Action Potentials Presentation
| Introduction to Action Potentials | ||
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| Action potentials are the electrical signals that transmit information in the nervous system. They are generated by the movement of ions across the cell membrane. Action potentials play a crucial role in the communication between neurons. | ||
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| Neuronal Membrane Potential | ||
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| Neurons have a resting membrane potential of around -70 millivolts. This is maintained by the uneven distribution of ions across the cell membrane. Sodium (Na+) and potassium (K+) ions are primary contributors to the membrane potential. |  | |
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| Depolarization Phase | ||
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| When a neuron receives a stimulus, it triggers the opening of sodium channels. Sodium ions rush into the cell, causing depolarization. This depolarization leads to a rapid change in the membrane potential. | ||
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| Threshold and Action Potential Initiation | ||
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| If the depolarization reaches a certain threshold, typically around -55 millivolts, an action potential is initiated. At this point, voltage-gated sodium channels open completely, allowing a massive influx of sodium ions. This causes a rapid and dramatic reversal of the membrane potential, known as the action potential. | ||
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| Rising and Falling Phases | ||
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| The rising phase of the action potential is characterized by the rapid depolarization. Sodium channels close, and voltage-gated potassium channels open during the falling phase. Potassium ions flow out of the cell, causing repolarization of the membrane potential. | ||
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| Hyperpolarization and Refractory Period | ||
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| After repolarization, the membrane potential briefly becomes more negative than the resting potential, leading to hyperpolarization. During this time, the neuron is in a refractory period, making it less likely to generate another action potential. The refractory period ensures the unidirectional transmission of action potentials. | ||
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| Propagation of Action Potentials | ||
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| Action potentials propagate along the axon of a neuron. The depolarization at the initial segment of the axon triggers adjacent sections to reach the threshold and generate their own action potentials. This allows the signal to travel rapidly from one end of the neuron to the other. | ||
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| All-or-None Principle | ||
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| Action potentials follow the all-or-none principle, meaning they either occur at full strength or do not occur at all. If the stimulus is strong enough to reach the threshold, the action potential will be generated; otherwise, it will not. The strength of the stimulus is represented by the frequency of action potentials. | ||
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| Action Potential Speed | ||
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| The speed of action potential propagation varies depending on factors such as axon diameter and myelination. Larger axon diameter and myelination result in faster conduction. This variation in speed allows for efficient communication within the nervous system. | ||
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| Summary | ||
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| Action potentials are electrical signals that transmit information in the nervous system. They are generated by the movement of ions across the cell membrane. Understanding action potentials is crucial for comprehending the functioning of the nervous system. | ||
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| References (download PPTX file for details) | ||
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| Alberts B, Johnson A, Lewis J, et al. Molecul... Section 21.2, Action Potentials and Synaptic ... Purves D, Augustine GJ, Fitzpatrick D, et al.... | | |
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