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Questions and Answers
What primarily prevents large influxes of water into the cell according to the Gibbs–Donnan model?
What primarily prevents large influxes of water into the cell according to the Gibbs–Donnan model?
Which ion has a permeability approximately 1/10 that of K+ according to the pump-leak model?
Which ion has a permeability approximately 1/10 that of K+ according to the pump-leak model?
The resting membrane potential in most resting neurons is typically within which range?
The resting membrane potential in most resting neurons is typically within which range?
What happens to the membrane when the potential becomes more positive than the resting potential?
What happens to the membrane when the potential becomes more positive than the resting potential?
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What is the main function of the sodium-potassium (Na⁺/K⁺) pump?
What is the main function of the sodium-potassium (Na⁺/K⁺) pump?
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What would likely occur if the sodium-potassium pump were inhibited?
What would likely occur if the sodium-potassium pump were inhibited?
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Which of the following accurately describes leak channels?
Which of the following accurately describes leak channels?
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How is the equilibrium potential of an ion quantitatively calculated?
How is the equilibrium potential of an ion quantitatively calculated?
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Which statement about voltage-gated channels is true?
Which statement about voltage-gated channels is true?
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In a normal resting state, what is the approximate resting membrane potential of a neuron?
In a normal resting state, what is the approximate resting membrane potential of a neuron?
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What is the equilibrium potential for potassium (K⁺) based on the Nernst equation?
What is the equilibrium potential for potassium (K⁺) based on the Nernst equation?
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What is the primary role of action potentials in the nervous system?
What is the primary role of action potentials in the nervous system?
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Which of the following best describes the resting potential of medium-sized nerves?
Which of the following best describes the resting potential of medium-sized nerves?
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What occurs during depolarization of an excitable tissue?
What occurs during depolarization of an excitable tissue?
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What changes occur in excitability during a monophasic action potential?
What changes occur in excitability during a monophasic action potential?
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Which term refers to the electrical state of a neuron at rest?
Which term refers to the electrical state of a neuron at rest?
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What is NOT a characteristic of monophasic action potentials?
What is NOT a characteristic of monophasic action potentials?
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Which phase is NOT typically included in a monophasic action potential?
Which phase is NOT typically included in a monophasic action potential?
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Which statement correctly describes the importance of the action potential?
Which statement correctly describes the importance of the action potential?
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At rest, which ion is the cell membrane most permeable to?
At rest, which ion is the cell membrane most permeable to?
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What effect would a toxin that blocks potassium channels have on the resting membrane potential?
What effect would a toxin that blocks potassium channels have on the resting membrane potential?
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Which of the following ions typically has a positive equilibrium potential in a neuron?
Which of the following ions typically has a positive equilibrium potential in a neuron?
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How does the Donnan effect contribute to ion distribution across a membrane?
How does the Donnan effect contribute to ion distribution across a membrane?
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What role does active transport play in maintaining resting membrane potential?
What role does active transport play in maintaining resting membrane potential?
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Which ion distribution is essential for the function of excitable cells like neurons?
Which ion distribution is essential for the function of excitable cells like neurons?
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What happens to the resting membrane potential when Na⁺ permeability is increased?
What happens to the resting membrane potential when Na⁺ permeability is increased?
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What is the primary mechanism responsible for the resting membrane potential in neurons?
What is the primary mechanism responsible for the resting membrane potential in neurons?
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How does an increase in extracellular K⁺ concentration affect the resting membrane potential?
How does an increase in extracellular K⁺ concentration affect the resting membrane potential?
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Study Notes
Course Information
- Faculty of Medicine
- Academic Year: 2024-2025
- Year: 1
- Semester: 1
- Module: Human Body Function (HBF) 102
Resting Membrane Potential
- Resting membrane potential (RMP) is the electrical potential difference across a cell membrane when the cell is at rest.
- The inside of the cell membrane is more negative than the outside.
- Normal range: -70 mV to -90 mV
- Important for neurons and muscle cells.
Objectives
- Define and list different membrane potentials.
- Recognize the driving forces behind the RMP development.
- Relate equilibrium potential of an ion to the RMP of the cell membrane.
- Identify the application of the Nernst equation in neurophysiology.
- Understand the role of the Na+/K+ pump in maintaining the RMP.
Cell Membrane
- The cell membrane acts as a selective filter.
- Allows the free movement of some molecules across it, but controls movement of others tightly.
- Uncharged molecules like oxygen (O2), carbon dioxide (CO2), urea, alcohol, and glucose move freely down their concentration gradient.
- Charged molecules (ions) cannot easily diffuse. They use ion channels, which are selective for specific ions.
