The adequate stimulus
is a property of a sensory receptor
that determines the type of energy to which a sensory receptor responds to with the initiation of sensory transduction
A sensory receptor's adequate stimulus is determined by the signal transduction mechanisms and ion channels incorporated in the sensory receptor's plasma membrane.
- Light - When the adequate stimulus of a sensory receptor is light, the sensory receptors contain pigment molecules whose shape is transformed by light. Changes in these molecules activate ion channels which initiate sensory transduction.
- Sound - When the adequate stimulus of a sensory receptor is sound, the sensory receptors are hair cells (mechanoreceptors). These hair cells contain stereocilia, which when bent, trigger the opening of ion channels. Thus hair cells transform the pressure waves of the sound into receptor potentials to initiate sensory transduction.
Although Muller proposed in his doctrine that any stimulus to a sensory receptor will invoke the same perception, we have now built on that theory by adding that an adequate stimulus is a type of stimulus for which a given sensory organ is particularly adapted towards.