Addiction and neural ageing
Addiction and neural ageing

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Glossary for SD805_2
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5-hydroxytryptamine (serotonin). Biologically active amine occurring as a hormone in plants and as both a hormone and a neurotransmitter in animals. Like acetylcholine, adrenalin and noradrenalin, serotonin acts on many organs of the body, either directly or by a neuronal reflex.


absorptive state

Period after a meal during which glucose is entering the bloodstream after its absorption from the gut.


A neurotransmitter. (Adj. cholinergic.)

action potential

A pulse of electricity that is generated in neurons and travels their length. The means of communication within neurons. Action potentials are ‘all-or-none’, meaning that they either occur in full or not at all.

active site

The region of an enzyme molecule where the substrate binds and catalysis occurs.

active transport

Transport processes across membranes that require the expenditure of energy and use specialised transport molecules.

adaptive characteristics

Variations in body structure, or function, or behaviour, which give some members of a species a survival advantage and hence increase their chances of leaving more surviving offspring than other members of the same species.

adenosine triphosphate



adipose tissue

Tissue composed of fat cells (adipocytes). The site of storage of fats (triacylglycerols).


Term used in psychology and psychiatry as a way of describing a person’s responses of emotion and attention to events in the world around them.


A process to do with sensations of pleasure and displeasure.

afferent neuron

A neuron that conveys information to a structure. Often used to mean neurons that convey information to the central nervous system, i.e. sensory neurons.


A substance that mimics the natural effect of a neurotransmitter by occupying receptor sites for the natural substance.


One of several alternative forms of a gene occupying a given locus on a chromosome.


Focused on an object in its own right, rather than in relation to oneself.

allosteric site

Region of an enzyme molecule where the regulatory molecule (often the end-product of a metabolic pathway) can reversibly bind. This results in a change in shape of the active site and so modifies substrate binding and enzyme catalysis.

amino acid

Building block of polypeptides and proteins, so named because of the presence of the amino, –NH2, and carboxylic acid, –COOH, groups of atoms in their structure. There are 20 common naturally occurring amino acids.


Brain structure with a primary role in motivation and emotion.

amyloid precursor protein (APP)

A large transmembrane glycoprotein, which has been shown to play a major role in the pathogenesis of Alzheimer’s disease, as well as other related cerebral amyloid diseases. APP is made of 695 amino acids (APP-695). In 1988, three research groups simultaneously reported the isolation of cDNA clones that were shown to contain one or two additional domains compared with original APP-695. One of them showed extensive similarity to the Kunitz family of serine protease inhibitors (KPI) and resulted in a 56 amino acid insertion within the extracellular domain of the precursor protein. Therefore, the APP gene transcript and the corresponding APP protein that contain the nucleotide sequence or amino acid sequence, respectively, encoding this insert are denoted as KPI-APP or APP-751. APP-695 is predominantly expressed in the brain during development. The level of KPI-APP or APP-751 increased during ageing.


Term describing metabolic reactions that result in the synthesis of materials and in which energy is consumed.


Reduction in the intensity of pain.


A means of specifically relieving pain, e.g. injection of morphine, as distinct from an anaesthetic, which reduces all sensations.

animal model

The study of a particular non-human animal in such a way as to reveal general properties, e.g. about how a human might function.

anorexia nervosa

The relentless pursuit of thinness through self-starvation, even as far as death.


A substance that occupies the nerve synapse receptor sites and blocks the natural transmitter’s receptor occupation and so inhibits its action.

anterograde amnesia

An inability to remember new information for any length of time.


The three-base sequence in a tRNA molecule that is complementary to a particular threebase sequence (the codon) in an mRNA molecule.


A molecule that opposes oxidation reactions brought about by free radicals, hence the name antioxidant. The term is often applied to substances that can trap free radicals; for example, vitamin E is an antioxidant.


That which produces, or increases, anxiety.


Tending to reduce anxiety.


American Psychological Association.


General medical term used to describe a disturbance of speech caused by damage to the brain; strictly, an absence of speech.

apolipoprotein E (ApoE)

The purified protein component of a lipoprotein particle. In mammals, a group of eight apolipoproteins will most often be present in a set ratio. This complex molecule serves a wide variety of functions in the blood, including transport of fat from tissue to tissue.


Amyloid precursor protein.


Something unnatural that arises as a result of an experimental intervention. For example, a structure that is seen when a cell preparation is examined under the microscope may appear to be a natural cell component, but may actually be the result of an alteration in the cell’s structure caused by the procedures used to prepare the specimen for microscopy.


Derived from a history of associations, as in Pavlovian conditioning.

associative conditioning

The process by which an organism forms an association between two events. The term covers both classical and instrumental conditioning. In either case, one event owes its strength to its pairing with some other event.

associative learning

Learning by experience to associate two events that have been paired (e.g. the sight of a needle with the effect of heroin).


The smallest particle of an element, consisting of a core of protons and neutrons (the nucleus) surrounded by electrons.


Adenosine triphosphate. Each molecule of ATP is made up of a nucleotide base, a sugar unit and a chain of three phosphate groups.  ATP is the energy currency of the cell.  Energy is stored as ATP in the reaction between ADP (adenosine diphosphate) and Pi (inorganic phosphate):

ADP + PiArrow ATP

and is made available as required via the breakdown of ATP to ADP and Pi.

autoimmune disease

Type of disease in which the immune system of an organism attacks the normal healthy body of the same organism. Autoimmunity or immunological reactions caused by antibodies or T lymphocytes can produce severe inflammation or be innocuous, as when directed to intracellular autoantigens. Autoimmunity can develop spontaneously or be induced experimentally by immunisation with autoantigens or with antigens that are cross-reactive with them.

autonomic ganglion

A collection of cell bodies of neurons within the autonomic nervous system.

autonomic nervous system (ANS)

That branch of the nervous system that is responsible for controlling the activity of smooth muscle, cardiac muscle and glands of the body.


Concerned with the theory of value.


basal metabolic rate (BMR)

The metabolic rate of an individual who has not eaten for 12 hours, and is at rest and at a comfortable temperature.


(in nucleotide) Nitrogen-containing, ring-shaped molecules in DNA and RNA. There are four different bases in a nucleic acid: two with a double-ring structure, called adenine (A) and guanine (G); and three with a single-ring structure, cytosine (C) and either thymine (T), in DNA, or uracil (U), in RNA. It is the sequence of bases which determines the information content of the molecule.


A school of psychology which advocated that only observable behaviour should form the data for a science of psychology.


The process by which stable chemicals, for example some pesticides, become increasingly concentrated in the tissues of animals as a consequence of their place in a food chain.


A broad term that includes the whole array of life forms and their component levels of organisation, from genes to ecosystems.

biological determinism

The view that every characteristic of an organism’s structure and functioning, including mental and emotional states in humans, is determined by the genes that an individual has inherited.

biological evolution

The gradual changes to the structures and functions of living things which have been occurring from the moment that the earliest life forms appeared on Earth, perhaps 3500–4000 million years ago.


The study of living organisms, their body structures and functions, and their interrelationships in natural environments.

biopsychosocial world

A conglomerate term which seeks to encompass all the influences on individuals and groups from their biological and psychological functioning and social interactions.


A form of vision in which brain-damaged subjects can show evidence of some level of perception (e.g. an ability to point correctly at targets) even though they are unconscious of any such visual stimuli.


A lower than normal heart rate.

brown adipose tissue (BAT)

Specialised form of adipose tissue which is present in newborn babies. The fat cells in BAT contain large numbers of mitochondria and are well supplied with blood. BAT is responsible for non-shivering thermogenesis.



A chemical agent that causes cancer.

cardiac arrhythmia

A disturbance to the normal beating of the heart.

cardiac muscle

The specialised muscle, found only in the heart, that is responsible for the regular contraction and relaxation of the heart (heart beat). It is under the control of the autonomic nervous system.

cardiovascular shock

A term used to describe insufficient blood flow to the tissues, such that tissue damage occurs.

Cartesian dualism

The principle, based on the theory of René Descartes, that mind and matter are qualitatively different, and that because the mind does not operate within the laws of physics it cannot be investigated scientifically. Descartes also postulated that the mind (or soul) was unique to humans.


