Which statement best describes tonic receptors?

• A. They respond only at stimulus onset
• B. They rapidly adapt to changes
• C. They do not respond to the duration of a stimulus
• D. They maintain signaling for the duration of the stimulus

Answer: (D)

Tonically responding receptors keep firing as long as the stimulus is present, providing ongoing information about both how strong the stimulus is and how long it lasts. This slow or minimal adaptation means their output reflects the duration of the stimulus, so signaling persists throughout the stimulus. That sustained activity is what distinguishes tonic receptors from phasic ones, which respond mainly at the moment of onset or after rapid changes and then diminish despite ongoing stimulation.