Detailed Notes: Nervous System - Notes | Study Science Class 5 - Class 5

You will learn about: 

• The brain 
• The spinal cord
• The nerves
• Reflex action

Our nervous system makes us aware of our surroundings. The nervous system controls all other body systems and the sense organs. It is an important organ system in our body. It helps us to see, read, write, think, learn, feel, respond, etc. The nervous system controls all other body systems and the sense organs. 

Brain

• The brain is the main organ of the nervous system. 
• It is the control center of our body. 
• It sends and receives messages from different parts of the body through spinal cord and nerves. 
• It is protected by a bony closed structure, the skull. 
• The space between the brain and the skull is filled with a fluid that acts as a shock absorber. 

The brain's average weight is about 1.5 kg.  

Parts of BrainCerebrum 

• The cerebrum is the largest and the main part of the brain. 
• It has many grooves and folds. 
• It controls our sense organs and is the center of intelligence.
• It controls our voice and also helps us to think, learn, remember and recall memories. It also controls our emotions 

Cerebellum 

• The cerebellum is an egg-shaped structure situated below the cerebrum. 
• It is the second largest part of the brain, also called the small brain. 
• It controls and coordinates the actions of voluntary muscles involved in activities like running, walking, dancing, and standing.
• It also helps in maintaining the balance of our bodies.  

Medulla Oblongata 

• The medulla oblongata is also called the brain stem. 
• It is a stem-shaped structure that lies below the cerebrum but in front of the cerebellum. 
• It connects the brain to the spinal cord. 
• It controls involuntary actions like the lungs' movement in breathing and the heart, etc.

Spinal Cord

• The spinal cord is a long, thick bundle of nerves that extends down from the medulla to the lower end of the backbone. 
• It is enclosed in the hard, bony vertebral column. 
• Nerves originate from the spinal cord and spread all over the body. 
• The spinal cord is responsible for carrying messages between the brain and the rest of the body through nerves. 
• It also controls the actions that do not involve the brain. These actions are called reflex actions.

Spinal cord in the human bodyNerves

• Nerves are thread-like structures extending from the brain and spinal cord to all body parts. 
• Each nerve is composed of bundles of fibers (neurons) through which impulses pass between the brain or other parts. 
• The network of nerve cells or neurons runs throughout the body. 
• The nerves from the head and the neck join the brain directly, while the nerves from the other parts of the body are connected to the spinal cord.

Types of Nerves

• Sensory Nerves- These nerves carry messages from the sense organs to the brain or the spinal cord. These messages are information about such things as temperature, smell, color or pressure. 
• Motor Nerves- These nerves send messages from the brain or the spinal cord to the muscles of different organs. These are the messages that make the muscles move. 
• Mixed Nerves- The mixed nerves connect the sensory and motor nerves. These nerves work both ways:
  They carry messages from the brain or spinal cord to different organs.
  They bring messages from the organs to the spinal cord or the brain. 

Structure of a Neuron

 Reflex Actions

• An automatic, quick action that our body makes, often without us even thinking about it, in response to a stimulus is called reflex action.  
• Some of our actions are involuntary and cannot be under our control. 
• These automatic actions are controlled by the spinal cord without any involvement of the brain. 
• The reflex actions are very fast.

Example: When we touch a sharp object, the nerve endings in the finger feel the pain as the message reaches the spinal cord through the sensory nerve. The spinal cord sends the command back through the motor nerve to the muscles of the hand to move away.