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Questions and Answers
Which channel type directly converts a chemical signal into a change in membrane permeability?
Which channel type directly converts a chemical signal into a change in membrane permeability?
What is the immediate effect of a mechanical stretch on a mechanosensitive channel?
What is the immediate effect of a mechanical stretch on a mechanosensitive channel?
If a cell's resting membrane potential becomes more positive than its typical resting value, this change is best described as:
If a cell's resting membrane potential becomes more positive than its typical resting value, this change is best described as:
The sodium-potassium pump contributes to the resting membrane potential primarily by:
The sodium-potassium pump contributes to the resting membrane potential primarily by:
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An outward flux of potassium ions ($K^+$) across the cell membrane through ion channels will cause the membrane potential (Vm) to become:
An outward flux of potassium ions ($K^+$) across the cell membrane through ion channels will cause the membrane potential (Vm) to become:
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Which of the following accurately describes the resting membrane potential (Vm) of a cell?
Which of the following accurately describes the resting membrane potential (Vm) of a cell?
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What is the primary distinction between intracellular recording and patch clamp recording techniques in electrophysiology?
What is the primary distinction between intracellular recording and patch clamp recording techniques in electrophysiology?
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In electrophysiological recordings, a 'downwards' trace in ionic current measurement typically signifies:
In electrophysiological recordings, a 'downwards' trace in ionic current measurement typically signifies:
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What is the effect of injecting a negative current into a cell during intracellular recording?
What is the effect of injecting a negative current into a cell during intracellular recording?
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Which of the following best describes a graded potential?
Which of the following best describes a graded potential?
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What is the key difference between current clamp and voltage clamp techniques in electrophysiology?
What is the key difference between current clamp and voltage clamp techniques in electrophysiology?
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Depolarization of a neuronal membrane is characterized by:
Depolarization of a neuronal membrane is characterized by:
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The patch clamp technique, which enabled the study of single ion channels, was developed by which Nobel laureates?
The patch clamp technique, which enabled the study of single ion channels, was developed by which Nobel laureates?
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Which of the following is measured using the current clamp technique?
Which of the following is measured using the current clamp technique?
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What is the immediate effect of membrane depolarization on a voltage-gated $Na^+$ channel?
What is the immediate effect of membrane depolarization on a voltage-gated $Na^+$ channel?
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What primary role does the lipid bilayer component of a nerve cell membrane fulfill?
What primary role does the lipid bilayer component of a nerve cell membrane fulfill?
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Nerve cell membrane pumps are primarily responsible for which function?
Nerve cell membrane pumps are primarily responsible for which function?
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Ion channels exhibit selectivity, meaning a $K^+$ channel is most likely to permit the passage of which ion?
Ion channels exhibit selectivity, meaning a $K^+$ channel is most likely to permit the passage of which ion?
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An inward current in a nerve cell membrane, mediated by ion channels, is characterized by the flux of which type of ion and in what direction?
An inward current in a nerve cell membrane, mediated by ion channels, is characterized by the flux of which type of ion and in what direction?
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Which of the following is classified as a biochemical stimulus that can gate ion channels?
Which of the following is classified as a biochemical stimulus that can gate ion channels?
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Ion channels in nerve cells play a crucial role in regulating which fundamental processes?
Ion channels in nerve cells play a crucial role in regulating which fundamental processes?
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What does selective permeability of a membrane primarily determine in the context of ion movement?
What does selective permeability of a membrane primarily determine in the context of ion movement?
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In the Nernst equation, what does the term '{ IONout } / { IONin }' represent?
In the Nernst equation, what does the term '{ IONout } / { IONin }' represent?
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According to the Goldman-Hodgkin-Katz equation, what is the membrane potential (EM) determined by?
According to the Goldman-Hodgkin-Katz equation, what is the membrane potential (EM) determined by?
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At resting membrane potential, why is the equilibrium potential for potassium (EK+) considered the most important factor?
At resting membrane potential, why is the equilibrium potential for potassium (EK+) considered the most important factor?
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In the equivalent circuit model of a nerve cell membrane, what does the transmembrane input resistance (RM) primarily represent?
In the equivalent circuit model of a nerve cell membrane, what does the transmembrane input resistance (RM) primarily represent?
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Which component of the nerve cell membrane is represented by capacitance (CM) in the equivalent circuit model?
Which component of the nerve cell membrane is represented by capacitance (CM) in the equivalent circuit model?
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How does the diameter of an axon affect the axoplasmic (internal) resistance (RA or RI)?
How does the diameter of an axon affect the axoplasmic (internal) resistance (RA or RI)?
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In the context of the nerve cell membrane as an equivalent electrical circuit, which component is analogous to a 'battery' that maintains ionic gradients?
In the context of the nerve cell membrane as an equivalent electrical circuit, which component is analogous to a 'battery' that maintains ionic gradients?
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Which of the following is a role of injected mRNA in oocytes?
Which of the following is a role of injected mRNA in oocytes?
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What measurement technique is used to study ion channels in oocytes?
What measurement technique is used to study ion channels in oocytes?
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During depolarization, what is the initial response of a sodium channel?
During depolarization, what is the initial response of a sodium channel?
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Which condition is associated with mutations in skeletal muscle Na+ channels?
Which condition is associated with mutations in skeletal muscle Na+ channels?
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When does a K+ channel typically close?
When does a K+ channel typically close?
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What is the role of oocytes in studying channelopathies?
What is the role of oocytes in studying channelopathies?
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Which mutation is related to sodium channels in the brain?
Which mutation is related to sodium channels in the brain?