Term describing metabolic reactions that result in the breakdown of materials and the release of energy.

catalase (CAT)

An enzyme involved in the process of the removal of highly dangerous hydrogen peroxide from the cell. Catalase catalyses the breakdown of H2O2 to H2O and O2.


A substance that speeds up a reaction without itself undergoing any overall change in the process.


A class of neurotransmitters and hormones, including dopamine and noradrenalin.


A causal explanation is one given in terms of the mechanisms that underlie behaviour in a given individual at a particular point in time. It should be distinguished from a functional explanation.

causal texture

The nature of relationships between events in the environment, e.g. that a bell predicts food, or that a lever-press is followed by delivery of food.


The unit of which all living things are composed.

cell cycle

The cycle of growth and division whereby one cell becomes two, involving the replication and exact partitioning of the chromosomes, duplication of all cell constituents and transmission of cellular organisation to the two new cells.

cell junctions

A variety of types of intercellular connections which may also allow cells to communicate with each other. Tight junctions (e.g. between epithelial cells) connect cells together to form a fluid-tight seal. Anchoring junctions, in which the cell’s cytoskeleton joins cells to one another, are found in tissues that are subject to friction and stretching (e.g. muscle tissue in the heart). In the third type, gap junctions, the adjacent cell membranes come extremely close to each other but do not actually touch. At gap junctions, pores in the cell membranes allow the transfer of material from cell to cell.

cell membrane

The boundary of a cell; a double layer of phospholipid molecules associated with other lipids (including cholesterol) and a variety of membrane proteins.

cell respiration

(cellular respiration) The complete oxidative catabolism of glucose (C6H12O6)to carbon dioxide and water according to the following equation, which summarizes a long sequence of reactions in which large amounts of energy are released (mostly as ATP):

C6H12O6 + 6O2arrow 6CO2 + 6H2O + energy

central nervous system (CNS)

The part of the nervous system that consists of the brain and spinal cord.


Concerning the brain, or mediated via the brain.


The term cerebrum is often used as a collective name for the left and right cerebral hemispheres of the brain.


A property of some objects that is responsible for electrostatic interactions (i.e. attraction or repulsion) between them. There are two types: positive and negative. Like charges repel and unlike charges attract each other. A stream of moving negative charges (electrons) through an electrical conductor produces an electric current.

chemical messenger

A chemical that serves a role of communication. In its broad definition, the term includes hormones. In its more narrow definition, it is synonymous with a neurotransmitter.

chemical reaction

A process in which a substance (or substances) is transformed to a different substance (or substances) by a rearrangement of the atoms and their accompanying electrons.

chemical synapse

A synapse at which communication is effected by a chemical that is released from a neuron and occupies receptors at the second cell.

chemical transmitter

A chemical that is released from a neuron and occupies receptors at a second cell, thereby effecting communication from the first cell to the second.


The DNAprotein complex that makes up chromosomes.


Structures inside the nucleus, made of DNA and protein, that carry the cell’s hereditary information.

chronic illness

A long-standing illness for which there is no known cure. It is not immediately life-threatening but can give rise to unpleasant and painful symptoms.

classical conditioning

A procedure whereby a neutral stimulus (e.g. a bell) is converted into a conditional stimulus by its pairing with an unconditional stimulus (e.g. food). Following classical conditioning, the neutral stimulus acquires a power (e.g. to evoke salivation).

classical contingency

A situation where a neutral stimulus is arranged to occur just before an unconditional stimulus.


A set of three bases in mRNA that corresponds to (i.e. codes for) a particular amino acid.


A non-protein molecule which is closely associated with, or in some cases covalently bound to, an enzyme, and helps catalyse a chemical reaction.


Facts about the world that can be utilised flexibly in behaviour, e.g. food is by the window.


Term describing a process of information storage and retrieval, which can be utilised flexibly in behaviour. In humans, ‘cognitive’ relates to mental operations sometimes termed thought processes, e.g. reasoning, calculation and planning.

cognitive map

A spatial representation in memory. Typically, a cognitive map would be of a particular environment and be used as an aid to navigation there.

cognitive psychology

A branch of psychology that is concerned with intelligence and thought processes. It tries to understand the complexity of the relationship between an individual’s thought and action.


A generation of people (or animals) all born during the same period of time.

cohort effects

Those aspects of a person’s biography that are common to the particular cohort or group to which they belong.


An enzyme that breaks down the protein collagen.


A substance made up of two or more types of atom.

compression of morbidity thesis

This claims that disease and decay have largely been eliminated until the very last few years of the lifespan.

concentration gradient

A gradient that exists when there is a difference in concentration of a particular substance, which results in the net movement of the substance from the region of high concentration to the one of lower concentration.


The extent to which halves of a twin pair correlate in some quality, e.g. height or IQ.

conditional/conditioned stimulus (CS)

A stimulus that owes its behavioural capacity to its association with an unconditional stimulus. For example, a CS (bell) might evoke salivation as a result of its earlier pairing with food.

conditional reflex

The reflex that links a conditional stimulus and a conditional response, e.g. the neurons that link the sound of a bell (after conditioning) with the production of saliva.

conditional response

The response triggered by a conditional stimulus, e.g. the salivation caused by a bell following conditioning.

conditioned place preference

A preference for a location associated with a drug. Suppose that a rat is injected with a drug in a distinctive (e.g. striped) arm of a T-shaped maze. It is then placed in the stem of the maze and given a choice of arm. A preference for being in the arm in which it experienced the drug is termed a conditioned place preference.


The term used to describe a procedure whereby an animal’s reaction to a situation is changed. For example, it might be conditioned to salivate to a bell or to press a lever to obtain food.

See classical conditioning; instrumental conditioning.

connective tissue

The packaging tissue that fills the space around the body’s internal structures. It is also present within internal structures.


An arrangement such that one event is arranged or programmed to follow another. For example, a classical contingency is where a neutral stimulus is arranged to occur just before an unconditional stimulus. In an instrumental contingency, it is arranged that an event (e.g. food presentation) occurs immediately after a response by the animal (e.g. lever-pressing).

continuous reinforcement

 A schedule of reinforcement in which each response is reinforced, e.g. each lever-press earns a pellet of food.


An animal is said to be contraprepared to learn something when it has a bias against learning it. For example, whereas rats are easily able to learn an association between a taste and gastrointestinal upset, it is difficult to teach them an association between a sound and gastrointestinal upset.

See also prepared.


The outer layer of grey matter of the brain.


A hormone secreted by the adrenal glands at times of challenge and stress. A member of the class of hormones known as corticosteroids.


One of the hormones belonging to the class called corticosteroids.

covalent bond

Chemical bond involving pairs of electrons shared between atoms; one pair of shared electrons constitutes a single bond, two pairs a double bond and three pairs a triple bond.

cranial nerve

A nerve conveying information between the brain and regions of the head, e.g. the optic nerve.

creatine phosphate

Molecule in skeletal muscle which phosphorylates ADP, thus producing ATP for use in muscle contraction:

creatine phosphate + ADP Equalibrium creatine + ATP

The reaction is reversible, and creatine phosphate is regenerated (by phosphorylation from ATP) when the muscle is at rest.


Folds of the inner mitochondrial membrane.

cross-sectional method

An experimental method which involves making comparisons between groups of people from different sections of the population made at the same point in time.

cultural evolution

The gradual changes to the customs, beliefs, values, knowledge and actions of human societies, which have been occurring for perhaps the last million years.


Technical name for the method (cell or tissue culture) used to study biological phenomena in the cell population that was, first, isolated from the animal of interest. A technique that allows living cells to be grown outside the body. Depending on the cell type, they might survive for a few days only, or they might differentiate and proliferate and continue the cell line for many years.

Cushing syndrome

A hormonal/metabolic disorder caused by hyperplasia of the pituitary gland, an increase in secretion of ACTH, and consequent hyperplasia of the adrenal gland.


The final stage of cell division; the separation into two cells, of a cell that has undergone nuclear division.


All the cell contents outside the nucleus, i.e. cytosol, organelles, intracellular membranes, cytoskeleton, ribosomes.


One of the nucleotide bases present in nucleic acids (DNA and RNA).


The intracellular scaffolding, composed of the structural proteins, actin and tubulin. Important in maintaining the cell’s shape and for movement of material within the cell as well as for movement of the cell itself.


