Sensory Receptors are responsive to a single type of stimulus energy
“It is often said that the power of the brain lies in the millions of neurons processing information in parallel. If we understand a muscle cell, we essentially understand how a whole muscle works. The power of the brain lies in the parallel action of millions of cells, each doing something different; to understand the brain we need to understand how its tasks are organized and how individual neurons carry out those tasks.
Functional differences between sensory systems arise from the different stimulus energies that drive them and the discrete pathways that comprise each system. Because of these characteristics each neuron performs a specific task, and the train of action potentials it produces has a specific functional significance for all postsynaptic neurons. This basic idea was expressed in the theory of specificity set forward by Charles Bell and Johannes Müller in the 19th century and remains one of the cornerstones of sensory neuroscience.
The richness of sensory experience begins with millions of highly specific sensory receptors. Each receptor responds to a specific kind of energy at specific locations on the body and sometimes only to energy with a particular temporal or spatial pattern. The receptor transforms the stimulus energy into electrical energy, thus establishing a common signaling mechanism in all sensory systems. The amplitude and duration of the electrical signal produced by the receptor, termed the receptor potential, are related to the intensity and time course of stimulation of the receptor. The process by which specific stimulus energy is converted into an electrical signal is called stimulus transduction.
Sensory receptors are morphologically specialized to transduce specific forms of energy, and each receptor has a specialized anatomical region where stimulus transduction occurs. Most receptors are optimally selective for a single type of stimulus energy, a property termed receptor specificity. We see particular colors, for example, because we have receptors that are selectively sensitive to photons with specific wavelengths, and we smell particular odors because we have receptors that bind specific odorant molecules”
Excerpt From: Kandel, Eric. “Principles of Neural Science”, 5th Edition