Electrophysiology Quiz: Membrane Potential

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

Which channel type relies on physical distortion to initiate its opening?

Voltage-gated

Mechanosensitive (correct)

Electrogenic pump

Ligand-gated

What term describes the state of a cell when its membrane potential becomes more positive than its resting membrane potential?

Hyperpolarized

Depolarized (correct)

Repolarized

Equilibrated

What is the primary direct contribution of the sodium/potassium pump to the resting membrane potential?

Creating a small negative membrane potential through its electrogenic nature (correct)

Preventing potassium ions from leaving the cell

Establishing high intracellular sodium concentration

Directly generating the majority of the resting membrane potential

Considering the distribution of ions across the cell membrane, which of the following statements is correct in a resting cell?

Sodium ion concentration is higher outside the cell than inside. (A) Signup and view all the answers

Which aspect of ion channel kinetics refers to the time taken for a channel to transition from a closed state to an open state upon stimulation?

Opening time (D) Signup and view all the answers

Which of the following best describes the state of a cell's membrane potential when it is at rest?

The inside of the cell is negatively charged relative to the outside. (A) Signup and view all the answers

What is the primary measurement in current clamp electrophysiology?

Changes in membrane potential (C) Signup and view all the answers

In electrophysiology, a 'downwards' deflection in a voltage recording trace is conventionally represented as:

Hyperpolarization (B) Signup and view all the answers

What is the effect on membrane potential when a positive current is injected into a cell during intracellular recording?

Depolarization, making the membrane potential more positive. (C) Signup and view all the answers

Which of the following is measured directly using the patch clamp technique?

Ionic current (B) Signup and view all the answers

In current recording conventions, an 'upwards' deflection in the trace indicates:

Outward positive current (A) Signup and view all the answers

What is required to reach the threshold level of depolarization in a neuron, leading to the generation of an action potential?

Sufficient depolarization (C) Signup and view all the answers

Which of the following changes in membrane potential is classified as an 'active response'?

Action potential (A) Signup and view all the answers

What is the primary value calculated by the Nernst equation in the context of neuronal membrane potential?

The equilibrium potential for a specific ion based on its concentration gradient. (D) Signup and view all the answers

According to the Goldman-Hodgkin-Katz (GHK) equation, what is the primary determinant of the membrane potential ($E_M$) in a cell permeable to multiple ions?

The weighted sum of the equilibrium potentials of all permeable ions, considering their relative permeabilities. (B) Signup and view all the answers

Which of the following factors is MOST crucial in establishing the resting membrane potential ($E_M$) in a neuron?

High permeability of the membrane to potassium ions ($K^+$) through non-gated channels. (A) Signup and view all the answers

At resting membrane potential, the neuronal membrane exhibits:

High permeability to potassium ions ($K^+$) and low permeability to sodium ions ($Na^+$). (B) Signup and view all the answers

In the equivalent circuit model of a nerve cell membrane, which component primarily represents the phospholipid bilayer's ability to store charge?

Membrane Capacitance ($C_M$). (B) Signup and view all the answers

Which of the following factors would primarily affect the axoplasmic resistance ($R_A$) in a neuron?

The diameter of the axon. (C) Signup and view all the answers

In the context of the equivalent circuit of a nerve cell membrane, ion channels are best represented as:

Resistors, influencing membrane resistance ($R_M$). (D) Signup and view all the answers

Myelination primarily affects which components of the equivalent circuit model of a nerve cell membrane?

Membrane resistance ($R_M$) and membrane capacitance ($C_M$). (B) Signup and view all the answers

For which contribution to the field of neuroscience were Sakmann and Neher awarded the Nobel Prize?

Pioneering the patch clamp technique for studying single ion channel currents. (C) Signup and view all the answers

What is the immediate effect of membrane depolarization on voltage-gated sodium (Na+) channels?

Channel opening, causing an influx of Na+ ions. (A) Signup and view all the answers

Which component of the nerve cell membrane primarily functions as a barrier to ion diffusion?

The phospholipid bilayer itself. (D) Signup and view all the answers

What is the principal role of ion pumps in the nerve cell membrane, in contrast to ion channels?

