Cell biological and electrical properties of neurons — Key Terminology (Vocabulary)

Vocabulary flashcards covering membrane transport, electrochemical gradients, resting potential, and electrical circuit models in neurons.

lipid bilayer

The plasma membrane (and organelle membranes) composed of a phospholipid bilayer that is impermeable to most ions and polar solutes, forming essential boundaries for cells and organelles.

channels

Transmembrane proteins with an aqueous pore that allows specific solutes to pass directly through when open, including ion channels.

transporters

Transmembrane proteins that move solutes across membranes via alternating opening gates; can act as pumps or cotransporters and are generally slower than channels.

passive transport

Movement of solutes down their electrochemical gradients without external energy input.

active transport

Movement of solutes against their electrochemical gradients using energy from sources such as ATP hydrolysis, light, or coupling to another transport process.

electrochemical gradient

The combined chemical and electrical gradients that determine the direction and magnitude of solute movement across a membrane.

chemical gradient

The difference in solute concentration across a membrane.

electrical gradient

The difference in electrical potential across a membrane.

equilibrium potential

The membrane potential at which there is no net movement of a given ion across the membrane (E_ion).

Nernst equation

E = (RT/zF) ln([outside]/[inside]); used to calculate the equilibrium potential for a given ion.

EK

Equilibrium potential for potassium (K+), approximately -85 mV in the model.

ENa

Equilibrium potential for sodium (Na+), approximately +58 mV in the model.

ECl

Equilibrium potential for chloride (Cl−), approximately -79 mV in the model.

Goldman-Hodgkin-Katz equation

Vm = (RT/F) ln[(PK[K+]o + PNa[Na+]o + PCl[Cl−]i) / (PK[K+]i + PNa[Na+]i + PCl[Cl−]o)]; Vm depends on permeabilities and ion concentrations.

driving force

The difference between the membrane potential Vm and the equilibrium potential of a given ion, indicating the tendency for that ion to move.

Na+-K+ ATPase

An ATPase pump that uses energy from ATP hydrolysis to move Na+ outward and K+ inward, maintaining Na+ and K+ gradients.

K+-Cl− cotransporter

A membrane transporter that moves K+ and Cl− together, helping maintain intracellular Cl− and overall ion gradients.

resting membrane potential

The steady-state membrane potential of a neuron at rest, typically around -50 to -80 mV, arising from ion gradients and membrane permeabilities.

permeability

Ease with which a solute (ion) can cross the membrane, determined by the presence and state of ion channels.

conductance

The inverse of resistance (g = 1/R); relates current to voltage via I = gV.

resistance

Opposition to current flow; in neurons, membrane resistance (Rm) determines how easily ions cross the membrane.

capacitor

An electrical component that stores charge; the neuronal membrane (lipid bilayer plus surrounding solutions) acts as a capacitor (Cm).

time constant

τ = Rm Cm; the time it takes for the membrane potential to approach about 63% of its final value after a change.

length constant

λ = sqrt((Rm d)/(4 Ri)); the distance over which a change in membrane potential decays to 1/e (~37%).

parallel RC circuit

A circuit model of the membrane where a resistor and a capacitor are in parallel, used to describe the membrane’s passive electrical properties.

Ohm’s law

I = V/R (or I = gV); fundamental relation relating current, voltage, resistance, and conductance.

uniporter

A transporter that moves a single species of solute across the membrane.

symporter

A cotransporter that moves two solutes in the same direction across the membrane.

antiporter

A cotransporter that moves two solutes in opposite directions (exchanger).

ATP-driven pump

A pump that uses energy from ATP hydrolysis to move solutes against their electrochemical gradients (e.g., Na+-K+ ATPase).

stimulating electrode

An electrode used to inject current into a neuron to evoke electrical responses.

recording electrode

An electrode used to measure membrane potential changes in response to stimulation.

action potential

A rapid, all-or-none depolarization that propagates along the neuron, typically triggered when membrane potential crosses a threshold.

gating

The opening and closing of ion channels, regulating membrane permeability and ionic flow.

membrane potential (Vm)

The electrical potential difference across the neuronal plasma membrane (inside versus outside).