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Questions and Answers
What is the extracellular concentration of potassium ions ([K+]e)?
Which of the following values represents the intracellular sodium ion concentration ([Na+]i)?
If the permeability of Cl- is denoted as PCl = 0.5, what does this imply about its relative permeability compared to potassium?
What is the reversal potential for an inhibitory channel given in the question?
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What should be ensured regarding the pages of the exam when submitting?
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During a resting state, what is the first voltage state before an inhibitory input arrives?
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Which ion has the highest intracellular concentration among Na+, K+, and Cl-?
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Based on the given parameters, which ion's reversal potential is not mentioned in the content?
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What will be the expected membrane voltage at a distance of 10 cm from the injection point after hyperpolarizing a cell to -100 mV?
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In the context of a squid giant axon, what does the conductance curve represent?
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What type of circuit configuration describes the op-amp in a Giga seal situation?
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What potential outcome can occur if the membrane is not opened during a patch clamp experiment?
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Which parameter impacts the voltage drop along the membrane the most when injecting a negative current?
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If injecting current into a neuron does not alter its resting potential, what could be inferred?
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Which factor contributes to the high resistance observed in a Giga seal during a patch clamp experiment?
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What effect do sodium and potassium conductance changes have on action potentials?
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Study Notes
Extracellular and Intracellular Ionic Concentrations
- Extracellular medium has following ionic concentrations:
- Na+: 120mM
- K+: 4mM
- Cl-: 110mM
- Cytoplasmic/intracellular ionic concentrations:
- Na+: 15mM
- K+: 120mM
- Cl-: 20mM
- Charge balance maintained by fixed negative charges in cytoplasm
Permeability Coefficients
- PNa = 0.02
- PK = 1
- PCl = 0.5
Reversal Potentials
- Reversal potential is the membrane potential at which there is no net movement of ions across the membrane.
- Calculated using the Nernst equation.
Resting Membrane Voltage
- Resting membrane voltage is the membrane potential of a cell when it is not being stimulated.
- Calculated using the Goldman equation, which takes into account the permeability of the membrane to different ions
- Can be influenced by factors like ion concentrations, membrane permeability, and temperature.
Excitatory and Inhibitory Inputs
- Excitatory inputs depolarize the membrane, making it more likely to fire an action potential.
- Inhibitory inputs hyperpolarize the membrane, making it less likely to fire an action potential.
- Reversal potential for excitatory channel: 0mV
- Reversal potential for inhibitory channel: -45mV
Voltage Dynamics During Inhibitory Input
- i) During rest: The inhibitory input would cause a hyperpolarization of the membrane.
- ii) During depolarization: The inhibitory input would still cause a hyperpolarization, but the amplitude of the hyperpolarization would be smaller due to the depolarized state of the membrane.
Whole-Cell Patch Pipette and Squid Giant Axon
- Whole-cell patch pipette is a technique used to study the electrical properties of cells.
- Squid giant axon is a large nerve fiber that is often used in electrophysiological studies.
Membrane Current
- Membrane current is the flow of ions across the membrane.
- Can be measured using a patch clamp.
- Can be affected by factors like the membrane potential, the conductance of the membrane to different ions, and the driving force on the ions..
Conductance Curves for Sodium and Potassium
- Conductance is a measure of the ease with which ions can flow across the membrane.
- Sodium and potassium conductances change during the action potential, which leads to the characteristic shape of the action potential.
Hyperpolarization of a Cell
- Hyperpolarization is a change in the membrane potential that makes the inside of the cell more negative.
- Can be induced by injecting negative current into the cell.
- The voltage recorded at a distance from the injection point will be less negative than the voltage at the injection point
- This is due to the resistance of the cell and the external medium.
Op-Amp Rules
- Op-amps are used in many electronic circuits and are often used to amplify signals.
- Op-amps have very high input impedance which means that they do not draw any current from the input signal
- Op-amps have very high open-loop gain which means that they can amplify small signals by large amounts.
- Op-amp circuit configurations are named based on the type of feedback used.
Giga Seal Formation
- Giga seal is a very tight seal that is formed between the pipette and the membrane.
- Measured in GΩ (gigaohms).
- Used in patch clamp electrophysiology.
Current Clamp vs Voltage Clamp Configurations
- Current Clamp configuration: the potential difference across the cell is controlled by the experimenter while the current flowing through the cell is measured.
- Voltage Clamp configuration: the current flowing through the cell is controlled by the experimenter while the potential difference across the cell is measured.
Patch Amplifier Output
- Patch amplifier measures changes in the current across the membrane.
- Current fluctuations are observed when ions move across the membrane
- The output of the patch amplifier reflects these fluctuations.
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Description
This quiz covers the concepts of extracellular and intracellular ionic concentrations, permeability coefficients, and the calculations of resting membrane voltage using the Nernst and Goldman equations. It also touches on excitatory and inhibitory inputs that affect membrane potential. Test your understanding of these critical topics in cellular physiology.
