Unit 2 The Biological Approach Content CNS, genes, neurotransmitters and hormones

We will be examining The role of the Central Nervous System and Neurotransmitters in human behaviour.

The Nervous System has 2 main parts – the Central Nervous System (CNS) and the Peripheral Nervous System (PNS) The CNS consists of the brain and the spinal cord. The brain is protected within the skull and the spinal cord is protected within the vertebrae.

Parts of the brain and spinal cord Remember to check out the brain tutorial on I Learn

Neurotransmitters Neurotransmitters are chemical messengers that act between the neurones in the brain. This allows the brain to process thoughts and memories. Neurones receive and transmit messages, passing them from cell to cell.

How Synapses work You need to be able to explain how messages are passed via neurotransmitters

Neurotransmitters continued: RECEPTORS can be thought of as locks – if a certain chemical (neurotransmitter) fits like a key, then the message is passed on: if it does not fit then the message is blocked.

Manufactured drugs work in this way they are made to mimic neurotransmitters, they more or less fit certain receptors and are received like neurotransmitters. Some drugs block the message – they fit the receptor, so the natural neurotransmitter cannot pass the message on because the receptor is not available.

Place the following in the correct order see worksheet The axon terminal of one neurone reaches to the dendrites of another. The synaptic gap or cleft sits between two neurones. At one end, a neurone has dendrites which surround the nucleus. On one side, at the dendrites, there are receptors of a certain shape, prepared to receive the neurotransmitter from another neurone. From the nucleus, there is a long extension called an axon, which reaches to an axon terminal. If the neurotransmitter fits the receptor the message is passed on; if it does not, the message is blocked. Between the terminal and the dendrites, there is a gap called a synapse.

This is an amazing site that will add to your understanding http://outreach.mcb.harvard.edu/animations/synaptic.sw If you missed the lesson this would be essential viewing!

Genes

A GENE contains a set of instructions. It is a carrier of information. A gene consists of a long strand of DNA A chromosome is a double chain of DNA Every nucleus in every cell in the body contains a set of 23 Chromosomes.

Each individual human has a genotype – this is the genetic composition Each person has a phenotype which is what the individual becomes when their genes interact with each other and the environment. I may have a genotype which indicates I will grow tall. However if I grow up without adequate nutrition this gene may never become my phenotype

Some genes always lead to certain characteristics; these are known as dominant genes – to produce a characteristic, dominant genes need to be on only one pair of chromosomes. Some genes need more than one copy to produce a characteristic; these are known as recessive genes – if a recessive gene is present on only one of the pair of chromosomes, the characteristic will not appear. However, they can be passed on and may appear in a future generation. Characteristics can be aspects of appearance, personality or behaviour.

Examples of the effects of genes on humans Some diseases and characteristics are sex linked – they are controlled by the sex genes. e.g. most colour blind people are men If one parent contributes two copies of chromosome 21, then the child has three copies and the consequence is Down’s Syndrome. Human chromosome 4 has a marker known as G8 – if a parent and child both have Huntingdon’s Disease, then in 98% of cases they both have the same form of G8 marker – suggesting that the gene for Huntingdon’s travels with the G8 marker

Huntingdon’s Disease

Environmental triggers on genes Sometimes genes do not influence physical characteristics unless the ‘right’ environmental conditions occur. These genes are known as epigenetic

PKU

The Nature – Nurture Debate What do psychologists mean when they talk about the nature – nurture debate? Write down some characteristics that you have which you believe are caused by nature. Write down some characteristics that you have which you believe are caused by nurture. Which characteristics may be caused due to an interaction between nature and nurture?

In this section we will examine the Biological explanations for gender development – we will…. Consider how biological psychologists might explain sex & gender Examine chromosomal influences on sex/gender development Examine hormonal influences on sex/gender development

Sex chromosomes The genetic blueprint for a person is organised into 23 pairs of chromosomes 22 pairs are both X shaped. The 23rd depends on whether the person is female or male XX – female XY - male

Sex chromosomes

Chromosomes & hormones You can read about this in more detail in your text book. An embryo will develop as a female unless instructed otherwise The Y chromosome contains instructions for the embryo to produce androgens (male sex hormones) These cause the embryo to develop along the ‘male path’

Sexual development At about 6 weeks gestation the GONADS or sex organs begin to develop but there is no difference between the developing sex organs of males and females at this stage. The SRY gene in the Y chromosome produces a protein called ‘testis-determining factor’ which instructs the gonads to develop into testes rather than ovaries. Once this has happened hormones take over….