To establish and maintain ion concentration gradients across the membrane. (B) Signup and view all the answers

Ion channels exhibit selectivity, meaning they are primarily permeable to:

Specific types of ions, such as K+, Na+, Ca++, or Cl-. (B) Signup and view all the answers

Which of the following stimuli is LEAST likely to directly gate an ion channel, based on the provided text?

Variations in ambient temperature. (B) Signup and view all the answers

An 'inward current' in the context of ion channels refers to the flux of:

Positive ions moving into the cell, contributing to depolarization. (C) Signup and view all the answers

Biochemical-gated ion channels are characterized by their direct activation through:

Intracellular signaling molecules such as G proteins, cyclic nucleotides, or Ca2+. (D) Signup and view all the answers

According to Ohm's Law as applied to ionic current across a membrane, what would decrease the ionic current ($I_{ION}$)?

A decrease in ionic conductance ($g_{ION}$). (A) Signup and view all the answers

If a membrane is hyperpolarized to a potential close to the equilibrium potential for potassium ($E_{K+}$), what is the expected driving force for potassium ions ($K^+$)?

Low driving force, resulting in minimal potassium efflux. (D) Signup and view all the answers

Which of the following best describes the relationship between ionic permeability ($P_{ION}$) and ionic conductance ($g_{ION}$)?

Ionic permeability is another term used to describe ionic conductance. (B) Signup and view all the answers

In the equation $V_M = \sum {P_{ION} imes E_{ION}}$, what does an increase in the permeability ($P_{ION}$) of a specific ion primarily contribute to?

A greater influence of the equilibrium potential ($E_{ION}$) of that specific ion on the membrane potential ($V_M$). (C) Signup and view all the answers

What is the significance of 'hydrophobicity plots' in the study of ion channels?

They indicate regions of a protein sequence that are likely to be located within the lipid bilayer of the cell membrane. (D) Signup and view all the answers

The Nobel Prize in Chemistry was awarded for the study of ion channels using X-ray crystallography, specifically for determining the structure of which ion channel?

KcsA bacterial $K^+$ channel. (D) Signup and view all the answers

Which technique is described as using crystals to measure distances between amino acids to infer the structure of ion channels?

X-ray crystallography. (B) Signup and view all the answers

What is the purpose of using the Xenopus oocyte expression system in ion channel research?

To express and study the function of ion channels by introducing foreign genetic material into Xenopus oocytes. (B) Signup and view all the answers

What is a primary advantage of using oocytes in the study of ion channels?

Oocytes do not express their own native ion channels, allowing researchers to study only the channels introduced via mRNA injection. (D) Signup and view all the answers

Which electrophysiological technique is specifically mentioned as being used to study ion channels in oocytes?

Patch clamp (A) Signup and view all the answers

Following membrane depolarization (VM+), what is the typical response of a Na+ channel expressed in an oocyte?

Initial inward flow of Na+ ions followed by inactivation. (D) Signup and view all the answers

How does the behavior of the K+ channel described in the content differ from the K+ channel responsible for the resting membrane potential?

The described K+ channel opens with depolarization (VM+), while the resting potential K+ channel is primarily involved in maintaining a stable negative membrane potential. (B) Signup and view all the answers

What process allows researchers to study channelopathies using oocytes?

Injecting mRNA coding for mutated ion channels into oocytes and observing their function. (B) Signup and view all the answers

Which of the following is listed as a channelopathy related to brain Na+ channels?

Generalized Epilepsy with Febrile Seizures Plus (D) Signup and view all the answers

According to the content, how do ion channels relate to Ohm's Law?

Ion channels may or may not obey Ohm's Law, suggesting their electrical conductance can be complex. (C) Signup and view all the answers

What happens to the Na+ channel described in the content when the membrane potential becomes more negative (VM-), moving towards hyperpolarization?

The Na+ channel closes. (C) Signup and view all the answers

Study Notes

Lecture 011625

Bioelectric Circuits and Ion Channels
- Electrophysiological Studies
- Molecular Approach
- Types of Channels and their Gating
Membrane potential
- Electrochemical equilibrium
- Resting membrane potential
- Selective permeability
- Driving Force
- Nernst and Goldman equations
Electrotonic (passive) properties
- Time and length constants - initial look
Action potential
- Introduction of the concept

Membrane Potentials

Recording of Membrane Potential (V_M)
- Changes in V_M from resting state include graded responses (synaptic potentials) and active responses (action potentials).
Synaptic Potential
- A graded response; a small, temporary change in membrane potential.
Action Potential
- A rapid, large change in membrane potential that is propagated along the axon.

