NEU 330 Exam 2 Study Guide Fall 2024 PDF

NEU 330 Fall 2024 Dr. Lee Exam 2 Study Guide General notes on the exam: The format and expectations are the same as for Exam 1. Things to Know Lecture 9: Explain the difference between what is recorded in current clamp and voltage clamp recordings...

NEU 330 Fall 2024 Dr. Lee Exam 2 Study Guide General notes on the exam: The format and expectations are the same as for Exam 1. Things to Know Lecture 9: Explain the difference between what is recorded in current clamp and voltage clamp recordings If given traces that correspond to currents with a scale bar with pA or nA, this is voltage clamp. If the traces are APs, EPSPs, or IPSPs, this is current clamp (scale bar should be in mV) From a family of current traces, be able to plot the current-voltage relationship (I-V plot) Current would be on y axis, voltage on x-axis. You should remember to label the axes. For any ion, start by plotting the Eion (should be at a voltage where y = 0 since there should be no current at that voltage). In the positive direction, ask yourself which way the ion would have to move so that the voltage goes to Eion. For example for Na+, at 0 mV, Na+ would have to move into cell (negative current) to make Vm move towards ENa (+60 mV). Then do the same at a voltage positive to the Eion. For Na+ at 80 mV, Na+ would have to move out of the cell (positive current) to make Vm move towards ENa. Describe how the properties of leak K+ channels and voltage-gated K+ (Kv) channels underlie the differences in their I-V plots The leak K+ IV will be linear and will have inward current more negative to -80 mV (EK). Kv channels will not have inward current at negative to -80 mV since they do not open until Vm is around -50 mV. Then the current will gradually slope upwards (not linear at first) because voltage sensors of the channel are being activated sequentially as Vm gets more depolarized. Lecture 10: Recognize the difference between I-V and G-V relationships for different types of ion channels Conductance refers to how many channels are open. It can be determined from the I-V plot. For voltage-gated channels, the G-V curve is sigmoidal at reaches a maximum at very depolarized voltages. This means that on the I-V plot, the conductance is low at -80 mV and increases as you move along the x-axis (all channels would be open somewhere between +30 and +50 mV (high G)). The amplitude of the currents in the I-V plot depends on the driving force AND the conductance. For Kv channels, since EK is -80 mV, the current will continue to increase as you move positive along the x-axis since G and driving force are always increasing. For Nav, since  ENa = +60 mV, driving force is very high at negative voltages and gets smaller as you go more positive, even though G is increasing. So the Na current is U-shaped, and is small at -30 mV because G is low, and is small at +30 mV since driving force is small. Describe how driving force, conductance, and Vm are affecting the currents in the I-V plot See above Explain what is being measured in an inactivation plot Nav channels become inactivated shortly after they open. Therefore you can measure the voltage-dependence of their inactivation by inducing them first to open with different voltages. Inactivation can be measured by holding Vm at “pre” voltages that cause different amounts of opening and therefore inactivation, and then stepping to a “test” voltage so you can measure the current through the channels that are not inactivated. For Nav channels, the more depolarized the “pre” voltages, the greater the inactivation, and the smaller the test current. When pre voltage= holding voltage (around -80 mV), there should be no inactivation so that is the maximum current you can get. Dividing the amplitude of each test current test current with that maximum current value will give you the fraction of current that is not inactivated. If you plot this against the pre voltage, you get the inactivation curve, which should be sigmoidal again since voltage sensors move sequentially to open the channels. Drugs like lidocaine that increase Nav inactivation often shift the inactivation curve to the left (inactivate more at negative voltages, which means GNa is low and this could shorten action potentials). Predict how changes in the I-V or G-V relationships for ion channels would affect action potentials How would increasing GK or decreasing GNa affect the action potential width, height, the AHP, frequency, the refractory period, etc. Lecture 11: Describe different electrophysiological recording methods (patch clamp, intracellular recording, extracellular recording, EEGs) and what information they provide (voltage, currents, patterns of activity) **Be able to recognize traces representing recordings using these methods** Explain the different configurations of the patch clamp method and the types of experiments they can be used for Inside out: inside facing part of channel (intracellular) is facing out towards the bath solution. Outside out: outside facing (extracellular) part of channel facing out (towards the bath solution) Cell-attached: outside part of channel facing into the electrode solution (not in the bat  Be able to match recordings of data with how they were obtained (for example, recognize single channel recordings vs whole-cell patch clamp recordings) Lecture 12: Describe the classes of channels that are activated by force, temperature, or neurotransmitters Explain how patch clamp methods can be used to study the properties of these channels TRP channels are sensitive to hot (chili oil) and cold (menthol), Piezo channels are activated by steps of force, and ligand gated channels are activated by neurotransmitters. For ligand gated channels, outside out or whole cell patch clamp recordings are easiest since you can apply the ligand in the bath solution. Describe 2-3 differences between voltage-gated and ligand-gated channels For example, their structures, what activates them, how selective they are for particular ions. Regarding the latter, you should be able to distinguish an IV plot for voltage-gated and ligand gated channels (Think reversal/equilibrium potentials, linearity) Explain the difference between ionototropic and metabotropic receptors Speed of signaling, general structural features, how they affect ionic conductances Lecture 13: Explain the steps in synaptic transmission and how EPSPs and IPSPs affect neuronal excitability Note what channels are involved and where For synapses