As the vesicle fuses, neurotransmitter is released into the synaptic cleft to signal one or more neighboring cells, usually other neurons or muscles. Specific neurotransmitters of C. elegans have been identified.

See Neuropeptide
See Receptor


A stage of development of the early embryo in which neurulation occurs. The comma stage is a landmark for the end of this stage of development (Wadsworth and Hedgecock, 1996).




The earliest stage in the development of the nematode nervous system, occurring between 230-340 min of embryogenesis, when epidermal blast cells ingress into the developing gastrula and divide to produce neuroblasts, which in turn begin to establish the early architecture of the nervous system by forming organized groups of cell bodies within the bodywall (Wadsworth and Hedgecock, 1992, 1996).


Nematode growth medium

A defined chemical medium which has proven to be adequate to produce a healthy culture of C. elegans when seeded with an E. coli OP50 lawn of bacteria and is typically poured into petri plates using a peristaltic pump. To reduce the grown of unwanted bacteria and fungi, drugs such as streptomycin or nystatin can be added to the solution before being poured (Stiernagle, 2006).

Nictation Waving (S)

A behavior seen in dauer larva in which they crawl up upon the substrate, such as a mold filament or a grass blade, and wave back and forth while standing on their tail, in search of a new arthropod host (Croll and Matthews, 1977; Kiontke and Sudhaus, 2006).

See Necromenic
See Phoretic
See Waving

NMJ Neuromuscular junction (S)

Nocioceptor/ Nocioceptive/ Nociception

A sensory receptor which is stimulated by painful stimuli. Whether the nematode can sense pain is difficult to ascertain, but certain sensory endings (ASH, PVD) in C. elegans have been ascribed to be homologous to nocioceptors because they are sensitive to a wide range of stimuli (Besson and Chaouch, 1987; Driscoll and Kaplan, 1997, Tobin and Bargmann, 2004 ).

Nomarski microscopy

DIC microscopy (S)

A form of high resolution interference optics (differential interference contrast, or DIC) that allows live nematodes to be observed at high magnification without staining, and to resolve individual cells and nuclei in thin optic sections (Allen, David and Nomarski, 1969).

See DIC microscopy

Normoxia/ Normoxic    

An environment containing the normal concentration of oxygen (21% O2).

See Anoxia
See Hypoxia

Nose Snout (S)  

The extreme anterior portion of the body

Nose touch

A behavioral response mediated by several neuronal sensilla in the head (ASH, OLQ, FLP) when the animal runs directly into a fine hair on the substrate; the response is to reverse direction and is often called “nose touch avoidance” (Kaplan and Horvitz, 1993; Hart et al., 1995; Hart, 2006).

See Mechanosensation


See Germ plasm


Cuticular nubbin (S)
CN (S)
Ciliary cap (S)


A very short lateral projection from the cilium of some sensory dendrites (CEP, OLL, OLQ, ADE) that embeds into the inner cuticle layer, presumably anchoring the cilium to the cuticle. The nubbin material is apparently an extracellular secretion from the cilium and is somewhat electron dense, but generally does not produce an external bump (papilla) on the surface of the animal. These sensory endings sometimes are open through the cuticle, but are more often closed (Perkins et al., 1986).

See Papilla

Nuclear envelope

Nuclear membrane (S)


Similar to that of vertebrates, the nuclear envelope of C. elegans has two concentric membranes (outer and inner) that enclose a lumenal space. Nuclear pore complexes mediate bidirectional transport between the nucleus and cytoplasm and a laminar network (Liu et al., 2000, Gruenbaum, 2002) provides support and for the proper segregation of the chromosomes (Oegema and Hyman, 2006). During mitosis, the nuclear envelope goes through a cycle of breakdown and reassembly.

See Lamin

Nuclear migration


Certain cell nuclei make characteristic movements during embryogenesis (at comma stage) or later during tissue morphogenesis. During embryonic closure, some hypodermal nuclei move within extended processes of the hypodermal cells to migrate from one side of the body to the other, crossing the dorsal midline. Similarly, in mid L1 stage, certain precursor nuclei (Pn cells) migrate from lateral positions to the ventral midline prior to dividing to produce neurons of the ventral nerve cord. It is most likely that nuclei may be actively moved via the internal cytoskeleton by motor proteins, or perhaps pushed passively by the squeezing actions of adjacent cells. Some mutants are known to block the normal progress of these migrations, including the lineage mutants unc-83,unc-84, and lin-3 (Sulston and Horvitz, 1981).

Nuclear pore  

Periodic, highly organized, channels (patent holes) in the nuclear membrane across which macromolecules including mRNAs and transcription factors can be transported between the nucleus and the cytoplasm. They are evenly spaced throughout the membrane and are most easily seen by freeze fracture.



A darkly staining part of the nucleus that is the site for the processing of rRNAs and their assembly into ribosomes.



The basic level of chromatin packing in which the DNA is wrapped around a protein core formed from histones. This gives a "beads on a string" look to the DNA. Each nucleosome core particle is separated from the next by a region of linker DNA. Nucleosomes are then usually packed together into compact stacks generating a condensed 30 nm fiber.


Membrane enclosed organelle which contains most of the cell's genetic material.

Nullo-X sperm    

A sperm cell that contains no copy of the normal X chromosome. Males produce equal numbers of haplo-X and nullo-X sperm so that half their progeny will also be male.

Nurse cells    

Germ cells in the somatic gonad are produced in excess numbers in comparison to the final yield of mature spermatocytes and oocytes, such that many individual germ cell nuclei undergo programmed cell death as they approach the loop of the gonad arm. Since all germ cells prior to this locale form a single syncytium, connected by a central rachis, it is postulated that the excess germ cells and especially their nuclei serve as nurse cells to those germ cells which do survive (Hengartner, 1997), synthesizing components which are delivered into the rachis to feed the surviving cells prior to their cellularization.


See Larva

Edited for the web by Laura A. Herndon. Last revision: January 27, 2010. This section should be cited as: Herndon, L.A. and Hall, D.H. 2010. Glossary N. In WormAtlas.  doi:10.3908/wormatlas.6.14