The fluid contents of the cell.


declarative memory


An intermediate in androgen and oestrogen biosynthesis.


A group of mental disorders characterised by progressive loss of cognitive and other intellectual functions associated with pathological ageing.

denervation supersensitivity

Increased sensitivity of the neurons of the CNS brought about by the proliferation of receptor molecules on the postsynaptic membrane following the loss of synaptic input.

Depression, the

A period in the 1930s in Western economies that was characterised by very high levels of unemployment and poverty.


A region of the body that is associated with a particular spinal nerve.


The lower layer of skin, beneath the epidermis, consisting mainly of loose connective tissue and fibroblasts, and containing nerves, vascular tissue (veins and lymphatics), hairs and sebaceous glands.

developmental psychology

A branch of psychology that sees human development as progressing in qualitative leaps or stages. This branch of psychology has mainly been concerned with childhood development but authors such as Eric Erickson have extended the analysis to the whole of the lifespan.

diabetes mellitus (types I and II)

Clinical condition in which either insulin is absent (type I, insulindependent) or in which insulin responsiveness is lost (type II, non-insulin-dependent). Characterized by the copious production of sweet urine.

dichotic listening

Listening to two different inputs simultaneously. This is a paradigm used very often to study attention where subjects listen to a series of two different things at the same time. Subjects are subsequently asked to repeat words previously presented.

differential gene expression

The expression of different sets of genes in different types of cell or at different stages of a cell’s life cycle.


Term describing cells that have become specialised into particular types.


The passive (i.e. non-energy-requiring) movement of a substance from a region where it is at a high concentration to a region where it is at a lower concentration.


A two-ring sugar, e.g. sucrose, lactose.


The ability to distinguish between two stimuli. It is measured by rewarding a response in the presence of one stimulus but not in the presence of the other and seeing whether behaviour shows a discrimination.

discriminative stimulus

A stimulus that is paired with either reward (i.e. reinforcer) availability (+) or its lack (−). An animal’s operant behaviour can be brought under the control of a discriminative stimulus such that it responds only in the presence of the reinforcer. In other words, discrimination training involves the association of a discriminative stimulus with a reinforcer.

disengagement theory

This theory suggests that older people voluntarily withdraw from society in preparation for death, and in order that society can continue to function.

disposable soma theory

A theory of the evolution of ageing and death, which suggests that organisms derive little benefit from investing resources in maintaining and repairing body tissues and thereby increasing their lifespan beyond a certain point. To do so would be inefficient as death is inevitable and resources that could have been put into reproduction would have been wasted.

disulphide bridge

An –S–S– covalent bond between two cysteine (Cys) units in a polypeptide chain, or between Cys units in different chains in the same protein.

diurnal (circadian) rhythm

Endogenous rhythmic changes, with a periodicity of approximately 24 hours, in the behaviour or physiology of animals and plants, such as the sleep/activity cycle in animals or growth movement in plants.

dizygotic twins

Non-identical twins. Two individuals that develop in one uterus from separately fertilised eggs. Also called fraternal twins.


Short for deoxyribonucleic acid. DNA is a macromolecule made up of individual units called nucleotides, and is found in all living cells and some viruses. The DNA molecule exists as a complex of two chains in an intertwined double helix. It is the carrier of genetic information that is passed on from generation to generation by replication of the DNA molecule.


One of the brain’s neurotransmitters (chemical messengers).

double aspect

The idea that mental events and brain events are two aspects of the same underlying reality.

double dissociation

The situation where a lesion at site A produces a disturbance in function X but not Y, and a lesion at site B produces a disturbance in function Y but not X.


The contribution of internal factors to motivation.


Diagnostic and Statistical Manual (of mental disorder). An American-based reference text; the ‘Bible’ of classification of psychological disorders. DSM I was first published in 1952 and has been updated several times since then. (The number, i.e. I, II, etc., denotes the edition.)


The idea that brain events and mind events are two distinct categories of existence. According to this, the mind can exist even in the absence of a physical brain.


Negative mood, e.g. depression; the opposite of euphoria. (Adjective: dysphoric.)



The scientific investigation of animals, plants and microbes in relation to their natural surroundings, both animate and inanimate.


System comprising living organisms and the physical and chemical factors that make up their environment.

efferent neuron

A neuron that carries information from a structure. Often used with respect to the central nervous system to refer to motor neurons.


A behaviour is described as elastic if its performance changes as a function of effort, e.g. if the demands made to gain access to a drug are increased and consumption falls. It is inelastic if, as the demands increase, consumption remains the same.


Concerned with the electrical properties of the skin. Electrical resistance changes with different emotions.

electroencephalography (EEG)

A technique in which electrodes are attached to the head, thus enabling the activity of populations of the brain’s neurons to be monitored. The record of such activity is called an electroencephalogram (also abbreviated to EEG).


Negatively charged particle present in all atoms. The electrons occur in shells surrounding the nucleus.

electron transport chain

Chain of molecules (electron carriers) in the inner mitochondrial membrane which are involved in oxidative phosphorylation. Electrons are transferred from NADH and FADH2 to these molecules, then from molecule to molecule along the chain, and are finally accepted by oxygen. ATP formation is coupled to this electron transfer.


A substance made up of only one type of atom.

elicited response

Response triggered by a stimulus.

embedded figures test

A test that measures a subject’s ability to distinguish figures from their context, e.g. a human face that is set in a number of disguising lines.


Properties are said to emerge at different levels of organization, i.e. they are emergent properties.

emitted response

This refers to a response for which there is no identifiable stimulus. (To some psychologists, the expression is a contradiction in terms.)

endocrine system

A general term to describe all of the hormones of the body, together with the glands that secrete them and the targets that are sensitive to them.


The process by which a cell engulfs and ingests extracellular material; the reverse of exocytosis.


One of the three germ layers (the basic layers of cells that arise early in embryonic development). It gives rise to the lining of the gut and also associated organs such as the liver and pancreas.


In a classification of depression, that which is caused by internal factors, e.g. a hormone imbalance.

endoplasmic reticulum (ER)

System of membranous sacs permeating the cytosol. Much of the ER has ribosomes attached, giving it a rough appearance in electron micrographs.

enteric nervous system

Intrinsic nervous system of the gut consisting of many small linked ganglia which contain neurons and glial cells. Enteric neurons play an essential role in the coordination of motility and secretion in the gut.

entorhinal cortex

Part of the lateral olfactory cortex in the temporal lobe that represents an important input to the hippocampus. Studies on humans and experimental animals indicate that the entorhinal cortex belongs to the memory system within the media temporal lobe.


A term used in this module to encompass geography, climate and physical surroundings, together with social circumstances, housing, diet, culture, politics, legislation, technology, religion, science, the media and so on – in fact, anything that could be considered as having an influence on health.


A class of proteins synthesised by living cells, all of which function as biological catalysts, i.e. they speed up biochemical reactions. A particular enzyme is specific for a particular reaction.


The study of how a condition is distributed within a population and how it changes over time, undertaken in order to understand the factors that contribute to the development of the condition.

epidermal proliferative unit

The hexagon-shaped structural unit of the epidermis consisting of a basal layer of dividing cells with layers of flattened, differentiating cells above.


The surface layer of skin, consisting of dividing cells next to a basement membrane and differentiating cells above, which become tough and impermeable.


A philosophically loaded term that is difficult to define; usually a mental state that is assumed to have no influence on behaviour or the brain. (Its mere postulation raises complex and highly controversial philosophical issues.)

episodic memory

Memory about things that an individual has done, or events that have affected that individual (memory of personal experience).


Relating to knowledge and the theory of how knowledge is acquired.


The bases and nature of knowledge that is employed in a branch of science. What constitutes its terms and preconceptions.

epithelial tissue (epithelium)

The tissue that covers all surfaces of the body and its organs, internal and external, including tubes and ducts.

excision repair

Name of one of the enzyme systems for repairing damaged DNA molecules. DNA repair occurs in several stages, each mediated by a specific enzyme: a specific endonuclease recognises the damaged region, cutting the relevant polynucleotide strand; an exonuclease digests away the nucleotides next to the cut; DNA polymerase binds 5′-nucleoside triphosphates to the resulting single-stranded region and, finally, the two ends of the strand are joined by the polynucleotide ligase.


