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The nervous system
- 2. Summary The nervous system and hormones enable us to respond to external changes. They also help us to control conditions inside our bodies. Hormones are used in some forms of contraception and in fertility treatments.
- 3. You should be able to: ■ evaluate the benefits of, and the problems that may arise from, the use of hormones to control fertility, including In Vitro Fertilisation (IVF)
- 4. Key terms Central nervous system Brain Spinal cord Stimulus / stimuli (plural) Receptor Impulse Neurones Nerve Sensory neurone Relay neurone Motor neurone Effector Synapse Reflex action Muscle
- 5. The Nervous System What are its component parts? • Brain • Spinal cord • Nerves What does it do? • Enables you to control your body • Gives you feedback about the world
- 6. Look away if you’re squeamish… A dissected brain, spinal cord and sections of major nerves.
- 7. The Cells of the Nervous System Neurones
- 8. The route impulses take
- 9. Receptors in the eyes are sensitive to ___________________ Receptors in the ears are sensitive to ___________________ Receptors in the ____________ are sensitive to changes in position Receptors in the _____________ and ___________ are sensitive to chemicals that enable us to taste and smell Receptors in the skin are sensitive to t________________, p_______________ and p_______
- 10. The route impulses take Sensory neurone Relay neurones (in brain or spinal cord) Effectors – Motor neurone
- 11. The Spine You don’t need to know any of these little details – just remember that the spinal cord carries messages to and from the brain.
- 13. Above: Sensory Neurone Below: Motor Neurone
- 14. Diagrams and Drawings in Biology
- 15. Nerves – bundles of neurones
- 16. Close-up of a nerve
- 17. Single neurones in cross-section
- 18. How Impulses Pass from Neurone to Neurone – the Synapse
- 19. Synapses
- 20. A Neuro-Chip
- 21. Reflex Reactions – bypassing the brain for extra speed
- 22. Reflex Reactions Can you think of any? • Startle reflex – moving away, contraction of arm and leg muscles, blinking, breathing changes • Withdrawal reflex – moving away from potentially harmful influences (e.g. high temperature) • Iris reflex – pupil becomes smaller in bright light
- 23. Knee Jerk Reflex
- 24. Why the knee jerk reflex? • This reflex is quite useful for walking. Every time you put weight on your foot, your muscles contract to support you. Without this reflex, we would all look silly staggering around, having to consciously think about working our muscles for each step, but with the muscles reacting too hopelessly late to be useful. Chewing gum at the same time would be out of the question.
Notas del editor
- (I don’t know why this image shows the pelvis – it isn’t part of the nervous system!) Ask students to discuss in groups what they think are the component parts of the nervous system. The brain and spinal cord make up the ‘central nervous system’ while the nerves comprise the ‘peripheral nervous system’. Students can then discuss what they think are the main functions of the nervous system before you reveal them.
- The nervous system – brain, spine and nerves - is made up of very specialised cells called nerve cells or neurones (also spelt ‘neurons’). They have all the main features of animal cells: cell membrane, cytoplasm, nucleus, etc. – but also some very specialised features which allow them to do their particular job. The large blob towards the lower left seems to be the cell body of a neurone, with an axon branching off to the right.
- Overview of the route signals take through the nervous system. The brain or spinal cord is sometimes referred to as the ‘co-ordinator’ in this process.
- Students must be clear about the types of neurones, in particular sensory neurones (from receptors to spine/brain, giving feedback on the outside world) and motor neurones (from brain/spine to effectors, which are usually muscles, enabling the brain/spine to control the body). These neurones are one-way only. For non-reflex reactions, there would be many relay neurones involved on the right, as the impulse from the sensory neurone enters the brain and the brain then makes decisions on how to respond, and sends impulses to the appropriate muscles.
- The key component here is the spinal cord, protected by the vertebrae of the spine. Nerves connect the spinal cord to all parts of the body.
- Not clear enough for students to copy, but gives them an idea of the two neurone types. Students could be asked to pick out similarities and differences between the two.
- More detailed – you may or may not wish to show this, as it shows more than students need to know at GCSE. For most syllabuses, they do not need to know the terms ‘synaptic endings’, ‘node of Ranvier’, ‘myelin sheath’ and ‘Schwann cell’.
- These are all images of motor neurones (except perhaps for the photo – I don’t know what type of neurones these two are…) This is to show students that there are many different ways of representing the same thing. Colours are not always realistic, but may be used in different ways for clarity.
- Again, notice that the colours do not necessarily reflect reality. Individual neurones are bundled together in nerves. The neurones do not interfere with each other, but all act independently, and each neurone is one-way only. A single nerve contains both motor neurones and sensory neurones. A nerve is a bit like a bundle of optical fibres used in telecommunications. Like all cells, nerve cells need energy to function. So the nerves also contain tiny blood vessels (capillaries) to carry oxygen and glucose to the cells.
- Magnified image showing neurones in a nerve.
- The axon (long part) of a neurone is surrounded by a fatty layer (called the myelin sheath). This acts as an electrical insulator. (Motor neurone disease is a disease which causes this insulator to break down. Signals leak out of the neurones and do not reach their destination muscles, so people with the disease gradually lose the ability to control their muscles.) The green bands in the image are the fatty insulation layer, highly magnified.
- The synapse is a tiny gap between one neurone and the next. The electrical signal reaches the end of the first neurone, and this triggers the release of chemicals. The arrival of these chemicals at the next neurone triggers the start of an electrical impulse. This is how the impulse gets from one neurone to the next. For most GCSE syllabuses, students do not need to know the terms ‘axon terminal’, ‘synaptic vesicles’ (‘sacs containing chemicals’ will do) or ‘neurotransmitter’ (‘chemicals’ is enough).
- Incidentally, you may be wondering why there should be synapses at all – why not have the neurones directly connected to one another, without a gap? One reason is to ensure that the flow of impulses is in one direction only. At a synapse, only one of the neurones contains sacs of chemicals for release, while the other is the only one with receptors for those chemicals.
- Not in GCSE, so you may want to hide this slide, but interesting to know that neurones can connect to each other in different ways. Taken from ‘Neuroscience For Kids’ at http://faculty.washington.edu/chudler/synapse.html
- It is just now becoming possible to take a single neurone and incorporate it into a microchip, in which the neurone acts as a tiny electrical connector. This may lead to some interesting possibilities in the future…mind-reading?...downloading your memories?
- Reflex reactions do not involve the brain; the brain is simply informed of them afterwards. The receptor causes an impulse along a sensory neurone, which connects to a relay neurone in the spine. Rather than taking the impulse up to the brain, it passes it directly to a motor neurone which causes a reaction in an appropriate muscle. Reflex reactions are usually there to protect the body from sources of danger, e.g. heat or injury. The body is full of ‘reflex arcs’ like this, ready for action should the need arise.
- Students can test out the iris reflex.
- Students could (carefully!) try this on themselves or each other. A hammer is not needed – the side of the hand works just as well. Gently tap just below the knee, and if you hit the right spot, the leg will jerk forwards. This movement is involuntary.