Generation of Action Potential Class notes
Generation of Action Potential Class notes BIOH 313-001
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This 6 page Class Notes was uploaded by Rebeka Jones on Tuesday September 27, 2016. The Class Notes belongs to BIOH 313-001 at Montana State University taught by Noudoost, Behrad in Fall 2016. Since its upload, it has received 4 views. For similar materials see Neurophysiology in Cell Biology and Neuroscience at Montana State University.
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Date Created: 09/27/16
Generation of the Action Potential Reminder: Several types of stimuli control the opening and closing of channels Ligand, phosphorylation, voltage, stretch or pressure Ligand and stretch channels on the dendrite side create local potentials The trigger zone is on the axon hillock and is controlled by voltage gated channels and create action potentials Voltage-Clamp Technique -How to study action potentials -set voltage across cell at certain level by injecting a current into the cell to achieve specific voltage -by measuring how much current you are sending into the cell you can measure how much the cell voltage changes -the amount of current you send in will compensate the currents in the cell You have a cell that is clamped at -60mV and you want to change it to - 50mV. Some positive ions in the cell now want to go out because it is not at resting membrane potential. You can now see a current be ing injected into the cell to keep it at -50mV. -first there will be a flux of cations outside the cell -then there will be a flux of cations inside the cell -a small depolarization is accompanied by capacitive and leakage currents -a larger depolarization results in larger capacitive and leakage currents, plus an inward current followed by and outward current -depolarizing the cell in the presence of tetrodotoxin (which blocks the Na+ current) and again in the presence of tetraethylammonium (which blocks the K+ current) reveals pure K+ and Na+ currents after subtracting Icand l I **review video on action potential and voltage clamp can be found on D2L under AP components 2 If the membrane is repolarized after a brief depolarization (line A) both gNa and gK return to their initial values. If the depo larization continues (line B) the Na+ channels close before depolarization is terminated, whereas K+ channels remain open and gK increases throughou t the depolarization. -Basically if you keep the voltage lo nger the sodium channel will open and close no matter but potassium channels will stay open until the current is removed. Also, the potassium channel closes slower than the sodium channel does. -sodium channel has two gates: one gate starts open (activation gate) and one starts closed (inactivation gate) …. there is a delay for the second gate……so the activation gate opens and then for a short time both gates 3 are open. Then at some point later the inactivation gate closes so both gates are closed…. then it returns to its resting form with one closed and one open…. this is why the sodium gate can only be open for a short amount of time and the flux is transient -The state when both gates are closed is called absolute refractory period just after the gate returned to its resting form it takes more depolarization to trigger the gate again. -potassium channel has one gate Both channels are triggered by changing the voltage enough to pass the threshold 4 The Sequential opening of voltage-gated Na+ and K+ channels generates the action potential Two similarities: -They both open in response to depolarization - The probability to open depends on the magnitude of depolarization Two difference: -The latency to open is different -Their response to long term depolarization i s different, Na channels inactivates but K channels stay open Two mechanisms to end up the depolarization 1) Gradual activation of voltage-gated channels 2) Late inactivation of voltage-gated channels Four important features 1) All or none behavior a. If the change in voltage does not meet the threshold the action potentials will not happen 2) Refractory period a. The absolute refractory period comes immediately after the action potential; during this period, it is impossible to excite the cell b. The relative refractory period follows and it is possible to trigger an action potential but only by applying stronger stimuli 3) Trigger zone 5 a. The trigger zone of the neuron has the lowest threshold for action potential generation, in part because it has an exceptionally high density of voltage- gated Na channels. In addition, it typically has voltage-gated ion channels that are sensi.ve to relatively small deviations from resting potential. These channels are important in determining whether synaptic input will drive the membrane potential to spike threshold 4) Variability/flexibility of action potentials a. Variations in the Proper.es of Voltage-Gated Ion Channels Increase the Signaling Capabili.es of Neurons b. The Nervous System Expresses a Rich Variety of Voltage - Gated Ion Channels c. Gating of Voltage-Sensitive Ion Channels Can Be Influenced by Various Cytoplasmic Factors d. Excitability Properties Vary Between Regions of the Neuron e. Excitability Properties Vary Among Neurons f. The Signaling Functions of Voltage-Gated Channels Can Be Related to Their Molecular Structures Repetitive firing properties vary widely among different types of neurons because the neurons differ in the types of voltage-gated ion channels they express. 6
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