Electrophysiology Review: Summation, Action Potentials, Myelination, Toxins, and MS

Vocabulary flashcards covering key concepts from the lecture: summation types, membrane potentials, ion channels and currents, action potential mechanics, myelination, MS, toxins, NMJ signaling, and channelopathies.

Temporal summation

Integration of multiple postsynaptic potentials in time from the same presynaptic neuron, allowing a larger net depolarization if excitatory signals accumulate.

Spatial summation

Integration of postsynaptic potentials from multiple presynaptic neurons arriving simultaneously at the postsynaptic cell to produce a combined depolarization.

EPSP (Excitatory postsynaptic potential)

A depolarizing postsynaptic potential that moves the membrane potential toward the threshold.

IPSP (Inhibitory postsynaptic potential)

A hyperpolarizing postsynaptic potential that moves the membrane potential away from the threshold.

Resting membrane potential (RMP)

The baseline electrical potential across the neuronal membrane when the cell is at rest, typically around -70 mV in motor neurons.

Threshold potential

The membrane potential at which voltage-gated ion channels open to trigger an action potential (about -55 mV in many neurons).

Sodium-potassium ATPase

Active transporter that pumps Na+ out and K+ in, maintaining the Na+/K+ gradient and contributing to the resting membrane potential.

Leak channels

Ion channels that are always open (non-gated), providing a continuous leak current and contributing to the resting membrane potential, especially K+ leak channels.

Equilibrium potential

The membrane potential at which the electrical gradient exactly balances the concentration gradient for a given ion (Nernst potential).

Sodium equilibrium potential

+60 mV; the potential at which Na+ would be in equilibrium across the membrane, indicating Na+ tends to be outside at rest.

Potassium equilibrium potential

≈ -75 mV; the potential at which K+ would be in equilibrium, indicating K+ tends to be inside the cell at rest.

Action potential

A rapid, transient depolarization and repolarization event that travels along the axon, primarily driven by voltage-gated Na+ influx (depolarization) followed by voltage-gated K+ efflux (repolarization).

Depolarization

Movement of the membrane potential toward a more positive value due to inward Na+ current through voltage-gated sodium channels.

Repolarization

Return toward the resting membrane potential after depolarization, mainly due to outward K+ current through voltage-gated potassium channels.

Hyperpolarization

A dip below the resting membrane potential caused by continued K+ efflux or delayed closing of K+ channels after an action potential.

Nodes of Ranvier

Gaps in the myelin sheath along a myelinated axon where ion channels are concentrated, enabling saltatory conduction and faster signal propagation.

Myelination

Insulation of axons by myelin; decreases capacitance and increases electrical resistance, enabling faster and more efficient action potential propagation.

Capacitance (neuronal)

The ability of the membrane to store charge; high in unmyelinated axons and reduced by myelination, which concentrates charging at nodes.

Electrical resistance (neuronal)

Opposition to current flow; increased by myelination in the internodes, boosting efficiency of signal travel at the nodes.

Multiple sclerosis (MS)

A demyelinating disease of the CNS, characterized by loss of myelin, formation of scar tissue, and slowed or disrupted action potential conduction.

Demyelination

Loss of myelin around axons leading to increased capacitance and decreased membrane resistance, causing slower or blocked action potential conduction.

Tetrodotoxin (TTX)

A toxin from pufferfish that blocks voltage-gated Na+ channels, preventing depolarization and abolishing action potentials.

Dendrotoxin

A presynaptic toxin from certain snakes that blocks voltage-gated K+ channels, prolonging depolarization, increasing excitability, and altering acetylcholine release.

Acetylcholine at the neuromuscular junction

The neurotransmitter that transmits signals from motor neurons to muscles at the NMJ to trigger muscle contraction.

Channelopathies

diseases caused by dysfunction or mutation in ion channels, which can be genetic or acquired and affect excitability and signaling.