Final answer:
A sensory receptor is the specialized nerve cell that detects stimuli from the external environment and initiates an electrical signal to the sensory neuron. Different types of receptors, such as free nerve endings and specialized cells, play a pivotal role in the reception and transduction of stimuli into signals transmitted to the central nervous system.
Step-by-step explanation:
The structure that receives a stimulus from the external environment and relays it to the sensory neuron is known as a sensory receptor.
Sensory receptors are specialized nerve cells that initiate a nerve impulse in response to environmental stimuli. This impulse travels via the sensory neuron to the central nervous system. For instance, when touching a hot stove, the sensory receptors in your skin detect the high temperature. They send an electrical signal through the sensory neurons to the spinal cord without the need for direct brain intervention. Here, it engages with interneurons and subsequently is communicated to motor neurons, causing a quick withdrawal of the hand - an action known as a reflex arc.
The body contains various types of sensory receptors—some are free nerve endings, while others are encapsulated or specialized. Reception is the first step in the sensory process, which involves activation of the receptors by external stimuli. Transduction follows, where the receptor converts the stimuli into electrical signals, also known as action potentials. The impulses then travel to the central nervous system for integration and processing, with pathways leading to the thalamus and then to specific regions of the cortex for certain sensory modalities, excluding olfaction.