Question

The organ A which is located inside the skull of our body is protected by a bony shell B. It is surrounded by three layers membranes C. The spaces between these layers are filled with a liquid D which protects organ A from mechanical shocks. Organ A in combination with another organ E makes up the central nervous system.

(a) What is organ A?
(b) What are B, C and D?
(c) Name the organ E.
(d) While walking barefoot, if we happen to step on a sharp piece of stone, we immediately lift our foot up. Which of the two organs: A or E, is directly involved in this action?
(e) If we step out from a darkened room into bright sunlight, we close our eyes for a moment. Which of the two organs: A or E, is directly involved in this action?

Answer 1

1. The organ A is the brain. The brain is located inside the skull of our body at the top of the spinal cord.
2. (i) B is the cranium. The brain is protected by a bony box in the skull called the cranium.

          (ii) C are meninges. The brain is surrounded by three layers of membranes called the meninges.
          (iii) D is the cerebrospinal fluid. It is present in between the meninges and protects the brain from mechanical shocks.

3. The organ E is the spinal cord. The brain (organ A) and the spinal cord (organ E) together make central nervous system.
4. A person walking barefoot lifts his foot at once on stepping on to a sharp piece of stone. The spinal cord (E) is involved in this action. Those reflexes that involve only the spinal cord are called spinal reflexes.
5. A person closes his eyes at once when he steps out from a darkened room to bright light. The brain (A) is involved in this action. Those reflexes that involve only the brain are known as cerebral reflexes.