Addiction and neural ageing
Addiction and neural ageing

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Glossary for SD805_2
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(chemical) Loss of oxygen, gain of hydrogen or gain of electrons in a chemical reaction.


An approach to describing or analysing complex phenomena from within a single, all-embracing level of explanation; all other apparent levels of explanation are reinterpreted as (‘reduced’ to) subsidiary manifestations of the fundamental explanatory level, or discarded as irrelevant.


An automatic, predictable and relatively stereotyped reaction to a particular stimulus.

reflex arc

Simple linkage between stimulus and response, in which presenting a stimulus triggers a response.

refractory period

A short time period which must elapse following an action potential before another action potential can be stimulated at the same location.


A stimulus given by an experimenter to an experimental animal contingent upon the animal performing a particular behaviour pattern. The stimulus is called a reinforcer.

Negative reinforcement encourages a particular behaviour pattern by making that behaviour pattern necessary if the animal is to avoid, or escape from, an unpleasant stimulus.

Positive reinforcement encourages a particular behaviour pattern by the presentation of a pleasant stimulus, such as food, every time the desired behaviour pattern is performed.

repair system

A system of enzymes that act sequentially to repair damaged or chemically modified DNA.

See also excision repair.

replication (cell)

The multiplication of cells in the body that occurs as part of development. Each cell division is preceded by copying of the genetic material (DNA replication).

replication (DNA)

The process of making new DNA molecules; each strand serves as a template for the synthesis of another, complementary strand. In this way, two new DNA double helices are formed, each having one strand from the ‘old’ original DNA double helix and one newly synthesised strand, i.e. DNA synthesis is semi-conservative.


The fusion of sex cells from a male and female to produce a new cell which goes on to develop into a viable offspring.

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