Learn Science [Form 2]

Chapter 1 - Lesson 2

CHAPTER 1: THE WORLD THROUGH OUR SENSES

1.2 The Sense of Touch

Structure of the human skin

The skin helps regulate body temperature. It is also a sensory organ that detects touch.

The skin has five different types of receptors.
These are:
◆ pain receptors
◆ touch receptors

◆ heat receptors
◆ cold receptors
◆

pressure receptors

The receptor in the skin are sensitive to the stimuli of pain, touch, heat, cold and pressure.

Figure 1.4 shows a cross section of the human skin. It shows the positions of the nerve endings of the five different receptors.

The pain receptors are stimulated in the epidermis of the skin. The touch, heat and cold receptors are situated in the dermis. The pressure receptors are found in the fatty layer.

◆ Pain receptor
~ Lie very close to the skin surface to detect even a slight pain.
◆ Heat receptor
~ Sensitive to heat and is able to detect the temperature when it is hotter than usual.
◆ Touch receptor
~ Detect any light touches and identify the texture of an object.
◆ Pressure receptor
~ Lie deep within the skin and can detect any forceful pressure against the skin.
◆ Cold receptor
~ Sensitive to cold and is able to detect the temperature when it is colder than usual.

Sensitivity of the skin

When the receptors are stimulated, they send out nerve impulses along the nerves to the brain. The brain interprets these impulses as the sensation of touch. It will then send suitable messages to the effectors as to how to react.

The skin on different parts of the body has different degrees of sensitivity. The fingertips, the lips, the tongue, the nose and the neck are more sensitive to touch. The legs, the elbows, the soles of the feet and the the back of the body are less sensitive.

SCIENCE ALERT!
• Our skin is 2 mm thick. It covers the whole body. It consists of two main layers, the outer epidermis and the inner dermis.
• The epidermis is made up of dead cells, and is waterproof. It is also a protective layer which prevents the entry of bacteria into the body tissues.
• The receptors in the dermis and epidermis enable the skin to detect various external stimuli.

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ACTIVITY 1.1 : Investigating the sensitivity of the skin at different parts of the body

Procedure:
1. Stick one toothpick into a piece of cork as shown in Figure 1.5 (a). Stick two toothpicks into another piece of cork as shown in Figure 1.5 (b).
2. Ask a friend to close his eyes. First prick the palm of his hand using the cork with one toothpick (a). Then prick his palm again, this time with two toothpicks (b). Record the results (whether the stimulus can be felt or not) in Table 1.2.
3. Repeat step 2 to test the skin in different parts of the body such as the fingertip, arm, neck and knee.

Results
• A tick (✔) indicates that skin can feel the stimulus.
• A cross (❌) indicates that the skin cannot feel the stimulus.

Conclusion
1. The sensitive of the skin on different parts of the body is different.
2. The skin on the neck and the fingertips is more sensitive than the skin on the palms, knees and arms.

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The sensitivity of the skin depends on
◆ the distance between the receptors
◆ the thickness of the epidermis

The skin on parts of the body which has thinner epidermis and more receptors is more sensitive to touch.
◆ Blind people use their sense of touch to identify objects in their environment.
◆ They use their fingertips to 'read' books in Braille.

Doctors usually give injections to their patients on their forearms or buttocks because these areas are less sensitive to touch and pain.

Science Blog
Louis Braille, who was blind, invented the Braille system. This system consists of raised dots and dashes that represent letters of the alphabet and numbers.

Here is an example of a Braille:

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So how is it so far? Any problems/questions/suggestions? Feel free to comment it all out! ☺😊😀😁

~ CutieKittyMe