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Welcome to 632 Nerve Muscle and Movement Chris Elliott - [email protected] Sean Sweeney [email protected] John Sparrow - [email protected] Web page: http://biolpc22.york.ac.uk/632/ Course Overview Lectures Chris 2 : Nerve and Synapse Sean 2: Synapse development Chris 2: Channels John 4: Muscle Chris 4: Movement Nerve & brain lectures In B006 Nerve 1 Ionic basis of Resting and Action potentials 2 Mechanism of synaptic actions and neuromodulation 3 The Patch clamp approach to Neurobiology 4 Effect of Insecticides on Neural function Movement lectures Neural Control of singing and hearing in insects Locomotion Types & Principles of locomotion Walking running & jumping Swimming floating Flying – birds, bats & insects Not only lectures… Practicals - No Group Case Study 30% Exam 70% paragraph answers; paper criticism Case Study group of 4 - 7 work on problem together submit single report choice of 4 Studies Group list: Wednesday 3 May 1115 e-mail appointment; or come Wed 31 May deadline : Friday 2 June Books, etc Purves, D (et al) (2001) Neuroscience Sinauer Simmons PJ and Young D (1999) Nerve Cells and Animal Behaviour CUP McNeill - Alexander R. How Animals Move [CD Rom borrow in teaching] Other books on nerve Shepherd, G. M. (1994) Neurobiology. OUP An excellent text Nicholls, J et al (2002) From Neuron to Brain (4th ed) Robinson, D. Neurobiology (ISBN 3-540-637788): (1998) What needs explaining? what are nerve cells like? what happens at rest ? Resting potentials dynamic equilibrium what happens when activated? Action potentials All-or-none speed comparative differences Mammalian cells Brain has neurons 109 glia 3 • 109 blood vessels Parts of a neuron dendrite soma axon Identifying cells silver staining fluorescent dyes antisera Invertebrate cells Ganglion 400 to 106 cells nerve or neuron? Summary so Far Brains made of neurons and glia Squid neurobiology Contract mantle as fast as possible Big axon (250µM) insert electrodes replace contents Resting potential Cells are all negative contain K+ outside Na+ anions e.g. Cl have semipermeable membranes Squid giant axon Animations of resting potential Bezanilla http://pb010.anes.ucla.edu/ Resting potential Balance between diffusion and electrical force? Use Nernst Equation to test this out Conclusion: passive balance is OK for squids Ediff K in RT ln zF K out Ediff 440 56 log mV 20 Ediff 75mV Summary so Far Brains made of neurons and glia All cells have resting potentials Normally maintained passively by balance of diffusion and electrical forces Action potential membrane becomes permeable to Na+ Na+ floods in diffusion electrical K+ still goes out Squid giant axon Action potential Two crucial properties of the Na+ current starts at a voltage threshold stops itself Arise from Na+ channel channel is voltage sensitive and opens closes with a second mechanism -30mV closed open 1ms inactivated -70mV How do we know ? (i) Hodgkin & Katz replaced Na+ in the seawater How do we know ? (ii) Hodgkin & Huxley devised the voltage clamp experiment separates the ionic and capacitative currents use replace ions to determine role of each Interlude What is resistance ? Write it down now What are current and voltage? Write it down now V R I Use V for voltage use I for current Rule (Ohm’s law) V = IR Interlude What is capacitance? Write it down now Resistance Rule (Ohm’s law) V = IR - + V R I Rule C Q=CV dQ/dt = CdV/dt I = dQ/dt = CdV/dt H&H Experiment Voltage Step the clamp from -70mV to different voltages Current H & H (ii) Add tetrodotoxin and block Na+ current tetra-ethylammonium and block K+ current H&H reconstruction H&H measured the kinetics of the currents used this to postulated the kinetics of channels used this to build a mathematical model Animations of H&H model Bezanilla see http://biolpc22.york.ac.uk/632 Summary so Far Brains made of neurons and glia All cells have resting potentials Normally maintained passively by balance of diffusion and electrical forces Properties of Na and K channels determine action potential How does it spread? electrostatically How fast is the action potential? Up to 100m/s major component of latency to respond for 2m high human, 2/100*1000 = 20ms for a 40m dinosaur... slowed by capacitance How do we know? Myelinated axons run faster, capacitance is reduced channels only at Nodes of Ranvier Myelination Schwann cell (blue) grows round axon (orange) In Multiple sclerosis (MS) myelin sheath is disrupted Comparative neurobiology Action potentials are not all the same in vertebrates K+ current is very small in molluscs, Ca++ current supplements the Na+ only vertebrates have myelination, but all animals have glia protozoa have action potentials too A word of caution students often write conductance when they mean conduction conductance is a measure of permeability how easy it is for ions to cross the membrane conduction is the process of movement along the axon e.g. conduction velocity Final Summary Brains made of neurons and glia All cells have resting potentials Normally maintained passively by balance of diffusion and electrical forces Properties of Na and K channels determine action potential Capacitance (myelination) determines speed Web page: http://biolpc22.york.ac.uk/632/