Membrane Potentials and Action Potential Mechanisms

What are chemically gated (ligand-gated) channels?

Channels that open only with the binding of a specific chemical, such as a neurotransmitter.

What are voltage-gated channels?

Channels that open and close in response to changes in membrane potential.

What are mechanically gated channels?

Channels that open and close in response to physical deformation of receptors, as in sensory receptors.

What is the role of membrane ion channels?

Large proteins serve as selective membrane ion channels, allowing specific ions to pass through.

What are the two main types of ion channels?

Leakage (nongated) channels, which are always open, and gated channels, which change shape to open or close.

What are the three main types of gated channels?

Chemically gated, voltage-gated, and mechanically gated channels.

What is an electrochemical gradient?

The combined electrical and chemical gradients that influence ion movement.

What does Ohm's law express?

The relationship between voltage (V), current (I), and resistance (R) in a circuit.

How is voltage measured?

Voltage is measured between two points in volts (V) or millivolts (mV) and is called potential difference.

What is current in the context of electrical charge?

The flow of electrical charge (ions) between two points.

What is resistance in electrical terms?

The hindrance to charge flow, with insulators having high resistance and conductors having low resistance.

What happens when opposite charges are separated?

The system has potential energy, and energy is required to keep them separated.

What is the difference in ionic composition between extracellular fluid (ECF) and intracellular fluid (ICF)?

ECF has a higher concentration of Na+ and is balanced chiefly by Cl−, while ICF has a higher concentration of K+ balanced by negatively charged proteins.

What is the resting membrane potential of neurons?

Unlike most cells, neurons can rapidly change their resting membrane potential and are highly excitable.

What stabilizes the resting membrane potential?

The sodium-potassium pump (Na+/K+ ATPase) maintains concentration gradients for Na+ and K+.

What are graded potentials?

Incoming signals that operate over short distances, resulting from changes in membrane potential.

What are action potentials?

Long-distance signals of axons that involve a brief reversal of membrane potential.

What is depolarization?

A decrease in membrane potential, making the inside of the membrane less negative and increasing the probability of an impulse.

What is hyperpolarization?

An increase in membrane potential, making the inside of the membrane more negative and decreasing the probability of an impulse.

What triggers graded potentials?

Stimuli that open gated ion channels, resulting in depolarization or hyperpolarization.

What is the principal way neurons send signals?

Through action potentials, which do not decay over distance.

What are the four main steps of action potentials?

1. Resting state: All gated channels are closed. 2. Depolarization: Na+ channels open. 3. Repolarization: Na+ channels inactivate, K+ channels open. 4. Hyperpolarization: Some K+ channels remain open.

What is the all-or-none principle of action potentials?

An action potential either occurs completely or does not occur at all.

What is the refractory period?

The time during which a neuron cannot trigger another action potential.

What are the two types of refractory periods?

Absolute refractory period, when Na+ channels are open, and relative refractory period, when most Na+ channels have returned to resting state but some K+ channels are still open.

How does the CNS differentiate between weak and strong stimuli?

By the frequency of action potentials received per second; higher frequencies indicate stronger stimuli.

What is the role of the sodium-potassium pump in action potentials?

It restores ionic conditions after repolarization by pumping Na+ out and K+ back into the cell.