Science Chapter 1 F2

Form 2
Chapter 1 The world through our senses yschow@smkbpj(a) 1

1.1 Sensory Organs and Their Functions • A sensory organ is an organ that enables the body to respond to stimuli. • A stimulus is a change in the surroundings that can be detected by the sensory organs. • The five sensory organs are eye, ear, nose, tongue and skin.

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• The ability of the sensory organs to detect stimuli is called senses.
Sensory organ Eye Ear Nose Tongue Skin Sense Sight Hearing Smell Taste Touch Stimuli Light Sound Chemical in air Chemical in foods Pressure, heat, cold, touch

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Pathway from stimulus to response.
Stimulus Response

Receptor in sensory organ

Effectors (muscle)

Sensory nerves

Brain yschow@smkbpj(a) Motor nerves
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1.2 Sense of Touch

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1.2 Sense of Touch
• The skin is a sensory organ which responds to the sense of touch. • There are five types of receptors in the skin.
Receptor Cold receptors Heat receptors Pain receptors Pressure receptors Touch receptors yschow@smkbpj(a) Stimuli (sensitive to) Cold substances Heat Pain Large pressure Small pressure (touch )
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• The sensitivity of the skin depends on (a) the thickness of epidermis (b) the number of receptors present • Fingertip and neck are more sensitive . • Elbow , knee and back side are not so sensitive to touch.

Braille letters are specifically designed symbols for stimulating the fingertips, which allows blind people to read yschow@smkbpj(a) 7

1.3 Sense of Smell

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1.3 Sense of Smell
• Mucus is produced to help keep the receptors moist. • When you inhale, the chemicals from the food enter the nasal cavity and dissolve in the mucus. • The smell receptors are stimulated. • The impulses from the smell receptors are sent to the brain by the olfactory nerves for interpretation. yschow@smkbpj(a) 9

• When we catch a cold, too much mucus is produced and this makes