Page 40 - Active Science 5 Ebook and Activity

Reflex Actions
Reflex actions are sudden, Interneuron

involuntary actions in response to Sensory
any change in the environment of an neuron
organism. So, reflex actions do not
Motor
require thinking. When messages are neuron
sent to and from spinal cord, reflex Spinal cord

actions take place. These responses Sensory
are very quick. If you touch a hot receptors
object accidentally, you withdraw

your hand almost immediately. The
sight of food makes your mouth
water immediately. Coughing and sneezing are also reflex actions. Stepping back when
something is about to fall on you is also a reflex action.

Nerves

All the parts of the nervous system contain cells called nerves or nerve cells. Nerves
are bundles of fibres that carry messages between the brain or spinal cord and other
parts of the body. There are three types of nerves.

1. Sensory Nerves: Sensory nerves carry signals from the sense organs and muscles

to spinal cord and then to the brain.

2. Motor Nerves: These carry messages from the brain and spinal cord to the muscles
and glands.

3. Automatic Nerves: The involuntary or slightly voluntary activities inside the body
are carried out by automatic nerves.

Activity 3.4

Hold your head with your right hand and rotate it. Make a circular motion on your stomach with
the left hand. Find out why the combined motion is difficult.

S ense Organs

Organs that carry messages about our environment to our nervous system are called
sense organs. Eyes, ears, nose, tongue and skin are our five sense organs.

Activity 3.5
Open a jar of pickle. Do you feel saliva coming out and filling your mouth? What kind of action
is this?

40 Active Science-5