Bioelectricity WSC331 Quiz
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Questions and Answers

What is the equilibrium transmembrane potential for a frog muscle cell if the membrane is only permeable to K+ ions?

  • -82.6 mV
  • 25 mV
  • +82.6 mV
  • -100.8 mV (correct)

Why do the equilibrium potentials for K+ and Na+ ions have different polarities?

  • They allow only positive charge movement.
  • They are influenced by the concentration gradients of each ion. (correct)
  • They maintain a constant membrane potential.
  • They are affected by the p-n junction effect.

In an electrical model of a single ion channel, what does Vm=Ek signify?

  • The equilibrium potential is equal to the transmembrane potential. (correct)
  • The ion influx exceeds the efflux.
  • The net ion flow is positive.
  • The membrane potential is at resting level.

What happens to potassium ions when Vm is greater than Ek?

<p>Potassium ions flow out of the cell. (C)</p> Signup and view all the answers

What does mobility (μ) represent in the context of charged particles in an electric field?

<p>The ability of particles to move freely (A)</p> Signup and view all the answers

Which of the following correctly describes what happens to diffusion in the presence of an electric field?

<p>An opposing conduction current develops. (D)</p> Signup and view all the answers

In the Nernst-Plank Equation, what does the term 'drift' refer to?

<p>Movement of charged particles in response to an electric field (A)</p> Signup and view all the answers

What is meant by 'concentration' in the discussed context?

<p>The amount of a substance in a given volume (B)</p> Signup and view all the answers

What can be inferred about ion permeability when large gradients exist across a thin membrane?

<p>Diffusion occurs more rapidly due to large gradients. (B)</p> Signup and view all the answers

Which statement is accurate regarding the valence of different types of particles?

<p>Cations are characterized by a positive valence. (B)</p> Signup and view all the answers

In terms of units, what distinguishes molarity from moles?

<p>Molarity refers to the number of moles per liter of solution. (A)</p> Signup and view all the answers

What can be a consequence of applying an electric field to charged particles?

<p>Development of an electric current (D)</p> Signup and view all the answers

What is the condition of net current in a system at equilibrium?

<p>J = 0 (D)</p> Signup and view all the answers

Which variable is NOT part of the Nernst equation for equilibrium potential?

<p>Electric field strength (E) (D)</p> Signup and view all the answers

In the context of Nernst equilibrium, what does the symbol 'Vm' represent?

<p>Equilibrium transmembrane potential (B)</p> Signup and view all the answers

What does the logarithmic form in the Nernst equation help to express?

<p>The relationship between ion concentration and transmembrane voltage (D)</p> Signup and view all the answers

Which variable corresponds to the concentration of ions inside the cell in the Nernst equation?

<p>C_p (B)</p> Signup and view all the answers

What does the 'Z' in the Nernst equation stand for?

<p>Charge of the ion (C)</p> Signup and view all the answers

At which temperature does the Nernst potential expression change, as mentioned?

<p>17°C (D)</p> Signup and view all the answers

What does the term 'steady state' imply in the context of Nernst equilibrium?

<p>No net change in concentration or voltage (D)</p> Signup and view all the answers

In the equilibrium condition for Nernst potential, what aspect does the induced conduction current counterbalance?

<p>Diffusion current due to concentration gradient (D)</p> Signup and view all the answers

What is needed for an ion to reach Nernst equilibrium according to the equilibrium potential formula?

<p>A specific concentration ratio across the membrane (B)</p> Signup and view all the answers

Flashcards

Diffusion

The movement of particles from an area of high concentration to an area of low concentration. It's driven by the random motion of particles, not by an external force.

Drift (Conduction)

The movement of particles due to an external force, such as an electric field. This force causes particles to move in a specific direction.

Concentration

The amount of substance per unit volume. It can be expressed in different units like moles per liter or grams per liter.

Mobility

A measure of the ability of a charged particle to move in an electric field. It indicates how quickly the particle responds to the applied force.

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Molarity

The number of moles of a substance dissolved in one liter of solution. It's a common unit to express concentration.

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Flux

The net movement of a substance across a boundary or surface. It usually refers to the amount of substance moving per unit time.

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Advection

The movement of particles carried by a flowing fluid. Think of leaves being swept away by a river current.

