In a sensory system, a sensory receptor is a structure that recognizes a stimulus in the internal or external environment of an organism. In response to stimuli the sensory receptor initiates sensory transduction by creating graded potentials or action potentials in the same cell or in an adjacent one.
The sensory receptor may be a specialized portion of the plasma membrane, or a separate cell associated with a neuron ending.
Some sensory receptors (i.e., taste and smell) contain receptors that bind to specific chemicals. Odor receptors in olfactory receptor neurons, for example, are activated by interacting with molecular structures on the odor molecule. Similarly, taste receptors in taste buds interact with chemicals in food to produce an action potential.
Other receptors such as mechanoreceptors and photoreceptors respond to physical stimuli. For example, photoreceptor cells contain specialized proteins such as rhodopsin to transduce the physical energy in light into electrical signals. Some types of mechanoreceptors fire action potentials when their membranes are physically streched.
The sensory receptor functions as the first component in a sensory system.
Sensory receptors respond to specific stimulus modalities. The stimulus modality to which a sensory receptor responds is determined by the sensory receptor's adequate stimulus.
The sensory receptor responds to its stimulus modality by initiating sensory transduction.
Classification by adequate stimulus
The sensory receptor's adequate stimulus is the stimulus modality to which a sensory receptor responds by initiating sensory transduction. Adequate stimulus can be used to classify sensory receptors:
- Chemoreceptors respond to chemical signals
- Mechanoreceptors respond to touch or pressure
- Thermoreceptors respond to heat
- Photoreceptor cells respond to light
Classification by location
Sensory receptors can be classified by location:
- Primary sensory cell
- Secondary sensory cell