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Questions and Answers
What best describes action potentials?
What best describes action potentials?
- They are the only signals generated by muscle cells.
- They are short-distance communication signals.
- They exclusively occur in connective tissue.
- They are long-distance signals characterized by reversal of charge. (correct)
What initiates the generation of an action potential?
What initiates the generation of an action potential?
- Changes in concentrations of ions across the membrane. (correct)
- A decrease in temperature affecting the membrane.
- Increase in extracellular calcium concentration.
- Stable ion concentrations within the neuron.
Which of the following is NOT a key characteristic of action potentials?
Which of the following is NOT a key characteristic of action potentials?
- They can be propagated over short distances. (correct)
- They are also known as spikes.
- They are based on frequency and pattern.
- They occur in both muscle and neuronal cells.
Which statement about graded potentials is true?
Which statement about graded potentials is true?
How is the neural code established for action potentials?
How is the neural code established for action potentials?
What happens to sodium channels during the resting state?
What happens to sodium channels during the resting state?
Which voltage-gated sodium channel gate is responsible for preventing further sodium entry after the channel is opened?
Which voltage-gated sodium channel gate is responsible for preventing further sodium entry after the channel is opened?
What is the threshold voltage that activates the main sodium channels during action potentials?
What is the threshold voltage that activates the main sodium channels during action potentials?
Which of the following statements regarding the absolute refractory period is true?
Which of the following statements regarding the absolute refractory period is true?
What is a characteristic of voltage-gated sodium channels?
What is a characteristic of voltage-gated sodium channels?
What effect does tetrodotoxin (TTX) have on sodium channels?
What effect does tetrodotoxin (TTX) have on sodium channels?
What role do voltage-gated sodium channels play during action potentials?
What role do voltage-gated sodium channels play during action potentials?
Which toxin blocks the inactivation of sodium channels, preventing them from closing?
Which toxin blocks the inactivation of sodium channels, preventing them from closing?
What is the primary effect of Na+ influx during depolarization?
What is the primary effect of Na+ influx during depolarization?
What occurs at the threshold potential of –55 to –50 mV?
What occurs at the threshold potential of –55 to –50 mV?
What is the role of K+ channels during repolarization?
What is the role of K+ channels during repolarization?
What happens to Na+ channels during repolarization?
What happens to Na+ channels during repolarization?
What is the membrane potential when the action potential spike reaches its peak?
What is the membrane potential when the action potential spike reaches its peak?
What is the role of potassium conductance during an action potential?
What is the role of potassium conductance during an action potential?
How do the activation gates of sodium channels behave at the resting state?
How do the activation gates of sodium channels behave at the resting state?
What is a defining characteristic of voltage-gated potassium channels compared to voltage-gated sodium channels?
What is a defining characteristic of voltage-gated potassium channels compared to voltage-gated sodium channels?
What happens to sodium channels after they have opened during depolarization?
What happens to sodium channels after they have opened during depolarization?
What maintains the resting membrane potential before an action potential occurs?
What maintains the resting membrane potential before an action potential occurs?
What occurs during hyperpolarization of the membrane?
What occurs during hyperpolarization of the membrane?
What is the threshold for initiating an action potential?
What is the threshold for initiating an action potential?
How does the frequency of impulses relate to stimulus strength?
How does the frequency of impulses relate to stimulus strength?
During which refractory period can an action potential be triggered only by an exceptionally strong stimulus?
During which refractory period can an action potential be triggered only by an exceptionally strong stimulus?
What is the role of sodium channels during the all-or-none phenomenon of action potentials?
What is the role of sodium channels during the all-or-none phenomenon of action potentials?
Which statement best describes how action potentials propagate in myelinated axons?
Which statement best describes how action potentials propagate in myelinated axons?
What mechanism prevents the back propagation of an action potential?
What mechanism prevents the back propagation of an action potential?
Which factors influence the rate of action potential propagation?
Which factors influence the rate of action potential propagation?
What is the consequence of depolarization not reaching the threshold voltage?
What is the consequence of depolarization not reaching the threshold voltage?
What is a characteristic of the absolute refractory period?
What is a characteristic of the absolute refractory period?
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Study Notes
Key Characteristics of Action Potentials
- Action potentials are crucial for long-distance cellular communication, primarily in neurons and muscle cells.
- They represent a reversal of charge relative to the extracellular space.
- Neural information is transmitted through the frequency and pattern of action potentials.
- Alternative names include "spike," "nerve impulse," and "discharge."
Generation of Action Potentials
- Changes in membrane potential occur when ion concentrations or membrane permeability alter.
- Two main types of signals:
- Graded potentials (short distances).
- Action potentials (long distances).
Steps of the Action Potential
- Resting State: All gated Na+ and K+ channels are closed; only leakage channels are open, maintaining the resting membrane potential.
- Depolarization:
- Voltage-gated Na+ channels open at -55mV, allowing Na+ influx; local currents cause adjacent channels to open.
- Membrane depolarizes to approximately +30mV.
- Repolarization:
- Na+ inactivation gates close, causing a decrease in Na+ permeability.
- Voltage-gated K+ channels open, allowing K+ to exit, leading the membrane back to resting potential.
- Hyperpolarization:
- Some K+ channels remain open, causing efflux that makes the inside of the membrane more negative, dipping below the resting potential.
All-or-None Principle
- Action potentials occur only if depolarization reaches a threshold of -55mV to trigger an AP.
- They either fully occur or not at all; varying stimulus strengths are encoded in the frequency of impulses.
Refractory Periods
- Absolute Refractory Period: No AP can be triggered; occurs from Na+ channel opening to resetting.
- Relative Refractory Period: Follows the absolute period; some Na+ channels are reset, but some K+ channels remain open, requiring a stronger stimulus for an AP.
Propagation of Action Potentials
- Initiated APs propagate along axons due to local currents causing adjacent areas to depolarize.
- In unmyelinated axons, each segment undergoes depolarization and repolarization.
- In myelinated axons, APs occur at nodes of Ranvier, allowing faster conduction.
Voltage-Gated Channel Dynamics
- Voltage-gated Na+ channels have activation and inactivation gates; dysfunction leads to channelopathies.
- Voltage-gated K+ channels open at +30mV to rectify membrane potential after an AP.
- Various toxins can affect channel functionality, highlighting their importance in neurotransmission.
Action Potential Characteristics
- All action potentials are identical in magnitude and duration, but the CNS differentiates stimulus intensity based on impulse frequency.
- Conduction velocities of APs vary widely among different axons, influenced by myelination and axon diameter.
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