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Channels: Single ion permeability

A type of transport mechanism where only one type of ion can pass through a membrane, effectively acting as a selective filter.

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Nernst Potential

A measurement of the electrical potential difference across a membrane when only one specific type of ion can move through it, reaching equilibrium.

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Equilibrium transmembrane potential for K+ in frog muscle

The Nernst potential for potassium (K+) ions in a frog muscle cell, calculated using the concentrations of K+ inside and outside the cell, assuming only K+ can move.

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Equilibrium transmembrane potential for Na+ in frog muscle

The Nernst potential for sodium (Na+) ions in a frog muscle cell, calculated using the concentrations of Na+ inside and outside the cell, assuming only Na+ can move.

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Why do K+ and Na+ have different polarity?

The difference in polarity for the potassium and sodium Nernst potentials is due to the different concentration gradients of these ions across the cell membrane.

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Nernst Potential vs. p-n junction voltage

The built-in voltage across a p-n junction in a semiconductor device is conceptually equivalent to the Nernst potential for a specific ion.

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Nernst Equilibrium

The state where there is no net movement of ions across a membrane. This means that the rate of ions moving in one direction is equal to the rate of ions moving in the opposite direction.

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Nernst Equation

The equation that describes the relationship between the concentration gradient of an ion and the electrical potential difference across a membrane at equilibrium. It is used to calculate the equilibrium potential for a specific ion.

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Conduction Current

A type of current that is driven by the movement of charged particles due to an electric field. Also known as conduction current.

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Diffusion Current

A type of current that is driven by the movement of particles due to a concentration gradient. Diffusion moves particles from high concentration to low concentration.

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Equilibrium Potential

The value of the Nernst potential for a given ion. It is expressed in millivolts (mV).

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Internal Concentration (Ci)

The concentration of an ion inside the cell. For example, the internal concentration of potassium (K+) in a nerve cell is much higher than the external concentration.

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External Concentration (Ce)

The concentration of an ion outside the cell. For example, the external concentration of sodium (Na+) in a nerve cell is much higher than the internal concentration.

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Ionic Charge (Zp)

The charge carried by an ion. For example, potassium (K+) has a charge of +1, while chloride (Cl-) has a charge of -1.

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Ion Flux

The movement of ions across a membrane. It can be either passive (driven by concentration gradient) or active (requires energy).

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Study Notes

Bioelectricity and Biophotonics Engineering

Recap of Last Lecture

  • Transport phenomena
  • Transport mechanisms
  • Nernst-Planck Equation (drift-diffusion equation)

Some Definitions

  • Concentration/units
  • Molarity: mol vs molar
  • Diffusion/advection/drift(conduction)
  • Flux/units

Mobility/Drift

  • In an electric field, charged particles experience an electrical force.
  • = sign(Z) μE (velocity is proportional to the electric field and valence)
  • μ: Mobility (m²/V-sec)
  • Z: valence (-1 for electrons, 0 for neutrals, >0 for cations, <0 for anions)

Diffusion

  • Transport from high to low concentration.
  • Random motion of particles results in this transport.
  • jd = − D ∇C (diffusion flux equation)
  • D = D0 exp(−ΔE / RT): diffusion coefficient

Osmosis

  • Solvent diffuses across a semi-permeable membrane.
  • Moves from low to high solute concentration.

Tonicity

  • Hypotonic: one solution has a lower solute concentration than another.
  • Hypertonic: one solution has a higher solute concentration than another.
  • Isotonic: both solutions have the same solute concentrations.

Recap from Previous Lecture- Nernst-Planck equation

  • Chemists count moles j = −D∇C + CZF∇Φ/RT (moles/m² sec)
  • Engineers measure currents J = −DFZ∇C + CZF∇Φ/RT (A/m²)

Today's Lecture

  • Transport phenomena across cell membranes
  • Cell Membrane (revisited)
  • Transport mechanisms
  • Nernst potential
  • Parallel-conductance model
  • Resting Potential

Transmembrane Potential

  • Vm = Φi − Φe (+/- 100 mV) (membrane potential)
  • Phospholipid bilayer + proteins, channels, pumps = Selective permeable

Equivalent circuit of a passive membrane

  • Intracellular and Extracellular medium are conductors.
  • The membrane is a lossy dielectric.
  • The Membrane capacitance is Cm = ε0εrA/d (Capacitance = permittivity*area/distance)
  • A large and important value for biological systems.

