Molecular Neurophysiology Quiz

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Questions and Answers

Which process is essential for determining the membrane potential across a cell's membrane?

Ion transport mechanisms (correct)

Temperature of the surrounding medium

Rate of cellular respiration

Presence of free radicals

What role does the membrane potential play in the nervous system?

It acts as a trigger for secretory processes (correct)

It prevents neurotransmitter release

It facilitates the growth of new neurons

It decreases the speed of nerve signal transmission

What condition is primarily responsible for the dissociation of salts in water leading to charge development?

High pH levels

Absence of temperature changes

Presence of ions

Polar nature of water (correct)

Which statement correctly describes cations and anions in a physiological salt solution?

Both cations and anions balance each other in terms of charge Signup and view all the answers

What does the term 'membrane voltage' refer to?

The difference in electric potential across the membrane Signup and view all the answers

What is a significant function of the membrane potential in muscle cells?

Triggering muscle activity Signup and view all the answers

What is the focus of the course 'Molecular Neurophysiology'?

The connections between molecular mechanisms and systems neuroscience Signup and view all the answers

In the context of bioelectrical processes, what does a defibrillator do?

Induces electrical stimulation to reset the heart's rhythm Signup and view all the answers

Which topic will be covered first in the lecture series?

Excitable Membrane and Action Potential Signup and view all the answers

Which component is NOT required for the generation of a membrane potential?

Presence of temperature variations Signup and view all the answers

Who is responsible for the lecture on 'Neuronal signaling 2: Gene expression'?

Prof. Gerhard Schratt Signup and view all the answers

What type of exam will be held for the course?

Electronic exam, multiple choice Signup and view all the answers

Which of the following topics will not be covered during the semester?

Neuromodulation in chronic pain Signup and view all the answers

On what date will the lecture on 'Postsynaptic responses, trans-synaptic signaling' take place?

30.09.2024 Signup and view all the answers

Which lecturer is presenting on 'Sensory Systems 1'?

Dr. Wolfger von der Behrens Signup and view all the answers

Which of the following weeks will have no lecture?

Week of October 21, 2024 Signup and view all the answers

During the absolute refractory period, which statement is true?

Action potentials cannot be generated, irrespective of stimulus strength. Signup and view all the answers

What is the role of local anesthetics in signal transmission?

Block Na+ channels. Signup and view all the answers

How do action potentials differ from electrotonic signal transmission?

Action potentials propagate without signal attenuation. Signup and view all the answers

What is primarily responsible for the recovery after inactivation of Na+ channels?

Restoration of resting membrane potential. Signup and view all the answers

Which part of a neuron is primarily responsible for receiving signals?

Dendrite. Signup and view all the answers

Which of the following describes the relationship between the central and peripheral nervous systems in terms of signal transmission?

CNS and PNS work together for muscle reflexes. Signup and view all the answers

What characterizes the relative refractory period in neurons?

A stronger-than-usual stimulus can trigger an action potential. Signup and view all the answers

Which process leads to distance-dependent signal attenuation in axons?

Electrotonic signal transmission. Signup and view all the answers

What initiates depolarization during the action potential generation?

Inward current due to sodium conductance Signup and view all the answers

What is the role of K+ conductance during the action potential?

It facilitates repolarization after the peak of the action potential Signup and view all the answers

What characterizes the 'all-or-nothing' principle of action potentials?

Threshold depolarization leads to full firing or none at all Signup and view all the answers

What determines the voltage-dependence of ion channels?

The presence of positively charged amino acids in S4-Helices Signup and view all the answers

What is the effect of delayed elevation of K+ ion permeability during an action potential?

It facilitates the repolarization phase of the action potential Signup and view all the answers

What happens during the inactivation of the Na+ conductance?

It halts depolarization and initiates repolarization Signup and view all the answers

What molecular structure acts as a voltage sensor in voltage-gated channels?

S4-Helix Signup and view all the answers

Why is the differential temporal behavior of Na+ and K+ conductances crucial?

It ensures the rapid initiation and cessation of action potentials Signup and view all the answers

What primarily contributes to faster action potential (AP) conductance in axons?

Increased axon diameter Signup and view all the answers

How does myelination affect the action potential transmission in axons?

Increases membrane resistance and enables saltatory conduction Signup and view all the answers

What role do nodes of Ranvier play in myelinated axons?

They concentrate voltage-dependent ion channels Signup and view all the answers

What is the effect of a high membrane resistance (rM) on action potential propagation?

Faster AP transmission as the threshold is reached at greater distances Signup and view all the answers

Which factor is least associated with the speed of signal transmission in axons?

Temperature of the environment Signup and view all the answers

What is the primary function of myelin in peripheral nerves?

To insulate axons and reduce ion exchange Signup and view all the answers

What defines the equilibrium potential for an ion?

The concentration gradient and selective permeability of the membrane for that ion Signup and view all the answers

Which statement correctly represents the relationship between action potential propagation and axon dimensions?

