Systems whose behavior is not predictable over long periods of time, either from its initial conditions or from its history of inputs. The equations of motion for such a system include threshold values that when breached result in sudden discontinuous changes to qualitatively different states. See Bifurcation, Catastrophe theory, Chaos, Complex system, Complexity, Control …
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Non-core concepts
Concepts that appear later in development and are shaped by experience. See Core concepts, Experience
Non-dysjunction
Failure of a pair of homologous chromosomes to separate during after cell division. It occurs during the anaphase of meiosis. It can also occur during and after mitosis when sister chromatids fail to separate. Non-dysjunction can result when daughter cells have a relative abnormal number of chromosomes. The outcomes include, for example, Down’s syndrome and …
Non-Communicating Children’s Pain Checklist (NCCPC-R)
Used to assess the pain experiencedby children who are unable to speak due to cognitive impairments ordisabilities. It has been validated for children aged 3 to 18 years. It hasbeen designed so that no specific training or previous experience with thespecific children being observed is required. There is one focused on severely disabled children’s experience of pain …
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Noggin
A protein, encoded by the NOG gene, secreted from the organiser tissue (i.e., the dorsal mesoderm) that blocks the transformation of ectoderm into epidermis and, by that, inducing the formation of neural tissue of the early nervous system. It is involved in the development of many body tissues, including bones, muscles and neural tissues (e.g., …
Nominal group
A word or group of words that names constituting a grammatical or linguistic unit that can be used as a noun in English. Such a group has three functions: interpersonal (how the use of the clause affects the interaction between two speakers, a reader or a writer), ideational (meaning of the clause), and textual (structure …
Nodes of Ranvier
Periodic gaps, about 1 micrometer wide, between myelin sheath (Schwann) cells on axons of particular neurons (see figure below). Fat being a good insulator means that the myelin sheaths facilitate the speed of an electrical impulse travelling along an axon. The impulse jumps from node to the next as a speed that can attain 120 …
Nicotine
The main alkaloid (a nitrogenous compound such as lipids) in tobacco, it is ingested when tobacco is smoked or chewed, or snuff taken. It is a strong stimulant of the nicotine acetylcholine receptors, especially those in the ganglia of the autonomic nervous system, that raises blood pressure, reduces sensory feedback from muscle spindles and muscle …
Nissl substance
`Also referred to as Nissl body and in the past as tigroid substance, but this term has now become obsolete. It has a granular structure made of clusters (rosettes) of ribosomes in ‘rough’ endoplasmic reticulum. In fact, the granular structures are proteins and the Nissl substance is the place where most of the synthesis of …
Niche (ecology)
In ecology, the status of organism in the ecosystem, including its habitat and its effect on other organisms and the environment. It includes the physical or abiotic environment that covers factors such as soil type and climate, as well as how a species has adapted to living in its habitat. According to the principle of competitive …