Pumps and Channels

  • Large polar molecules can't cross a phospholipid bilayer, so pumps and channels are required to move them in and out of the cell.
  • Pumps move ions against their concentration gradient (require energy).
  • Channels allow ion's flow with their concentration gradient (no energy required).

Membrane Conductance

  • The cell has many channels, but each operates discretely; macroscopically, the membrane exhibits a particular ion conductance.

Channels: Single ion permeability

  • Some channels are permeable to certain ions while impermeable to others.
  • P+ permeates, Q+ doesn't.
  • [P+]i > [P+]e ⇒ Diffusion is favored.

Channels: Single ion permeability (continued)

  • Diffusion of one ionic species in an ideal channel leads to the creation of an electric field.
  • The electric field opposes diffusion and eventually no net flow occurs.

Nernst equilibrium

  • In equilibrium, net current = 0
  • Jp = −DpF Zp(∇Cp + CpZp∇Φ)/RT = 0
  • Gradients perpendicular to the membrane – 1D.

Nernst Equilibrium (continued)

  • Veq = (RT / ZpF) ln(Cp,e / Cp,i) = 23mV ln (Cp,e / Cp,i)
  • For T ≈ 17°C or 25mV ln (Cp,e / Cp,i)
  • Equilibrium transmembrane potential

Nernst Potential

  • Equilibrium transmembrane potential of an ion.
  • Potential where induced conduction current counterbalances diffusion current.
  • Electrical measure of diffusion strength.

Examples (Frog Muscle Cell)

  • Intracellular and extracellular concentrations of K+, Na+, Cl-.

Answers & Notation

  • Transmembrane potential, given permeability of just Potassium or Sodium ions, calculated using Nernst potential formula.

p-n Junction

  • Nernst potential is equivalent to the built-in voltage in a p-n junction.

Channel – Electrical model (single ion)

  • Interior/cytoplasm, exterior/medium models.
  • Vm = Ek ⇒ Equilibrium, Im = 0
  • Vm > EK ⇒ Ik > 0, K+ flows outwards
  • Vm < EK ⇒ Ik > 0, K+ flows inwards

Multiple ions: Parallel conductance model

  • In reality, more than one ion passes the membrane at a time, and their currents combine to produce a net current across the membrane.

Resting potential

  • Each ion's Nernst potential is different.
  • Resting potential = transmembrane potential making total current = 0.
  • Weighted average of each ion's Nernst potential (Goldman-Hodgkin-Katz equation).

Example (Squid axon)

  • Intracellular and extracellular concentrations of K+, Na+, and Cl-
  • Conductivities of those ions
  • Resting potential calculation
  • Determine if any net current is produced at resting potential.
  • Determine if any net flow of ions occurs at resting potential.

Answer (Squid axon)

  • Nernst equation for K+, Na+, Cl- calculate equilibrium potentials.
  • Resting membrane potential calculated summing all potentials given by Goldman-Hodgkin-Katz relation.

Ions currents

  • Vm>Ek ⇒ Ik>0 ⇒ efflux of potassium ions
  • Vm<ENa ⇒ INa<0 ⇒ influx of sodium ions
  • Vm<ECl ⇒ ICl<0 ⇒ efflux of chlorine ions

So far...

  • Capacitive nature of bilayer (Cm).
  • Transport through ion channels (diffusion and conduction (gp)).
  • Nernst potential for each ion (Ep).

Today's lecture

  • Review of processes/topics previously discussed.

Next Lecture

  • Transport phenomena across cell membranes
  • Quasineutrality
  • Donnan equilibrium
  • Role of pumps

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Bioelectricity and Biophotonics Engineering Lecture Notes PDF

Description

Test your understanding of bioelectricity and biophotonics engineering concepts covered in course WSC331. This quiz includes topics such as transport phenomena, the Nernst-Planck equation, and definitions related to mobility and diffusion. Assess your knowledge on the principles governing the behavior of charged particles in electric fields.

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