Final answer:
A sensory receptor is a specialized neuron or a specialized cell associated with a neuron that responds to specific environmental stimuli by converting them into nerve impulses for the nervous system.
Step-by-step explanation:
A sensory receptor is often a modified version of a neuron, which is a specialized nerve cell. These receptors convert stimuli from the environment (both internal and external) into electrical signals in the nervous system. They are specialized for the type of stimulus they detect, such as light, sound, touch, or chemicals, and are responsive only within their specific receptive field. Different sensory receptors exist, including encapsulated endings and specialized neurons like photoreceptors in the eyes (rod cells) which synapse with bipolar cells and then the optic nerve neurons. Sensory receptors play the crucial role of initiating the sensory transduction process by activating the associated sensory neuron and conveying information to the central nervous system.
The classification of sensory receptors can be based on structural aspects such as the presence of free nerve endings or encapsulated endings, as well as functionally based on how they change cell membrane potential in response to mechanical, light, or chemical stimuli.