1. The World Through Our Senses

2. SENSORY ORGANS

3. Sensory Organs
 They all contribute to us something special. And that
is our senses.
 Changes in the surrounding are called stimuli.
 Each sensory organ has special structures that are
very sensitive to stimuli.
 These structures are called receptors.
 For example, our ears detect stimuli when we hear
something. The way the stimulus travels through our
body is described below.

4. Sensory Organs
Stimulus > Receptors > Nerves > Brain > Nerves
>Effectors

5. Sense of Touch
 The skin is the sensory organ for touch
 It is the largest organ in the body
 The skin can detect changes in temperatures,
pain, touch and pressure.
 The skin has special receptors to detect each of
these stimuli.

6. The Sense of Touch
c Slight pressure is detected by the Touch
Receptor.
u Pain Receptors detect the slightest pain as
they lie very close to the surface of the skin.
o Heat Receptors are sensitive to heat.
The cold is detected by Cold Receptors.
i Pressure Receptors are only sensitive to
heavy pressure as they lie deep within the
skin.

7. The Skin

8. The Nose

9. The Nose
 Mucous in the nasal cavity lines warms and moistens the
air before it enters the lungs.
 The roof of the nasal cavity has many receptors and
sensory cells to detect smell.
 Chemicals released by food, perfume and flowers into the
air are known as smells.

10. The Nose
 The chemicals dissolve in the mucous lining
and stimulate the sensory cells which in
turn, send out nerve impulses to the brain
which interpret them as a smell.

11. The Tongue
 Our tongue is the sensory organ for taste.
It can detect four basic tastes :
• Salty
• Sweet
• Sour
• Bitter

12. The Tongue

13. The Tongue
 The chemicals of the food dissolve in our saliva as
we chew. The dissolved chemicals then stimulate
the taste receptors in our taste buds to produce
nerve impulses, which are then sent to the brain
where they will be identified as tastes.

14. The Tongue
 Our sense of smell improves our sense of taste. As we chew,
some chemicals from the food dissolve in our saliva and
stimulate the taste buds. But there are also some chemicals
that move into our nasal passages. These chemicals stimulate
the sensory cells in our nose.

15. Taste
 The food is tasteless when you have a cold. Why?
 It's because the smell from the food cannot reach the sensory
cells in the nose.
 This is because the passages in your nose are blocked.
 Since you cannot smell it, food seems tasteless.

16. The Ear
 The ear is the sensory organ of sound.
 The sense of hearing is sensitive to the sound
stimuli.
 The human ear can be divided into three main
parts. These are known as the outer ear, the
middle ear and the inner ear.
 Every structure of the ear has their own functions and
are very important.

18. The Ear
 Outer Ear
Structure
Function/Explanation
Pinna
Made of cartilage and skin and shaped like a funnel. It collects and
directs sounds into the ear canal.
Ear canal
A long tube lined with hairs. It directs sounds to the eardrum.

19. The Ear
Middle Ear
Structure
Function/Explanation
Eardrum
A thin membrane that seperates the outer ear from the middle ear. It vibrates
and transmits sound waves to the ossicles.
Ossicles
Made up of three small bones which is the hammer, the anvil and the stirrup.
It intensifies the vibrations of the sound waves by 22 times before
transmitting to the oval window.
Eustachian tube
A narrow tube that joins the middle ear to the throat that balances the air
pressure at both sides of the eardrum.
Oval window
An oval-shaped, thin membrane between the middle ear and the inner ear. It
transmits sound vibrations from the middle ear to the inner ear.

20. The Ear
 Inner Ear
Structure
Function/Explanation
Cochlea
Filled with liquid and contains the ends of nerve cells. The vibration of
the oval window causes this liquid to vibrate. The vibration is detected
by the nerve cells and are then changed into impulses.
Auditory nerve
It carries the impulses to the brain which then interprets the impulses as
sound.
Semicircular canals
For body balance

22. How Do We Hear
1. The pinna collects sound waves and directs them along the
ear canal to the ear drum.
2. When the sound waves hit the eardrum, it vibrates.
3. The ossicles amplify the vibrations about 20 times before
transferring them to the oval window.

24. How DO We Hear?
1. Vibrations of the oval window set up waves which travel
through the fluid in the cochlea.
2. Receptors in the cochlea are stimulated to produce nerve
impulses.
3. The auditory canal nerve carries the impulses to the brain.
4. The brain interprets the impulses as sounds.

