Lecture Notes: Graded Potentials

Overview

• Graded potentials are short-lived, localized changes in membrane potential or voltage.
• The stronger the stimulus, the more significant the voltage change and the farther the current flows.

Characteristics

• Graded potentials are akin to a wave of voltage.
• They are triggered by a stimulus that opens gated ion channels.
• Result in depolarization and sometimes hyperpolarization.

Types of Graded Potentials

1. End Plate Potential

   • Occurs at the motor end plate.
   • A type of graded potential in the neuromuscular junction.

2. Receptor Potential (Generator Potential)

   • Formed in the receptors of sensory neurons.
   • Example: Smelling an odorant molecule creating a receptor potential.
   • May or may not trigger an action potential.

3. Postsynaptic Potential

   • A neuron graded potential occurring in dendrites and cell bodies.
   • May or may not lead to an action potential.

Mechanism

• Graded potentials occur as a local area of membrane potential change.
• A stimulus causes local depolarization, which can spread.
• As depolarization spreads, it diminishes over time and distance, similar to a wave in a pond.

Behavior

• Caused by gated ion channels opening, leading to depolarization or hyperpolarization spreading across the membrane.
• Depolarization causes local areas of positive charge.
• As depolarization spreads, the effect on local voltage decreases.
• Current flows but decays quickly over short distances.

Key Points

• Graded potentials decay over time and distance.
• Initial depolarization may be strong but weakens as it spreads;
• As ions dissipate, the membrane potential returns closer to resting potential.