HORMONES Read p106 In your text book

There are a number of hormones involved in sex development H-Y antigen hormone – stop ovaries developing and starts testes development Anti Mullerian Hormone –prevents the further development of female genitals Hormones dictate gender differences and cause male and female brains to develop differently!!!! g

The Male Brain - Joke!!

The Female Brain -Joke!!

Seriously though! Abnormal sex differentiation and development Problems with sex differentiation can occur at any time during development. Problems can arise at fertilisation – e.g. boys with XXY chromosomes develop Klinefelter’e syndrome and girls with XO chromosomes have Turner’s syndrome. Incorrect Mullerian or Wolffian duct development can also cause problems – the foetus might not respond to androgens, in which case the foetus will have neither male nor female internal duct structures and lack of the Mullerian (female) inhibiting substance but with androgen secretion can lead to a foetus having both male and female duct structures.

Klinefelter’s syndrome Physical differences (stature, limbs) Underdeveloped genitalia Gynaecomastia in some cases Poor language abilities, learning difficulties ‘Shy and passive’ temperament

Klinefelter’s syndrome

Klinefelter’s syndrome

Turner’s syndrome

Turner’s syndrome Physical differences (neck, stature) Underdeveloped ovaries, lack of menstruation at puberty Poor spatial and mathematical abilities Poor social adjustment

Turner’s syndrome

Hormones Like neurotransmitters, hormones carry messages However, the messages are passed much more slowly because hormones travel in the bloodstream They affect numerous processes such as growth, development, mood and metabolism

Hormones are produced by endocrine glands, which are groups of cells and include the pituitary, thyroid and adrenal glands They are also produced by males in the testes and females in the ovaries The female hormones are oestrogen and progesterone The male hormones are androgens such as testosterone

Hormone differences can affect health and lifestyle throughout a person’s life. For example – more females develop pain syndromes like fibromyalgia and they also tend to suffer more from mood disorders such as depression and anxiety. On the other hand, more men than women are likely to develop alcoholism and to abuse drugs.

A great deal of research into hormones and gender development is conducted on animals!

Brain Lateralisation see p106 What is meant by the term brain lateralisation? What are the 2 parts of the brain known as? What connects the 2 parts of the brain? It is claimed that the left and right sides of the brain are concerned with different things – what are these? What evidence is there for brain lateralisation? You will need evidence from studies e.g.Pfeiffer

Test your Brain Sex You can do this by logging on to the following link and completing the test – it will take about twenty minutes. http://www.bbc.co.uk/science/humanbody/sex/index_cookie.shtml Have a go, you may be surprised by what you find out!

Evaluation of biological explanations for gender development We can use the case of David Reimer The results of biological explanations are based on tests that can be repeated e.g. injecting rats with additional testosterone or using MRI scanning in humans to detect blood flow. The results are replicable and can be shown to be reliable

Different research methods are used and tend to come up with similar results e.g. sex differences in brain lateralisation. There is a problem with generalisability because many findings come from animal studies; there are important differences in the human brain, so some findings may not be relevant to humans and may not be credible. Biological aspects are difficult to study without reference to the environment; for example male and female children are reinforced for different behaviour; this may mean that they use different strategies to do tasks rather than that they have different brain structures (SLT)

Think about Pseudo hermaphrodites – e. g Think about Pseudo hermaphrodites – e.g. Daphne Went – this evidence refutes the genetic explanation of gender development. How? Androgenital syndrome and Androgen sensitivity syndrome support the argument that pre natal exposure to certain hormones determines gender development – hormone exposure can override genetic sex. There is an argument that gender is a result of interaction between biology and environment. From the moment a child is conceived it is subject to influence from the environment…can you think of an example?