8/3/2019 Chapter 1 f2

1/19

CHAPTER 1CHAPTER 1

THE WORLD THROUGH OURS

SENSES

8/3/2019 Chapter 1 f2

2/19

SENSORY ORGANS & THEIRSENSORY ORGANS & THEIR

FUNCTIONSFUNCTIONS

Sensory organs are organs that allow organisms to

detect changes in their surroundings

Any change that is picked up by a sensory organ is

called stimulusThe five sense, sensory organs and stimuli are:

SENSORY ORGAN STIMULI SENSE

Eye Light Sight

Ear Sound Hearing

Nose Chemical vapour smell

8/3/2019 Chapter 1 f2

3/19

Skin Touch Touch

Tongue Chemicalsubstances

Taste

PATHWAY FROM STIMULUS TO REPONSE

When there is any change in environment that is

dangerous, an organism can detect the danger and react

to save itself

The reaction of an organism to a stimulus is known as

a response

8/3/2019 Chapter 1 f2

4/19

The pathway from stimulus to response can be

summarised as:a) Stimulus is detected by the receptors in sensory

organ

b) The sensory organ sends a message through the

nerves to the brain. This message is in the formof electrical signals called impulses

c) When the brain receives the messages, it

interpret the message and decide on the proper

response to stimulus through the effectors

8/3/2019 Chapter 1 f2

5/19

8/3/2019 Chapter 1 f2

6/19

SENSE OF TOUCHSENSE OF TOUCH

The skin is the sensory of touchThe skin can detect pain, pressure, touch and changes

in temperature (hot or cold)

It has two layers, the dermis and epidermis

a) Dermis (inner layer)

Consists of a layer of thick connective tissues

Rich with blood capillaries

Has receptors to detect pain, touch, pressure, coldand hot

8/3/2019 Chapter 1 f2

7/19

Other structures: sweat glands, fatty layer and

muscle fibres

b) Epidermis (outer layer)

It has a thin layer

Composed of a layer of tough cells

8/3/2019 Chapter 1 f2

8/19

8/3/2019 Chapter 1 f2

9/19

TYPE OF RECEPTOR FUNCTION

Pain receptor Sensitive to pain

Heat receptor Sensitive to hot objects

Pressure receptor Sensitive to heavy

pressureCold receptor Sensitive to cold objects

Touch receptor Sensitive to slight

pressure

8/3/2019 Chapter 1 f2

10/19

SENSITIVITY OF SKINSENSITIVITY OF SKIN

The skin has different degrees of sensitivity at

different parts of the body

The degree of sensitivity depends on:

a) Thickness of the epidermis

Thinner part of the skin is more sensitive towards

stimulus

b) Number of receptors

The part of the skin that has more receptors ismore sensitive towards stimulus

8/3/2019 Chapter 1 f2

11/19

APPLICATIONS OF THE SENSITIVITYAPPLICATIONS OF THE SENSITIVITY

OF SKINOF SKIN

A patient is normally given an injection on the forearm

or hip which have thicker epidermis. So the patient will

feel less pain when injected

The blind people use their fingertips to identify letters

and read Braille. This is because the fingertips have thin

epidermis and have many receptors that are sensitive to

touch

8/3/2019 Chapter 1 f2

12/19

SENSE OF SMELLSENSE OF SMELL

Nasal cavity

Nostril

Olfactory bulb

Smell

receptor

Smell receptors or sensory cells are found on

the top of the nasal cavity

8/3/2019 Chapter 1 f2

13/19

PATHWAY OF SMELL DETECTION

Chemical substances enter thenasal cavity

Chemical substances dissolve inmucus and stimulate smell

receptors

Impulses sent to the brainthrough the nerves

8/3/2019 Chapter 1 f2

14/19

Brain interprets the impulses

Smell identified

8/3/2019 Chapter 1 f2

15/19

The sensitivity of the nose is affected by:

a) The strength of the smell- A stronger smell will be detected by the nose

easily compared to a weaker smell

b) The presence of mucus in the nose- A lot of mucus will reduce the sensitivity of

the nose

- This is because very little of the chemical

vapour stimulate the smell receptors- Example: when a person has a flu

8/3/2019 Chapter 1 f2

16/19

SENSE OF TASTESENSE OF TASTE

The tongue is the sensory organ for taste

It can detect sweet, salty, sour and bitter tastes

The surface of the tongue has many taste buds

Each taste bud has many taste receptors fordetecting the flavour of a chemical substances

8/3/2019 Chapter 1 f2

17/19

Taste bud

8/3/2019 Chapter 1 f2

18/19

PATHWAY OF TASTE DETECTION

Chemicals in the food dissolve in thesaliva and stimulate the taste buds

Impulses sent to brain through thenerves

Brain interprets the taste and thentaste is identified

8/3/2019 Chapter 1 f2

19/19

The sense of taste is influenced by the

sense of smell because as we chew our food,chemicals from the food also move into the

nasal cavity and stimulate the smell receptors