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Questions and Answers
During which period is it impossible to generate an action potential regardless of stimulus strength?
How does an action potential propagate in unmyelinated axons?
What differentiates the relative refractory period from the absolute refractory period?
Which factor most significantly increases the speed of action potential conduction?
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What is the primary way in which stronger stimuli are interpreted within the nervous system?
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Study Notes
Refractory Periods
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Absolute Refractory Period: No action potential can be generated regardless of stimulus strength; occurs during sodium channel activity (open/inactivated).
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Ending of Absolute Refractory Period: Concludes when sodium channels reset near resting membrane potential.
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Relative Refractory Period: An action potential can occur but requires a stronger stimulus due to hyperpolarization from K+ efflux; may result in a weaker action potential compared to the first.
Stimulus Strength
- All-or-None Response: Action potentials have a uniform size once the threshold is achieved; stronger stimuli do not increase amplitude but lead to a higher frequency of action potentials.
- Frequency Coding: The body perceives stronger stimuli through increased frequency of action potentials rather than changes in amplitude.
Action Potential Propagation
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Continuous Conduction: Occurs in unmyelinated axons; sodium ions diffuse to adjacent membrane areas, leading to gradual depolarization. Backward diffusion is prevented by the refractory period.
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Saltatory Conduction: Found in myelinated axons where action potentials "jump" between Nodes of Ranvier, enhancing propagation speed.
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Myelination Effects: Myelination significantly increases conduction speed; larger diameter axons further enhance conduction efficiency.
Disease Example
- Multiple Sclerosis (MS): An autoimmune disorder causing degradation of myelin in the central nervous system, resulting in reduced signal transmission speed.
Key Concepts Likely to be Tested
- Differences between absolute and relative refractory periods.
- Mechanisms and significance of saltatory conduction versus continuous conduction.
- Influence of axon diameter and myelination on conduction speed.
- How stronger stimuli are represented through increased frequency rather than amplitude.
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Description
Explore the concepts of absolute and relative refractory periods in neurophysiology. This quiz will assess your understanding of how action potentials are generated and the role of sodium and potassium channels in this process. Test your knowledge on stimulus strength and the all-or-none response.
