Electrical Signaling, Membrane Potentials & Ion Effects

20 question-and-answer flashcards covering resting membrane potential, depolarization/hyperpolarization, ion concentrations, graded vs. action potentials, and how altered K⁺ or Ca²⁺ levels affect excitability.

What is the main purpose of electrical signaling in nerve and muscle cells?

To allow rapid communication by using ion movements across the membrane to create electrical signals.

What is the typical numerical range for a resting membrane potential (Vm) in most neurons?

Approximately –70 mV to –85 mV.

Define “resting membrane potential.”

The membrane voltage of a cell when it is not actively transmitting a signal (at rest).

What is meant by “depolarization”?

A change in membrane potential that makes the interior more positive (less negative) than the resting level.

What is meant by “hyperpolarization”?

A change in membrane potential that makes the interior more negative (farther from zero) than the resting level.

Where is K⁺ concentration highest—inside or outside the cell?

Inside the cell.

In the Na⁺/K⁺ ATPase pump, how many K⁺ ions are moved into the cell for every three Na⁺ ions moved out?

Two K⁺ ions.

What is the normal extracellular potassium concentration ([K⁺]ₒᵤₜ)?

Around 4 mEq/L.

What is the equilibrium potential for potassium (Eₖ)?

Approximately –94 mV.

Where is Na⁺ concentration highest—inside or outside the cell?

Outside the cell.

What is the equilibrium potential for sodium (Eₙₐ)?

Approximately +61 mV.

What term describes small, local membrane potential changes that can be either excitatory or inhibitory?

Graded potentials.

Opening Na⁺ channels usually generates which type of graded potential?

An excitatory postsynaptic potential (EPSP) that depolarizes the membrane.

Opening K⁺ or Cl⁻ channels usually generates which type of graded potential?

An inhibitory postsynaptic potential (IPSP) that hyperpolarizes the membrane.

What principle states that once threshold is reached an action potential will occur fully and uniformly?

The all-or-none principle.

Describe the basic ion sequence of a typical action potential.

Voltage-gated Na⁺ channels open (Na⁺ influx), Na⁺ channels inactivate, voltage-gated K⁺ channels open (K⁺ efflux), membrane repolarizes/hyperpolarizes and then resets.

How does low extracellular potassium (hypokalemia) affect membrane excitability?

It makes Vm more negative (farther from threshold), so cells are harder to stimulate.

How does high extracellular potassium (hyperkalemia) generally affect membrane excitability?

It makes Vm less negative (closer to threshold), so cells are easier to depolarize (though severe hyperkalemia can eventually impair conduction).

What effect does HIGH extracellular calcium have on threshold and excitability?

It raises the threshold, leading to a loss of cellular excitability.

What effect does LOW extracellular calcium have on threshold and excitability?

It lowers the threshold, increasing cellular excitability.