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7.7 Neurogenesis

Brains contain within them the seeds of their own salvation and the seeds of their own destruction. In its early stages, the brain produces vast numbers of neuroblasts as stem cells divide at a huge rate, churning out millions of potential neurons. By birth in humans, this process of neuronal proliferation has virtually stopped. There are, however, some localised areas of the brain, in the olfactory lobe and the hippocampus, for example, where neuronal stem cells survive well into adulthood.
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7.2 Selected to survive: studies of the PNS

Viktor Hamburger carried out a series of classic embryologieal experiments over a period of about 30 years. He investigated the relationship between the size of target tissue in chick embryos and the size of the pool of neurons that innervated it. His technique was to remove or add target tissue to the tissue which would eventually form a limb, usually the hind limb, and is called the limb bud. A few days later he observed the effect of the tissue addition or removal on the pool of neurons de
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6.4 Crossing the midline: a case study

Many neurons on the left side of the body make contact with targets on the right, contralateral, side of the body, and vice verse. Crossing the midline is particularly prevalent in descending neurons (e.g. the Betz cells mentioned earlier) and interneurons in the spinal cord which form part of the sensory pathways. However, not all spinal cord interneurons cross the midline: short distance interneurons which influence motor neurons and certain neurons of the spinoreticular tract are ipsilater
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4.3 Small babies: the sequel

Evidence that some of the consequences of being born prematurely were enduring was discussed in Section 3.2. However, what emerges from Section 4.2 is that the quality of maternal care can alter the course of development. So the question arises as to whether the course of development of premature babies can, likewise, be altered
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1.1 Introduction

This unit addresses the question of how the differences between individuals, especially in behaviour, arise during development. Development, the transformation of the single cell, the zygote, into an adult organism with billions of cells, numerous organs and an intricate, functioning nervous system, is one of the most remarkable feats of living systems. The process begins when an egg cell, or ovum, is fertilised by a sperm, or spermatozoon. The resultant single cell, the zygote, divides to pr
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Introduction

This unit examines issue of nature and nurture, how genes and the environment interact in the development of the nervous system to make each of us unique. In particular it looks at the period from conception to birth. It is a topic that should be of wide interest to students.

This unit is an adapted extract from the Open University course Biological psychology: Exploring the brain(SD
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3.8 Key points about vitamins

  1. Vitamins A, D, E and K are fat-soluble; the remainder are water-soluble.

  2. Adequate amounts of vitamins are required, many on a regular basis, though some can be stored.

  3. A balanced diet should provide the necessary amounts of vitamins, but people on a restricted diet need to take particular care to ensure an adequate intake of all of them.

  4. Deficiency diseases can occur when vitamins are absent or in short sup
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Introduction

In this unit you will find out that the sensation of pain is caused by the release of a chemical called prostaglandin that stimulates the nerve endings and sends an electrical message to the brain. Inhibiting the formation of prostaglandin reduces pain and we will see, by looking at the specific shape of the molecules involved, how aspirin can so inhibit the formation of prostaglandin. To make the most of the material of this unit you will need to use an organic molecular modelling kit such a
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Introduction

Genes are units of inheritance that contribute to a person’s behaviour and health. In this unit you will learn what genes, DNA and chromosomes are and how they combine to make the human genome. You will also learn how the principles of inheritance work, the effect that our genetic make-up has on health, and how genetic material is passed on from generation to generation.

This unit is an adapted extract from the course Author(s): The Open University

3 The flow of information from DNA to RNA to protein

The information flow from DNA to protein is more complex than shown in Figure 1. The genetic information encoded within the DNA of a gene is carried via an intermediary molecule, RNA (ribonucleic acid). Information within a cell can therefore be seen as passing from DNA, via RNA, to a protein. This flow of information can b
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1.1.6 Late-onset multifactorial disorders

It is becoming clear that many, if not most, of the common diseases that affect the Western world are multifactorial disorders with some inherited genetic component. Some of the genes that render individuals susceptible to diabetes, coronary heart disease, hypertension and many cancers, including breast cancer, have been identified and can be tested now for the presence of mutations. Multifactorial disorders present a real challenge for genetic medicine. For example, while it may be true that
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1.1 What is genetic testing?

When most people encounter genetic testing today, it is usually in a medical context. We may be referred by our GPs to a regional genetics unit, or we may approach our doctors, asking for genetic tests because we suspect something about our family history. In this unit we look at the issues and problems facing individuals and families when confronted with genetic testing.

The technologies that make genetic testing possible range from chemical tests for gene products in the blood,
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Introduction

This unit looks at three different uses of genetic testing: pre-natal diagnosis, childhood testing and adult testing. Such tests provide genetic information in the form of a predictive diagnosis, and as such are described as predictive tests. Pre-natal diagnosis uses techniques such as amniocentesis to test fetuses in the womb. For example, it is commonly offered to women over 35 to test for Down's syndrome. Childhood testing involves testing children for genetic diseases that may not
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Acknowledgements

The content acknowledged below is Proprietary (see terms and conditions) and is used under licence. This content is made available under a Creative Commons Attribution-NonCommercial-ShareAlike 2.0 Licence

Grateful acknowledgement is made to the following sources for permission to reproduce material in this unit:


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4.3 Type-II superconductors

For decades it was assumed that all superconductors, elements and alloys, behaved in similar ways, and that any differences could be attributed to impurities or defects in the materials. However, in 1957, Abrikosov predicted the existence of a different sort of superconductor, and Figure 23 shows direct evidence for the existence of what are now known as type-II superconductors. A comparison of Figures 23 and 22 indicates that the effect of an applied field on a type-II superconductor is rath
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3.3 The London equations

A simple but useful description of the electrodynamics of superconductivity was put forward by the brothers Fritz and Heinz London in 1935, shortly after the discovery that magnetic fields are expelled from superconductors. Their proposed equations are consistent with the Meissner effect and can be used with Maxwell's equations to predict how the magnetic field and surface current vary with distance from the surface of a superconductor.

In order to account for the Meissner effect, the L
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3.2 Magnetic field in a perfect conductor

When discussing the Meissner effect in Subsection 2.3, we argued qualitatively that a material that just had the property of zero resistance – a perfect conductor rather than a superconductor – would maintain a constant magnetic field in its interior, and would not expel any field that was present when the material became superconducting. We shall now show how that conclusion follows from an application of Maxwell's equations to a perfect conductor. We can then see what additional assumpt
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3.1 A two-fluid model

As was mentioned earlier, a substantial dose of quantum mechanics would be required to provide a full explanation of the properties of superconductors. This would take us too far away from electromagnetism, and we shall therefore restrict our discussion to aspects that can be discussed using classical concepts of electromagnetism.

We shall model the free electrons within a superconductor as two fluids. According to this two-fluid model, one fluid consists of ‘normal’ electron
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2.2 Persistent currents lead to constant magnetic flux

An important consequence of the persistent currents that flow in materials with zero resistance is that the magnetic flux that passes through a continuous loop of such a material remains constant. To see how this comes about, consider a ring of metal, enclosing a fixed area A, as shown in Figure 6a. An initial magnetic field B0 is applied perpendicular to the plane of the ring when the temperature is above the critical temperature of the material from which the rin
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2.1 Zero electrical resistance

In this section we shall discuss some of the most important electrical properties of superconductors, with discussion of magnetic properties to follow in the next section.

The most obvious characteristic of a superconductor is the complete disappearance of its electrical resistance below a temperature that is known as its critical temperature. Experiments have been carried out to attempt to detect whether there is any small residual resistance in the superconducting state. A sensitive t
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