18.2: Introduction to Sensory Receptors
Sensory receptors are vital in our ability to perceive and interpret the world. Sensory receptors are specialized cells in the peripheral nervous system that respond to various stimuli and enable one to experience different sensations. Based on specific criteria, sensory receptors are classified into distinct types.
The first classification criterion is based on cell type, position, and function. Some receptor cells are neurons with free nerve endings, where their dendrites are embedded in the tissue that receives the sensation. Others are neurons with encapsulated endings, surrounded by connective tissue, enhancing their sensitivity to stimuli. The third category of cells consists of specialized receptor cells, which are equipped with unique structural elements designed to detect and interpret specific kinds of stimuli. For example, photoreceptors are located in the eyes, while gustatory receptors can be found within the taste buds.
Receptors can also be classified based on their location relative to the stimuli. Exteroceptors, such as somatosensory receptors in the skin, are located near stimuli in the external environment, enabling us to perceive touch and pressure. Conversely, interoceptors interpret stimuli from internal organs and tissues, like receptors that sense changes in blood pressure in the aorta or carotid sinus. Finally, proprioceptors are located near moving body parts, such as muscles, and help us interpret body positions as they move, contributing to our sense of balance and coordination.
Physical stimuli, such as pressure, vibration, sound, and body position, are interpreted through mechanoreceptors. Temperature, a critical sensory aspect, is sensed through thermoreceptors sensitive to temperatures above or below normal body temperature.
