Which of the following is true of pain receptors?

A) Pain receptors differ anatomically.
B) Pain receptors are similar in the type of physical stimuli to which they most readily react.
C) Pain receptors have a much lower threshold for firing than receptors for temperature and touch.
D) Pain receptors react mainly to physical stimuli that distort them or to chemical stimuli that irritate them into action.

Pain receptors, also known as nociceptors, are specialized sensory receptors that react to physical stimuli that distort or damage the tissue or to chemical stimuli that irritate them into action. Unlike receptors for temperature and touch, pain receptors have a much lower threshold for firing. Furthermore, pain receptors differ anatomically, which means that different types of pain may be sensed by different receptors in different parts of the body. Therefore, option A and B are incorrect.