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29 Cards in this Set
- Front
- Back
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1. What are the two types of signals that neuron participate in?
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1) Graded Potentials
2) Action Potentials (a.k.a. spikes, nerve impulses) |
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2. How do action potentials differ from graded potentials?
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1) Action potentials only occur along the axon, where Graded potentials can occur anywhere on the neuron.
2) Action potentials are ALWAYS depolarizing, whereas Graded potentials can be either depolarizing or hyperpolarizing. 3) Action potentials are only initiated at the Axon Hillock, whereas Graded potentials occur Postsynaptically. 4) Action potentials are all-or-none, whereas Graded Potentials decay with distance. 5) All Action Potentials are identical for any given neuron (all have same amplitude, travel at the same speed etc.), whereas Graded potentials are variable. |
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3. Where is the only place where Action potentials begin?
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At the Axon Hillock
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4. Why don’t dendrites have Action potentials?
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Action potentials require particular channels called “Voltage Gated Channels”, and these are only found in the axon.
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5. How does an Action Potential begin at an Axon Hillock?
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It is all related to this voltage gating property in particular Na+ channels and Threshold
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6. Threshold Potential, is a membrane potential, which is typically how many milli-Volts above RMP?
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+15 mV (a depolarizing event).
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7. If the Axon Hillock region is depolarized to threshold, what will be the result?
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The voltage gated Na+ channels open, and if enough of them open, we will have the initiation of an Action Potential (only 50% of the time).
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8. Will Subthreshold depolarizations, cause an Action Potential?
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No, they never cause an Action potential.
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9. Will Suprathreshold depolarizations, cause an Action Potential?
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Always
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10. How many gates does a Voltage-gated Na+ channel have?
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2 Gates, which both need to be open in order for the channel to be open
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11. What are there names(two voltage-gated Na+ channels?
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1) Activation Gate (opens quickly)
2) Inactivation Gate (closes slowly) |
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12. What are the 3 different states in which this channel can exist?
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1) Resting State
2) Open State 3) Inactivated State. |
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13. How can we get these 3 different states, if at no time both gates are closed?
1) Resting State 2) Open State 3) Inactivated State. |
1) Resting State: Activation gate closed & Inactivation gate open.
2) Open State: Both gates are open (at threshold -55mV). 3) Inactivated State: Activation gate open & Inactivation gate closed. Inactivation gate closes slowly (slow response ~1 millisecond). |
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14. The channel stays in the inactivated state until?
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Repolarization to about -50mV, and then it goes completely from the inactivated state back to the resting state.
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16. What is the clinical importance of the Na+ channel?
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Involved in the action of local anesthetics (ex. Lidocaine). Local anesthetics bind to the inactivated form of the voltage gated Na+ channels, and at high concentrations the block action potential propagation or generation.
Small diameter, and slowly conducting axons are the axons that carry pain information, and these are the ones local anesthetics bind better to. |
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17. What are other examples of voltage gated Na+ channel blockers (Na+ channel antagonists)?
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Japanese puffer Fish (tingling sensation in the mouth), neurotoxin “tetroto toxin”, scorpion venom, anemone venom.
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18. What are the three phases of Action Potentials?
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1) Depolarization phase
2) Repolarization phase 3) Hyperpolarization phase |
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19. Where is the only place, were you see both Graded potentials and Action potentials?
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At the Axon Hillock.
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20. What is happening during Depolarization?
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A massive number of open Na+ channels are open during an Action potential than during a Graded potential (Na+ is rushing into the cell, down its concentration gradient, thus, depolarizing the inside of the cell).
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21. What occurs at the peak of an Action potential?
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The Na+ channels inactivate (the go from the open state to the inactivated state), and Na+ stops rushing into the cell, thus signaling the end of the depolarization period. – BOTTOM LINE: The beginning of the depolarization phase is the opening of the voltage Na+ channels, and the end of depolarization is the inactivation of the voltage Na+ channels.
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22. What occurs about this same time of the peak of an action potential?
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The voltage gated K+ channels open, this begins the Repolarization phase. – BOTTOM LINE: the beginning of the repolarization phase is the opening of the voltage K+ channels, and when these voltage gated channels open, K+ is rushing out of the cell, down its concentration gradient.
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23. Why does hyperpolarization occur?
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Because, the voltage gated K+ channels are slow to close.
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24. Why does this graph look different from the other one?
(needs image) |
Because, this action potential is not measured at the Axon Hillock were you would also show the Graded potentials.
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25. The frequency of Action Potentials generation is limited by?
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Refractory Periods.
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26. What are the 2 kinds of Refractory Periods?
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1) The Absolute refractory period
2) The Relative refractory period |
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27. What is the Absolute refractory period?
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No additional Action Potentials can be generated during this time. This is when the Axon Hillock region is in the Depolarization phase and most of the Repolarization phase. The end of the Absolute refractory period is when the voltage gated Na+ channels return to their resting state.
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28. What is the clinical significance of the K+ channel?
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A rare neo-natal seizure disorder, due to altered voltage gated K+ channel, this is a genetic mutation, which causes these channels to close earlier than normal. As a result the neurons fail to hyperpolarize, which leads to shorter refractory periods. (neurons are hyper-excitable and thus generate more action potentials than normal), thus leading to seizures.
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29. What don’t Action Potentials go in both directions?
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Because, the back part of the membrane is in a refractory period. Therefore, the membrane at rest, which is in front reacts to this Action Potential, hence, the way they travel.
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30. What are the 2 main factors involved in the conduction speed of an Action Potential?
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1) Diameter of the Axon – the larger the diameter, the Faster the Action Potential will travel.
2) The Degree of Myelination – In a myelinated axon, the Action Potential travels significantly faster, than in an Unmyelinated axon. |
