Form 2 Scientist : Sensory Organs Part 2

1.3 The Sense of Smell

Structure of The Nose

1. The nose is the sensory organs for smell.
2. The upper part of the nasal cavity  of the nose has many sensory cells or receptors to detect smell.
3. These smell receptors are sensitive to all kinds of smells.

Detection of Smells

1. Certain chemicals particles present in the air circulate the smells in the air. For example flowers, food and perfume release chemicals into the air.
2. When these chemicals particles enter the nasal cavity, they dissolves in the mucus lining that coats the smell receptors in the nasal cavity.
3. The dissolved chemicals particles stimulate the smell receptors.
4. The smell receptors then send out nerve impulse to the brain. The brain identities the smell.
5. When a person has a cold, he is unable to detect smells well. This is because too much mucus is being produced. The mucus prevents the chemicals from stimulating the smell receptors. 
6. Structural adaptions of the nose to detect smells:           

• Smell receptors are located at the roof of the nasal cavity. This enables the receptors to have maximum exposure to the air that enter the nasal cavity. 
• The smell receptors are always covered in moist mucus which is secreted by the glands in the nasal cavity.
• Figure 1.6 shows how smell are detectedChemicals in the air.

(a) Chemicals enter the nasal cavity and are dissolved in the mucus lining. Upon dissolving, they stimulate the smell receptors.
(b) Messages are sent to the brain along the nerves.
(c) The brain interprets the messages.
(d) Smells are identified.

Figure 1.7 Structure of the nose

1.4 The Sense of Taste 

1. The tongue is the sensory organs that gives us the sense of taste. It is sensitive to sweet, salty,sour, and bitter taste.
2. The upper surface of the tongue is rough. This is because it is covered with taste buds.
3. Taste receptors can be found in the taste buds. They responds to various chemicals in food. Each type of taste receptors is sensitive to a certain type of taste.
4. The tongue has four types of taste receptors.
5. These are ; sweet receptors, sour receptors, salty receptors and bitter receptors.
6. Each receptor is located in a particular area of the tongue. Thus, each area of the tongue able to detect a certain type of taste.
7. Figure 1.8 shows the location of the various taste receptors.

Sense of Taste and Smell

1. Both the sense of taste and smell are needed to detect the flavors of food accurately.
2. The nasal cavity and the mouth are connected.
3. Chemicals from food that stimulated the taste receptors also move into our nasal passages. These chemicals stimulated the sensory cells in the nose.
4. If a person has a cold or closes his nose, the air passages in the nose are blocked. This reduces the sensitivity of the smell receptors. Food becomes less tasty or different from its original taste. This is because the sense of taste and smell are closely related