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The Biological Approach Notes

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The biological approach Define the biological approach A person's thoughts feelings and actions are determined by….


His/her genetic inheritance; we all inherit genes from our parents and these genes determine key features regarding not only appearance and health status but also psychological variables such as intelligence, aggression and ability to relate to others and many human behaviours such as attachment, communication and our ability to remember and learn. Hormones and neurotransmitters, which are chemical messengers which tell our body how to react The central nervous system, including neuroanatomy and neuronal organisation, nowadays it is understood that our environment/ experiences affect how our brains work and concepts such as neuroplasticity and epigenetics are exiting areas to explore

Terminology Central nervous system (CNS)


The central nervous system comprises the spinal cord and the brain. The brain is made of nerve cells called neurons At the end of the neurons, structures called receptors receive chemical signals (via neurotransmitters)from other neurons

Synapse

Gap between the axon of one neuron and the dendrite of the next neuron.

Receptor

A molecular structure or site on the surface or interior of a cell that binds with substances such as hormones, antigens, drugs, or neurotransmitters

Neurone

A specialized, impulse-conducting cell that is the functional unit of the nervous system, consisting of the cell body and its processes, the axon and dendrites.

Neurotransmitter


Genes

Chemicals produced by neurons that pass on nerve signals across a synapse between two neurons Examples: dopamine, serotonin, adrenalin





Contains a set of instructions and is a carrier of information Each individual has a genotype, which is genetic constitution. Each person also has a phenotype, which is what the individual becomes when their genes interact with each other and with the environment Genes are inherited, 50% from each biological parent Consists of a long strand of DN; a chromosome is another chain of DNA, one of the functions of DNA is to control gene activity

Hormones

Chemical produced by the endocrine system and released in the bloodstream. Hormones are transported to targets organs which they affect in different ways. Examples: testosterone produced by the testis affects the growth of facial hair for example Oestrogen produced by the ovaries affects the growth of breasts

Brain lateralisation

The brain is organised in highly specialised areas which are located on various sides of the brain. Brain lateralisation is the difference between the right and the left hemisphere of the brain

Content Briefly describe the role of the central nervous system and neurotransmitters in human behaviour

The nervous system has 2 main parts, the CNS and PNS The CNS consists of the brain and the spinal cord and there are then further subdivisions

Brain part Striatum

Function Important role in controlling movement and thinking

Hippocampus Ventricles Corpus callosum, connects the two hemispheres Amygdala Hypothalamus

STM occurs Schizophrenia Brain lateralisation, sex differentiation

Hemispheres

Emotions and aggression Regulating eating and drinking and motivated behaviours Brain lateralisation

Other parts of the brain include:

Approach Biological, effects of antipsychotic drugs; use of animal lab experiments Cognitive A2 Biological

Biological- Raine et al Biological

Biological

o o o

The thalamus- near the base; passes information on from the senses The cerebellum- stores well learned practical skills The cortex- the most recent development of the brain for humans, which stores information and is involved in problem solving and decision making

Neurotransmitters











Neurotransmitters are chemical messengers (e.g. dopamine and noradrenaline) that act between neurones in the brain This allows the brain to process thoughts and memories The nervous system consists of neurones and glia Glial cells carry out repairs, act as insulators and remove waste products from the brain; research is still going on into the role of glia Neurones are cells that receive and transmit messages, passing them from cell to cell At one end, a neurone has dendrites, which are finger-like structures surrounding the nucleus From the nucleus there is a long extension called an axon, which reaches to an axon terminal The axon terminal of one neurone reaches to the dendrites of another neurone Between the terminal and the dendrites there is a gap called the synapse The synaptic cleft sits between two neurones On one side, at the dendrites, there are receptors of a certain shape prepared to receive the neurotransmitter from the other neurone If the neurotransmitter fits it will trigger and electrical impulse in the cell body, which then travels down the neurones axon so the message continues, if not, the message is blocked Manufactured drugs work in this way, they mimic natural neurotransmitters, more or less fit certain receptors, and are received like neurotransmitters and the message from them 'works'. Some drugs block the message. They fit the receptor, so the natural neurotransmitters cannot pass the message on because the receptor is not available (competitive inhibition)

