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BioKnowledgy Presentation on 6.5 Neurons and synapses

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BioKnowledgy Presentation on 6.5 Neurons and synapses

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BioKnowledgy Presentation on 6.5 Neurons and synapses

  1. 1. Essential idea: Neurons transmit the message, synapses modulate the message. 6.5 Neurons and synapses By Chris Paine https://bioknowledgy.weebly.com/ The image shows a tiny segment of a human brain the lines show neurons and the dots show synapses. The image is intended to illustrate both the how complex even a small mammal's brain is and additionally how important the synapses between neurons are; it is the synapses that drive communication and conscious thought. With the exception of the memory centre the number of cells in the human brain does not increase after birth, what increase is the number of connections and hence synapses between neurons. http://med.stanford.edu/mcp/_jcr_content/hero/hero_banner/images/ima geSlide8.img.620.high.jpg
  2. 2. Understandings Statement Guidance 6.5.U1 Neurons transmit electrical impulses. The details of structure of different types of neuron are not needed. 6.5.U2 The myelination of nerve fibres allows for saltatory conduction. 6.5.U3 Neurons pump sodium and potassium ions across their membranes to generate a resting potential. 6.5.U4 An action potential consists of depolarization and repolarization of the neuron. 6.5.U5 Nerve impulses are action potentials propagated along the axons of neurons. 6.5.U6 Propagation of nerve impulses is the result of local currents that cause each successive part of the axon to reach the threshold potential. 6.5.U7 Synapses are junctions between neurons and between neurons and receptor or effector cells. Only chemical synapses are required, not electrical, and they can simply be referred to as synapses. 6.5.U8 When presynaptic neurons are depolarized they release a neurotransmitter into the synapse. 6.5.U9 A nerve impulse is only initiated if the threshold potential is reached.
  3. 3. Applications and Skills Statement Guidance 6.5.A1 Secretion and reabsorption of acetylcholine by neurons at synapses. 6.5.A2 Blocking of synaptic transmission at cholinergic synapses in insects by binding of neonicotinoid pesticides to acetylcholine receptors. 6.5.S1 Analysis of oscilloscope traces showing resting potentials and action potentials.
  4. 4. 6.5.U1 Neurons transmit electrical impulses. Schwan cell
  5. 5. 6.5.U5 Nerve impulses are action potentials propagated along the axons of neurons. http://outreach.mcb.harvard.edu/animations/actionpotential_s hort.swf
  6. 6. 6.5.S1 Analysis of oscilloscope traces showing resting potentials and action potentials. https://phet.colorado.edu/en/simulation/neuron Use the PhET simulation to build an understanding of resting and action potentials and how they relate to the voltage changes in the axon membrane. The neuron lab worksheet activity acts as a guide for the investigation: https://phet.colorado.edu/en/cont ributions/view/3608 Investigate how neurons generate electrical impulses
  7. 7. 6.5.U3 Neurons pump sodium and potassium ions across their membranes to generate a resting potential. Plasma membrane is 50 times more permeable to K+ ions than Na+ n.b. proteins inside the nerve fiber are negatively charged which increases the charge imbalance. -70mV
  8. 8. 6.5.U4 An action potential consists of depolarization and repolarization of the neuron. The sodium-potassium pump (Na+/K+ pump) maintains the electrochemical gradient of the resting potential. Some K+ leaks out of the neuron (making the membrane potential negative, -70mv). 1 In response to a stimulus (e.g. change in membrane potential) in an adjacent section of the neuron some voltage gated Na+ channels open and sodium enters the neuron by diffusion. If a sufficient change in membrane potential is achieved (threshold potential) all the voltage gated Na+ channels open. The entry of Na+ causes the membrane potential to become positive (depolarisation) http://www.ib.bioninja.com.au/_Media/action_potential_med.jpeg 2 Action potential is the reversal (depolarization) and restoration (repolarization) of the membrane potential as an impulse travels along it.
  9. 9. Action potential is the reversal (depolarization) and restoration (repolarization) of the membrane potential as an impulse travels along it. 6.5.U4 An action potential consists of depolarization and repolarization of the neuron. The depolarisation of the membrane potential causes the voltage gated Na+ channels to close and the voltage gated K+ channels open. K+ diffuses out of the neuron rapidly and the membrane potential becomes negative again (repolarisation) 3 http://www.ib.bioninja.com.au/_Media/action_potential_med.jpeg 4 Before the neuron is ready to propagate another impulse the distribution of Na+ (out) and K+ (in) needs to be reset by the Na+/K+ pump, returning the neuron to resting potential. This enforced rest (refractory period) ensures impulses can only travel in a single direction.
  10. 10. Action potential is the reversal (depolarization) and restoration (repolarization) of the membrane potential as an impulse travels along it. 6.5.U4 An action potential consists of depolarization and repolarization of the neuron. http://www.ib.bioninja.com.au/_Media/action_potential_med.jpeg From McGraw Hill: http://goo.gl/tI2MD http://www.wiley.com/WileyCDA/