Someone who believes that individuals are free to choose what they are, rather than having to follow a predetermined blueprint. The most famous existentialist, Jean-Paul Sartre, declared that for the existentialist ‘existence preceded essence’, by which he means that we invent ourselves through our actions, our ‘essence’ is not given.


Extrusion of material from the cell via vesicles which fuse with the cell membrane thereby releasing their contents to the outside (e.g. hormones, extracellular enzymes). The reverse of endocytosis.


In a classification of depression, refers to that caused by an external factor, e.g. divorce.


Coding sequence in a gene. The whole gene is transcribed, and sections of the primary transcription product (RNA) are cut out and the cut ends rejoined (spliced) to make the functional mRNA molecule. The parts of the RNA molecule retained are those transcribed from the exons.


A term meaning that an animal (e.g. a rat) has some knowledge of what is at the goal and acts as if it expects to receive this.

explicit memory

Memory that is revealed when performance of a task requires conscious recollection of a previous experience (e.g. whether a word or a picture has been seen already). Also called declarative memory.

exteroceptive stimulus

A stimulus arising in the external environment, e.g. a light or sound.


A term used in behavioural studies to describe both a procedure and a result. It is the procedure whereby the strengthening agent is omitted in a conditioning situation (CS). For example, after an animal has been classically conditioned to respond to a bell by salivating, extinction consists of omitting the food but still presenting the bell. As a result, extinction is seen when the animal ceases to respond to the CS. Similarly, in instrumental conditioning, an extinction procedure consists of omitting the food. Extinction is observed when the animal ceases to respond.


extracellular matrix

The material between cells in tissues. It consists mainly of polysaccharides and proteins, the latter often in fibrous form (e.g. collagen and elastin). It provides a strong, flexible matrix within which cells are embedded and can move.



Federal Drugs Administration. The US drugs policy and control organisation.


The number of fertilised eggs that a sexually reproducing organism produces.


A process whereby action is taken in anticipation of what might happen in the future. It is usually contrasted with negative feedback in which action depends upon error signals.


A sustained increase in body temperature above normal. It is usually the result of infection but can be due to physical trauma.


Type of differentiated cell in the dermis (and elsewhere in the body) that produces collagen and other proteins of the extracellular matrix. Fibroblasts are connective tissue cells.

filial piety

The dutifulness that a son or daughter displays to his or her parents.


Ability of an organism to survive and produce offspring that can themselves produce viable offspring. The term should not be confused with the common use, which refers specifically to physical bodily fitness.

flavin adenine dinucleotide (FAD)

A hydrogencarrying coenzyme derived from vitamin B2 (riboflavin).

free radicals

Atoms or group of atoms that contain unpaired electrons and are therefore unstable and highly reactive. They are produced both via metabolism and by exposure to harmful substances. Free radicals acquire electrons from other molecules around them, thus creating another unpaired electron in that molecule, and so on, resulting in a chain reaction. This chain reaction can cause considerable damage to living material. Free radicals can be inactivated by antioxidants.

functional explanation

An explanation given in terms of how something appeared in evolution. It explains how something contributed to evolutionary success in evolutionary history. It should be distinguished from a causal explanation.



An enzyme that breaks down lactose.

Garcia effect

A variety of rapid learning which occurs when ingestion of a characteristic food is followed by gastrointestinal upset. The flavour is avoided in the future. The effect is named after its discoverer, John Garcia, and is also termed taste-aversion learning.

gastric inhibitory peptide (GIP)

Hormone released by endocrine cells in the small intestine in response to the presence of fats and glucose. GIP stimulates insulin release.


The unit of genetic information. Most genes code for the production of proteins.

Genetic developments

We must consider mitosis and meiosis when looking at any pphysiological and psychological development. Meiosis is particular responsible for deciding on the birth sex, in that it passes either the XX or the XY gene into the fertilisation process. 


The total genetic material of a cell or organism.


The specific composition of alleles of a single gene, or the entire complement of genes of an organism. The information content that is inherited.

germ cells

The cells in sexually reproducing organisms that give rise to gametes (ova in females and sperm in males). The gametes contain half the number of chromosomes of the somatic cells. When a sperm fuses with an ovum, a zygote is formed which goes on to develop into a new individual.

germ line

The line of cells that give rise to gametes, i.e. synonymous with germ cells. The term expresses the continuity of inheritance via the germ cells as a result of sexual reproduction.


Technical name for the scientific study of the elderly.

Gestalt psychology

A school of psychology which emphasised that our perception of an image is more than the sum of our perception of component features within an image. (‘Gestalt’ is German for ‘pattern or configuration’.) These days, Gestalt is more commonly used to apply to a form of therapy.


Structure from which substances are secreted by the body. Glands can be endorine, secreting hormones into the bloodstrean, or exocrine, secreting (for example) digestive juices into the gut or sweat onto the surface of the skin.

glia (glial cells)

Cells in the nervous system, found in close physical association with neurons. They are not directly involved in transmission of information along neurons, but have a supporting role. Their functions are both metabolic, e.g. regulating the chemical composition of the nervous system, and structural – they are often wrapped tightly around neurons, where their fatty membranes, called myelin, act as electrical insulation.


Hormone produced by alpha cells of the pancreas in response to lowering of blood glucose level. Glucagon stimulates the release of glucose from glycogen and triacylglycerol stores (via glycogenolysis and lipolysis respectively) and also the new synthesis of glucose (gluconeogenesis).


A group of steroid hormones, the most important being cortisol and corticosterone, synthesised by the adrenal gland; they are involved in the regulation of metabolism and resistance to stress conditions.


The new synthesis of glucose from other small molecules (e.g. lactate, pyruvate, glycerol).


A neuron whose activity is particularly sensitive to local glucose level or rate of glucose metabolism.

glucose sparing

Production of ATP by catabolism of fuel molecules other than glucose, e.g. fatty acids.


An amino acid which is not only a constituent of proteins, but also functions as a neurotransmitter; a derivative of glutamine (also an amino acid).

glutathione peroxidase (GPx)

An enzyme that catalyses the oxidation of two molecules of glutathione, a tripeptide made of three amino acids (γ-glutamyl-cysteinyl-glycine) by hydrogen peroxide, to form oxidised glutathione and two molecules of water. This enzyme is very important in protection of haemoglobin from oxidative breakdown.


The polysaccharide storage molecule in humans and other mammals. It is made up of many glucose units joined together. Glycogen is formed predominantly in the liver and in skeletal muscle and is broken down to glucose to provide energy as required.


Breakdown of glycogen to release glucose.


Lipid with covalently attached sugar chains.


First stage in the catabolism of glucose. The end-product of glycolysis is pyruvate.


Protein with covalently attached sugar chains.

Golgi complex

Stack of flattened membranous sacs in which proteins manufactured by the ribosomes are processed and packaged for export out of the cell in secretory vesicles.

grey matter

Part of the brain and spinal cord that is characterised by a relatively greyish appearance. The appearance is due to the high concentration of cell bodies in this region.

See also white matter.

growth hormone

Also called somatotropin. Fundamentally important hormone, which in conjunction with other hormones (insulin, thyroxin, etc.) controls growth, differentiation and the continual renewal of body substances.



The environment in which an organism lives.


An enzyme that, during the process of replication, breaks the hydrogen bonds linking the two strands of double-stranded DNA.


(1) broad (H2): the proportion of total phenotypic variation in a particular trait at the population level that is attributable to variation in the 10 genotype;

(2) narrow (h2): the proportion of phenotypic variation that can be attributed to additive genetic variation, and which can be used to predict the response of the population to natural selection or selective breeding.


A single-ring sugar with six carbon atoms; all hexoses have the molecular formula C6H12O6.

high density lipoproteins (HDL)

Molecular aggregates in the bloodstream consisting of about equal proportions of protein and lipid (i.e. 50 per cent protein and 50 per cent lipid, of which about two-fifths is cholesterol). HDL returns cholesterol to the liver where it is broken down to waste products that are excreted in bile. The proportion of HDL in the circulation is increased by the consumption of unsaturated fatty acids.


The evolutionarily oldest part of the cerebral cortex, which has become folded under the temporal lobe. It is involved in memory processes.


(noun: holism) A type of approach to describing or analysing a complex phenomenon, which takes account of all possible levels of explanation and their interactions; the phenomenon itself is considered as a ‘whole’ which is more than the sum of its component parts or influences.


