Sense organs. Senses are the means by which many-celled animals tell what is happening in their environment

Senses are the means by which many-celled animals tell what is happening in their environment. Many people think that human being have only five senses – sight, hearing, smell, taste and touch. But scientists have found that human beings also have other kinds of senses that give information about the body needs. These senses include hunger, fatigue, pain and thirst. Scientists divide the senses into two groups. External senses receive information about the outside environment. These senses include hearing, vision, smell, taste and touch. They also include the sense of heat which is felt by special receptor cells in the skin. Internal senses detect changes that take place in the tissues and organs inside the body and send messages about these changes to the brain. The internal senses respond to chemical and physical stimuli in the circulatory, digestive, excretory, respiratory and central nervous systems. They control such feelings as hunger, fatigue, pain and thirst. The internal senses also respond to the position and movement of the joints, to tension in the muscles, and to the position of the head. By responding to these chemical and physical changes internal senses help maintain a proper environment inside the body.

Answer the questions:

1. What is the difference between these groups of senses?

2. What senses do these groups include?