Questions and Answers
What is the primary reason for the opening of sodium channels in the membrane during the initiation of an action potential?
What is the term for the change in membrane potential when it moves towards zero?
What is the approximate voltage of the resting membrane potential?
What is the function of voltage-gated potassium channels during the repolarization phase?
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Why does the sodium cation continue to enter the cell even after the membrane potential has become zero?
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What is the term for the movement of the membrane potential back towards its resting voltage?
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What is the approximate voltage reached by the membrane potential during the action potential?
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What happens to the membrane potential after repolarization?
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What is the minimum voltage required to reach the threshold of an action potential?
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What is the function of the inactivation gate of the voltage-gated Na+ channel?
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What occurs during the hyperpolarizing overshoot?
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Why does a stronger stimulus not make a 'bigger' action potential?
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What is the function of the voltage-gated K+ channel?
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What happens during the absolute refractory period?
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What is the duration of an action potential?
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What is the voltage at which the voltage-gated K+ channel opens?
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What happens to the voltage-gated Na+ channel during repolarization?
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Why does a stronger stimulus initiate multiple action potentials more quickly?
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What causes the membrane potential to return to its resting voltage after hyperpolarization?
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What is the name of the voltage at which voltage-gated Na+ channels open?
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Which of the following statements accurately describes the action potential?
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What is the main difference between the driving force for Na+ and K+ during an action potential?
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What is the role of the voltage-gated Na+ channels in initiating an action potential?
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Which of the following is NOT a type of Na+ channel that can contribute to depolarization?
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What happens if a stimulus does not depolarize the membrane to -55 mV or higher?
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What is the significance of the threshold in the context of action potential generation?
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What is the term used to describe the period after an action potential when the membrane potential is more negative than the resting potential?
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How does the action potential differ from the charge stored in a battery?
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Study Notes
The Action Potential
- The resting membrane potential is the steady state of the cell, which is a dynamic process balanced by ion leakage and ion pumping.
- To get an electrical signal started, the membrane potential has to change, which starts with a channel opening for Na+ in the membrane.
- The concentration of Na+ is higher outside the cell than inside the cell by a factor of 10, causing ions to rush into the cell driven largely by the concentration gradient.
- The sodium ion entering the cell will cause the membrane potential to become less negative, known as depolarization, moving toward zero.
Depolarization and Repolarization
- The concentration gradient for Na+ is so strong that it will continue to enter the cell even after the membrane potential has become zero, so that the voltage immediately around the pore begins to become positive.
- The electrical gradient also plays a role, as negative proteins below the membrane attract the sodium ion.
- As the membrane potential reaches +30 mV, other voltage-gated channels open in the membrane, specific for the potassium ion.
- A concentration gradient acts on K+, and as K+ starts to leave the cell, taking a positive charge with it, the membrane potential begins to move back toward its resting voltage, known as repolarization.
- Repolarization returns the membrane potential to the -70 mV value that indicates the resting potential, but it actually overshoots that value, resulting in hyperpolarization.
Characteristics of the Action Potential
- The action potential is the electrical signal that nervous tissue generates for communication.
- The change in the membrane voltage from -70 mV at rest to +30 mV at the end of depolarization is a 100-mV change.
- The membrane potential can be described as a battery, with a charge stored across the membrane that can be released under the correct conditions.
Initiation of the Action Potential
- The description above conveniently glosses over the initiation of the action potential, which is vital to understanding what is happening.
- The membrane potential will stay at the resting voltage until something changes, such as a Na+ channel opening.
- There are a few different types of channels that allow Na+ to cross the membrane, including ligand-gated Na+ channels, mechanically gated Na+ channels, and voltage-gated Na+ channels.
- A stimulus, such as a neurotransmitter binding to its receptor protein or a sensory stimulus activating a sensory receptor cell, gets the process started.
Threshold and the All-or-None Principle
- The threshold is the voltage at which the voltage-gated Na+ channels open, which is -55 mV.
- Any depolarization that does not change the membrane potential to -55 mV or higher will not reach threshold and thus will not result in an action potential.
- If the threshold is reached, then the action potential continues and runs all the way to +30 mV, at which K+ causes repolarization, including the hyperpolarizing overshoot.
- The action potential is an all-or-none event, meaning that either the membrane reaches the threshold and everything occurs as described above, or the membrane does not reach the threshold and nothing else happens.
Refractory Period
- While an action potential is in progress, another one cannot be initiated, which is referred to as the refractory period.
- There are two phases of the refractory period: the absolute refractory period and the relative refractory period.
- During the absolute phase, another action potential will not start, and during the relative phase, a new action potential could be started, but only by a stronger stimulus than the one that initiated the current action potential.
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Description
Learn about the dynamic process of resting membrane potential and how it changes to generate an electrical signal, involving ion leakage, pumping and channel opening for sodium ions.