Study of ion channels - electrophysiology

Intracellular recording
- Current clamp: measures membrane potential (V_M).
- Recordings conventionally show depolarization (V_M increases) as upward traces and hyperpolarization (V_M decreases) as downward traces:
Patch clamp recording
- Form of voltage clamp: measures ionic current.
- Recordings conventionally show inward current (downwards trace) and outward current (upwards trace).
Membrane Potential = V_M
Ionic Current = I(ION)

Intracellular recording of resting and action potentials

Injecting positive current: depolarization
Injecting negative current: hyperpolarization
A threshold level of depolarization can trigger an action potential.

Patch clamp recording of single voltage-gated Na+ channels

Stimulus: membrane depolarization
Effect: channel opening, Na⁺ influx

Nerve cell membrane

Lipid bilayer: barrier to ion diffusion
Pumps: transport ions to create concentration gradients
Channels: embedded in the phospholipid bilayer; selective for K⁺, Na⁺, Ca²⁺, or Cl^-; passive flux of ions; gated by varied stimuli (e.g., changes in V_M, neurotransmitters, etc.)

Study of Ion Channels - X-ray crystallography

KcsA bacterial K⁺ channel structure determined by X-ray crystallography.
Bacterial voltage-gated channels and eukaryotic channels have also been studied via other techniques.

Study of ion channels - Molecular Biology

Gene sequences predict association of subunits to cell membranes.
Hydrophobicity plots can be used to understand the protein's structure.

Study of ion channels - Electrophysiology

Xenopus oocyte expression system: oocytes are used to study ion channels because they do not express native ion channels, can express injected exogenous mRNA coding for channel proteins, and traffic and insert functional channels into the cell membrane.
This system useful to compare normal channel function to those mutated in disease—channelopathies.

Na and K channel responses to V_M

Na+ channels: Na⁺ enters (open) then inactivates (closed) when V_M changes.
K+ channels: K⁺ exits (open) when Vm changes.

Expression of Na⁺ channels in frog egg

RNA is inserted into the frog egg
The channels are recorded using patch clamp.

Channelopathies

Genetic defects in ion channels can lead to various diseases. Examples are presented for skeletal muscle Na+ channels and brain Na+ channels.

Electrotonic (passive) membrane properties

Time constant: time taken for the potential change to reach approximately 63% of the final value.
Length constant: distance over which the potential change is approximately 37% of its initial value.

Basis of Membrane Potential

Role of sodium/potassium pump
- Maintains ion distribution (high Na⁺ outside, high K⁺ inside)
- Creates a charge difference across the membrane
- Is electrogenic (creates a small negative membrane potential)
Role of ion channels
- Allows ion movement down electrochemical gradients
- Permeability of specific ions determines the resting membrane potential
Nernst equation: Predicts the equilibrium potential for an ion.
Goldman-Hodgkin-Katz equation: Calculates the membrane potential based on the permeability of multiple ions

Resting membrane potential (EM) versus equilibrium potential (Eion)

Ionic concentration gradients
Selective ionic permeabilities
- At rest, non-gated K channels are open, with high K⁺ permeability and low Na⁺ permeability.
- K⁺ efflux is the major contributor to RMP
- Equilibrium potential for Potassium (E_K) is most important at rest.

Equivalent circuit of nerve cell membrane

Ohm's law : voltage = current * resistance.
Resistance, capacitance, and current relate to ion channel function.

Ion channels as conductors of electricity

Ohm's law (V = IR): channels obey Ohm's law (are "ohmic") if their current is directly proportional to voltage; channels don't always follow the law; rectifying channels don't follow Ohm's law and conductance is not constant).

Action Potentials

Why? To quickly transmit information over distances (axons, muscle).
How? Voltage-gated Na⁺ and K⁺ channels; these channels provide the rapid, propagating "all or none" action potential.

Studying That Suits You

Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

Description

Test your knowledge on electrophysiology concepts, particularly focusing on membrane potential, ion channels, and their dynamics. This quiz covers essential aspects of how ion distribution and channel kinetics influence a cell's electrical state. Perfect for students in advanced biology or physiology courses.