Addiction and neural ageing
Addiction and neural ageing

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Glossary for SD805_2
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An antagonist to opioids. It can cause distress and some signs of withdrawal if injected by heroin users, a so-called naloxone challenge.


An opioid (opiate) drug, e.g. morphine or heroin.

natural selection

Driving force of evolution as described by Darwin. In the competition for resources between individuals in an environment that cannot support all of a population, a natural process of ‘selection’ occurs in which individuals with the most adaptive characteristics are more likely to survive and reproduce.

nature–nurture debate

This refers to debates about the relative contributions of genetic inheritance (nature) and environmental influences (nurture) to the physical/ behavioural characteristics of an organism or species.

negative cognitive set

Tendency to construe the world in negative terms; characteristic of a depressed mood.

negative feedback

(in cell metabolism) Also called end-product inhibition. It is the mechanism by which a metabolic pathway is regulated: when the product of the pathway exceeds a critical concentration, it ‘switches off’ an enzyme early in the pathway, thereby preventing further synthesis of the regulatory end-product.

negative feedback system

A system in which a displacement of a variable from a state causes corrective action such as to return the variable to that state.

negative reinforcement

nerve cell

Another name for a neuron.

nervous system

The collection of all of the neurons of the body, in brain, spinal cord and periphery.


Adjective describing the nervous system and its constituent cells (neurons).

neural pathway

A pathway of neurons over which information is transmitted.

neural sensitisation

A process by which the efficacy of processes within the nervous system are strengthened. For example, taking a drug into the body might sensitise those processes that underlie drug craving, thereby creating a vicious circle (or ‘positive feedback’ effect).


The central nervous system as seen in the spatial dimension, extending from the cerebral cortex to the lower end of the spinal cord.


Dendrites or axons grown from neurons.

neurofibrillary tangles

Dense bundles of long unbranched filaments in the cytoplasm of some neurons. Made exclusively of microtubule-associated proteins (MAPs).


The process of proliferation of a neuronal progenitor cell.


A type of drug that is antagonistic to dopamine

neurological disorder

A disorder of behaviour or personality brought about by damage to the brain. Sometimes called an organic disorder.

neuromuscular junction

A special type of synapse formed by the junction between a motor neuron and a muscle fibre.


A cell that serves to communicate and process information within the nervous system.


A small molecule synthesised and released by the nerve endings of nerve cells in the process of transmission of nerve impulses.

neutral stimulus

A stimulus that has no obvious effect in terms of evoking a response. A conditional stimulus prior to conditioning.


Particle with no electric charge which is present in atomic nuclei.

nicotinamide adenine dinucleotide (NAD+)

Hydrogencarrying coenzyme derived from the vitamin niacin.

N-methyl-D-aspartate (NMDA) receptor

One subtype of glutamate receptor, which binds the amino acid glutamate (a major excitatory neurotransmitter) and mediates its effect in neurotransmission. It is named after the dicarboxylic amino acid N-methyl-D-aspartate (NMDA), an agonist of glutamate used extensively to characterise different isoforms of glutamate receptor.


A neuron that is sensitive to tissue damage at its tip. Normally, the first stage in the process of pain.

non-insulin-dependent diabetes mellitus (NIDDM)

The most common form of diabetes mellitus, in which the responsiveness of cells to insulin is diminished. Thus, although insulin may be present at normal (or near-normal) levels, it is not able to effect its normal regulatory role.

See also diabetes mellitus (type II).

non-manual social classes

Those who fall into this social class are from professional and managerial occupations; sometimes called white-collar workers.

non-shivering thermogenesis

Generation of heat in brown adipose tissue (BAT) by the uncoupling of ATP formation from the electron transport chain. This is an important mechanism for the maintenance of body temperature in newborn babies.

norm of reaction

The range of phenotypes that may arise from the interplay between a given genotype and various environments.

nuclear envelope

The double layer of membranes that surrounds the nucleus.

nuclear pores

Perforations in the nuclear envelope which allow communication between the cytoplasm and the nucleus.


The repeating unit in nucleic acids (DNA and RNA); composed of a base, a sugar and a phosphate group.


A word that has two different meanings in biology, as follows.

  1. The organisational centre of a cell, which contains its genetic material.
  2. A collection of neuron cell bodies in the central nervous system.

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