The process of maintaining the stability of important internal variables and the instigation of corrective action when these deviate from optimum.


The condition in which the two alleles at a particular locus on a pair of homologous (matching) chromosomes are the same.


A chemical that is secreted into a blood vessel at one location and carried in the blood to effect action at some other site, which may be a large distance away.

humanistic psychology

A branch of psychology which emphasises that humans are free agents in possession of consciousness and able to influence events in the world.

hydrogen bonding

An important type of intra- and intermolecular attraction which is particularly important in and between biological molecules. Hydrogen bonds occur between H atoms that are attached to O or N atoms, and O or N atoms elsewhere in the same molecule or in an adjacent molecule.


Literally, ‘water-loving’, i.e. having a tendency to associate with (polar) water molecules.


Literally, ‘water-hating’, i.e. having a tendency to associate with non-polar molecules (such as each other) and away from water.


Excessive pain sensitivity to a given noxious stimulus. (Adjective: hyperalgesic.)


Elevated concentration of glucose in the circulation (above about 140 mg ml-1).


The state of the body resulting from elevated temperature. Fever is the usual index of hyperthermia but there can also be heat exhaustion and heat stroke.


Lowered concentration of glucose in the circulation (below about 70 mg ml-1).

hypothalamo-pituitary-adrenal (HPA) axis

The hypothalamus is the brain region that lies at the base of the thalamus and is involved in the control of the body’s endocrine secretion. It is linked to the pituitary and adrenal glands through neuroendocrine links and the portal blood system.


The collection of nuclei below the thalamus which, amongst other things, helps to regulate the activities of the hormonal system and the autonomic nervous system.


Reduction of body temperature below the normal range of values (i.e. 36–38 °C).



International Association for the Study of Pain.


An effect that arises as an unwanted consequence of a medical intervention


International Classification of Diseases (10th edition).


Intracranial self-stimulation. Pressing a lever in a Skinner box to deliver electric shocks to the brain via implanted electrodes.


The philosophy that the mind (and spirit) is fundamental to the world and cannot be reduced to a product of the brain.

identity theory

The idea that brain events and mind events are two different languages for describing the same reality, i.e. mind events do not have an existence apart from brain events.


Concerned with the measurement and analysis of individual differences.

implicit memory

Memory that is revealed when performance on a task is facilitated without conscious recollection (such as when naming an object).


A measure of the external contribution to a motivation as a result of the intrinsic properties of an object, e.g. a food.


The number of new cases occurring per thousand of the population in any given period.

index of learning

The behavioural measure of learning. For example, the strength of a hungry rat’s tendency to turn to the food side of a maze might be used as the index of its learning the maze.

inhibitory synapse

Synapse at which electrical activity in one neuron reduces the excitability of another cell.


When a neuron (or group of neurons) is said to innervate a particular muscle or gland, it means that they provide a motor input to that muscle or gland, i.e. they activate it.


Term that describes compounds that do not contain carbon. (Note: this classification is not precise: there are some carbon-containing compounds that are also described as inorganic, e.g. CO2, carbonates.)

insensible water loss

Passive loss of water by evaporation from the skin and from the lungs during exhalation.

instinctive drift

A shift of behaviour towards speciestypical behaviour. For example, an animal might learn a task that is unnatural but then behaviour can shift to something that is typical for the species and thereby disrupt the learning.

instrumental act

An act that is assumed to occur (or to occur more frequently) because of the positive consequences that arise from it, e.g. euphoria after taking a drug.

instrumental conditioning

A process whereby behaviour is changed as a result of its consequences. Thus an animal might turn left in a maze and thereby get to food. This will increase the chances that it will turn left in the future. A special kind of instrumental conditioning is termed operant conditioning.

instrumental contingency

A contingency that is arranged such that for a particular response (e.g. lever pressing) an event occurs (e.g. food arrives).

insulin-dependent diabetes mellitus (IDDM)

One of the two types of diabetes mellitus, affecting about 15 per cent of diabetic individuals. In IDDM, insulin is lacking, completely or almost completely, because of the destruction of the pancreatic beta cells by an autoimmne reaction. Also called type I diabetes mellitus.

insulin resistance

Insensitivity of cells to insulin, which occurs in non-insulin-dependent diabetes mellitus (type II).

intelligence quotient (IQ)

The score that is the result of a standard intelligence test.


Neurons that are neither sensory nor motor but lie somewhere between these.


Arising from within the body, e.g. the stretch of the stomach.


By means of injection into a vein.


Non-coding sequence in a gene – the whole gene is transcribed, and sections of the primary transcription product (RNA) are cut out and the cut ends rejoined (spliced) to make the functional mRNA molecule. The parts of the RNA molecule removed are those copied from the introns.


The process of reflecting upon the contents of one’s own conscious mind. A tool used in psychological investigation.


An ion is formed when an atom or molecule either loses or gains one or more electrons, leaving it with a positive or negative charge, respectively.

ionic bonding

Chemical bonding between ions of opposite charge. Also called electrostatic interaction.


A pair of molecules are isomers if they have the same molecular formula but differ in the way in which the atoms are joined together, or in the orientation of particular atoms or groups in space.


Isotopes are atoms of the same element with different numbers of neutrons in their nuclei.


kainate receptor

A type of excitatory amino acid receptor for which glutamate may be the endogenous ligand. It is named after its specific agonist ligand, kainate. The receptor is coupled to Na+/K+ channels in the cell membrane, which are opened when activated by the agonist. Activation by the agonist is indirect, through the action of G-protein, or guanine nucleotide binding protein, which acts as a transducer of information between the receptor and the ion channel. For more details on the structure and mechanism of signal transduction, see Carlson, Ch. 4; or Oxford Reference Online.

kin selection

Natural selection operating indirectly on a character by favouring the relatives of the individual having that character. For example, the genes that cause a woman’s reproductive activity to be switched off at a certain stage will be favoured by natural selection if, as a result of her post-reproductive behaviour, her progeny and those of other close relatives are more likely to survive.



(social) Describes some aspect of an individual’s condition such that it becomes a way of defining that individual’s relationship with the rest of the world.


The asymmetrical distribution of function between the two hemispheres of the brain, e.g. localisation of language in the left hemisphere.


A mixture containing opium, which was widely available in Britain in the Victorian period.

law of effect

The law that states that behaviour is strengthened by its consequences.


The process by which a memory of experience is acquired that will modify behaviour.

learning curve

A graph showing an index of learning as a function of the number of trials over time.

level of explanation

A term applied to explanations for a certain phenomenon which are derived from a coherent body of concepts, hypotheses and knowledge associated with a particular academic discipline or subdiscipline; the term signifies the existence and value of other levels of explanation of the same phenomenon.

life expectancy

The average number of years a person can expect to live from birth.


The length of life of the longest-lived member of a species.

light receptors

Cells located at the retina of the eye and specialised for the detection of light.


(genetic) The situation in which alleles of different genes do not assort independently; they are held together, or linked. The degree of linkage is greater the closer together the genes are on the chromosome because, the closer they are, the less likely they are to be separated during the process of crossing over.


A class of hydrophobic organic molecules that form large aggregates; includes fats and oils (triacylglycerols), phospholipids and steroids.


A yellow pigment of lipoprotein found in aged cells and contributing to the slowing of their metabolism. By-product of inefficient protein recycling.


Breakdown of fats to release fatty acids and glycerol.

lipoprotein lipase

Enzyme that breaks down lipoproteins and is situated on the lumenal surface of capillary endothelial cells.


Multicomponent complexes of proteins and lipids which form distinct molecular aggregates. They serve a variety of functions in transporting lipids and participating in lipid metabolism.

longitudinal method

An experimental method that involves testing and retesting the same subjects at different ages over a long period of time.

long-term memory

Memory that is stored by the brain for long periods of time.

low density lipoproteins (LDL)

Molecular aggregates of lipid and protein in the circulation which consist of much more lipid than protein (80 per cent lipid). The proportion of LDL in the circulation is increased by the consumption of saturated fatty acids.


Organelle responsible for intracellular digestion, which is required for the destruction of pathogenic microbes and the recycling of materials.