25. HOW DO We HEAR
 The pinna collects sound waves and directs them along the
ear canal to the ear drum.
 When the sound waves hit the eardrum, it vibrates
 The ossicles amplify the vibrations about 20 times before
transferring them to the oval window.
 Vibrations of the oval window set up waves which travel
through the fluid in the cochlea
 Receptors in the cochlea are stimulated to produce nerve
impulses.

26. HoW Do We HEAr
 Vibrations of the oval window set up waves which travel
through the fluid in the cochlea
 Receptors in the cochlea are stimulated to produce nerve
impulses
 The auditory nerve carries the impulses to the brain
 The brain interprets the impulses as sounds.

27. Facts about Sight
 Most people blink every 2-10 seconds.
 Each time you blink, you shut your eyes for 0.3 seconds,
which means your eyes are closed at least 30 minutes a
day just from blinking.
 If you only had one eye, everything would appear two-
dimensional. (This does not work just by closing one
eye.)

28. Facts about Sight
 Owls can see a mouse moving over 150 feet away
with light no brighter than a candle.
 The reason cat's and dog's eyes glow at night is
because of silver mirrors in the back of their eyes
called the tapetum. This makes it easier for them to
see at night.
 An ostrich has eyes that are two inches across. Each
eye weighs more than the brain.

30. Sense of Sight
Sclera
Protect and maintains the shape of the eyeball.
Choroid
Absorbs light and prevents internal reflection of
light. Supplies the eye with nutrients and oxygen.
Retina – Detects light and produces nerve impulses. Cones
Detect colours in bright light. Rods detect shades of grey in
Dim light

31. Sense of Sight
Lens
Focuses light onto the retina
Vitreous humour
Helps in reflecting light, maintains the shape of the eyeball.
Suspensory ligaments
Hold the lens in its position

32. Sense of Sight
Ciliary body
Contracts and relaxes to change the thickness of the
lens.
Conjunctiva
Protects the cornea
Aqueous humour
Helps in refracting light, maintains the shape of the
eyeball.

33. Sense of Sight
Cornea
Refracts light onto the retina
Pupil
Controls the amount of light that’s enters the eyes.
Iris
Controls the size of the pupil

34. Sense of Sight
Yellow spot
Detects light or any images that fall on it.
Blind spot
It is the spot where the optic nerve leaves the
eyeball
Optic nerve
Carries nerve impulses from the retina to the brain

35. HOW DO WE SEE

36. HOW DO WE SEE

38. HOW DO WE SEE
1. LIGHT RAYS TRAVEL FROM THE OBJECT
TO THE EYE.
3. AS THE LIGHT PASS THROUGH THE EYE,
THEY ARE REFRACTED (BENT) BY THE
CORNEA, AQUEOUS HUMOUR, LENS
AND THE VITREOUS HUMOUR.

39. HOW DO WE SEE
1. AN UPSIDE DOWN IMAGE (PICTURE) IS
FORMED ON THE RETINA.
3. THE PHOTORECEPTORS ON THE RETINA SEND
NERVE IMPULSES ALONG THE OPTIC NERVE TO
THE BRAIN.
5. THE BRAIN INTERPRETS THE IMPULSES AND
ALLOWS US TO SEE THE OBJECT THE RIGHT
WAY UP.

41. Short- sightedness

42. SHORT SIGHTEDNESS
 A person can see near objects clearly but
cannot focus on distance objects.
 Light from distance object is focused in
front of the retina, so the image become
blur.
 This is because the lens is too thick or
eyeball too long
 Short sightedness can be corrected using
concave lens.

43. Normal focus
Short sightedness (Myopia)
• Distance vision blurry, near usually OK.
Short- Short-sighted
sighted focus correction

44. Long-sightedness

45. LONG SIGHTEDNESS
 A long sighted person can see distant
objects clearly but cannot focus on near
objects.
 Light from a near object converges to a
point behind the retina, so the image is
blur.
 This is either because the lens is too thin or
the eyeball is too short.
 Long sightedness can be corrected using

46. Long-sightedness
(Hyperopia)
• Difficulty seeing clearly and comfortably
up close.
Long-sighted
Long-sighted
correction
focus

47. ASTIGMATISM

48. Astigmatism
• Irregular curvature of the eye (shaped
more like a football than a basketball)
• Light in different planes focuses at
different points
A
B
90
180