2 2 Neurons Passive Potentials BIO 361T Fall 2014 1 Calculate the equilibrium potentials for Na and K in mV Show your work Na 61 mV K 90 mV 2 On the graph draw two horizontal lines representing the Keq values you calculated 3 In order to depolarize does the neuron increase its membrane permeability to Na or K assume all transport is passive For whichever ion you did not choose explain why Na If it were K it would go in causing hyperpolarization 4 In order to hyperpolarize does the neuron increase its membrane permeability to Na or K assume all transport is passive For whichever ion you did not choose explain why K If it were Na it would go out causing depolarization 1 2 5 Would your answer to either 3 or 4 change if active transport were a possibility Why or why not Yes both Active transport is against the electrochemical gradient so either ion could be responsible Rewrite 3 without assume all transport is passive and answer it 6 In the boxes above the graph draw arrows that illustrate the direction and relative magnitude of the chemical and electrical gradients for Na and K Each of the four boxes should have four arrows the first one is done for you For each box label which direction Na and K will each tend to flow i e the direction of the electrochemical gradient for each Confirm that this matches the relative magnitude of the gradients as indicated by the arrows you drew Na in K out for all panels 7 Look at all four panels and identify any patterns in the direction of the electrical gradient for each ion Identify patterns in the direction of the chemical gradient for each ion Electrical gradient is always into the cell Chemical gradient for Na is always in chemical gradient for K is always out 8 Given your answer to 6 explain how the membrane changes potential in terms of electrical and chemical gradients Changes in DIFFERENCE between electrical and chemical gradients 9 Imagine you have a neuron that hyperpolarizes when exposed to a particular neurotransmitter due to binding a ligand gated K channel Give three mechanisms by which the magnitude of hyperpolarization can be varied Number of channels number of neurotransmitters affinity of neurotransmitter for channel length of time it remains bound changing the resting potential changing intra or extra cellular K 10 Graded potentials are initiated at the dendrite or soma membrane and must travel to the axon hillock How does the nature of graded potentials exert a functional limit on soma size They decay over space so the soma cannot be too big or the graded potential will never reach the axon hillock 11 In the graph below label each panel as either spatial summation temporal summation or no summation Some terms may be used more than once or not at all
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