**Core Concept**
Generatory potential, also known as generator potential, is a local electrical change in the membrane of sensory receptors in response to a stimulus, such as pressure, light, or sound. This potential is the initial step in the transduction process that ultimately leads to the generation of an action potential in sensory neurons.

**Why the Correct Answer is Right**
The generator potential is a graded potential that varies in amplitude depending on the strength of the stimulus. It is generated by the opening of ion channels in the sensory receptor membrane, leading to a change in the membrane potential. The type of ion channels involved and the direction of the potential change depend on the specific type of sensory receptor and the nature of the stimulus. For example, in photoreceptors, the generator potential is a hyperpolarization that is generated by the closure of sodium channels in response to light.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because generator potential is not a type of action potential, but rather a graded potential that can lead to the generation of an action potential.
* **Option B:** This option is incorrect because generator potential is not directly related to synaptic transmission, although it can ultimately lead to changes in synaptic strength.
* **Option C:** This option is incorrect because generator potential is not a type of receptor potential, but rather a local electrical change in the sensory receptor membrane.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that generator potential is a graded potential, meaning its amplitude varies with the strength of the stimulus, whereas action potentials are all-or-nothing electrical impulses.

**Correct Answer: C. Generator potential is a local graded electrical change in the sensory receptor membrane in response to a stimulus.**