10 9 14 Are your 100 billion neurons ring How to Communicate Coordinate Electrical Signals Lesson 21 BIOL 1108 10 October 2014 1 Unit Animal Form and FuncIon Today s Topic Electrical Signals Today s learning objecIves Be able to describe the range of vertebrate nervous systems describe informaIon processing idenIfy neuron structure and funcIon describe the basis of membrane potenIal 2 1 10 9 14 This is your brain This is your brain on colored proteins 3 B SEASTAR C CRICKET A HYDRA cnidarian D SQUID E SALAMANDER 4 2 10 9 14 Central Nervous System CNS Brain Peripheral Nervous System PNS Cranial Nerves Spinal Cord Ganglia Outside CNS Spinal Nerves 5 Sensory Input Integration Center Sensor Motor Output Effector Peripheral nervous system Central nervous system 6 3 10 9 14 Organelles 1 Dendrites 2 Cell Body 3 Axon Hillock Signals generated 4 Myelin Sheath Insulation increases speed Schwan Cell The funcIonal unit of the nervous system Neuron 5 Node of Ranvier Gap helps signal leap down axon 6 Axon transmits signal from cell to cell 7 Axon terminal 7 Figure 48 9 TECHNIQUE Microelectrode Voltage recorder Reference electrode 8 4 10 9 14 Membrane potenIal The charge di erence or voltage mV between the inside and outside of the axon Measured relaIve to the extracellular uid How is a negaIve charge built up inside the axon ResIng potenIal Between a60 mV and a80mV 9 Why is the axon resIng membrane potenIal a70mV Electrical Charge Active transport Net movement of K out of the cell since there are more K channels More diffusion out less diffusion in Pumps in more K than Na 3 Na out 2 K in keeps charge inside 10 5 10 9 14 Equilibrium PotenIal Eion when the electrical gradient opposes the concentraIon gradient a Calculated using the Nernst EquaIon a Depends on the concentraIon gradient EK a90mV ENa 60 mV E ion 62 mV log ion inside ion outside E Na 62 mV log 150 mM 15 mM 60 mV 11 WORKSHEET Experiment in Ion Flow Across Semiapermeable Membranes Experiment Potassium K Flow IdenIfy the process draw the ion distribuIon and predict the voltmeter reading less negative Becomes less positive 0 mV mV Less mV Voltmeter mV Voltmeter mV Voltmeter mV Measuring electrode Na Step 1 K T Diffusion t Step 2 Semiapermeable membrane perm to K only Electrical Force Net flow of K t Step 3 Equilibrium potential for K Process underlying the movement of all molecules What is the process by which the ions move Draw the resulIng ion distribuIon in step 2 When there is no nemlow i e the system has reached equilibrium is the voltmeter reading posiIve or negaIve When charged ions are involved a second process becomes important What happens when similar charges are genng close to each other This process is driven by Combined e ect Predict what will happen in step 3 Draw the ion distribuIon How does the voltmeter reading compare to step 2 When the ions moved by process 1 are equal to the amount of ions moved by process 2 no nemlow occurs and the system has reached equilibrium The voltmeter reading at this point is the equilibrium potenIal for K EK PracIce Sodium Na Flow On a separate sheet of paper draw the expected outcomes if the membrane were only permeable to Na 6 10 9 14 Animal Form and FuncIon Electrical Signals Today s learning objecIves Be able to describe the range of vertebrate nervous systems describe informaIon processing idenIfy neuron structure and funcIon describe the basis of membrane potenIal Think about How does the nervous system aid in homeostasis 13 7