Function of Nerves and Membrane Potentials - Vocabulary Flashcards

Vocabulary flashcards covering resting potential, graded potentials, action potentials, gating mechanisms, summation, refractory periods, and conduction.

Resting membrane potential

Electrical potential difference across the cell membrane when the cell is at rest; typically around -70 mV, established by leak channels and the Na+/K+ pump maintaining ion gradients.

Na+/K+ pump

Active transporter that moves 3 Na+ out and 2 K+ in, helping maintain resting membrane potential and ion concentration gradients.

Leak channels

Non-gated ion channels that allow ions to diffuse down their concentration gradients, contributing to the resting membrane potential.

Electrochemical gradient

Combined effect of a ion's concentration difference and electrical difference across the membrane that drives ion movement.

Graded (local) potentials

Small, localized changes in membrane potential that decay with distance and can be depolarizing or hyperpolarizing; depend on stimulus strength.

Depolarization

Membrane potential becomes less negative (more positive) as Na+ enters the cell.

Repolarization

Return of the membrane potential toward the resting value, mainly due to K+ efflux and inactivation of Na+ channels.

Hyperpolarization

Membrane potential becomes more negative than resting potential, often because K+ channels remain open after repolarization.

Gated ion channels

Ion channels that open or close in response to stimuli such as voltage, ligands, or mechanical forces.

Mechanically gated channel

Ion channel opened by mechanical deformation (e.g., pressure or stretch).

Ligand-gated channel

Ion channel opened by binding of a chemical messenger (ligand) such as acetylcholine.

EPSP (excitatory postsynaptic potential)

Depolarizing graded potential that increases the likelihood of an action potential.

IPSP (inhibitory postsynaptic potential)

Hyperpolarizing graded potential that decreases the likelihood of an action potential.

Temporal summation

Addition of graded potentials occurring at the same site in rapid succession, increasing the chance to reach threshold.

Spatial summation

Addition of graded potentials arriving at different locations on the neuron, combining to influence the membrane potential.

Threshold

Membrane potential at which voltage-gated Na+ channels open, triggering an action potential (approximately -55 mV).

Action potential

All-or-none electrical impulse that propagates along the axon, initiated when the membrane reaches threshold.

Voltage-gated Na+ channel

Channel with activation and inactivation gates; opens with depolarization, then inactivates to stop Na+ influx.

Activation gate

Gate of the voltage-gated Na+ channel that opens during depolarization.

Inactivation gate

Gate of the voltage-gated Na+ channel that closes after a short time, inactivating the channel.

Voltage-gated K+ channel

Channel that opens with depolarization to allow K+ efflux, contributing to repolarization.

Refractory period

Time after an action potential during which a second one cannot or is harder to initiate.

Absolute refractory period

Phase when Na+ channels are open or inactivated; no new action potential can be fired.

Relative refractory period

Phase when Na+ channels are closed and K+ channels may be open; a stronger stimulus is needed to trigger an AP.

Continuous conduction

Propagation of an action potential along an unmyelinated axon as a wave of depolarization.

Saltatory conduction

Rapid conduction of an action potential along a myelinated axon where the impulse 'jumps' between nodes of Ranvier.

Phases of an action potential

Depolarization (Na+ influx), repolarization (K+ efflux and Na+ inactivation), hyperpolarization, and return to resting potential.

Ionic concentrations (inside vs outside)

Typical differences that create the resting potential: high outside Na+ (≈150 mM) and high inside K+ (≈150 mM); Cl− higher outside; large anions inside.