General name for a very large molecule; often used interchangeably with ‘polymer’.

manual social classes

The Registrar General’s social classification of the population is based on occupational status. The manual social classes are made up of people whose work is manual, e.g. building or plumbing work, and are sometimes referred to as blue-collar workers.


A change in the nervous system as a consequence of learning, by which information is stored; the inferred process that connects learning to recall.

mesolimbic/mesotelencephalic dopamine system/ pathway

The set of dopaminergic neurons that originate in the midbrain, substantia nigra and ventral tegementum (immediately beneath the nigra), and which project axon terminals to a wide set of forebrain structures, chiefly the nucleus accumbens and striatum, the amygdala, and the frontal cortex.

messenger RNA (mRNA)

A single-stranded molecule of RNA produced by the transcription of DNA. A particular mRNA molecule carries the code for the amino acid sequence of a particular protein.

metabolic pathway

A group of sequential metabolic reactions.

metabolic rate

The rate at which energy is used by the body. It is usually expressed in kilocalories per hour.


The sum of all the chemical reactions that take place in an organism.


The term refers to when a cancerous tumour spreads out to establish satellite tumours elsewhere.


A substance that is prescribed for heroin addicts. It is believed to have a less-addictive potency than heroin, though in this regard its use is controversial.


A group of peptide hormones, the most important being aldosterone, synthesised by the adrenal gland, which regulates the balance of water and electrolytes in the body.


Organelles present in almost all eukaryotic cells in which molecules derived from food are oxidised to provide energy for all kinds of vital activities. (Singular: mitochondrion.)


Type of cell division that occurs in growth and repair – one cell divides into two identical cells. Mitosis involves chromosome condensation, separation of duplicated chromosomes by means of the mitotic spindle, formation of two identical nuclei, and finally cytokinesis.

molecular formula

A representation using chemical symbols for the atoms contained in one molecule of a covalent compound; it gives the types of atoms and the numbers of each present; for example, the molecular formula of water is H2O.  (Formulae for ionic compounds are also given using the same shorthand convention, e.g. sodium chloride is NaCl.)


A group of atoms bound together by covalent bonds.

monism / monistic

A philosophical view that there is just one kind of matter in existence, e.g. materialism.


A single-ring sugar, e.g. glucose, fructose, ribose.

monozygotic twins

Genetically identical twins. Two individuals that developed in one uterus from a singe zygote by separation of the embryo after the two-cell stage.


Occurrence of illness. Specifically, the reported incidence of illness per 1000 of the population.


The tendency of an animal to engage in a particular behaviour, e.g. a feeding motivation or a sexual motivation.

motor neurons

Neurons that convey information that activates muscles or glands.

See also efferent neurons.


Magnetic resonance imaging. A non-invasive technique employed to detect hydrogen atoms and also to map the internal structure of a living organism.


Describes an agent that can cause mutations (e.g. UV radiation and certain chemicals).


An organism or cell carrying a mutation.


An alteration in the genetic material. This can be a change in chromosome number or structure, or a change the DNA base sequence of a gene.


A coating that covers the axons of some neurons. It is part of a glial cell.



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.

‘nothing but’

The idea that something is nothing but its component parts and can be explained simply in terms of them, e.g. that humans are ‘nothing but’ a collection of physical components.


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.



Term describing behaviour that is freely emitted by an animal and can be reinforced by the experimenter.

operant conditioning

A variety of instrumental conditioning in which an animal emits a behaviour at a time it decides and that behaviour is then reinforced by its consequences. For example, an animal might press a lever in a Skinner box to earn a pellet of food. Not all instrumental conditioning can be described as operant. For instance, where an experimenter puts a rat in a maze and then removes it after its choice, is not described as operant since the timing of behaviour is not under the control of the rat.

operant learning

Learning based upon consequences. Certain classes of behaviour are said to be emitted and, if the consequences are favourable, there is an increase in the tendency to repeat the behaviour.


A class of drug that includes opium, morphine and heroin.


A distinct structure in the body serving a particular function, e.g. brain or kidney.


Membrane-bound structure in the cytosol, e.g. mitochondrion, lysosome, chloroplast (in plant cells only).


Term used to describe the majority of compounds that contain carbon. (Some carboncontaining compounds are classified as inorganic, e.g. carbon dioxide, carbonates.)

organ system

A group of organs that all work together, e.g. the cardiovascular system, the urinary system, the digestive system. Also sometimes called body system.


The movement of water across a membrane that is freely permeable to water but not to solutes (dissolved substances), from a region of low solute concentration to one where the solute concentration is higher.


A disease of bones. It is brought about when old bone is lost faster than new bone is gained in the remodelling process.


Gain of oxygen, loss of hydrogen or loss of electrons in a chemical reaction.

oxidative phosphorylation

The process coupled to electron transport which is last of the series of reactions in which energy is derived from glucose. It takes place at the inner mitochondrial membrane. Electrons are transferred from NADH and FADH2 (formed by reduction of NAD+ and FAD during glycolysis and the TCA cycle) along a series of electron carrier molecules, and are eventually passed to oxygen.  The process generates large quantities of ATP.

oxygen radical



A measure of the attraction value of a food.


The relief of pain and suffering.

palliative care

The care of patients with active, progressive, far advanced disease and limited prognosis and for whom the focus of care is the quality of life.

paranoid psychosis

Behaviour that is out of touch with conventional reality. Bizarre behaviour in which the sufferer feels persecuted by others and can be dangerous to others.

parasympathetic nervous system

One of the two divisions of the autonomic nervous system. Its activity has a calming effect, e.g. to lower heart rate.

See also sympathetic nervous system.

partial reinforcement

A schedule of reinforcement in which not every response is reinforced. For example, only one in 10 responses made by a rat might earn a pellet of food.

pathogenic paradigm

The conceptualisation of health in terms of disease.


(of nervous system) A collection of axons physically located together within the central nervous system, rather like wires in a cable. An alternative name is tract.

Pavlovian conditioning

peptide bond

The covalent link between adjacent amino acids in peptides and proteins.

peripheral nervous system

That part of the nervous system that is outside of the brain and spinal cord. That is to say, the collection of neurons and parts of neurons that extend between the central nervous system and the various regions of the body.


Endocytosis of solid material. This is the process whereby a phagocytic cell (e.g. macrophage) adheres to a target (which may be another body cell, a bacterium or inert cell debris), engulfs it and then destroys it by means of enzymes and other biochemically active molecules.


As it appears to the subject who experiences a particular effect.


A psychologist who studies the contents of conscious experience by means of asking subjects to introspect.


The study of one’s conscious experiences of the world, e.g. how it feels to experience addiction.


The sum of all the characters that an organism possesses; or one particular character, e.g. blue eyes or brown eyes. The phenotype is determined by the interaction of the genotype and the environment.


One of the most important membrane lipids; the polar phosphate ‘head’ groups are on the outside and the fatty acid ‘tails’ cluster together in the membrane interior.


The process in plants by which solar energy is captured and used to synthesize organic molecules, such as sugars, from simple inorganic chemicals.

phylogenetic scale

A scale that refers to different species in the context of their emergence in evolution.


The process whereby characteristics appear as a result of evolution.


Endocytosis of liquid.

pituitary gland

A hormone-producing gland situated at the base of the brain.


A neutral substance that can none-the-less have a specific effect, especially if a subject believes that it will do so, e.g. to reduce pain.


(neuronal) A property of neurons whereby the connection between a neuron and a target is neither specified nor fixed; confers the ability of neurons to change their connections.

polar covalent bond

Covalent bond in which there is substantial charge separation; occurs when the combining atoms have different electronegativities.

political economy

This approach to analysing society is concerned with the unequal distribution of wealth.


The introduction into the environment (air, water or land) of contaminants, the quantities, characteristics and duration of which are likely to be injurious to humans, animal, or plant life.


A large molecule formed by the linking together of many small-molecule ‘building blocks’ (called monomers).


A chain of amino acids joined together by peptide bonds. A protein is made up of one or more polypeptide chains held together by weak, non-covalent interactions.

positive feedback

A process in which a deviation from some condition tends to promote further deviation.

positive reinforcement


A reference to a philosophical position which considers only observable and measurable phenomena (e.g. movement, quantity of saliva produced) to be the basis of science.

post-absorptive state

Period starting about 4 hours after a meal and continuing until the next meal, during which no glucose is entering the circulation from the gut, and hence during which glucose must be derived from energy stores laid down during the absorptive state.


