This is a slideshow about The Nervous System for grade 7th, 8th and 9th. It includes definitions, questions and pictures to enhance it.

1. THE NERVOUS SYSTEM
-For Grade 8

2. What is the nervous system?
The nervous system is the highway along which
your brain sends and receives information about
what is happening in the body and around it.
This highway is made up of billions of nerve
cells, or neurons (say new-rons) which join
together to make nerves.

3. • A nerve is a fibre that sends impulses through the body.
• These fibres are covered by fatty substance called myelin
(say my-e-lin). Myelin helps the messages go fast through
the neurons.
• Nerve cells work by a mixture of chemical and electrical
action.
The two main parts of the nervous system are
the central nervous system and the peripheral
(say per-if-er-al) nervous system.

4. The Central Nervous System
• The brain and the spinal cord make up the
central nervous system. The brain lies
protected inside the skull and from there
controls all the body functions by sending
and receiving messages through nerves.

5. The Peripheral Nervous System
• The peripheral nervous system carries messages to
and from the central nervous system. It sends
information to the brain and carries out orders from
the brain. (All the nerves)
• Messages travel through the cranial nerves, those
which branch out from the brain and go to many
places in the head such as the ears, eyes and face.
Messages can also travel through the spinal nerves
which branch out from the spinal cord.

6. The basic unit of Our Nervous System
“Nerve Cell Or Neuron”
• Neuron is a specialized cell that carries messages between
the brain and other parts of the body and that is the basic
unit of the nervous system.

7. Type of Neurons
There are 3 types of Neurons:
1. Sensory Neurons
Sensory Neurons Pick up stimuli from the outside environment or from inside
the body. These are found in organs called receptors (skin, eyes, ears, nose,
tongue, and glands.) They transmit the message to Inter neurons.
2. Inter Neurons
Inter neurons Receive messages from the sensory neurons and interpret
them. They then decide where they should be sent.
3. Motor Neurons
Motor Neurons Receive messages from inter neurons and sends them to
organs called effectors (muscles and glands).

8. Receptors
Information about your surrounding is
collected by receptor cells. These are usually
grouped together in sense organs i.e eyes,
nose, tongue, ears and skin. Each type of
receptor is sensitive to a different kind of
change or stimulus.

9. Think…
You are ironing your school uniform. Suddenly, your hand touches the hot
iron. What will you do? Will you keep your hand on the iron and think
whether you should remove it or not- Or- will you take it away
spontaneously?
Obviously you will take it away as soon as it touches the hot iron!
How did this response take place itself? Lets see…

10. This is what happens…
7 STEPS
1. The heat on the object stimulates the receptors in the skin.
2. Impulses (electrical messages) are produced.
3. Sensory neurons pick up the impulses and transmit it to
intermediate or relay neuron.
4. The impulses travel from the intermediate neuron to the
motor neuron.
5. The impulses leave the spinal cord along the motor
neuron to the effector.
6. The effector is the biceps muscle which then contracts.
7. This brings about a sudden withdrawal of the hand.

11. Interval Questions
Q1. What do you understand by the term “Nervous system”.
Q2. What does the basic unit of the nervous system do?
Q3. How many types of Neurons are there? What are their
functions?
Q4. You spot a spider of your leg. Explain how your body takes
an action to remove it instantly.
Q5. What is the difference between the Central and Peripheral
nervous system?

12. Moving Forward
Scientists use proper scientific terms while talking about the
Nervous system. The ones you need to know are…
 The Reflex action
 The Reflex arc
 Spinal reflex
 Cranial reflexes

13. “Reflex action” and “Reflex Arc”
The body’s automatic, involuntary response to a stimulus or
change in it’s environment is called the “Reflex action”. It
protects the body from harm.
So how did that reflex happen after you touched the stove? In
your hand are nerve endings that pick up a stimulus and carry it
to the spinal column and brain. The nerve ending (in this case of
burning your hand) is called a sensory neuron because it takes
the stimulus - heat to the hand – to the spinal column and brain
for interpretation. The brain then interprets the stimulus and
sends a message back to the muscles in the hand by a motor
Neuron (also called an efferent neuron).
The process of the sensory neuron carrying the stimulus to the
spinal column and brain, and then the brain sending a message
to the motor neuron is called a reflex arc.

14. “Spinal reflex” and “Cranial Reflex”
 A reflex action where the reflex arc is through the spinal
cord is called the Spinal reflex.
Whereas,
 A reflex action of the head, such as sneezing or blinking,
which only involves a small section of the brain is called the
Cranial reflex.

15. THAT’S ALL FOR NOW.
THANK YOU.