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What function does hyperpolarization serve in the action potential process?
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Hyperpolarization makes the membrane more negative than its resting potential, contributing to the relative refractory period.
What is the difference in opening dynamics between voltage-gated sodium and potassium channels?
Sodium channels open rapidly at threshold, whereas potassium channels open slower and are responsible for repolarization and hyperpolarization.
What defines a stimulus as excitatory in the context of graded potentials?
An excitatory stimulus causes depolarization of the membrane potential.
What are the equilibrium potentials represented by the green and purple dashed lines?
The green line represents Sodium's equilibrium potential, and the purple dashed line represents Potassium's equilibrium potential.
Explain the significance of the 'all-or-none' characteristic of action potentials.
It means action potentials occur with a consistent size and strength once the threshold is reached and do not weaken as they propagate.
What physiological changes occur when a stimulus reaches the threshold potential?
Voltage-gated channels open, allowing specific ions to move across the membrane.
What prevents an action potential from reversing direction along the axon?
The absolute refractory period prevents an action potential from reversing direction by ensuring that recently activated sodium channels remain inactivated.
What role does the axon hillock play in action potential initiation?
The axon hillock has a high density of voltage-gated sodium channels and is the site where action potentials first initiate.
How do graded potentials differ from action potentials?
Graded potentials are small changes in membrane potential and can be excitatory or inhibitory, whereas action potentials are larger, all-or-none responses that are always excitatory.
Describe the three conformations of voltage-gated sodium channels.
1. Closed but capable of opening, 2. Open, 3. Inactivated (closed and incapable of opening).
Define the absolute refractory period in terms of sodium channel state.
During the absolute refractory period, sodium channels are either open or inactivated preventing a new action potential.
What occurs during the relative refractory period?
The membrane can initiate an action potential only if a stronger than normal stimulus is applied.
Why is action potential propagation unidirectional in axons?
The refractory periods (absolute and relative) prevent the action potential from propagating backward.
How does the membrane potential return to resting level after an action potential?
The sodium-potassium pump and leak channels restore the resting membrane potential by pumping sodium out and potassium in.
How does potassium movement contribute to the phases of the action potential?
Potassium movement out of the cell leads to repolarization and hyperpolarization of the membrane.
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