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KA 3: The cells of the nervous system and neurotransmitters at synapses (a) Structure and function of neurones NS cells and neurotransmitters at synapses (b) Neurotransmitters at synapses (e) Mode of action of recreational drugs (d) Neurotransmitters, mood and behaviour (c) Function of converging, diverging and reverberating pathways By the end of this section you will be able to ….. • Be able to identify the following structures in a diagram: – Dendrites – Cell body – Axons – Myelin sheath • State the function of the above structures • State what is what meant by myelination • State the difference in impulse conduction between 2 year olds and adolescents and adults • Describe the effects of destroyed myelin sheaths • State 4 functions of glial cells Neurones • The CNS is complex network of: – Nerve cells called NEURONES • They receive and transmit electrical signals – Glial cells • Support and maintain the neurones Neurones • The human body contain billions of neurones, which must all be coordinated to provide the body with rapid means of communication and control. • There are 3 types of neurones which are structurally adapted to suit their function: – Sensory neurones – Inter neurones – Motor neurones Structure of a Neurone Cell body Axon Direction of impulse Dendrites Myelin Sheath Node (gap lacking myelin) • Axon – a single nerve fibre that carries impulse away from cell body to the next neurone (or in the case of motor neurone, to the muscle or gland) • Cell body – control centre of cell’s metabolism, contains a nucleus and clusters of ribosomes • Dendrites – (several) receive nerve impulses and pass them onto the cell body • Myelin Sheath - fatty material which surrounds the axon which: – Insulates the axon and – Increases speed of conduction from node to node Remember the pathway! DENDRITES CELL BODY AXON Myelination • Myelination is the development of myelin around axon fibres • It is a long process – myelination is not complete at birth, so continues from birth to adolescence. • As a result, responses to stimuli in the first two years of life are not as rapid or coordinated as those of an older child or adult Myelination Destruction of myelin sheaths • In some diseases (such as polio, multiple sclerosis and Tay-Sachs disease) the myelin sheath around the axons becomes destroyed or damaged. • This can cause a loss in coordination and therefore affects physical movement Name of Disease Polio Multiple Sclerosis Tay-Sachs disease Causes Symptoms Treatment Polio • Caused by virus • Virus spreads along nerve pathways destroying motor neurones • Fever, neck and back muscle pain, asymmetrical weakness of certain muscles, paralysis of 1 or more limbs • No cure • Only pain treatment • Polio vaccine for prevention Multiple Sclerosis • Unknown cause • Some studies suggest autoimmune destruction of myelin sheaths • The demyelinated nerve fibres are unable to transmit nerve impulses efficiently • Numbness, walking difficulties, impaired vision, progressive loss of coordination, can be persistent or sudden attacks • No cure • Helping to regain functions after attacks • Other treatments to reduce attacks available, but they have adverse side effects Tay-Sachs Disease • Caused by a genetic disorder where by the sufferer will inherit a defective recessive allele from both parents • Sufferer cannot make an enzyme which breaks down a fatty material, so this fatty substance builds up around the neurones – they become swollen (distended) and incapable of functioning • Region of retina shows up as a red spot • Infantile TSD = continuous deterioration of physical and mental abilities from 6 months, deaf, blind, paralysis, death at 4 years • No cure. Care can be given to ease symptoms Glial Cells • Several types of glial cells • Physically support neurons and produce the myelin sheath. • They also maintain a homeostatic environment around the neurones and remove debris by phagocytosis. Task: use page 248 to label your diagram Summary • https://www.youtube.com/watch?v=cUG uWh2UeMk