Gibbs-Donnan Effect
- The Donnan effect is the phenomenon of a predictable unequal distribution of permeant charged ions on either side of a semipermeable membrane in the presence of impermeable charged ions.
- Ionic distribution across cell membranes, which is critical in maintaining the cell's resting membrane potential.
Ion Concentration
- Large anion proteins are not permeable to cell membranes.
- Small cations are attracted but are not bound to proteins.
- Small anions cross the capillary walls away from anionic proteins more readily than small cations.
- Intracellular concentration of K+ is much higher than extracellular. ( 150 mmol vs 5mmol )
- Extracellular concentration of Na+ is much higher than intracellular.(150mmol vs 15mmol ).
- Extracellular concentration of Cl- is much higher than intracellular. ( 125mmol vs 9mmol ).
The Donnan Effect on Ionic Distribution in Cells
- Cells contain impermeant anions (proteins/nucleic acids).
- These negatively charged ions create a tendency for positively charged ions, like potassium (K+), to enter the cell to balance the negative charges.
- If too many ions move across, osmotic balance is disrupted, leading to potential swelling (water entering).
Ion Movement
- Three factors induce ion movement through channels:
- Concentration gradient
- Electrical gradient
- Ion channels
Interrelation of Donnan Effect and Resting Membrane Potential
- The Donnan effect influences the distribution of ions across the cell membranes.
- Large intracellular proteins (anions) cannot cross the membrane and contribute to overall negative charge inside the cell.
- This is essential in maintaining the resting membrane potential.
Resting Membrane Potential Values
- In most resting neurons, the potential difference across the membrane is about 30 to 90 mV.
- Inside the cell is more negative than outside.
- Excitable tissues (nerves and muscles) have higher potentials than other cells.
- Dead cells do not have membrane potentials.
Basic Physics of Resting Membrane Potential
- Contribution of K+ diffusion potential: The cell membrane tends to pump K+ out (positive charge) from high to low concentration.
- Electro-positivity outside; electro-negativity inside
- RMP is much more permeable to K+ than Na+.
- K+ diffusion contributes far more to resting membrane potential.
Basic Physics of Resting Membrane Potential
- Contribution of Na+ diffusion: A small amount of Na+ diffuses into the cell down its concentration gradient.
- The membrane is only slightly permeable to Na+ through K-Na leak channels.
Contribution of Na+/K+ Pump
- This is a powerful electrogenic pump on the cell membrane.
- Maintains concentration gradients of K+ and Na+ between the two sides of the membrane.
- Pumps 3 Na+ out and 2 K+ in, causing a net loss of positive charge from inside, returning the nerve fibre to the resting state.
Membrane Ion Channels
- Leak channels (passive channels) are always open and ions diffuse through them according to the ion concentration gradient.
- Voltage-gated channels open when the cell membrane is electrically activated.
- Chemically-gated channels open when a neurotransmitter binds to the receptor.
Equilibrium Potential
- The electrical potential difference across the cell membrane that exactly balances the concentration gradient for an ion is known as the equilibrium potential.
- The Nernst equation is used to calculate the equilibrium potential of a particular ion.
The Potassium Nernst (Equilibrium) Potential
- At rest, the intracellular K+ concentration (inside the cell) is significantly higher than the extracellular K+ concentration (outside the cell).
- K+ leak channels are much more permeable to K+ than Na+ (K+ molecules are smaller).
- This results in a net outward diffusion of K+ and negative charge inside. (-94mV).
The Sodium (Equilibrium) Potential
- The inside-to-outside ratio of Na+ is much less inside vs. outside (0.1).
- Na+ leak channels are relatively less permeable.
- This results in a net positive potential for Na+, as it would rush into the cell (+61mV).
Action Potential
- A series of brief, self-propagated electrical changes in excitable tissue when stimulated by adequate stimuli.
- Action potentials are responsible for communication between neurons and other cells,
- Action potentials exhibit multiple phases which include: depolarization, repolarization, and hyperpolarization.
Electrical Activities of Excitable Tissues
- Resting membrane potential.
- Electrotonus
- Action potential
Clinical Significance of Action Potentials
- Nerve impulse transmission.
- Excitation-contraction coupling.
- Excitation-secretion coupling.
- Medical diagnosis (ECG, EEG, EM).
- Research in neuroscience and artificial intelligence (AI) fields.
Question Answers
- Most permeable ion at rest is potassium (K+).
- Blocking potassium channels leads to depolarization (positive).
- Sodium (Na+) has a positive equilibrium potential.
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Description
Test your knowledge on membrane dynamics with this quiz focusing on the Gibbs-Donnan model, resting membrane potential, and the functions of ion channels. Answer questions on the sodium-potassium pump and the equilibrium potential of various ions. Ideal for students studying cell biology or physiology.
