Which of the following is NOT a type of mechanoreceptor?

• A. Meissner corpuscles
• B. Pacinian corpuscles
• C. Nociceptors
• D. Merkel's receptors

Answer: (C)

Mechanoreceptors are specialized to convert mechanical energy—touch, pressure, vibration—into electrical signals. The three classic mechanoreceptors each focus on a different aspect of touch: Meissner corpuscles detect light, dynamic touch and have small receptive fields; Pacinian corpuscles sense deep pressure and high-frequency vibration with rapid adaptation; Merkel’s receptors respond to steady pressure and texture, providing fine spatial details with slow adaptation. Nociceptors, on the other hand, are pain receptors that signal tissue damage or potentially harmful stimuli. They are not classified as mechanoreceptors, even though some can respond to mechanical injury, because their primary role is signaling pain rather than encoding ordinary mechanical touch. Therefore, the one not fitting as a mechanoreceptor is the nociceptor.