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Questions and Answers
What is the typical resting membrane potential of a cell?
What determines the equilibrium potential of an ion?
What is the primary function of the Na+/K+-ATPase pump?
What type of recording is used to measure electrical potentials from inside a cell?
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What is the primary component of the membrane that provides a hydrophobic barrier?
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What is the result of the inside of the cell becoming very negative?
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What is the purpose of the ion channels in the membrane?
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What is the result of depolarization of the cell membrane?
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What is the primary function of the sodium pump in establishing the membrane potential?
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What is the term for the period of time during which an action potential cannot be generated?
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What is the purpose of patch clamping in measuring electrical potentials?
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What is the property of the cell membrane that allows it to store charges?
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What is the term for the difference in electrical potential between the inside and outside of a cell?
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What is the role of voltage-dependent ion channels in generating the membrane potential?
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What is the term for the minimum amount of electrical potential required to generate an action potential?
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What is the purpose of extracellular recording in measuring electrical potentials?
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What is the primary function of sodium channels in a cell?
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What is the result of the rapid influx of sodium into the cell through sodium channels?
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What is the primary function of potassium channels in a cell?
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What is the result of the rapid efflux of potassium out of the cell through potassium channels?
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What determines the resting membrane potential?
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What are the two specific forces that ions are under?
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What is the equation used to calculate the resting membrane potential?
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What is the value of the resting membrane potential under physiological conditions?
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What is the primary cause of the depolarization of the neuron beyond the threshold?
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What is the effect of the inactivation of sodium channels?
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What is the purpose of the relative refractory period?
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What is the typical resting membrane potential of a neuron?
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What happens to the potassium channels during the hyperpolarization phase?
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What is the primary function of the leak channels?
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What is the result of the rapid entry of sodium ions into the neuron?
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What is the purpose of the voltage-gated sodium channels?
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What is the typical voltage at which the voltage-dependent, transient Na+ channels open?
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What is the primary function of the V-gated K channels?
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What is the term for the period of time during which the V-gated Na channels are inactivated?
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What is the primary difference between the conduction of action potentials in non-myelinated and myelinated axons?
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What is the term for the ability of an excitable cell to generate an action potential?
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What is the typical concentration of Na+ ions inside a cell?
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What is the term for the movement of ions across the cell membrane?
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What is the term for the ability of a cell membrane to store electrical energy?
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What is the term for the flow of electrical charge across the cell membrane?
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What is the term for the difference in electrical potential between the inside and outside of a cell?
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Study Notes
Establishing Electrochemical Potentials and Axon Potentials
- Electrochemical equilibria and membrane potential:
- The membrane separates and stores charges
- Na+ and K+ ion channels contribute to generating the membrane potential (MP)
- The differential permeability of the membrane to Na+ and K+ ions is significant
- Electrochemical gradients are established through the sodium pump, voltage-dependent ion channels, and membrane capacitance
- Action potential, propagation, and nerve conduction:
- Properties of the action potential (AP):
- Voltage and conductance changes during the AP
- Capacitance
- Threshold and refractory periods:
- What is meant by 'threshold' and 'refractory periods'
- Importance of myelin in nerve conduction
- Properties of the action potential (AP):
Measuring Electrical Potentials
- Methods of measuring electrical potentials:
- Extracellular recording (electrode outside the cell)
- Intracellular recording (electrode inside the cell)
- Patch clamping (electrode sealed to the cell surface)
- Measurement units:
- 100 mV (intracellular recording)
- 0.1 mV (extracellular recording)
Basic Principles
- At rest, the inside of the membrane is more negatively charged than the outside (hyperpolarized)
- When cells become activated, the inside of the membrane becomes more positively charged (depolarized)
The Resting Membrane Potential
- The resting membrane potential (Vm) is typically around -70 mV
- It is determined by Na+ and K+ ions (and Ca2+ ions)
- Equilibrium potential of an ion is the membrane voltage required to prevent movement of an ion down its concentration gradient
- If the inside of the cell is very negative, K+ will be prevented from leaving; if the inside of the cell is very positive, Na+ will be prevented from entering
The Membrane
- The membrane surrounds the entire neuron, providing a hydrophobic, relatively impermeable barrier
- Composed of lipids and proteins, with ion channels and pumps providing entry and exit routes for ions
- Na+/K+-ATPase pump:
- Uses energy (ATP) to actively pump three sodium (Na+) and two potassium (K+) ions out and into the cell, respectively
- Maintains a more depolarized internal environment
- Sodium channels:
- Permit the rapid influx of sodium into the cell upon opening, resulting in depolarization
- Potassium channels:
- Permit the rapid efflux of potassium out of the cell upon opening, resulting in hyperpolarization
The Action Potential
- The action potential is generated by the rapid influx of sodium ions and the rapid efflux of potassium ions
- The Nernst equation is used to calculate the equilibrium potential of an ion
- The action potential has five stages:
- Depolarization reaches threshold
- Voltage-gated sodium channels (NaV) open, and sodium ions (Na+) enter the neuron
- Rapid Na+ entry depolarizes the neuron further
- NaV channels inactivate, and slower (0.5 mS) potassium channels (Kv) open
- Potassium ions (K+) move out of the neuron, repolarizing it
Refractory Periods
- Absolute refractory period:
- Results from the inactivation of Na+ channels
- Lasts until the resting membrane potential is restored
- Relative refractory period:
- Results from the hyperpolarization phase
- During which a greater stimulus is needed to reach threshold
Functional States of Ion Channels
- Ion channels have three states:
- Closed (resting)
- Open (active)
- Inactive (refractory)
- V-gated Na channels have all three states, while V-gated K channels have no inactivation state
Action Potential Conduction
- Action potential conduction in non-myelinated axons:
- Involves the continuous generation of action potentials along the length of the axon
- Action potential conduction in myelinated axons:
- Involves the saltatory conduction of action potentials between nodes of Ranvier
- The myelin sheath insulates the axon, increasing the speed of transmission
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Description
This quiz covers the physiology of electrochemical potentials and axon potentials, including the concentrations of Na+ and K+ ions inside and outside of cells and how electrical events are measured.
