The world through our senses

Chapter 1

1.1 Sensory organs and their functions

• Sensory organs = detect changes that happen in its environment.eg/ eye

• Stimulus (s) / stimuli (p) = change in the environment that causes the body to respond.eg/ light

• Senses = ability of a sensory organ to detect stimuli.eg/ sight

Sense

Touch

Smell

Taste

Hearing

Sight

Sensory organs

Skin

Nose

Tongue

Ears

Eyes

Types of

stimuli Pressure, pain, heat, cold

Chemicals in the air

Chemicals in food

Sound

Light

The pathway from stimulus to response

Stimulus Sensory organs

Nerves impulse

Brain Nerves impulseRespons

e

1.2 The sense of touch

Types of receptors in the skin

Pain Touch

Heat Cold

Pressure

Cross section of human skin.

Doctors usually give injections on the patients

forearms. Why???

Think!!!

The skin on the area is less sensitive to touch and pain

compared to the skin on other parts of the body

Answer

Sensitivity of the skin depends on:

The distance between

receptors.

The thickness

of epidermis.

1.3 The sense of smell

Detection of smells

Chemicals in the air

Chemicals dissolve in mucous lining

Stimulate smell receptors

Messages

Brain interprets the messages

Smell identified

Structural adaptations of the nose to detect smell

1) Smell receptors located at the roof of nasal cavity → maximum exposure to the air that enter nasal cavity.

2) Smell receptors are covered by mucus → keep nasal cavity moist.

When a person had a cold, they cannot

detect smell very well. Why?

THINK!!!!

This is because too much mucus produce in the nasal

cavity and it prevent chemicals in the air to stimulates the smell

receptors.

Answer

1.4 The sense of taste

Taste receptors

Sour

Sweet

Salty

Bitter

Salty Salty

Location of various taste receptors.

Detection of tastes

Sense of taste and smell

• The nasal cavity and mouth are connected.

• The sense of taste is influenced by the sense of smell.

• When nose is blocked, food become tasteless or different from its original taste.

Exercise 1. Name 5 senses in our body.2. State the pathway from stimulus to

response. Give example.3. Name 5 receptors found in the skin. 4. What are the 2 factors that

influence the sensitivity of skin?5. Name receptors found in:

a) epidermis layerb) dermis layerc) adipose/fatty layer

6. The smell receptor is always dampened by mucus liquid. What is the mucus function?

7. The smell receptors in the nose are sensitive to the ……

8. What tastes can be detected by the taste buds in the tongue?

9. Why is it dry tongue cannot taste food well?

10. Why is it a person who has cold seems to find his food less tasty?

touch

Sensory

organs

Stimuli

Senses

Conclusion

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