Sensory receptors are specialized, excitable cells that are designed to convert a physical stimulus into an electrical signal that can be transmitted to other nerve cells in the nervous system. The physical stimulus interacts with a specialized receptor protein embedded in the membrane of the sensory receptor leading to a change in membrane potential. Sensory receptors typically respond to only one type of stimulus and that specificity is conserved as the signal is propagated along neural pathways in the spinal cord and brain. The series of neurons that are connected by synapses from the sensory receptor to secondary sensory and third order sensory neurons in the nervous system is referred to as a ‘labeled line’. The labeled lines enable the brain to distinguish and process information about different types physical stimuli. In response to a constant stimulus, the response most sensory receptors declines over time, as process called adaptation. Some sensory receptors adapt slowly to a constant stimulus and others adapt more rapidly.

(Unless otherwise noted, all figures are from:  Kandel ER, Schwartz JH, Jessell TM 2012, Siegelbaum SA, Hudspeth AJ. ‘Principles of Neural Science, 5th ed. McGraw-Hill, New York.)