Signal propagation speed increases with increasing axon diameter Signup and view all the answers

Which of the following describes the all-or-nothing principle of action potentials?

APs occur once a certain threshold potential is reached Signup and view all the answers

What is a primary consequence of saltatory conduction in myelinated axons?

Increased energy efficiency and speed of signal transmission Signup and view all the answers

How is the equilibrium potential for K+ calculated given a concentration of 145 mM inside and 4.4 mM outside?

EK = -61 mV * log(33) Signup and view all the answers

What occurs during the overshoot phase of an action potential?

The membrane is rapidly depolarized beyond the threshold potential Signup and view all the answers

Which factor does NOT affect the equilibrium potential of an ion?

The membrane thickness Signup and view all the answers

What role did Hodgkin & Huxley play in the study of action potentials?

They conducted classical experiments on ionic mechanisms in giant axons Signup and view all the answers

During what physiological condition are intra- and extracellular ion concentrations typically unchanged?

While generating diffusion potentials Signup and view all the answers

What is the mathematical representation of the Nernst equation for an ion?

Eion = -61 mV * log([ci]/[ca]) Signup and view all the answers

Study Notes

Lecture Molecular Neurophysiology "Excitable Membranes"

The lecture was held at ETH Zurich on the topic of excitable membranes.
The professor is Dr. Gerhard Schratt.
The semester is FS 2024.

Molecular Neurophysiology: From Molecules to Systems

The course covers molecular neurophysiology from molecules to systems.
The exam is scheduled for January 13, 2024.
The exam is online, multiple choice.
Lecture schedule covers topics like introduction, excitable membranes, action potential, neurotransmitter release, postsynaptic responses and trans-synaptic signaling.
Other topics include: neuronal signaling, synaptic plasticity.

Books

Neuroscience, 5th edition, edited by Purves, Augustine, Fitzpatrick, et al.
Cellular and Molecular Neurophysiology, 5th edition, by Constance Hammond.

The Functioning of the Nervous System

The nervous system relies on electrical processes.
Luigi Galvani's experiments with frog legs demonstrated "animal electricity."
The biological basis of "animal electricity" involves charged ions, the membrane, and muscle contraction.

Bioelectrical Processes: Electrophysiology

Electrophysiology measures electrical activity in cells and organs.
ECG (electrocardiography) measures heart activity.
EEG (electroencephalography) measures brain activity.
Electrical stimulation can be used to induce or modulate cellular processes.
Examples include pacemakers, defibrillators, and cochlear implants.

Basis of Bioelectrical Processes

The membrane potential underlies bioelectrical processes.
The membrane voltage is approximately -70mV.
Inside the cell is negative relative to the outside.
Nomenclature: membrane voltage is the difference in potential.
Symbol: Vm = Um = Em.
Unit is mV.
Inside vs. outside convention uses the outside as the reference potential (mass = 0 mV).

Functions of the Membrane Potential

The membrane potential drives transport across membranes (like in the small intestine and kidneys).
It triggers secretory processes (e.g., insulin secretion).
It drives ATP synthesis in mitochondrial membranes.
It is involved in electrical signaling.
It is a direct trigger for muscle activity

Requirements for Generating a Membrane Potential

Essential for membrane potential are electrical charges, electrical insulation, and a mechanism to transport charges across the membrane.

Ions: Electrically Charged Molecules

Salts dissociate into electrically-charged ions in water (cations + and anions -).
Physiological salt solutions have equal amounts of positive and negative charges.

Intra- and Extracellular Ion Concentrations

Intracellular and extracellular environments have different ion concentrations.
Specific concentrations are listed for various ions (Na+, K+, Ca2+, Mg2+, Cl-, HCO3-, A- (e.g., proteins)).

Requirements for Membrane Potential (repeat)

Electrical charges, electrical insulation, mechanism for moving charges across the membrane.

Intra- and Extracellular Environment

The plasma membrane separates the intracellular and extracellular environments.
The membrane is a key component to maintain gradients.
Hydrophobic nature of the membrane makes it a good insulator for charged ions
Various principles apply across membranes.

Permeabilities of Physiologically Relevant Solutes

Cell membranes act as barriers for most polar molecules.
Permeabilities vary significantly for different types of molecules (gases, small uncharged molecules, water, large uncharged molecules, ions, charged polar molecules)
Specific values (1 cm/s to 10-12cm/s) are examples of permeability.

How is a Membrane Potential Generated?

Two essential factors are concentration gradients of specific ions and selective permeability of membranes.
The result leads to an electrical gradient (membrane potential)
Other relevant factors are: the concentration difference and the permeability of the membrane.

How Are Concentration Gradients Generated?

Concentration gradients are the result of transport mechanisms across membranes including diffusion, carrier-mediated transport, facilitated diffusion and active transport (like Primary and secondary active transporters).

How is a Membrane Potential Generated (Repeat)

The key factors that drive formation of a membrane potential are concentration gradient for a given ion and selective permeability of the membrane to the same ion.

