Membrane Potentials and Action Potentials

These flashcards cover key concepts related to membrane potentials and action potentials, focusing on ions, types of potentials, mechanisms, and refractory periods.

What ions are most important for membrane potentials?

Sodium (Na⁺), Potassium (K⁺), Chloride (Cl⁻), Calcium (Ca²⁺)

Which ion is most responsible for resting membrane potential?

Potassium (K⁺)

Which ion is most responsible for depolarization?

Sodium (Na⁺)

What is the resting membrane potential (RMP)?

Stable negative charge (~ -70 mV) when neuron is inactive

What are graded potentials?

Small, local changes in membrane potential that vary in strength

Where do graded potentials occur?

Dendrites and cell body

What is an action potential?

Rapid, all-or-none electrical signal along the axon

Key difference between graded and action potentials?

Graded = variable strength; Action = all-or-none

What creates the resting membrane potential?

Unequal ion distribution + selective permeability

Role of the Na⁺/K⁺ pump?

Pumps 3 Na⁺ out, 2 K⁺ in (uses ATP)

Why is the inside of the neuron negative at rest?

More K⁺ leaks out + negative proteins remain inside

What is an electrochemical gradient?

Combined effect of concentration gradient + electrical charge

What happens when membrane permeability changes?

Different ions flow, changing membrane potential

Function of leak channels?

Allow passive movement of ions (especially K⁺)

Function of chemically (ligand)-gated channels?

Open in response to neurotransmitters

Function of voltage-gated channels?

Open in response to changes in membrane potential

What triggers an action potential?

Reaching threshold (~ -55 mV)

What happens if threshold is not reached?

No action potential occurs

What is depolarization?

Na⁺ channels open → Na⁺ enters → membrane becomes positive

What is repolarization?

K⁺ channels open → K⁺ leaves → membrane becomes negative again

What is hyperpolarization?

Membrane becomes more negative than resting potential

Order of events in an action potential?

Resting → Threshold → Depolarization → Repolarization → Hyperpolarization → Resting

How do action potentials travel in unmyelinated axons?

Continuous conduction (slow)

How do action potentials travel in myelinated axons?

Saltatory conduction (jumping between nodes, fast)

Why is myelination faster?

Signal skips across nodes of Ranvier

What is the absolute refractory period?

No second AP can occur (Na⁺ channels inactivated)

What is the relative refractory period?

AP possible, but requires stronger stimulus

Why is the absolute refractory period important?

Ensures one-way signal travel

Why is the relative refractory period important?

Controls frequency of action potentials