Science: Control and Coordination: Divisions of Nervous System (For CBSE, ICSE, IAS, NET, NRA 2022)

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The Nervous System

It Ensure that the body works in a controlled and coordinated manner. The nervous system includes the brain, spinal cord, sense organs and nerves. The functioning of the nervous system depends on detecting a stimulus in the internal or external environment and responding to it.

Nervous System

It Consists of Three Parts

  • Dendrites are branched cytoplasmic projections from the cell body. The dendritic tip of the nerve cells receive impulses and sets off a chemical reaction that creates an electrical impulse which is further transmitted to the cell body.
  • The cell body contains a well-defined nucleus, surrounded by cytoplasm. It has cell organelles like any other cells. The cell body further transmits the impulse to the axon.
  • Axon: One branch arising out of the cell body is very long in comparison to others. This branch is called axon.

There Are Three Types of Neurons

  • Sensory neurons convey the impulse from receptor (sense organ) to the main nervous system. (brain or spinal cord) .
  • Motor neurons carry the impulse from the main nervous system to an effector (muscle or gland) .
  • Association (Connecting) neurons are located in the brain and spinal cord and interconnect the sensory and motor neurons nerve fiber.
Types of Neurons
  • Nerves: A nerve is formed of a bundle of nerve Fibres (axons) enclosed in a tubular sheath.

There Are Three Kinds of Nerves

  • Sensory nerves that contain sensory Fibres. These nerves bring impulse from the receptors (sense organs) to the brain or spinal cord. Example: Optic nerve arising from the eye and ending in the brain.
  • Motor nerves which contain motor Fibres. These nerves carry impulse from the brain or spinal cord to the effector organ like muscles or glands. Example: a nerve arising from the brain and carrying impulse to the muscles of the eye.
  • Mixed nerves are those that contain both sensory and motor Fibres and perform a mixed function. Example: a spinal nerve.

Divisions of Nervous System

The nervous system has two main divisions: Central Nervous System (CNS) that includes brain and spinal cord and Peripheral Nervous System (PNS) which includes the nerves arising from the brain and spinal cord.

Central Nervous System (CNS)

The central nervous system in human beings consists of brain and spinal cord.

Brain

Brain is the highest coordinating center in the body. It is covered by meninges, which is made up of three layers. It is protected by cranium. Brain is broadly divided into:

  • Forebrain: The forebrain includes cerebrum and olfactory lobes. Cerebrum is the largest part of the brain. It consists of two cerebral hemispheres. Sensory and motor receptors are present in the brain. There are various regions for reception of vision (occipital lobe) , reception of sound (temporal lobe) , touch, smell, temperature (parietal lobe) and muscular activities (frontal lobe) . Olfactory lobes are one in pair and receives olfactory nerves.
  • Midbrain: It is the small portion of the brain that connects cerebrum with the other parts of the brain and spinal cord.
  • Hindbrain: It consists of cerebellum, pons and medulla oblongata. Cerebellum is responsible for coordination and adjustment of movement and posture. Pons regulate respiration. Medulla oblongata regulates swallowing, coughing, sneezing and vomiting.
  • Spinal cord: Medulla oblongata extends downwards, enclosed in vertebral column to form a cylindrical structure known as spinal cord. It is also covered by meninges. It is the reflex center of the body.
Central Nervous System

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