Iodine is necessary for the synthesis of which hormone?

$(a)$ Name the part of the brain which controls:
$(i)$ voluntary actions,
$(ii)$ involuntary actions.
$(b)$ What is the significance of the peripheral nervous system? Name the components of this nervous system and distinguish between the origin of the two.

Which of the following statements are true about the brain?
$(i)$ The main thinking part of the brain is the hindbrain.
$(ii)$ Centres of hearing,smell,memory,sight,etc.,are located in the forebrain.
$(iii)$ Involuntary actions like salivation,vomiting,and blood pressure are controlled by the medulla in the hindbrain.
$(iv)$ The cerebellum does not control posture and balance of the body.

$(a)$ An old man is advised by his doctor to take less sugar in his diet. Name the disease from which the man is suffering. Mention the hormone due to imbalance of which he is suffering from this disease. Which endocrine gland secretes this hormone?
$(b)$ Name the endocrine gland which secretes growth hormone. What will be its effect on a person of:
$(i)$ Deficiency of growth hormones?
$(ii)$ Excess secretion of growth hormones?

What is a tropic movement? Explain with an example.

Name the system which facilitates communication between the central nervous system and the other parts of the body. Mention two types of nerves it consists of along with their organ of origin.