  11. 11. http://highered.mheducation.com/ol c/dl/120107/bio_d.swf 6.5.U6 Propagation of nerve impulses is the result of local currents that cause each successive part of the axon to reach the threshold potential. Propagation of a nerve impulse in un-myelinated axons http://cnx.org/resources/0d4d8e978090c5adf07cc1661372b69be3496ec6/Figure_35_02_04.png Cell body
  12. 12. 6.5.U4 An action potential consists of depolarization and repolarization of the neuron. http://www.psych.ualberta.ca/~ITL/ap/ap.htm http://www.mrothery.co.uk/images/nerveimpulse.swf More action potential resources: http://www.sumanasinc.com/webco ntent/animations/content/actionpot ential.html http://highered.mheducation.com/olc/dl/12 0107/anim0013.swf
  13. 13. 6.5.U2 The myelination of nerve fibres allows for saltatory conduction. http://cnx.org/resources/1a264d4943c1148665b7216c649d72ad774fc80b/Figure_35_02_05.jpg http://antranik.org/wp-content/uploads/2012/04/conduction-in-a-myelinated-nerve-fiber-saltatory-conduction.jpg myelination and saltatory conduction *The jump along the axon is actually just the very rapid conduction inside the myelinated portion of the axon. As myelin acts as an insulator myelinated axons only allow action potentials to occur at the unmyelinated nodes of Ranvier. This forces the the action potential to jump* from node to node (saltatory conduction). The result of this is that the impulse travels much more quickly (up to 200 m/s) along myelinated axons compared to unmyelinated axons (2 m/s). Saltatory conduction from node to node also reduces degradation of the impulse and hence allows the impulse to travel longer distances than impulses in unmyelinated axons. The myelin sheath also reduces energy expenditure over the axon as the quantity of sodium and potassium ions that need to be pumped to restore resting potential is less than that of a un-myelintated axon
  14. 14. 6.5.U7 Synapses are junctions between neurons and between neurons and receptor or effector cells. To function the nervous system needs to receive input/stimuli and then to coordinate a response to it. For this to happen impulses need to travel from sensory receptor cells via a series of nerve cells to effectors, which are commonly muscles and glands. There are junctions between each cell called synapses across which impulses cannot travel. A special group of molecules called neurotransmitters move across the synapse to effect an impulse in the adjacent cell.
  15. 15. http://outreach.mcb.harvard.edu/animations/synaptic.swf 6.5.U7 Synapses are junctions between neurons and between neurons and receptor or effector cells.
  16. 16. 6.5.U8 When presynaptic neurons are depolarized they release a neurotransmitter into the synapse. AND 6.5.U9 A nerve impulse is only initiated if the threshold potential is reached.
  17. 17. 6.5.U8 When presynaptic neurons are depolarized they release a neurotransmitter into the synapse. AND 6.5.U9 A nerve impulse is only initiated if the threshold potential is reached.
  18. 18. 6.5.U8 When presynaptic neurons are depolarized they release a neurotransmitter into the synapse. AND 6.5.U9 A nerve impulse is only initiated if the threshold potential is reached.
  19. 19. 6.5.U8 When presynaptic neurons are depolarized they release a neurotransmitter into the synapse. AND 6.5.U9 A nerve impulse is only initiated if the threshold potential is reached.
  20. 20. 6.5.U8 When presynaptic neurons are depolarized they release a neurotransmitter into the synapse. AND 6.5.U9 A nerve impulse is only initiated if the threshold potential is reached.
  21. 21. 6.5.A1 Secretion and reabsorption of acetylcholine by neurons at synapses. http://faculty.pasadena.edu/dkwon/chap%208_files/images/image61.png Acetylcholine is a neurotransmitter used in many synapses through the nervous system One use is at the neuromuscular junction, i.e. it is the molecule that motor neurons release to activate muscles. Interfering with the action of acetylcholine can cause a range of effect from paralysis to convulsions.
  22. 22. 6.5.A2 Blocking of synaptic transmission at cholinergic synapses in insects by binding of neonicotinoid pesticides to acetylcholine receptors.
  23. 23. Nature of science: Cooperation and collaboration between groups of scientists - biologists are contributing to research into memory and learning. (4.3) Gero Miesenböck FRS Waynflete Professor of Physiology, Wellcome Investigator Martin Booth Professor of Engineering Science Tim Vogels Sir Henry Dale Fellow (physicsist) Stephen Goodwin Professor of Neurogenetics, Wellcome Investigator Korneel Hens Group Leader (Biochemist) Scott Waddell Professor of Neurobiology, Wellcome Trust Senior Research Fellow in Basic Biomedical Sciences http://www.cncb.ox.ac.uk/team/ Nowadays scientists often work in multidisciplinary teams for example the Centre for Neural Circuits and Behaviour (CNCB) The aim of the CNCB is to understand how intelligence emerges from the physical interaction of nerve cells. Studying the brain from this top- down approach to answer such fundamental questions requires techniques and understanding from a range of disciplines.
  24. 24. Bibliography / Acknowledgments Bob Smullen

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