CHAPTER 1

The World Through Our Senses

Sense of Touch

1. Skin is the sensory organ that can detect touch, pain, pressure, heat and cold.

2. Consist of 3 main layer:a. Epidermis- outer layerb. Dermis- inner layerc. Fatty layer- insulator

Structure of human skin

4. Function of different receptors:a. Pain receptors - detect painb. Touch receptors - detect light touchesc. Heat receptors - detect heatd. Cold receptors - detect colde. Pressure receptors- detect pressure

Sense of Smell

1. Nose is the sensory organ for smell that can detect chemicals in the air

2. Smell receptors located at the top of nasal cavity

3. The nasal cavity lined with mucus that is important to dissolve chemicals

Structure of nose

4. Detection of smellsChemicals in the air enter the nasal cavity, dissolve in the

mucus to stimulate smell receptors

Smell receptors produce impulse and send the massage to the brain

Brain interprets the massage

Smell identified

Sense of Taste

1. The tongue is sensory organ related to the sense of taste

2. There are 4 basic taste:i. Sweetii. Saltyiii. Souriv. bitter

3. The surface of tongue covered with taste buds

4. Saliva dissolve chemicals to be detect by taste receptors

5. Sense of taste is helped by sense of smell

Sense of Hearing

1. Ears are the sensory organs of hearing that can detect sound.

2. Human ears has 3 main parts:a. Outer ear; pinna, ear canal, eardrumb. Middle ear; ossicles (hammer, anvil & stirrup), oval

window and Eustachian tube.c. Inner ear; cochlea, auditory nerve and semicircular

canals.

Structure of human ear and their function

Sense of Sight

1. Sensory organs for sight are the eyes, which sensitive to light

2. The wall of the eyeball is made up of 3 layers:a. Sclera – tough, outer layerb. Choroid – black, middle layerc. Retina – sensitive to light, innermost layer

Front View of Human Eye

Cross-section of the human eye

Understanding Light and Sight

1.7.1 Reflection and refraction of light

1. Take place when light rays fall on the surface of an opaque object and bounce off it.2. Plane mirrors and shiny metals are good light reflectors3. Flat and smooth surface reflects light in regular patterns (regular reflection)

4. Irregular surfaces like paper and cloth will reflects scattered in different directions of reflected light(diffused reflection)

5. The law of reflection states: i) angle of incidence = angle of reflection i = r ii) Incident ray, reflected ray and normal are

at the same plane

6. Applications of the reflection of light a) Periscopes – used in submarines b) Kaleidoscope c) Mirrors

7. Refraction of light occurs when light travels through different media at certain angle8. Refraction occur when the speed of light changes9. The speed of light decreases when light enters a denser medium10.The speed of light increases when light enters a less dense medium

A) From less dense to a denser medium i) The light refracted towards the normal ii) Angle of incident is bigger than the angle

of refraction

B) From denser to a less dense medium i) The light refracted away from normalii) Angle of incident is smaller than the angle

of refraction

11. Phenomena of the refraction of light:

1.7.2 Vision defects and ways to correct them1. Normal vision can see close and near objects clearly2. The thickness of the lens is changed when looking

at near or distant object3. Focusing object:

4. Short-sightedness (myopia)a. See near objects clearly but distant objects are

blurredb. The lens is too thickc. The eyeball is too long

5. Correcting short-sightedness

6. Long-sightedness (hypermetropia) a) See distant objects clearly b) Can’t focus on near object c) The eye lens too thin d) Eyeball too short

7. Correcting long-sightedness

8. Comparison between short-sightedness and long-sightedness

9. Astigmatism• Caused by the irregular surface of the cornea or lens not

evenly curve• Image cannot be focused at same time• Image formed distorted and not clear• Can be corrected by wearing cylindrical lenses

1.7.3 Limitation of Sight

A. Blind spot - the point where the optic nerve enters the retina; not sensitive to light

B. Optical illusions- Caused by disturbances to the impulses going to

the brain- The brain cannot interpret accurately the

information sent bye eye.

C. Stereoscopic and monocular vision

i) Stereoscopic vision Both eyes in front of the

head Overlapping Smaller field of vision Give 3 dimensional (3D),

can estimate distance accurately

Most predators and human

ii) Monocular visionOne eye at each side of

the head Do not overlapWider field of visionDoes not give 3D view,

cannot estimate distant accurately.

Most prey

1.7.4 Device to overcome limitation

Magnifying glass

Binocular

Microscope

1.8 Understanding sound and hearing

1. Properties of sound Sound is a form of energy Produced by vibrations When an object vibrates, kinetic energy is changed to sound

energy Medium (solid, liquid, gas) is needed for sound to travel Sound cannot travel through vacuum Sound can be reflected by hard and smooth surfaces. (metal,

glass, brick wall) Reflection of sound is called echoes Soft and porous surface can absorb sound. (carpets,

curtains, cotton, sponge

2. Hearing defectsi. temporary loss - the earwax in the auditory

canal block sound waves

ii. total hearing loss - ossicles fused together, damaged cochlea by local infections or by exposure to loud sound

3. Ways to rectifying hearing defects

uses syringes and warm water to remove wax

punctured eardrum can be repair by surgery

implanted electronic gadget

4. Limitation of hearing

5. Ways to overcome hearing limitationsEarphone

Stethoscope

Loud speaker

6. Stereophonic hearingAbility to hear using both earsEnables to detect the direction of the sound

accuratelyImportant for the survival of animals especially for

prey