Neuron Excitability (3)

A set of flashcards reviewing saltatory conduction, graded vs. action potentials, ion imbalances, neurotransmitters, and refractory periods.

What membrane potential (in mV) must the axon hillock reach to trigger an action potential (threshold)?

−55 mV

How does potassium leakage at the soma influence a spreading depolarization?

It weakens the graded potential by allowing positive charge to leak out, making the interior more negative.

Which ion’s leakage is generally negligible in weakening a graded potential?

Sodium (Na⁺) leakage

Which glial cells create myelin in the central nervous system (CNS)?

Oligodendrocytes

Which glial cells create myelin in the peripheral nervous system (PNS)?

Schwann cells

What are the gaps between adjacent myelin sheaths called?

Nodes of Ranvier

Where are voltage-gated sodium channels concentrated on a myelinated axon?

At the nodes of Ranvier

What term describes an action potential “jumping” from one node to the next along a myelinated axon?

Saltatory conduction

List two primary benefits of myelination.

1) Greatly increases conduction velocity; 2) Reduces ATP use by limiting the number of Na⁺/K⁺ pumps required.

Which enzyme restores sodium and potassium gradients after an action potential?

Sodium-potassium pump (Na⁺/K⁺-ATPase)

Where in a neuron do graded potentials occur?

Soma (cell body) and dendrites

Where do action potentials propagate in a neuron?

Along the axon to the axon terminals

Can graded potentials be depolarizing, hyperpolarizing, or both?

Both

Is an action potential an all-or-nothing event?

Yes

What property allows several subthreshold graded potentials to combine into a larger one?

Summation

Which disease results from demyelination of CNS axons?

Multiple sclerosis

How do local anesthetics block pain transmission?

They block voltage-gated sodium channels on nociceptive neurons, preventing action potentials and neurotransmitter release.

What happens to the resting membrane potential during hypokalemia?

It becomes more negative (hyperpolarized), moving further from threshold and lowering neuronal excitability.

How does hyperkalemia affect neuronal excitability?

It makes the resting membrane potential less negative (closer to threshold), increasing excitability.

Which neurotransmitter opens chloride channels to hyperpolarize CNS neurons?

GABA (gamma-aminobutyric acid)

Are glutamate and aspartate excitatory or inhibitory neurotransmitters?

Excitatory

During which refractory period can NO new action potential be generated, regardless of stimulus size?

Absolute refractory period

What is required to elicit an action potential during the relative refractory period?

A larger-than-normal (stronger) stimulus to reach threshold

Name the two gates found on a voltage-gated sodium channel.

Activation gate (extracellular side) and inactivation gate (intracellular side)

Which gate opens first during depolarization, allowing Na⁺ influx?

The activation gate

Why can’t a neuron fire another action potential during the absolute refractory period?

Sodium channel inactivation gates are closed and the membrane has not yet fully repolarized, preventing Na⁺ influx.