What is the generator potential and how does it relate to action potential initiation?

• A. A short, all-or-none signal in a neuron.
• B. A hyperpolarizing event that prevents firing.
• C. A chemical signal released by receptor cells.
• D. A graded depolarization in a sensory neuron that may trigger an action potential if threshold is reached.

Answer: (D)

The main idea is that a generator potential is a graded depolarization produced by a sensory receptor in response to a stimulus, and it can trigger an action potential if it reaches threshold. This depolarization varies in size with the strength of the stimulus, unlike an action potential, which is a uniform all-or-none event. When the generator potential is large enough to reach the axon hillock, voltage-gated Na+ channels open and an action potential is initiated and then propagates along the neuron. If the generator potential doesn’t reach threshold, no action potential occurs. This concept sits between the initial, local depolarization at the receptor and the all-or-none spike that carries the signal.