PSYB32H3 Chapter Notes -Posttraumatic Stress Disorder, Action Potential, Sympathetic Nervous System

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4 Jun 2011
A paradigm is a set of basic assumptions, a general perspective, that defines how to conceptualize and
study a subject, how to gather and interpret relevant data, even how to think about a particular subject.
Central to any application to of scientific principles, in Kuhns view, is the notion of paradigm, the
conceptual framework or approach within which the scientists work. Paradigms specify what problem
scientists will investigate and how they will go about the investigation.
Five paradigms: biological, psycho analytic, humanistic and existential, learning, and cognitive.
Current thinking about abnormal behaviour tends to be multi-faceted, and contemporary views of
abnormal behaviour and its treatment tend to integrate several paradigms.
The biological paradigm of abnormal behaviour is a continuation of the somatogenic hypothesis. This
broad perspective holds that mental disorders are caused by aberrant biological processes. This paradigm
has often been referred to as the medical model or disease model.
Heart disease is one example. May factors—genetic makeup, smoking, obesity, life stress, and perhaps
even a persons personality—are causes of heart disease. Medical illness can differ widely from one
another in their causes. However, they all share one characteristic: in all of them some biological process
is disrupted or not functioning normally. That is why we call this the biological paradigm.
The biological paradigm was the dominant paradigm in Canada and elsewhere from the late 1800s until at
least the middle of the 20th century
More sophisticated approaches are used today, and there is now an extensive literature on biological
factors relevant to psychopathology. Heredity probably predisposes a person to have an increased risk of
developing schizophrenia, depression may result from clinical imbalances within the brain, anxiety
disorders may stem from a defect within the autonomic nervous system that causes a person to be easily
aroused, and dementia can be traced to impairments in structures of the brain. In each case, the
psychopathology is viewed as caused by the disturbance of some biological process. Those working with
the biological paradigm assume that answers puzzles of psychopathology will be found within the body.
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Behaviour genetics is the study of individual differences in behaviour that are attributable in part to
differences in genetic makeup. The total genetic makeup of an individual, consisting of inherited genes, is
referred to as the genotype. Individual genotype is his or her unobservable genetic constitution; in
contrast, an individuals phenotype is the totality of his or her observable, behavioural characteristics,
such as level of anxiety.
It is critical to recognise that various clinical syndromes are disorders of the phenotype, not the genotype.
Thus, it is not correct to speak of the direct inheritance of schizophrenia or anxiety disorders; at most,
only the genotypes for these disorders can be inherited.
The study of behaviour genetics has relied of four basic methods to uncover whether a predisposition for
psychopathology is inherited: comparison of members of a family, comparison of pairs of twins, the
investigation of a adoptees and the linkage analysis. The family method can be used to study a genetic
predisposition among members of a family because the average the number of genes shared by two blood
relatives is known.
The starting point in such investigations is the collection of a sample of individuals who bear the
diagnosis in question. These people are referred to as index cases, or probands. Then, relatives are studied
to determine the frequency with which the same diagnosis might be applied to them.
In the twin method, both monozygotic (MZ) twins and dizygotic (DZ) twins are compared. MZ, or
identical, twins develop from a single fertilised egg and genetically the same. DZ, or fraternal, pairs
develop from separate eggs and are on average only fifty percent alike genetically, no more alike then any
other two siblings. MZ twins are always the same sex but DZ twins can be either the same or the opposite
sex. When the twins are similar diagnostically, they are said to be concordant.
The ability to offer a genetic interpretation of data from twins studies hinges on what is called the equal
environment assumption. The equal environment assumption is that environmental factors that are partial
causes of concordance are equally influential for MZ pairs and DZ pairs.
Other factors can also complicate the results of twin research. In a study of post-traumatic stress disorder
in community residence, identified three factors as biasing heritability estimates: violation of equal
environments assumption, the sex of the participant and his or her age when the assumption took place.
When the controlled statistically for the effects of age and sex differences, they found that genetic and
non- shared environmental factors contributed to symptoms of post-traumatic stress disorder.
Researchers using the adoptees method study children who were adopted and reared apart from the
parents with abnormal disorders. Though infrequent, this situation has the benefit of eliminating the
effects of being raised by disordered parents.
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Molecular genetics is a highly advanced approach that goes beyond mere attempts to show whether a
disorder has a genetic component; it tries to specify a particular gene or genes involved and the precise
function of these genes. The term “allelerefers to any one of several DNA codings that occupy the same
location on a chromosome. A persons genotype is his or her set of allele.
The term “genetic polymorphism refers to variability among members of the species. It involves
differences in the DNA sequence that can manifest in very different forms among members in the same
habitat. It entails mutations in a chromosome that can be induced or naturally occurring.
Linkage analysis is a method in molecular genetics that is used to study people. Researchers using this
method typically study families in which a disorder is heavily concentrated. They collect diagnostic
information in blood samples from affected individuals and their relatives and use the blood samples to
study the inheritances pattern characteristics whose genetics are fully understood, referred to as genetic
markers. Eye colour, for example, is known to be controlled by a gene in a specific location on a specific
Note that researchers in this area often hypothesize gene-environment interactions. This is the notion
that a disorder or related symptoms are the joint product of a genetic vulnerability in specific
environmental experiences or conditions.
The nervous system is composed of billions of neurons. Although neurons differ in some respects , each
neuron has four major parts: (1) the cell body; (2) several dendrites (the short and thick extensions); (3)
one or more axons of varying lengths (usually only one long and thin axon extending a considerable
distance from the cell body); and (4) terminal buttons on the many end branches of the axon. When a
neuron is appropriately stimulated at its cell body or through its dendrites, a nerve impulse, which is a
change in the electric potential of the cell, travels down the axon to the terminal endings. Between the
terminal endings the sending axon and the cell membrane of the receiving neuron, there is a small gap,
called the synapse.
The terminal buttons of each axon contains synaptic vesicles, small structures that are filled with
neurotransmitters, chemical substances that allow a nerve impulse to cross the synapse. Nerve impulses
cause the synaptic vesicles to release molecules of their transmitter substances, and these molecules flood
the synapse and diffuse toward the receiving, or postsynaptic, neuron.
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