Membrane Potential and Excitability (Flashcards)

Vocabulary flashcards covering membrane potential, excitability, ion channels and pumps, and related concepts from the lecture notes.

Membrane potential

Electrical potential difference across a cell’s plasma membrane; reflects charge separation between cytoplasm (inside) and extracellular fluid (outside); also called transmembrane potential or membrane voltage.

Excitability

Intrinsic property of nerve and muscle membranes to generate an electrical signal (action potential) in response to a stimulus that depolarizes beyond a threshold.

Action potential

A rapid, transient electrical signal produced by the concerted action of ion channels in response to depolarization, allowing propagation of the signal along the membrane.

Resting membrane potential (RMP)

Steady-state membrane potential of a cell at rest (commonly around -70 mV in neurons); largely maintained by K+ leak channels and ion gradients.

Na+/K+-ATPase (Sodium-Potassium Pump)

Energy-consuming pump that moves 3 Na+ out and 2 K+ in per cycle; electrogenic and maintains Na+ and K+ gradients; uses ATP; consumes 20-40% of brain energy.

Antiporter

Transporter that moves ions/molecules in opposite directions; Na+/K+-ATPase is described as an anti-porter.

Electrogenic

Processes or transporters that generate net charge movement across the membrane, contributing to membrane potential.

Ion gradient

Difference in ion concentration across the membrane maintained by pumps; stores chemical potential energy for signaling.

Ion channel

Protein that forms a pore allowing ions to move passively down their electrochemical gradient; can be gated.

Channel

Gated pores that provide a continuous aqueous pathway through the membrane for ions when open.

Transporter

Membrane protein that moves substrates by undergoing conformational changes; includes facilitated diffusion and active transport.

Ligand-gated ion channel (LGIC)

Ion channel opened by binding of a chemical ligand (e.g., neurotransmitter) to its site.

Voltage-gated ion channel (VGIC)

Ion channel that opens/closes in response to changes in membrane potential; includes NaV, KV, CaV channels.

Permeability

Ease with which ions pass through the membrane; depends on channel state and properties; quantified by permeability coefficients.

Reversal potential

Membrane potential at which the net flux of a given ion is zero; electrical and chemical gradients balance.

Nernst equation

Equation to calculate the equilibrium (reversal) potential for a single ion from its intracellular and extracellular concentrations.

Goldman-Hodgkin-Katz equation

Equation that estimates the resting membrane potential considering multiple ions and their permeabilities (P values).

Selectivity filter

Structure in K+ channels that allows dehydrated K+ to pass while excluding Na+; enables high selectivity and single-file ion passage.

Voltage-sensing domain (S4)

Transmembrane segment with positively charged residues; moves in response to depolarization to trigger opening of voltage-gated channels.

Activation gate

Gate in voltage-gated channels that opens in response to voltage changes to allow ion flow.

Inactivation

Process by which Na+ channels close despite maintained depolarization, creating a refractory period.

Piezo-2

Mechanosensitive, non-selective cation channel in nociceptive nerve endings; senses membrane tension and allows Na+/Ca2+ influx.

NaV channels

Voltage-gated sodium channels; open with depolarization to drive the AP upstroke; subject to inactivation.

Kv channels

Voltage-gated potassium channels; activate to repolarize/hyperpolarize the membrane; slower and require larger depolarization.

Ca2+ channels

Voltage-gated calcium channels; permit Ca2+ entry; triggers neurotransmitter release and Ca2+-dependent processes.

Action potential propagation

Depolarization from the initial site spreads to adjacent membrane, triggering NaV channels; back-propagation is limited by inactivation and Kv recovery.

Nicotinic acetylcholine receptor (nACh receptor)

Excitatory ligand-gated non-selective cation channel at the neuromuscular junction; binds acetylcholine to cause depolarization.

Tetrodotoxin (TTX)

NaV channel blocker derived from pufferfish; used to study NaV channel function.

Lidocaine

Local anesthetic that blocks NaV channels; use-dependent blocker—binds more when channels are open.

hERG (Kv11)

Potassium channel (human ether-a-go-go-related gene) involved in cardiac repolarization; dysfunction linked to arrhythmias.

TRP channels

Transient receptor potential channels; non-selective cation channels involved in sensory perception, including pain.