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How can ion channels be described in terms of Ohm's law?
How can ion channels be described in terms of Ohm's law?
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What is the driving force for ion flow according to Ohm's Law?
What is the driving force for ion flow according to Ohm's Law?
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In a hyperpolarized membrane (near $E_{K^+}$), what is the characteristic of the driving force for potassium ions?
In a hyperpolarized membrane (near $E_{K^+}$), what is the characteristic of the driving force for potassium ions?
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Which property of the depolarized membrane near $E_{Na^+}$ affects its potential?
Which property of the depolarized membrane near $E_{Na^+}$ affects its potential?
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What technique was used to determine the structure of eukaryotic ion channels?
What technique was used to determine the structure of eukaryotic ion channels?
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How do gene sequences predict the association of ion channel subunits?
How do gene sequences predict the association of ion channel subunits?
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How is the increase or decrease in membrane potential represented in electrotonic properties?
How is the increase or decrease in membrane potential represented in electrotonic properties?
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What is the purpose of using the Xenopus oocyte expression system in electrophysiology?
What is the purpose of using the Xenopus oocyte expression system in electrophysiology?
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Study Notes
Lecture 011625
- Bioelectric circuits and ion channels are studied through electrophysiological studies and a molecular approach
- Different types of channels and their gating mechanisms are investigated
- Membrane potential, electrochemical equilibrium, resting membrane potential, selective permeability, and driving force are crucial concepts
- Nernst and Goldman equations are used to model these concepts
- Electrotonic (passive) properties, such as time and length constants, are explained in terms of first looks.
- Action potentials are introduced.
Membrane Potentials
- Changes in membrane potential (Vm) influence graded and action potentials.
- Synaptic potentials are a graded response, while action potentials are an active response.
- Resting membrane potential (Vm) is negative relative to the outside of the cell at rest.
Study of Ion Channels - Electrophysiology
- Intracellular recording measures membrane potential (Vm) using a current clamp.
- Patch clamp recording measures ionic current using a voltage clamp.
- Depolarization (Vm ↑) is represented by an upward trace.
- Hyperpolarization (Vm ↓) is represented by a downwards trace.
- Conventions for recording ion currents are similar, with inward currents represented downwards and outward currents upwards.
Intracellular Recording of Resting and Action Potentials
- Injecting positive current causes depolarization and negative current causes hyperpolarization.
- A threshold level of depolarization triggers an action potential.
- The lecture introduces the concepts of resting potential (RP) and action potential (AP), asking for their basis and role.
Patch Clamp Recording of Single Voltage-Gated Na+ Channel
- Membrane depolarization triggers Na+ channel opening and influx.
- Ionic current is the sum of flux through ion channels.
Nerve Cell Membrane
- Lipid bilayer forms a barrier to ion diffusion.
- Pumps actively transport ions to create concentration gradients.
- Ion channels are embedded in the phospholipid bilayer and are selective.
- Channels are gated by various stimuli (e.g., voltage, chemicals).
Study of Ion Channels - X-ray Crystallography
- Techniques like X-ray crystallography reveal detailed structures of ion channels, including the KcsA bacterial K+ channel.
- Structure determination and the implication of the analysis method are discussed.
Study of Ion Channels - Molecular Biology
- Gene sequences reveal the relationship between channel subunits and the cell membrane.
- Hydrophobicity plots aid in understanding the domains of channels, which form the pore, receptor, and/or accessory units.
- Specific examples like acetylcholine receptors (AChR) and sodium channels are given.
Study of Ion Channels - Electrophysiology (Xenopus Oocyte Expression System)
- Xenopus oocytes are used to study ion channels as they express proteins in the membrane.
- Exogenous mRNA coding for channel proteins can be inserted into oocytes, allowing for study with patch clamp techniques
- These experiments can compare normal ion channels to disease-causing mutated forms (channelopathies).
Na and K Channel Responses to Vm
- The responses of Na+ and K+ channels to changes in membrane potential (Vm) are explained.
- Different phases of channel activation and inactivation are described.
Expression of Na+ Channels in Frog Eggs
- Na+ channels are studied by recording using patch clamp methods. This involves expressing the channel protein in the egg, and subsequent analysis.
Channelopathies
- Skeletal muscle Na+ channel diseases like Hyperkalemic Periodic Paralysis, Hypokalemic Periodic Paralysis, Paramyotonia Congenita, or Potassium Aggravated Myotonia are examined. Similar investigation is done for brain Na + channels, which lead to similar conditions in brain.
Electrotonic (Passive) Membrane Properties
- Time Constant: The time required for a membrane potential change to reach around 63% of its final value, as well as calculating this value
- Length Constant: The distance along the membrane over which a potential change is able to spread, and how this measurement is calculated.
Basis of Membrane Potential
- The role of the Na+/K+ pump in establishing ion concentration gradients and membrane potential is explained.
- The contribution of ion channels to the resting membrane potential (Vm) and their selective permeability are discussed.
- Nernst and Goldman-Hodgkin-Katz equations are used to model ionic fluxes and membrane potentials under these conditions.
Action Potentials
- Action potentials are described as rapid changes in membrane potential that are used to quickly transfer information over distance.
- Frequency, recruitment, and place coding are described as factors for information transmission using action potentials
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Description
Explore the complex world of bioelectric circuits and ion channels through your understanding of electrophysiology. This quiz covers essential concepts such as membrane potentials, gating mechanisms, and action potentials, backed by key equations like Nernst and Goldman. Test your knowledge on how changes in membrane potential influence both graded and action potentials.
