8th science Biology Nervous System
Class 8th Science
ICSE/ CBSE Notes
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By Er. Amit Sir
5-Nervous System
- Your nervous system is your body's command center.
- Originating from your brain, it controls your movements, thoughts and automatic responses to the world around you.
- It also controls other body systems and processes, such as digestion, breathing and sexual development (puberty)
- Your nervous system uses specialized cells called neurons to send signals, or messages, all over your body.
- These electrical signals travel between your brain, skin, organs, glands and muscles.
- The messages help you move your limbs and feel sensations, such as pain.
- Neurons consists of three main parts cyton, axon , dendrites.
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By Er. Amit Sir
- Different kinds of neurons send different signals.
- Motor neurons tell your muscles to move.
- Sensory neurons take information from your senses and send signals to your brain.
- Other types of neurons control the things your body does automatically, like breathing, shivering, having a regular heartbeat and digesting food.
Nerve fibers
- Nerves cells are joined end to end forming long nerve fibers.
- A number of nerve fibers or axon part are bundled together in a tubular sheath forming a nerve.
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By Er. Amit Sir
Types of Nerves
There are three types of nerves in the human body which are classified based on their functions. These are the
- sensory nerves
- motor nerves
- mixed nerves.
Sensory Nerves
- These are the nerves that send messages to the brain or the spinal cord from the sense organs.
- These are enclosed in the form of a bundle like structures or nerve fibres in the peripheral nervous system.
- They carry information from the PNS to the CNS( Central Nervous System).
Motor Nerves
- Motor nerves are those nerves those that carry the messages in the form of a response from the brain or the spinal cord to other parts of the body such as the muscles and glands.
- They are responsible for carrying the information from the CNS to the PNS.
Mixed Nerves
- Mixed nerves are the nerves that perform both the action of sensory nerves as well as a motor nerve.
- They transform electrical impulses from the central nervous system to the muscles of the body.
- Generally, the mixed nerves transmit impulses at the rate of 120 metres per second or 432 kilometres per hour.
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By Er. Amit Sir
Parts of the nervous system
- The nervous system has two main parts.
- Each part contains billions of cells called neurons, or nerve cells.
- These special cells send and receive electrical signals through your body to tell it what to do.
The main parts of the nervous system are:
1- Central nervous system (C.N.S.)
- Your brain and spinal cord make up your CNS.
- Your brain uses your nerves to send messages to the rest of your body.
- Each nerve has a protective outer layer called myelin. Myelin insulates the nerve and helps the messages get through.
Brain
- The brain is one of the largest and most complex organs in the human body.
- It is made up of more than 100 billion nerves that communicate in trillions of connections called synapses.
- The cortex is the outermost layer of brain cells. Thinking and voluntary movements begin in the cortex.
- The brain stem is between the spinal cord and the rest of the brain. Basic functions like breathing and sleep are controlled here.
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By Er. Amit Sir
Brain consists of three main centers
- Cerebrum
- Cerebellum
- Brain Stem or Medulla oblongata
Cerebrum
- It is the upper most and largest part of the brain.
- Its surface has many grooves and ridges. by which surface area is increased for more nerve cells.
- It is divided into right and left cerebral hemispheres.
Functions of cerebrum
- It control mental activities like thinking and reasoning.
- It is center for intelligence and memory.
- Its function is perceiving pain ,sound, touch,taste and smell.
Cerebellum
- The cerebellum is at the base and the back of the brain. The cerebellum is responsible for coordination and balance.
- It has many furrows but lacks convolutions.
Functions of cerebellum
- It maintain balance of the body.
- It coordinates muscular activity.
Brain Stem
- It is lowest part of the brain.
- It join the brain to spinal card.
Functions of brain stem
- It control the activity of internal organs.
- Heartbeat , breathing and all involuntary movements.
Spinal cord
- The spinal cord is a long, thin, tubular structure made up of nervous tissue.
- which extends from the medulla oblongata in the brainstem to the lumbar region of the vertebral column.
- The spinal cord is a long bundle of nerves and cells that extends from the lower portion of the brain to the lower back.
- It carries signals between the brain and the rest of the body.
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By Er. Amit Sir
- Gray matter: The gray matter is the dark, butterfly OR H shaped region of the spinal cord made up of nerve cell bodies.
- White matter: The white matter surrounds the gray matter in the spinal cord and contains cells coated in myelin, which makes nerve transmission occur more quickly. Nerve cells in the gray matter are not as heavily coated with myelin.
The spinal cord plays a vital role in various aspects of the body’s functioning. Examples of these key functions include:
- Carrying signals from the brain: The spinal cord receives signals from the brain that control movement and autonomic functions.
- Carrying information to the brain: The spinal cord nerves also transmit messages to the brain from the body, such as sensations of touch, pressure, and pain.
- Reflex responses: The spinal cord may also act independently of the brain in conducting motor reflexes. One example is the patellar reflex, which causes a person’s knee to involuntarily jerk when tapped in a certain spot.
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By Er. Amit Sir
B - Peripheral nervous system (P.N.S.)
- Your peripheral nervous system consists of many nerves that branch out from our CNS all over our body.
- This system relays information from our brain and spinal cord to our organs, arms, legs, fingers and toes.
- Somatic nervous system, which guides your voluntary movements.
- Autonomic nervous system, which controls the activities you do without thinking about them.
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