5 Electricity in Biological Systems Free Online FlashCards

What does an electric field describe?

An electric field is force per unit charge: $\mathbf{E}=\frac{\mathbf{F}}{q}$.

Why does a cell membrane act like a capacitor?

The lipid bilayer separates charge across an insulating layer, so it acts approximately like a capacitor.

How is membrane potential defined?

The membrane potential is the voltage inside a cell relative to the outside: $V_m=V_{inside}-V_{outside}$.

What initiates the depolarizing phase of an action potential?

Rapidly increased sodium permeability lets Na⁺ enter the cell, depolarizing the membrane.

What is a voltage difference?

Voltage difference is a difference in electric potential energy per unit charge.

How is field magnitude related to voltage difference and distance?

In a roughly uniform field, its magnitude is approximately $E=\frac{\Delta V}{d}$, where $d$ is the distance across which voltage changes.

What circuit element do ion channels resemble?

Ion channels act as conductances, providing pathways for particular ions to cross the membrane.

What does a circuit time constant describe?

The time constant is $\tau=RC$; it describes how quickly voltage changes when current flows through resistance and capacitance.

What creates a cell's membrane potential?

It arises from uneven ion distributions across the membrane and the membrane's selective permeability to those ions.

What does the Nernst equation determine?

The Nernst equation gives the equilibrium potential of a single ion species, where electrical force balances its concentration-driven tendency to diffuse.

Does resting membrane potential usually equal one ion's Nernst potential?

Usually not: real membranes are permeable to multiple ions, so resting membrane potential is not generally equal to any one ion's Nernst potential.

How does a neuron help repolarize after depolarization?

Sodium channels inactivate and potassium permeability rises; K⁺ leaves the cell, helping repolarize the membrane.