that use acetylcholine (Ach) or glutamate, list the key components and understand their roles in synaptic transmission NMJ vs neuron-neuron synapses—what do they have in common, what are the differences? For the I-V plot for Ach and glutamate receptors, explain the reversal potential and how it predicts the movement of Na+ and K+ ions and their effects on EPSPs What happens if the receptors had mutations that affected their permeability to Na or K? Why is the IV different for NMDA receptors after strong depolarization or with low Mg2+? Which glutamate receptor (AMPA or NMDA) is responsible for most of the EPSC? Lecture 14: Describe the Ca2+ hypothesis for neurotransmitter release and the evidence supporting it  How do we know it is Ca2+ and not Na+ in or K+ out that causes the release ? How does Ca2+ and causing vesicles to fuse with the membrane? Explain the difference between miniature EPPs and evoked EPPs and how they are studied mEPPs represent fusion of individual vesicles which occurs randomly. Evoked EPPs are triggered by presynaptic APs which increase Ca2+ in the nerve terminal which increases the probability that the vesicles will fuse with the membrane. Recognize the I-V plot for voltage-gated Cav channels and implications for neurotransmitter release Does it look like a Na+ channel or K+ channel IV? Where is the equilibrium potential? List the steps involved in synaptic vesicle release and the role of Ca2+ in this process In cases where synaptic transmission is impaired (e.g., myasthenia gravis) what steps could you interfere with or enhance to improve it? Lecture 15: Describe the effects of passive and active properties of dendrites in regulating the propagation of electrical signals Note that potentials get smaller and slower as they spread (recall why!) Note that action potentials can spread (backpropagate) from the axon hillock to the dendrites, causing Ca spikes in the distal dendrites. The Ca spikes always occur later than the somatic AP since Na channels activate faster and generally have a lower threshold for activation than Ca channels Explain the differences in temporal and spatial summation and recognize how the passive properties of dendrites affects them as well as some examples of each Make a chart summarizing these differences Lecture 16: Describe the I-V plot for GABA receptors and use it to predict how the currents would affect the membrane potential Remember that Cl- moving into the cell is the same as an outward (positive) current! Follow the steps under Lecture 9 above to plot the IV for GABA receptors. Explain how IPSPs occurring in different parts of the neuron would affect the summation of EPSPs Whenever an IPSP occurs between the site of the EPSP and the axon hillock, it will have a strong inhibitory effect If the IPSP and EPSP occur in different dendrites, the IPSP will have a small inhibitory effect  Explain the concept of shunting inhibition This is when the inhibitory input occurs between the site of the EPSP and the soma or axon hillock. Because the reversal potential for Cl- is around the resting potential, not much Cl- will move into the cell if GABA binds to the receptor at this voltage. However, because of the increase in conductance (lowering of Rm) caused by the open GABA receptors, the EPSP coming down the dendrite will not be able to depolarize Vm much (think V = I/G). At the same time, if the EPSPs end up depolarizing the membrane near the GABA receptors, that driving force will move Cl- into the cell which will also inhibit depolarization. Describe when the GABA conductance would have a depolarizing effect Early in development, the Cl- gradient changes so that the ECl gets more positive (to around -60 or -50 mV). Because of this, the Cl- current is moving out of the cell around at the resting potential (around -70 mV) when GABA binds to GABA receptors. This would mean GABA is excitatory rather than inhibitory. Lecture 17: Explain the significance of residual Ca2+ and different pools of synaptic vesicles for synaptic plasticity Describe the differences between short-term depression (STD) and short-term facilitation (STF) Explain what causes these forms of synaptic plasticity and what might increase or decrease them STD : characterizes synapses with high probability of release, is caused by the smaller RRP remaining after an initial AP Stronger STD could result from things that decrease residual Ca like Ca-dependent inactivation of Cav channels (decreasing their conductance), increasing Ca binding proteins, increasing Ca pump activity. Also anything that further decreased the RRP. STF: characterizes synapses with low probability of release, is caused by residual Ca2+ that can trigger the release of the larger RRP remaining after an initial AP Stronger STF could result from things that increase residual Ca like Ca-dependent facilitation of Cav channels (increasing their conductance), decreasing Ca binding proteins, decreasing Ca pump activity. Lecture 18: Describe what happens during long term potentiation (LTP) and long term depression (LTD)– the initial events that lead to them (the induction) and the events that cause the increase or decrease in the synaptic response (the expression) Explain how NMDA receptor can cause LTP or LTD LTP: Strong depolarization of presynaptic and postsynaptic neurons causes Mg2+ unblock of NMDA receptor, and the Ca2+ influx activates CaMKII and helps more AMPA receptors into the membrane and may phosphorylate these receptors to increase their function. These effects cause a longlasting increase in the EPSP. LTD: Weak depolarization of presynaptic and postsynaptic neurons causes Mg2+ unblock of NMDA receptor, and the Ca2+ influx activates phosphatases that dephosphorylate AMPA receptors, and also causes endocytosis of AMPA receptors out of the membrane. These effects cause a longlasting decrease in the EPSP. Explain the concepts of input-specificity, cooperativity, and associativity with respect to LTP Input specificity: LTP only occurs at synapses that were stimulated by an LTP inducing stimulus Cooperativity: need strong postsynaptic as well as presynaptic depolarization to get LTP (can be from strong stimulation of one presynaptic input or weaker stimulation of multiple synaptic inputs that spatially summate) Associativity: Weakly activated synapses near a strongly activated synapse can undergo LTP possibly because backpropagating action potentials would produce a strong depolarization affecting the neighboring dendritic spines