Ion Channels and Neuronal Excitability Flashcards

Vocabulary-style flashcards covering the phases of action potentials, ion channel mechanics, refractory periods, and related clinical channelopathies.

Resting potential

The difference in voltage across the neuronal membrane while at rest, typically measured at $-70\,mV$.

Threshold

The voltage level of $-55\,mV$ that must be reached by EPSPs to trigger the opening of $Na^+$ channels and start an action potential.

Depolarisation

The phase of the action potential where the voltage rises to $+30/+40\,mV$ due to a sudden rush of $Na^+$ ions into the cell.

Voltage sensor

A component of the ion channel that moves outward in response to an increase in voltage to $-55\,mV$, causing the channel to open.

Sodium ($Na^+$) equilibrium potential

The theoretical membrane potential at which there is no net movement of sodium ions, which the membrane rapidly approaches at approximately $+60\,mV$ during the rising phase.

Repolarisation

The phase where the membrane potential lowers back down because $Na^+$ channels inactivate and $K^+$ channels activate, causing $K^+$ to leave the cell.

Hyperpolarisation

Also known as the undershoot, this occurs when $K^+$ efflux moves the membrane potential close to the $K^+$ equilibrium potential of approximately $-90\,mV$.

Absolute Refractory Period

A time during the action potential when it is absolutely not possible to generate another action potential due to the inactivation of sodium channels.

Relative Refractory Period

A period following an action potential where the membrane is less excitable because $K^+$ channels are open, but an action potential can be generated by a greater stimulus because sodium channels are reactivated.

Channelopathy

A medical condition caused by the disruption of the function of ion channels or the proteins that produce them.

Lidocaine

A local anesthetic that prevents pain by prolonging the inactivation of voltage-gated $Na^+$ channels, thereby preventing the generation of an action potential.

Tetrodotoxin (TTX)

An extremely toxic substance produced by puffer fish that blocks $Na^+$ channels and prevents $Na^+$ from entering the neuron; a dose of $1\,mg$ is lethal.

2 amino-pyridine (4-AP)

A potassium channel blocker used in demyelinated axons as a potential treatment for multiple sclerosis by reversing the effects of increased extracellular $K^+$.

Na+ channelopathies

Disruptions specifically in sodium channels that can result in generalised epilepsy with febrile seizures.

K+ channelopathies

Disruptions specifically in potassium channels that result in seizures.