Properties of the Resting Membrane, Action Potential, and Nerve Impulse Conduction

Vocabulary practice flashcards covering resting membrane potentials, ion gradients, gating mechanisms of transport channels, action potential phases, and continuous versus saltatory conduction.

Electrical Current (Cell Membrane)

The flow of electrical charge across cell membranes carried by the movement of major inorganic ions in physiological fluids ($Ca^{2+}$, $Na^+$, $K^+$, $Cl^-$, and $HCO_3^-$), in contrast to the flow of electrons in a metal wire.

Resting Membrane Potential (RMP)

The potential difference between the inner and outer surfaces of the membrane present in all animal cells at rest, produced by a small accumulation of negative charges on the inner side and an equal accumulation of positive charges on the outer side.

Excitable Cell

A specialized cell capable of altering its membrane potential to generate an electrical impulse or action potential, such as neurons and muscle cells.

Organic Anions

Large impermeable negatively charged intracellular molecules, such as proteins, nucleic acids, and amino acid residues, that cannot cross the plasma membrane and largely cause the cell interior to be negative relative to the outside.

Microelectrode

A microscopic recording probe inserted into a neuron that, alongside an extracellular reference electrode, is connected to a voltmeter to measure the electrical potential difference across the plasma membrane.

$K^+$ Leak Channels

Channels that open and close randomly to allow continuous passive outward diffusion of $K^+$ ions down their concentration gradient, dominating the membrane permeability and resting membrane potential of most vertebrate cells.

$Na^+/K^+$ Pump ($Na^+/K^+$-ATPase)

An active transport carrier protein that hydrolyzes ATP to export $3\,Na^+$ ions out of the cell and import $2\,K^+$ ions into the cell, counterbalancing ion leakage to maintain stable transmembrane concentration gradients.

Depolarization

The phase during which the membrane potential becomes less negative and more positive than the resting value, occurring when $Na^+$ channels open and $Na^+$ rushes into the cell.

Repolarization

The process by which the membrane potential returns toward its negative resting membrane potential value following depolarization, primarily driven by the closure of $Na^+$ inactivation gates and the outward movement of $K^+$ through voltage-gated $K^+$ channels.

Hyperpolarization

A condition in which the membrane potential temporarily becomes more negative than the baseline resting potential due to prolonged outflow of $K^+$ ions before channels fully close.

Ligand-gated Channels

Membrane ion channels that open or close in direct response to the binding of a specific chemical messenger, such as a neurotransmitter or receptor ligand.

Mechanically-gated Channels

Membrane transport channels that open in response to mechanical deformation of the membrane, such as physical pressure or stretch.

Voltage-gated Channels

Ion channels equipped with voltage sensors that open or close in response to alterations in transmembrane electrical potential.

Threshold

The critical membrane potential level (approximately $-55\,\text{mV}$ in neurons) required to activate voltage-gated $Na^+$ channel activation gates and trigger an all-or-none action potential.

Subthreshold Stimulus

A weak stimulus that depolarizes the membrane locally but fails to reach the firing threshold (about $-55\,\text{mV}$), resulting in no action potential generation.

Suprathreshold Stimulus

A stimulus that exceeds threshold strength, producing action potentials of unchanged amplitude and duration but at an increased firing frequency (more spikes per second).

Continuous Conduction

The relatively slow mode of nerve impulse propagation found in unmyelinated axons, where the action potential must be sequentially regenerated at every adjacent patch of the axonal membrane.

Myelin Sheath

A lipid-rich insulating layer enclosing an axon that prevents current leakage across the membrane, allowing electrical local circuits to spread faster and further down the fiber.

Nodes of Ranvier

Periodic unmyelinated interruptions along a myelinated axon where voltage-gated ion channels are concentrated and action potentials are regenerated.

Saltatory Conduction

The rapid and energy-efficient mode of action potential propagation in myelinated axons, where electrical depolarization jumps from one node of Ranvier to the next.