A term referring to physical life that continues despite serious progressive mental disability. The term is used to describe the state of people with Alzheimer’s disease or other types of neurodegenerative conditions.


An animal is said to be ‘prepared’ to learn something if it has a bias in favour of learning it. For example, animals are prepared to learn relationships between food and gastrointestinal upset. It is easy to teach them such an association.


A family of highly conserved transmembrane proteins with a variety of biological functions. Mutations in presenilin genes are most likely to act as dominant negative gene defects, which may ultimately lead to proteolytic processing of APP and activation of caspases. Mutations in presenilins account for up to 40 per cent of early-onset Alzheimer’s disease.


The number of individuals per thousand of the population actually showing a disease or trait at any given point in time.

primacy effect

Effect observed in investigations of short-term memory. Subjects are presented with a sequence of 15–30 unrelated words. Immediately after the last word, they are asked to recall as many words as they can in any order they wish. Performance on this task shows that the first-presented words are recalled reasonably well – the primacy effect.

See also recency effect.

primary structure

The sequence of amino acids in a polypeptide chain.


A term with two meanings in behavioural biology:

  1. Test used very often to study non-declarative, implicit, forms of memory. In this paradigm a subject see the list of words, pictures or objects, or non-verbal material such as novel objects or designs. Subsequently, subjects are tested with both old and new items and asked to name words or objects, previously presented, as quickly as possible.
  2. The revival of a particular behaviour pattern performed as an operant task by presenting, under the control of the experimenter, the reward normally obtained in the task. A particular behaviour pattern that is undergoing extinction as a result of omission of reward can often be revived in strength in this way.


A biological relative against which comparisons can be made.

procedural memory

Memory that includes knowledge of skills, of ‘knowing how’ (such as swimming, riding a bike, driving a car).


Term describing a large group of enzymes that digest (break down) proteins and peptides into their constituent amino acids, by hydrolysing the peptide bonds between them.


A protein molecule comprises one or more chains of amino acids joined together by peptide bonds. In proteins made up of more than one polypeptide chain, the chains are held together by non-covalent interactions.


Positively charged particle present in all atomic nuclei.

psychiatric disorder

A disorder of behaviour or personality without obvious brain damage. Sometimes called a functional disorder.

psychic secretions

Term used by Pavlov to describe secretions of saliva evoked by such stimuli as people entering the room. We would now see these as a type of conditional stimulus.

psychological life-history explanation

Explanation that seeks the origins of a disorder within an individual’s own life history.


The study of the behaviour of humans (and other animal species) and of their mental states.


The link between sensory information and motor reactions made on the basis of it. A process impaired by, for example, alcohol.

psychomotor stimulant

A class of drug (including amphetamine), which has the effect of increasing the level of activity in a given situation.


Behaviour that is out of touch with conventional reality. (Adjective: psychotic.)


A consequence that is contingent upon a particular response and which reduces the frequency of exhibiting that response in the future. An example of a punishment is an electric shock.


Describes behaviour directed to obtaining a goal and guided by a representation of the goal.


quaternary structure

The overall shape of a protein made up of two or more polypeptide chains.


recency effect

Effect observed in investigations of short-term memory. Subjects are presented with a sequence of 15–30 unrelated words. Immediately after the last word, they are asked to recall as many words as they can in any order they wish. Performance on this task shows that the last few words are recalled extremely well – the recency effect.

See also primacy effect.

receptive field

The area of sensory surface which, when stimulated, changes the activity of a neuron in a sensory system.


A term with two very different meanings in neurobiology:

  1. A sensory neuron or that part of one which is responsible for sensing information in the environment (e.g. light receptors in the eye).
  2. Protein molecule embedded within a cell membrane which when occupied by a particular hormone, drug, or neurotransmitter initiates a change in cell function.


A return to drug taking after a period of abstinence.

rectangularisation of mortality

Term referring to the observation that a plot of percentage survival against age for populations of modern Western societies is roughly rectangular in shape. This indicates that the average lifespan is approaching the maximum lifespan. The maximum lifespan is presumed to remain fairly constant.


(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.


The behavioural reaction of an animal to a stimulus.

resting potential

The state of a neuron when it is not exhibiting an action potential. It corresponds to a voltage in which the inside of the neuron is −70 mV with respect to the outside.

retrograde amnesia

Impairment of memory for events that happened prior to the event causing the amnesia.

R group

Amino acids have the same general formula, possessing an amino group, a carboxylic acid group, and a group of atoms that is different for each amino acid; this is called the R group. The shape and properties of a protein, and hence its function, are determined by the R groups of their constituent amino acids.


A subcellular structure composed of RNA and protein, at which protein synthesis takes place.


Ribonucleic acid; biopolymer of ribonucleotides present in all living cells and some viruses. There are three main types of RNA classified on the basis of their function: messenger RNA (mRNA), ribosomal RNA (rRNA) and transfer RNA (tRNA).

Rorschach test

A test in which subjects are shown ink blots and asked to describe what images they perceive. It is said to give insights into personality.


The abbreviation for reactive oxygen species, such as hydroxy, nitric and superoxide radicals.


salivation reflex

The reaction of an animal’s salivary glands to a stimulus (measured in drops of saliva). Normally, the stimulus is the presence of food in the mouth.


A state of loss of motivation as a result of completing a session of a particular behaviour. For example, after food deprivation an animal might be given food and then achieve a state of satiety as a result of free ingestion.

schedules of reinforcement

The nature of the relationship between an animal’s behaviour and the reinforcing agent that is contingent upon it. This might be continuous reinforcement or partial reinforcement.

secondary structure

Regular structure within a polypeptide chain. There are two main types: the α-helix and the β-sheet.


A family of enzymes involved in the processing/proteolysis of APP.


A term that refers to the capacity of an individual to set goals and to meet them. A capacity to obtain satisfaction in realising ambitions.

semantic memory

Memory that includes general knowledge of the world acquired through education and experience, including the use of language.

senile/neuritic plaques

Extracellular structures composed of complex and incompletely characterised molecular and cellular constituents. Amyloid β peptide, produced by proteolytic cleavage of APP, and ApoE are the major components of the plaques.

sensory neurons

Neurons that convey information to the central nervous system.

See also afferent neurons.


An adjective describing a neuron that synthesises, stores and releases serotonin or a synapse at which serotonin is the neurotransmitter.


One of the brain’s neurotransmitters.


A procedure whereby an experimenter rewards successive approximations to a desired operant response. For example, if lever-pressing is the desired operant, an experimenter might offer reward for first touching the lever and then for lowering the lever slightly. Finally, reward would be given only for fully lowering the lever.

short-term memory

Memory where information is only stored for a limited period of time, e.g a phone number.

See also working memory.

skeletal muscle

The muscles that are associated with the skeleton and responsible for changing the position of the body or parts of the body (e.g. legs and arms) in relation to the external environment.

Skinner box

An apparatus in which an animal obtains a reward, usually food or water, for emitting a response. In the case of pigeons, a key is pecked; and for rats, a lever is pressed.

smooth muscle

Type of muscle controlled by the autonomic nervous system and which determines such things as the state of contraction of the gut and the diameter of blood vessels.

social death

A term used to describe patients who are treated by others as if they were not there.

socio-economic groups

Classification of groups in society in terms of social characteristics (e.g. marital status) or economic determinants (e.g. income level).


The study of human interactions and social relationships, their organisation, functions, development and significance.

somatic cell

Any cell of a living organism, except the reproductive cells (gametes).

somatic nervous system

That part of the nervous system that controls the activity of the skeletal muscles of the body.


A peptide hormone synthesised in a distinct region of the brain and released into the capillaries of the brain blood vessels. Somatostatin regulates (inhibits) the secretion of some other hormones (somatotropin, insulin, thyrotropin, glucagon, gastrin and cholecystokinin).


To do with the internal organs of the body, e.g. heart, gut.


A population of similar organisms, which usually interbreed in their natural habitat and produce fertile offspring.

spinal reflex

A reflex involving sensory neurons and motor neurons organised at a particular level within the spinal cord.

spinal system

A system involving the spinal cord, the collection of nervous system pathways and processes located within the backbone.


