BIOL325 - Graded Potential

Graded potential

Local membrane voltage change whose size depends on stimulus strength.

Depolarization

Membrane potential becomes less negative.

Hyperpolarization

Membrane potential becomes more negative.

Triggering event

Stimulus that opens gated channels and changes membrane potential.

Chemically (ligand)-gated channels

Channels opened when a chemical messenger binds.

Mechanically gated channels

Channels opened by membrane deformation or pressure.

Voltage-gated channels

Channels whose opening depends on membrane voltage.

Receptive region

Dendrites and soma where graded potentials typically begin.

Trigger zone

Axon hillock/initial segment where threshold can start an AP.

Conducting region

Axon that propagates action potentials.

Secretory region

Axon terminal where neurotransmitter release occurs.

Active area

Membrane region where a stimulus changes ion permeability.

Inactive area

Nearby membrane not directly stimulated.

Local current

Charge flow from an active membrane area toward neighboring areas.

Decremental spread

Graded signal weakens with distance due to current loss.

Why are graded potentials short-range?

Current leaks across membrane and encounters internal resistance.

What causes depolarizing graded potentials?

Opening channels that allow net positive charge inward, often Na+.

What causes hyperpolarizing graded potentials?

Opening channels favoring K+ exit or Cl− entry.

Opening gated Cl− channels

Usually drives voltage toward ECl; may inhibit depolarization.

Excitatory graded potential (EPSP)

Depolarization that brings trigger zone closer to threshold.

Inhibitory graded potential (IPSP)

Signal that moves voltage away from threshold or opposes excitation.

Stimulus intensity vs. graded potential size

Stronger stimulus usually produces a larger voltage change.

Stimulus duration vs. graded potential duration

Longer stimulus can produce a longer graded potential.

Why are graded potentials analog?

Amplitude varies with stimulus intensity.

Threshold potential

Voltage at which inward Na+ current can trigger regenerative AP.

Graded potential vs. action potential

Graded: variable and decremental; AP: all-or-none and nondecremental.