Ion Channels and Resting Membrane Potential

Questions and Answers

What primarily determines the selectivity of ion channels for specific ions?

The chemical interactions with polar amino acid residues (correct)

The temperature of the surrounding environment

The thickness of the membrane surrounding the channel

The type of ion flowing through the channel

What is the main role of ion channels in the nervous system?

To store neurotransmitters

To transport glucose across the membrane

To change the membrane potential (correct)

To facilitate hormone production

What effect does an increase in ion charge concentration have on solvation?

It reduces the number of surrounding H2O molecules.

It increases the solvation radius. (correct)

It has no effect on solvation.

It decreases the solvation radius.

Which type of ion channels allows the passage of a variety of ions, including Na+, K+, and Ca2+?

Heteromeric channels Signup and view all the answers

How do the atomic radii of Na+ and K+ compare?

Na+ has a smaller atomic radius than K+. Signup and view all the answers

What effect do ionic fluxes across the membrane have on neurons?

They cause rapid changes in membrane potential Signup and view all the answers

Which statement about intrinsic membrane proteins is true?

They form pores to allow specific ions to pass Signup and view all the answers

What characterizes voltage-gated ion channels?

They have a specific activation threshold that must be reached. Signup and view all the answers

What type of conductance do rectifying channels exhibit?

Variable conductance depending on membrane potential. Signup and view all the answers

What triggers the opening of the Na+ channel gate?

A change in membrane potential Signup and view all the answers

What is the role of segment S4 in Na+ channels?

It functions as the voltage sensor Signup and view all the answers

What happens to the conductance of a high conductance channel?

It has a positive slope indicating increasing current. Signup and view all the answers

What is true about the inactivation gate of the Na+ channel?

It occludes the pore from the internal side Signup and view all the answers

Which statement accurately describes the functional properties of K+ channels?

They exhibit slow inactivation kinetics and help repolarize action potentials Signup and view all the answers

What inhibits the Na+ channels mentioned in the content?

TTX (tetrodotoxin) Signup and view all the answers

What is the primary characteristic of high threshold activation (HVA) channels?

They activate at potentials around -20mV. Signup and view all the answers

What is the typical membrane potential range in mammal cells?

-65mV to -70mV Signup and view all the answers

Which channel is categorized as a low threshold activation (LVA) channel?

Cav3 Signup and view all the answers

What primarily determines the resting potential in excitable cells?

The distribution of electric charges across the membrane Signup and view all the answers

Which of the following describes the action potential?

It occurs in response to specific stimuli causing ion fluxes. Signup and view all the answers

What is the equilibrium potential for K+ defined by?

Nernst's equation Signup and view all the answers

What occurs when the electric force inside the cell opposes the chemical gradient?

The tendency for K+ to enter the cell equals its tendency to exit Signup and view all the answers

At 25 °C, what is the value of RT/F used in Nernst's equation?

25.2 mV Signup and view all the answers

For a cation with a higher extracellular concentration than intracellular concentration, what is the sign of the equilibrium potential (Ex)?

Ex > 0 Signup and view all the answers

What generates the membrane potential?

Resting membrane permeability and ion concentration gradient Signup and view all the answers

Study Notes

Neurons and Membrane Potential

Neurons generate, transmit, and process nervous information through changes in membrane potential.
Membrane potential changes result from the opening and closure of ion channels.

Ion Channels

Intrinsic membrane proteins formed by subunits creating a pore for specific ions (Na+, K+, Ca2+).
Ionic fluxes across the membrane lead to rapid membrane potential changes.

Ion Channel Selectivity

Ion channels exhibit varying selectivity; some allow passage of different ions while others are highly selective.
Selectivity is influenced by chemical interactions in the P domain and pore size.
Hydration of ions affects their movement, where smaller ions like Na+ carry higher charge concentrations than larger ions like K+.

Channel Conductance

Ohmic channels maintain constant conductance with a linear relationship between membrane potential (Vm) and current.
Rectifying channels have variable conductance, optimizing conduction for specific membrane potentials.

Voltage-Gated Ion Channels

Remain closed at resting potential, require membrane potential changes to open.
Feature a voltage sensor composed of charged amino acid sequences crucial for activation.

Sodium Channels

Na+ channels include the S4 segment as the voltage sensor, a selectivity filter, and an inactivation gate.
Membrane depolarization displaces the S4 segment, leading to channel activation.
Inactivation occurs through folding of a loop between specific domains, occluding the channel.

Functional Properties of Sodium Channels

Multiple subtypes (Nav1.1-Nav1.9) exist, requiring specific subunits for functional performance.
Key in generating action potentials, characterized by a low activation threshold and rapid ion flow.

Potassium Channels

K+ channels activated by voltage and Ca2+, formed by four identical subunits with six segments.
Critical for repolarization during action potentials and possess slower inactivation kinetics.

Calcium Channels

Three families (Cav1, Cav2, Cav3) with various isoforms.
Comprised of subunits forming the pore and additional subunits affecting channel properties.

Membrane Potential

Refers to the electric potential difference across the cell membrane, typically negative inside.
In mammalian cells, it generally ranges from -65mV to -70mV.
Alterations in membrane potential are essential for nerve transmission and muscle contraction.

Equilibrium Potential

Defined by Nernst's equation, providing the equilibrium potential for ions based on concentration gradients inside and outside the cell.
Determines the driving force for ion movement when membrane permeability is selective.

Nernst Equation

Ex = (RT/F) * ln([X]out/[X]in), with a simplified version at 25°C resulting in Ex = 58 mV * log([X]out/[X]in).
Indicates conditions under which the equilibrium potential exceeds or is less than zero based on ion concentrations.

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Description

Explore the critical role ion channels play in the generation and transmission of nerve signals. This quiz delves into the mechanisms of how membrane potential changes affect neuronal activity, contributing to the overall function of the nervous system.