An array of cytoskeletal protein fibres present in a dividing cell, which joins the chromosomes, present at the cell equator, to the poles and is involved in chromosome separation during meiosis and mitosis.

split-brain individual

An individual in whom the corpus callosum has been cut. Under certain conditions, such individuals behave as if they had two brains with separate consciousnesses.

S–R psychology


Unusual repetitive behaviour such as picking a part of the skin repeatedly.


Class of lipids characterised by their four fused-ring structure. The steroid cholesterol is a component of cell membranes, conferring rigidity; some other steroids function as hormones.


Something that impinges upon an animal's sense organs.

stimulus–response psychology

An outlook within psychology which suggested that learning consists in forming relationships between stimuli and responses.

stress-induced analgesia

Analgesia (a process acting in opposition to pain) that arises as a result of the exposure of an animal to a fear-eliciting stimulus.

stress reaction

The response of the body to shock caused by damage to tissues and organs, involving the release of stress hormones which increase metabolic rate and initiate repair activities. Often accompanied by fever.

structural formula

A representation of a molecule that shows the order in which the atoms are connected together as well as all the bonds involved.

substrate-level phosphorylation

Formation of ATP by addition of a phosphate group from the reaction substrate, to ADP. (Compare with oxidative phosphorylation, which is ATP formation by addition of inorganic phosphate (Pi) to ADP.)

successive approximations

In the context of operant conditioning, a process whereby the demand is made more stringent before reward is given. This is a process of shaping.


Sulci (plural) are folds in the cerebral cortex. They serve as landmarks for identifying brain regions.

superoxide dismutase (SOD)

An enzyme belonging to a large family of enzymes that catalyse the formation of dioxygen and hydrogen peroxide from even more dangerous superoxide radicals.

sympathetic nervous system

One of two divisions of the autonomic nervous system, it is responsible for activation of the body, e.g. sympathetic activity increases heart rate.

See also parasympathetic nervous system.

sympathetic overactivity

Overactivity of the part of the nervous system that controls such processes as heart rate, sweating and digestion. A consequence of its overactivity is a higher than normal heart rate.


Junction between cells in the nervous system, and also between such cells and their target organs, e.g. muscles. A synapse consists of a specialised presynaptic membrane from which molecules of neurotransmitter can be released, a gap across which the neurotransmitter diffuses (synaptic cleft) and a postsynaptic membrane that has receptor molecules on it which are specific for and so bind the neurotransmitter.

synaptic cleft

Space between two cells at a synapse.


Process of new synapse formation.


Combining of effects. A synergism of cannabis and alcohol would be a combination of effects, each reinforcing the other, e.g. in producing the incapacity to drive a car.



An instrument for very brief measured exposure of objects to the eye.


Abnormally high heart rate.

taste reactivity test

A test in which substances are placed on the tongue of a laboratory animal (e.g. a rat) by means of an implanted tube. The reaction of the animal to the substance (e.g. swallowing, mouth wiping) is usually monitored by video.

TCA cycle

Tricarboxylic acid cycle (also citric acid cycle or Krebs cycle.) Second of three consecutive metabolic pathways involved in energy production from glucose. Acetyl CoA, formed from pyruvate in the link reaction, is catabolised via a cyclic series of reactions, in which CO2 and reduced coenzymes are produced. The former is excreted via the lungs and the latter reoxidised via the electron transport chain.

T cell

A white blood cell known as a lymphocyte that matures in an organ called the thymus and is responsible for much of the biological response against pathogens.


Guided by a goal or end-point. For example, some have suggested that evolution is guided in this way (though this is not a mainstream view).


An enzyme that replicates telomeres. Telomerase is a specialised reverse transcriptase able to replicate without loss the 5′ end (in a 5to 3end direction) of each DNA strand in the chromosome.


A term used for the end of the chromosome; simple tandem DNA repeat sequences that make the end of a eukaryotic chromosome.

temperature acclimatisation

Adjustment to a different (i.e. higher or lower) environmental temperature. For example, heat acclimatisation involves a more rapid sweating response, an increase in the volume of sweat produced and a reduction in the amount of salt (NaCl) lost via sweating.

temporal contiguity

The presentation of two stimuli (e.g. a conditional and an unconditional stimulus) at the same time.

terminal drop

This describes the state of affairs when the body finally wears out.

tertiary structure

The overall shape unique to a particular macromolecule, such as a polypeptide chain.

thermoneutral zone

Range of environmental temperatures that can be adjusted to by control of the blood supply to the skin (via the state of contraction of the blood vessels in the skin). In adults, this range is between 25 and 30 °C.


The maintenance of body temperature within its normally narrow range (36–38 °C.).

tissue culture

Growing cells that have been isolated from the body, in dishes containing all the nutrients necessary for survival and growth.


A decreasing response to an interventio (e.g. drug injection) as a function of its repeated presentation.

total energy expenditure

Total energy used by the body over a period of time. It is the sum of the heat energy generated plus the external work done plus the energy stored.

trace elements

Elements that are needed in very small quantities in the diet.


(neural) A collection of axons physically located together within the central nervous system rather like wires in a cable. Also called a pathway.


The synthesis of an RNA molecule using DNA as the template.

transfer RNA (tRNA)

Small RNA molecules involved in protein synthesis. Each one carries a particular amino acid to a ribosome, which is itself attached to an mRNA molecule. Every tRNA molecule has an anticodon which recognizes a specific codon on the mRNA.

transgenic animal

An animal whose genome has been modified artificially by the addition of genes (DNA) from another organism. The transgenic animal has the ‘foreign’ genes incorporated into its genome.


The synthesis of a protein, whereby the information encoded in a sequence of mRNA bases determines the amino acid sequence of the corresponding protein product.


Chemical name for fats and oils; also commonly called triglycerides. Made up of one molecule of glycerol and three fatty acid molecules.

trophic factors

Term used for factors that exert a nutritive, or trophic, effect on cells.



A small, highly conserved protein which derives its name from its widespread distribution – it is present in all eukaryotic cells and is located in both the nucleus and the cytoplasm. Ubiquitin becomes covalently attached to other intracellular proteins, thereby tagging them for breakdown.

unconditional reflex

The reflex that links an unconditional stimulus and an unconditional response, e.g. a series of neurons that links the presence of food in the mouth to secretion by the salivary glands.

unconditional response (UCR)

The response evoked by an unconditional stimulus. An example is salivation triggered by the presence of food in the mouth.

unconditional/unconditioned stimulus (UCS)

A stimulus that evokes a response even in the absence of a history of conditioning, e.g. food in the mouth with regard to salivation.

uracil (U)

One of the four nucleotide bases that occur in RNA. Uracil is not present in DNA (thymine (T) occurs in its place).



The number of covalent single bonds that an atom can make. For example, from the formula of methane, CH4, a carbon atom can be seen to have a valency of 4.


(neural) A nodule on an axonal branch which contributes to the postsynaptic influence of the neuron by releasing large quantities of transmitter. This type of synapse is characteristic of neurons projecting to the striatum from the substantia nigra.

venous cannula

A tube passing into a vein through which a drug can be passed into the body.

very low density lipoproteins (VLDL)

Molecular aggregates of lipids and proteins. VLDL are formed in the liver. They contain much less protein than lipid.


The probability that a fertilized egg will go on to develop into an individual that can reproduce.


white matter

Parts of the central nervous system characterised by their relatively whitish appearance. The appearance is due to the presence of a large percentage of myelinated axons and the myelin contributes to the whitish appearance.

See also grey matter.

word completion task

In this test, subjects are presented with a three-letter word-fragment and asked to write down the first word they think of, or that had appeared on the previously presented list. Subsequently, subjects are asked to complete fragments. The score is the number of completed words that were elicited.

working memory

Memory where information is only stored for the period of time in which it is needed.

See also short-term memory.

wound contraction

Closure of a wound by contraction of a ring of contractile cells differentiated from fibroblasts, producing a continuous layer of dermis which covers the wound.



Also referred to as amyloid-

β (abbreviated to Aβ). It is a peptide derived from the larger amyloid precursor protein (APP) and is the principal component of amyloid fibrils. The specific role of β-amyloid is unclear, but it is thought that amyloid deposits may cause neurons to degenerate. Amyloid deposits also occur in the brains of older Down’s syndrome patients.

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