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The central nervous system consists of:
A. Brain
B. Spinal cord
C. Nerves and ganglia
D. Both A and B

Last updated date: 13th Jun 2024
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Hint: The organ system in animals that contain networking of neurons which are specialized cells and these specialized cells coordinate the actions and transmit signals between various parts of the animal’s body. It is the most important controlling and regulatory system in the body of the animal. The nervous system is classified as the Central nervous system (CNS) and the Peripheral nervous system (PNS).

Complete Answer:
- The central nervous system is made up of the brain and the spinal cord. The name ‘Central’ suggests that it combines information from the entire body and coordinates activity across the whole body of an animal.
- The brain controls all the activities of the body and it uses most of the body's energy.
- The brain and spinal cord are connected through a part of the brain called the brainstem.
- The spinal cord, a tubular structure consisting of nervous tissues runs from the head and middle of back in downward direction. The spinal cord runs through the spinal canal. The main function of the spinal cord is to transmit signals to and fro between the brain and the peripheral nervous system.
- The smallest unit of the Central nervous system is the neuron.

Therefore, option (D) is correct.

Note: Though most animals have brains, but there are few exceptions. For example, sponges don’t have any kind of nervous tissue or brain. The jellyfishes don’t have a brain, heart or even blood. Some of the animals without brains are sea star, sea cucumber and sea anemone.