Course Notes: Week of September 14
Course Notes: Week of September 14 NSCI 3310
Popular in Cellular Neuroscience
Joseph Merritt Ramsey
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Popular in Neuroscience
This 3 page Class Notes was uploaded by Joseph Merritt Ramsey on Friday September 25, 2015. The Class Notes belongs to NSCI 3310 at Tulane University taught by Jeffery Tasker in Fall 2015. Since its upload, it has received 82 views. For similar materials see Cellular Neuroscience in Neuroscience at Tulane University.
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Date Created: 09/25/15
Action Potential Generation and Propagation 0 Voltage Gated Channels 0 Sodium I Trangent Nature turns o on its own closing despite the fact that the system remains depolarized 0 Closes on its own I Contains a Voltage Sensor that responds to the voltage change 0 This dynamic of opening and closing is actually what effects the channel s opening 0 Channel open randomly but with MUCH higher frequency in proper voltage 0 So the opening and closing and therefore action potential of a neuron is random and based on probability 0 Patch Clamp Gaygone s Seal Channel Clamped I No cellular ow occurring through a single isolated channel 0 This allows us to study a single channel and its nature helping figure out how it all works as a whole I Voltage Diagram 0 We see that the level reached as a result of the single channel opening is ALWAYS THE SAME on a per channel basis 0 Known as Conductant State they are either open all rushes in or not nothing comes in o In the Inward Mediated Current we see the cessation of channel entrance despite the sustained charge 0 But that experimental diagram only describes the negative nature of the current ow positive ow is entering the cell 0 But we can use Tetrodoxin to assess the Voltage Gated Sodium Channels 0 But we also see that they have a range of conditions under which they will open 0 Patch ClampVoltage Clamped Experiments I Now we control the Membrane Potential I Diagrams 0 Through these wee see a trend 0 The more Depolarized the cell is the I A Higher the amplitude of Response I B More of a consistent opening in channelsHigher positive currentMore outward ow of positive charge 0 Think about it I Chloride wants to get to its 60mV Potential but as we get further away the cell is becoming positive so Chloride will ow in to Polarize which is a Positive Current Positive is Exiting I Potassium wants to reach 80Mv Potential but further away the cell is positive so Potassium will rush out of the cell so a Positive Current positive Charge is leaving I Sodium the channel is still open under the mV environmental conditions so Sodium is still owing inward as it reaches for the 62mV charge Potential 0 Whole Cell Patch Clamp I Now we essentially pop the membranechannel so the channel is the electrode so we can now read and gauge the whole cell s current and response to stimuli o Allows for MacroscopicW hole CellEnsemble Current to be Read 0 From this observation we see how Single Channels accumulate to the Ensemble reading 0 Single channels have a at level reading but they stack and have similar tendencies 0 So with enough of them we have a linear curve Reiman Sums within the cell membrane I Negative Flow Positive Charge Entering the Cell 0 Quick and Trangent cause a Rising Phase almost immediately after injected Current I Positive Flow Positive Charge Leaving the Cell 0 Much more delayed and elongated 0 Potassium o Sustained Current Nature I They Open but also Close slowly so even after 65mV is restored some continue to remain open and Potassium continues to ow out 0 Results in Hyperpolarization State 0 They also want to keep moving out to attain the Eion of Potassium 80mV 0 But due to Leak Channels reaching 65mV restores the regular steady state of the cell 0 Components I Known as a Sustained Current 0 Keeps goingstays open until the voltage dictates otherwise 0 By this logic it is known as a Noninactivating Channel 0 It does not eventually shut off on its own as does Sodium I How Is This its Response 0 Potassium Voltage Gates Cannels contain 1 Voltage Sensitive Gate that responds to depolarization o Repolarization to Subthreshold Level closes the channel 0 With one channel it stays open and on as long as the proper depolarization is present 0 Only Contains and Activation Gate M Gate 0 Sodium o Trangential Nature I Inactivating Temporary 0 Components How can it be Inactivated despite Threshold Levels I Has two gates o 1 MGate Activation Gate 0 2 HGate Inactivation Gate 0 Responses to Depolarization I How 0 MGate responds by opening 0 HGate responds by closing I Each involve the movement of Positive Amino acids in the protein structure that shift as a result of the new positive surrounding 0 Ball and Chain on the HGate I Diagram 0 Positive Ball oats around attached to the Chain free oating in the negative cytoplasmic environment 0 But when the positive Sodium in ux occurs it repels the Positive Ball and blocks the channel nds af nity for a negative spot on the channel I The opening is extremely rapid but the closing is slower 0 Could not be at the same time they would cancel 0 So with Two Options for Two Gates M and H We have Four States I 1 Activated MGate I 2 Deactivated MGate I 3 Inactivated HGate I 4 Deinactivated HGate 0 Conductance o A large amount of channels contribute o Refractory Periods I Occur because of Ion Channels Nature and Timing I Absolute Refractory 0 Sodium channels are still closed as the cell is Polarizing again 0 Because of this no new action potential can be generated I Relative Refractory 0 Sodium has now Deinactivated action potential is possible again 0 But Potassium continues to ow out and hyperpolarize the cell so it may be around 75mV o In essence we now need more of a depolarizing effect to overcome the larger threshold difference