Learn Science [Form 2]

Chapter 1 - Lesson 1

CHAPTER 1: THE WORLD THROUGH OUR SENSES

1.1 Sensory Organs and Their Functions

Sensory Organs enable an organism to detect changes that occur in its environment.

A change in the environment that causes the body to react or respond to it is called a stimulus (plural: stimuli). Examples of stimuli are chemical substances and changes in temperature and light intensity.

Human beings have five sensory organs. They are the skin, nose, tongue, ears and eyes.

Human beings have five different types of senses. They are touch, smell, taste, hearing and sight.

◆ eye
~ sensitive to light.
◆ skin
~ sensitive to touch
◆ nose
~ sensitive to chemicals in the air (smell)
◆ ear
~ sensitive to sound
◆ tongue
~ sensitive to chemicals in food and liquids (taste)

Table 1.1 shows the relation between the sensory organs, senses and the stimuli.

Sensory organs have specialised receptors and means of converting stimuli into nerve impulses that travel to the brain.

Table 1.1

The pathway from stimulus to response

The nervous system of humans consists of the brain, the spinal cord and nerves.

A receptor is a special sensitive tissue or organ which detects stimuli.

The nerves carry information from the receptor to the spinal cord and the brain, and from the brain to the spinal cord and to the muscles or glands.

The nerves carry information
• from the receptors to the spinal cord and the brain
• from the brain and the spinal cord to the muscles or glands.

The brain and the spinal cord work together to
• process the stimuli detected by the receptors
• inform the muscles or glands to respond to the stimuli

Figure 1.1 Functions of the nervous system in humans

Figure 1.2 How we respond to a stimulus

Example:

1. A woman's handbag is snatched by a thief. (Stimulus)

2. The sound of the woman shouting is detected by your ears. (Receptors in a sensory organ)

3. Nerve impulses are sent along the nerves to your brain.

4. The brain interprets the message and decides what to do.

5. Nerve impulses are sent to other parts of your body. You quickly go over to help the woman. (Effectors)

Figure 1.3 Reacting to a stimulus

SCIENCE ALERT!
The nerves carry information
• from the receptors to the spinal cord and the brain, and
• from the brain and spinal cord to the muscles and glands

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Hey guys! This is all from my revision book so the credits are all to the publisher of the book. Hope it helps and if you have some questions or suggestion, feel free to comment out your thoughts. ♡

~ CutieKittyMe