Electrochemical Equilibria and Membrane Potentials

Diffusion Potential

Potential difference due to ion concentration gradients.

Equilibrium Potential

Membrane potential where ion concentrations stabilize.

Membrane Potential

Voltage difference across a cell's plasma membrane.

Nernst Equation

Calculates equilibrium potential for specific ions.

Goldman Equation

Calculates membrane potential considering multiple ions.

Resting Potential

Stable membrane potential in a non-active cell.

Depolarization

Decrease in membrane potential, making it less negative.

Hyperpolarization

Increase in membrane potential, making it more negative.

Overshoot

Membrane potential exceeds zero during action potential.

Repolarization

Return of membrane potential to resting state.

Graded Potentials

Local changes in membrane potential, not all-or-nothing.

Action Potentials

Rapid, all-or-nothing electrical signals in neurons.

Voltage-Gated Sodium Channels

Channels that open during depolarization phase of action potential.

Sodium Permeability

Increases during depolarization phase of action potential.

Potassium Permeability

Increases during repolarization phase of action potential.

Myelinated Axons

Faster action potential conduction due to insulation.

Unmyelinated Axons

Slower action potential conduction without insulation.

Concentration Gradient

Difference in ion concentration across a membrane.

Electrical Potential

Voltage difference caused by ion distribution.

Compartment 1 and 2

Two areas separated by a permeable membrane.

Cl- Diffusion Rate

Chloride ions diffuse faster than sodium ions.

Diffusion

Movement of Cl- from area 1 to 2.

Em

Membrane potential affecting ion movement direction.

Equilibrium

State with no net flux of Cl-.

ECl

Equilibrium potential for chloride ions.

Ion Flux

Movement of ions across a membrane.

Membrane Potential (Em)

Voltage across a cell membrane.

ENa

Equilibrium potential for sodium ions, +58 mV.

EK

Equilibrium potential for potassium ions, -81 mV.

Driving Force

Difference between Em and Eion for ion movement.

Membrane Permeability

Ease of ion passage through membrane channels.

Conductance (gion)

Ease of ion movement through channels.

Channel Selectivity

Preference of channels for specific ions.

Channel Conductance (gs)

Index of ion flux through a channel.

Open Probability (Po)

Likelihood of ion channels being open.

Channel Density (N)

Number of ion channels per membrane area.

Electrochemical Gradient

Combined effect of concentration and electrical gradients.

Resting Membrane Potential

Typical Em value around -70 mV.

Steady State

Condition where sum of ionic currents equals zero.

Permeant Ion

Ion that can cross the membrane.

Dominant Ion

Ion with greater influence on Em.

Cl- Current

Negligible current due to chloride ions in resting state.

Goldman-Hodgkin-Katz Equation

Predicts membrane potential from all permeant ions.

Permeability Ratio (b)

Ratio of K+ to Na+ permeability affecting Em.

Equilibrium Potential (Eion)

Membrane potential where ion's net movement is zero.

Nernst Potential

Equilibrium potential calculated for a specific ion.

Action Potential

All-or-none electrical signal triggered by depolarization.

Threshold

Minimum depolarization needed to trigger an action potential.

Absolute Refractory Period

Time after AP when another cannot be generated.

Facilitated Diffusion

Passive transport of ions across a membrane.

Graded Depolarization

Increase in membrane potential due to Na+ influx.

Graded Hyperpolarization

Increase in membrane potential due to K+ efflux.

Steady State Membrane Potential

Stable membrane potential during constant ion permeability.

Ion Concentration Gradient

Difference in ion concentration across a membrane.

Voltage-gated Ion Channels

Channels that open/close in response to voltage changes.

K+ Dominance

K+ permeability is greater than Na+ at rest.

b Value Change

Alters membrane potential based on ion permeability.

Undershoot

Phase where membrane potential becomes more negative post-AP.

Summation of Graded Potentials

Combining multiple graded potentials to affect membrane potential.

Action Potential (AP)

Rapid change in membrane potential during neuron firing.

Ion Permeability (Pion)

Changes in ion flow affecting membrane voltage.

Depolarizing Stimulus

Initial change that raises membrane potential to threshold.

Voltage-gated Na+ Channels

Open during depolarization, allowing Na+ influx.

Voltage-gated K+ Channels

Open during repolarization, allowing K+ efflux.

After-hyperpolarization

Period following AP where membrane potential is below resting.

Rising Phase

Initial increase in membrane potential during action potential.

Falling Phase

Decrease in membrane potential after peak of action potential.

Refractory Period

Period post-action potential where neuron is less excitable.

Inactivation Gate

Closes Na+ channels rapidly after action potential peaks.

Activation Gates

Open Na+ channels allowing Na+ influx during depolarization.

PNa

Permeability of the membrane to Na+ ions.

PK

Permeability of the membrane to K+ ions.

Cytosol

Intracellular fluid within the neuron.

Extracellular Fluid

Fluid outside the neuron, rich in Na+.

Plasma Membrane

Barrier separating cytosol from extracellular fluid.

Sodium Channel

Channel that selectively allows Na+ ions to pass.

Potassium Channel

Channel that selectively allows K+ ions to pass.

Closed State

Condition of channels when they are not conducting ions.

Open State

Condition of channels when they allow ion flow.

Inactive State

Condition of channels when they cannot open despite depolarization.

Na+ Channels

Voltage-gated channels allowing sodium entry into neurons.

K+ Channels

Voltage-gated channels allowing potassium exit from neurons.

Relative Refractory Period

Only stronger stimulus can initiate action potential.

Ion Permeability

Ability of ions to cross the neuronal membrane.

Dendrites

Branch-like structures receiving signals from other neurons.

Cell Body

Contains nucleus and organelles of the neuron.

Axon

Long projection transmitting electrical impulses away from the cell body.

Myelin Sheath

Insulating layer increasing conduction speed of action potentials.

Nodes of Ranvier

Gaps in myelin sheath where ion channels are concentrated.

Saltatory Conduction

Rapid transmission of action potentials along myelinated axons.

Trigger Zone

Region where action potential is initiated in the axon.

Local Current Flow

Movement of charge that depolarizes adjacent membrane sections.

Refractory Region

Period preventing backward propagation of action potentials.

Active Region

Area of axon currently undergoing depolarization.

Inactive Region

Area of axon not currently conducting action potentials.

Tetrodotoxin (TTX)

Neurotoxin blocking voltage-gated Na+ channels.

Tetraethylammonium (TEA)

Compound blocking voltage-gated K+ channels.