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PSL300 Midterm study guide

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University of Toronto St. George
Michelle French

PSL300 1 Term Test Study Guide Page | 1 Membrane Potential Na+/K+ pump 3 Na out, 2 K in Inequality creates potential difference (pd) of -10mV Measured from inside of cell with regards to outside Pump creates concentration gradient for K+ Resting potential Due to K+ diffusing out of cell through K+ channels Channels are 2-pored Cations gather outside of cell At diffusion equilibrium net charge across membrane calculated by Nerst equation EK+ = (RT/F) ln([K+]o /[K+]i) But K+ is not the only thing that diffuses Use Goldman Equation Where concentration ratio for Cl- is reversed since it is an anion (gradient reversed) Resting potential -70mV Action Potential Membrane properties change to make the membrane more permeable to Na+ Net inward Na+ current ENa+=+60mV Voltage-Gated Na+ channels MW 2011 PSL300 1 Term Test Study Guide Page | 2 Opened by depolarizing membrane to threshold of -50mV Channels rapidly inactive ENa+never reaches 60mV: 30mV instead Na inactivation leaves K+ leakage to restore resting potential Refractory Period After potential drops below threshold channels can reconfigure Absolute None of channels reconfigured Relative Some of channels reconfigured but not all Depolarization Block If membrane is kept depolarized (eg. Excess extracellular K+) Na inactivation persists Membrane remains in absolute refractory state After-hyperpolarization Some membranes have voltage-gated K+ channels Opened by depolarization to threshold (like Na channels but slower) Outward K+ current occurs after Na inactivation Conduction Na channels of adjacent membrane opens Cable properties Conduction velocity along axon depends on the membrane length constant Measures how quickly a pot. Difference decays to zero as a function of distance Increased by increasing axon diameter or membrane resistance MW 2011 PSL300 1 Term Test Study Guide Page | 3 Myelination Increasing membrane resistance is easiest Specialized glial cells wrap around axon Creates a myelin sheath Small gap between are called nodes of Ranvier Has high density of voltage-gated Na channels No voltage-gated K channels These are found at paranodes In myelinated axons only nodes are excitable Saltatory conduction Jumping of a.p. from one node to next 5-10 nodes In unmyelinated axons Na and K voltage-gated channels are intermixed Remak bundle is slower One Schwann cell engulfs 5-30 axons Axon terminal A.p. cannot turn around due to refractory period Axons end in boutons filled with vesicles (of neurotransmitters) Bouton membranes have voltage-gated C++ channels Opened by depolarizing a.p. currents Vesicles released by inward C++ flow Vesicles usually docked around a polyhedral scaffold 1 a.p. has 10-90% chance of releasing 1 vesicle Synapse Gap between axonal bouton and adjacent neuron (200A wide) Ionotropic effect Ligand (neurotransmitter) binding opens ion channel Acetylcholine Nicotinic receptors Important for movements Glutamate GABA GABA-gated Cl- channels used for presynaptic inhibition Glycine Serotonin 5-HT3 ATP P2X Depending on channel (not ligand) Generates EPSP (Excitatory Post Synaptic Potential) Na+, K+ (in) MW 2011 PSL300 1 Term Test Study Guide Page | 4 Depolarizes membrane (starts a.p.) Or an IPSP (Inhibitory Post Synaptic Potential) Cl- (in), K+ (out) Maintains resting potential of membrane (inhibits a.p.) PSPs generated in inexcitable membranes (dendrites and cell bodies) Passive conduction of PSP to initial segment of axon Spatial summation 10-30 synchronous EPSPs in dendritic tree (each at different synapse) Temporal summation Few active synapses generating EPSPs at high frequency (summated over time) More than 50% of EPSP amplitudes reach initial segment IPSPs located close to initial segment easily polarizes cell Spike Trains Summated PSPs remain above threshold Voltage-gated K+ channels at initial segment: afterhyperpolarizations Hyperpolarization after each spike insures Na+ channels reconfigure Metabotropic effect Ligand-receptor binding activates an enzyme Usually via G-protein coupling Acetylcholine muscarinic receptors Peptides: substance P, -endorphin, ADH Cetecholamines: noradrenaline, dopamine Serotonin Glutamate mGluR GABA GABA reBeptors Purines: adenosine, ATP Free radicals: NO, CO Enzyme then catalyzes production of second messenger cAMP, cGMP, InP 3 2 messenger actives other enzymes Eg. Phosphokinases which phosphorylate ionotropic receptors Eg. -adrenoceptor Binding of noradrenaline activates adenylyl cyclise via G-protein alteration nd Creats cAMP (2 messenger) from ATP cAMP activates kinases Kinases phosphorylates membrane Ca++ channels Influx of Ca++ (important in heart muscles) For gaseous transmitters NO, CO, H2S Synthesized on demand by Ca++ influx into cell Eg. NO synthase, which catalyzes NO production from L-arg, activated by Ca++ NO binds to haem in guanylyl cyclise MW 2011
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