24 Questions
What is the primary function of the Nernst Equation in the context of membrane potential?
To determine the equilibrium potential for a single ion
What is the effect of increasing external potassium on the membrane potential?
It depolarizes the membrane
What is the valency of potassium ions in the Nernst Equation?
1
What is the significance of tight regulation of neuronal K+ concentrations?
It maintains the membrane potential particular sensitive to changes in potassium
What is the consequence of hyperkalemia on the heart?
It can cause the heart to stop beating
What is the threshold level of depolarization required to trigger an action potential?
-55 mV
What is the primary role of ligand-gated cation channels in the initial stimulus of an action potential?
To allow the movement of sodium ions into the neuron
What is the concentration of potassium ions in the blood?
4mM
What is the primary function of non-gated (leak) ion channels in regulating membrane potential?
To set the resting membrane potential by allowing the efflux of K+ ions
Which of the following factors contributes to the unequal distribution of inorganic ions between intracellular and extracellular fluid?
Permeability, concentration gradient, and electrical gradient of Na+, K+, Cl- and organic ions
What is the value of the resting membrane potential (RMP) in millivolts?
-65mV
What is the primary function of voltage-gated ion channels?
To generate action potentials in response to changes in voltage
What is the result of the movement of K+ ions down their concentration gradient out of the cell?
The cell becomes more negatively charged
Which of the following types of ion channels is responsible for generating potential changes at synapses?
Ligand-gated (chemical) ion channels
What is the term for the potential difference at which there is no net movement of ions across the membrane?
Equilibrium potential
What is the term for the movement of ions across the membrane driven by the combination of electrical and chemical gradients?
Electrochemical gradient
What is the initial effect of K+ exit on the charge distribution inside and outside the cell?
Excess negative charge inside and positive charge outside
What is the primary reason for the opposition to the movement of remaining K+ ions down the concentration gradient?
Electrostatic repulsion
What is the term for the joint effect of electrical and diffusional forces on the movement of K+ ions?
Electrochemical gradient
What is the state achieved when the electrical force driving K+ back into the cell equals the chemical force driving K+ out?
Equilibrium
What is the relationship between the net concentration and net electrical forces at Ek?
Net concentration equals net electrical
What is the value of the resting membrane potential (RMP) when it equals the equilibrium potential for potassium (Ek)?
-75 mv
What is the term for the continuous balance between K+ ions leaving and entering the cell, maintaining equilibrium?
Continuous balance
What is the likely effect of hyperkalemia on the membrane potential of a cell?
Depolarization
Study Notes
Charge Imbalance and Electrical Potential Difference
- Excess positive charge outside the cell creates a slight excess of negative charge inside, making the inside of the cell negative relative to the outside.
- This charge imbalance establishes an electrical potential difference across the membrane.
Electrochemical Gradient
- Electrical and diffusional forces jointly form the electrochemical gradient for K+.
- The electrochemical gradient determines the spontaneous direction of K+ movement.
Equilibrium
- As the electrical potential difference builds up, it opposes further K+ movement out of the cell.
- The electrical force driving K+ back into the cell equals the chemical force driving K+ out, resulting in equilibrium.
- At equilibrium, there is no net movement of K+ in either direction.
- Every time one K+ leaves, another enters, maintaining the equilibrium.
Nernst Equation
- The Nernst equation calculates the equilibrium potential for a single ion.
- The equation includes constants R and F, body temperature T, valency z, and outside and inside ion concentrations [ion]o and [ion]i.
Significance of Potassium
- Membrane potential is particularly sensitive to changes in potassium.
- Increasing external potassium depolarizes the membrane.
- Neuronal K+ is under tight regulation.
- The concentration of K+ in the blood is 4mM.
Action Potential
- The action potential has three stages: initial stimulus, depolarization, and repolarization.
- The initial stimulus is an initial depolarization that triggers the movement of Na+ into the neuron by ligand-gated cation channels.
- Depolarization occurs when the initial depolarization reaches the threshold level, opening voltage-gated Na+ channels and resulting in rapid depolarization.
- The resting membrane potential (RMP) is -65mV.
Factors Responsible for Unequal Distribution of Inorganic Ions
- Permeability, concentration gradient, and electrical gradient of Na+, K+, Cl-, and organic ions are responsible for the unequal distribution of inorganic ions between intracellular and extracellular fluid.
Ion Channels
- Non-gated (leak) ion channels set the resting membrane potential and are always open, with more K+ channels than Na+ channels.
- Voltage-gated ion channels change in voltage, causing ion channels to open, generating action potentials.
- Ligand-gated (chemical) ion channels generate potential changes at synapses.
Electrical Gradient
- The electrical gradient is self-limiting due to the movement of K+ down its concentration gradient, which exits the cell and creates a charge imbalance.
This quiz explores the concept of charge imbalance in cells, where a slight excess of positive charge outside and negative charge inside leads to an electrical potential difference across the membrane.
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