Chapter 1 The World Through Our Senses
1.1 Sensory Organs
1. Humans have five sensory organs.
2. They are eye, ear, nose, tongue and skin.
3. The sensory organs enable an organism to detect changes in the surrounding.
4. Sense is the ability of the sensory organ to detect a stimulus.
5. Our five senses are the sense of sight, hearing, touch, taste and smell.
6. A stimulus is a change in the environment that produces a reaction in a living organism.
7. Examples of stimulus are light, sound, heat, taste, smell.
Relation between sensory organ, senses and stimulus
| Sensory organs
| Senses
| Stimulus
|
| Eye | Sight | Light |
| Ear | Hearing | Sound |
| Nose | Smell | Smells (Chemicals in the air) |
| Tongue | Taste | Sweet, sour, bitter, salty (Chemicals in food) |
| Skin | Touch | Pain, pressure, heat, cold, touch |
Stimulus to response
1. Response is the way an organism reacts to a stimulus.
2. The pathway from stimulus to response is shown as below:
3. Stimulus Sensory organ Nerves Brain Nerves Effectors Response
4. A stimulus will stimulate the sensory organ to produce nerve impulses.
5. These impulses are sent to the brain through the nerves.
6. The brain receives the messages and interprets them.
7. The brain then decides what to do and sends out nerve impulses through the nerve to effectors.
8. Effectors are parts of the body that carry out responses. For example, muscles or organs.
9. A response is a reaction produced in answer to a stimulus.
10. The brain controls all the actions and responses of the body.