Describe the role of genes in behaviour (including the nature/nurture debate). Examples of the effects of genes on humans

Human chromosome 4 has a marker known as G8. It is not yet known what G8 contributes, but the gene for Huntington's disease lies close to it. If a parent and child both have Huntington's disease, then in 98% of cases they both have the same G8 marker. This suggest the gene for Huntington's disease travels with the G8 marker


Some diseases and characteristics are sex linked in that they are controlled by the sex genes. This is why some diseases/ characteristics are more common in one particular sex e.g. colour blindness is most common in men if one parent contributes two copies of chromosome 21, then the child has three copies and the consequence is downs syndrome Cancer involves damage to the DNA and he damage occurs as the cells divide. For example in the form of leukaemia, almost every white blood cell carries an unusually small chromosome 22. The bone marrow produces damaged cells that reproduce more quickly than other cells and the disease spreads. It appears that chromosome 22 is smaller because part has broken off and transferred to chromosome 9. This transfer leads to a new abnormal protein being produced that speeds up cell division. However, there may be other factors involved when cancer develops, such as environmental triggers.

Environmental triggers on genes

Sometimes genes do not influence physical characteristics unless the 'right' environmental conditions occur One example is phenylketonuria (PKU), babies once born in the UK have a blood sample taken from their heels. This is to test for PKU, a disease that leads to brain damage. It is known that if a child's diet is carefully controlled the damage from PKU can be averted, i.e. the effect of the gene can be avoided.

The nature- nurture debate

The effects of nature on behaviour o Consider the effects of neurotransmitter functioning, brain structure, genetic makeup and other related issues The effects of nurture o Consider style of upbringing, experience of schooling, peer-group influences, position in family (e.g. middle child), social and cultural influences etc. o E.g. children who watch a lot of violent television may be more likely to act aggressively; children who have not made secure attachments with their main care givers may find it less easy to form secure relationships when they are older

With regard to gender development, describe the role of genes, hormones, and brain lateralisation.

Gender- in the term used when referring to the development and behaviour of different sexes in relation to environmental and social aspects. Sex- usually used when referring to biological aspects, whether XX or XY

Genes and sex determination





Apart from sperm and egg cells, every cell in the human body contains 46 chromosomes (23 pairs) Sperm and egg cells have unpaired 23 chromosomes To form a new organism, 23 chromosomes come from the fathers sperm cell and 23 come from the mothers egg cell The two unpaired sets combine to make 23 unique pairs Male get X from mother and Y from father, female gets X from each

Genes and gender development Normal sex differentiation in humans

1.

Fertilisation determines genetic sex, according to the chromosomes contributed from sperm and egg cells. The 23 chromosomes in an egg cell include and X chromosome and the 23 chromosomes in a sperm cell include either an X or Y chromosome

2.


3.

The fertilised egg divides to form a large number of identical cells. During the development of the embryo the cells differentiate to form the various body organs, including the sex organs. Both males and females at this stage have to gonadal and after 6/7 weeks gestation, two sets of internal ducts, the mullarian (female) and wolffian (male) ducts. At this stage the external genitalia appear female.


The gonadal ridge either becomes either ovary or testis. In males, it develops into testis because of a product from a gene on the Y chromosome. In females there is no Y chromosome; other genes trigger the gonadal ridge to develop into ovaries.


Hormones then act to enable the different sexes to develop. Mullarian inhibiting substance (MIS) and androgens (male hormones) are the two important hormones. MIS prevents the growth of female mullarian ducts (the uterus and fallopian tubes) which are present in all foetuses up to this point. Androgens are also secreted and affect the growth of wolffian ducts. Ovaries do not produce androgens, but testes do. The Wolffian duct do not grow when ovaries develop; MIS is not produced either, so the female mullarian ducts can develop. For male development, MIS is needed to stop female duct growth. External genitalia remain feminine in the absence of androgens; in males, androgens allow masculine external genitalia to develop.

4.






Abnormal development

There are a large number of potential problems with sex differentiation. They can occur at any of the four stages described above. An example is

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