Which statement regarding graded potentials is correct?

• A. Both receptor potentials and generator potentials are graded depolarizations that can trigger an action potential if threshold is reached.
• B. Only receptor potentials are graded.
• C. Generator potentials are not related to sensory transduction.
• D. Receptor potentials always cause immediate action potentials.

Answer: (A)

Graded depolarizations in sensory transduction determine whether an action potential will be produced. Both receptor potentials and generator potentials are depolarizing, graded in amplitude with stimulus strength. When the depolarization reaches threshold, voltage-gated Na+ channels open and an action potential is generated. In receptor potentials, the receptor cell depolarizes and releases neurotransmitter onto a sensory neuron; in generator potentials, the sensory neuron itself depolarizes to threshold and fires an action potential. Therefore, the statement that both are graded depolarizations that can trigger an action potential if threshold is reached captures the essential idea. The other options misstate the graded nature, the relation to sensory transduction, or the conditions under which action potentials occur.