Question

P is a cell (or group of cells) in the human body which is sensitive to a particular type of stimulus and conveys the messages to CNS through nerves Q. On the other hand, R is a part of the human body which can respond to a stimulus according to the instructions sent from the CNS through nerves S.
(a) What is P? Name five organs which contain cells (or group of cells) like P.
(b) Name the nerves Q.
(c) What is R? Give two examples of R.
(d) Name nerves S.
(e) How do messages travel through the nerves Q and S?

Answer 1

(a) P is a receptor. The five organs which contain receptors are: eyes, ears, nose, tongue and skin.

(b) Q represents sensory nerves. Sensory nerves bring impulses from sensory organs to the CNS. 

(c) R is an effector organ. Effectors are part of the human body which can respond to a stimulus according to the instructions sent from the CNS though the motor nerves. Two examples of effector organs are the muscles and glands.

(d) S represents motor nerves. Motor nerves carry impulse from the CNS to the effector organs like the muscles or glands.

(e) Messages travel in the form of electrical impulses or nerve impulses through sensory nerves (Q) and motor nerves (S).