Action Potential Propagation and Membrane Dynamics

Vocabulary flashcards covering membrane potential values, ion equilibrium potentials, voltage-gated channel structures, refractory periods, and types of nerve impulse conduction.

Nodes of Ranvier

Unmyelinated sites along an axon containing voltage-gated sodium and potassium channels where the action potential is actively recharged during saltatory conduction.

Contiguous Conduction

The continuous, unidirectional propagation of an action potential along every segment of an unmyelinated axon due to the sequential opening and closing of membrane channels.

Saltatory Conduction

The rapid "jumping" conduction of an action potential along a myelinated axon, where local electrical current travels through the cytoplasm under myelin sheath sections and re-generates at the nodes of Ranvier.

Conduction Velocity Factors

The two primary physical characteristics of an axon that determine the speed of action potential propagation: 1. Myelination and 2. Axon diameter.

Absolute Refractory Period

The period during which an action potential is actively occurring and the membrane is entirely incapable of conducting another action potential.

Relative Refractory Period

The timeframe following an action potential where channel gates are closed but capable of opening again if triggered.

Fast Gate (Activation Gate)

Gate 1 of the voltage-gated $\text{Na}^+$ channel, which opens rapidly at the threshold potential to increase sodium permeability and initiate depolarization.

Slow Gate (Inactivation Gate)

Gate 2 of the voltage-gated $\text{Na}^+$ channel, which begins closing at threshold to decrease sodium permeability and stop the positive movement of the membrane potential at peak depolarization.

Voltage-Gated Potassium Channel

A single-gated, slow-opening channel that increases $\text{K}^+$ permeability, allowing potassium ions to leave the cell and drive the membrane potential back toward resting potential.

Threshold Potential

The membrane potential value (approximately $-50\,mV$) at which voltage-gated $\text{Na}^+$ gates respond, initiating rapid depolarization.

Resting Membrane Potential

The baseline electrical charge across the cell membrane, established at $-70\,mV$, where voltage-gated sodium channels are closed but ready to open.

Sodium Equilibrium Potential

The electrical equilibrium potential for sodium ions, defined as $+60\,mV$.

Potassium Equilibrium Potential

The electrical equilibrium potential for potassium ions, defined as $-90\,mV$.

One-Way Conduction Mechanism

The process ensuring action potentials move strictly from the trigger zone to the end of the axon, maintained because the active membrane region behind the propagating signal enters a refractory period and cannot immediately conduct another action potential.