Potential Equilibrium

The equilibrium potential is a specific voltage at which there is no net ion flux.
The Nernst equation defines this voltage.

Example Calculation of Equilibrium Potentials

Illustrates the Nernst equation calculation for specific ions (K+, Cl-).

Summary Equilibrium Potential

The voltage across a membrane is the equilibrium potential if there is a concentration gradient for an ion.
The membrane is selectively permeable to the ion.
Magnitude is defined by the Nernst equation.
Value depends only on concentration gradient.
Ion fluxes during potential generation don't significantly change intra/extracellular concentrations.

Signal Transmission: The Action Potential

Neurological signal transmission utilizes action potentials.

When Does a Cell Fire an Action Potential (AP)?

Action potentials are triggered by depolarization.
A threshold potential must be reached for an action potential to occur.

The Action Potential

Action potentials are characterized by amplitude and kinetics.
Described as all-or-nothing. The action potential and the phases (rising phase, overshoot, falling phase, and after-hyperpolarization).

Basic Properties of Action Potentials

Cause of rapid depolarization phase (including membrane potential reversal).
Triggering of action potentials by depolarization.
Significance of the threshold potential and the "all-or-nothing" principle.

Classical Experiments on Ionic Mechanisms of APs

Hodgkin and Huxley's experiments using giant squid axons provided insights into the ionic mechanisms behind action potentials
Awarded a Nobel Prize.

Mechanistic Principles of Depolarisation and Repolarisation

Changes in membrane potentials involve ion fluxes that reverse the charge across the membrane.
The inward current during depolarization, and the outward current during repolarization.

Na+ and K+ Currents

Na+ and K+ currents are characteristic of action potentials.
These currents are measured using a voltage-clamp technique.
The currents result from selective channel openings.

Summary: Generation of an AP

Depolarization is caused by voltage-gated Na+ channel activation.
Repolarization involves voltage-gated K+ channel activation and inactivation of Na+ channels.
The crucial factor is the differential timing of Na+ and K+ conductances.

Why Are Aps Following the "All-or-Nothing Principle?"

Depolarization increases Na+ permeability, leading to more depolarization (positive feedback).
The delayed increase in K+ permeability causes repolarization (negative feedback).

Why Are Na+ and K+ Currents Voltage-Dependent?

The question of the mechanism behind the voltage-dependence of currents.

The Architecture of Voltage-Gated Na+ and K+ Channels

The structure of voltage-gated channels, including the S4 helix and other domains, and their role in conductance.

Voltage-Dependence of Single Ion Channels

The open probability of ion channels increases with increasing depolarization.

Molecular Basis of Voltage-Dependent Switch Behaviour

S4-Helices, with their charged amino acids, act as voltage sensors within voltage-gated channels.

Voltage-Dependent Na+ Channels Adopt States

Na+ channels cycle through three states: closed, open, and inactivated.
Inactivation is essential for the action potential.
The recovery from inactivation.

Consequence of Na+ Current Inactivation

Describes the absolute and relative refractory periods.

Local Anesthetics Block Na+ Channels

Local anesthetics block voltage-gated Na+ channels.

How is Signal Transmission Within Neurons Achieved?

Signal transmission in neurons involves action potentials and synapses

The Function of Nerve Cells

Signal transmission (action potentials) in neurons.
Signal transfer (synapses) between neurons.

In Electrically Excitable Cells

Electrical signals are used for information transfer in nerve cells, heart and other excitable structures.

Signal Transmission without Action Potentials

Passive properties of axons.
Signal attenuation along the axon.

Signal Transmission with Action Potentials

Action potentials enable long-distance signal transmission.
Signal transmission is not attenuated by action potentials.

Continuous, Regenerative Spread of APs along the Axon

Action potentials propagate along the axon.
The spread is regenerative at each segment of the axon membrane.

What Determines the Speed of Signal Spread?

Factors influencing action potential speed: the axon's diameter and myelination.

Axons with Large Diameter Conduct Faster

Larger diameter axons conduct faster because of reduced internal resistance.

What Determines the Speed of Signal Spread (repeat)

Factors impacting AP conduction speed: fiber diameter, membrane resistance and myelination.

Myelinated Axons

Myelinated axons increase the speed of conduction.
Myelination involves Schwann cells in the peripheral nervous system, and oligodendrocytes in the central nervous system.

Consequence of Myelination: Saltatory Signal Transmission

Action potential propagation in myelinated axons.
Saltatory transmission means jumping across the myelin segments.

Summary Conductance Speed

Factors affecting action potential speed include axon diameter, membrane resistance and myelination.

Fiber Types and Conductance Speeds

Different types of nerve fibers (A, B, C) have varying myelination and conduction speeds.

Demyelination Diseases

Demyelination diseases like Multiple Sclerosis and Guillain-Barré Syndrome impair action potential transmission.

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Description

Test your knowledge on the essential concepts of membrane potential and its significance in the nervous system. This quiz covers various topics including bioelectrical processes, neuronal signaling, and muscle cell function, specifically designed for students studying Molecular Neurophysiology.