Chapter 1: The World through Our Senses

Chapter 1: The World through Our Senses

Flash Review

1.1| Sensory Organ

        1)    Five Sensory organs are skins,nose,tongue and ear

·         Skin detects: heat, cold, touch, pain and pressure

·         Nose detects: smells

·         Tongue  detects: taste, sweet, sour and bitter

·         Ear detects: sound and sense of balance

·         Eye detects: sight, depend on light

        2) Sensory organ has receptor.

        3)   Stimulus - Receptor - Nerves - Brain - Nerves - Effectors - Response

1.2| Sense of touch

    1) Contain two main layers:

Epidermis- Outer layer. Proof and tough-Protective layer

Dermis-Contain blood vessel, sweet gland and receptor.

   2) Five type of receptor:

       Touch receptor- sensitive to slight pressure, tell something is rough or smooth.

Pain receptor- detect pain,close to skin surface-slightest pain can detect

Heat receptor-these are sensitive to heat

Cold receptor-sensitive to cold

Pressure receptor-sensitive to pressure

1.3| Sense of smell

1)    Nose is sensory organ for smell

2)   Two holes is nostrils

3)   Inside nose is hollow space know as nasal cavity

4)   Nasal cavity covered by layer known as mucous lining

5)   Receptor cell found in roof of nasal cavity

1.4| Sense of taste

1)    Tongue is sensory organ for taste

2)   Four basic taste is issweet,salty,sour and bitter

3)   Food chewed in the mouth dissolve in saliva will stimulate the receptors.

4)   Receptors of taste are found in the taste buds. Taste buds can be grouped into four  types for sweet, salty, sour and bitter .

5)   Taste buds for the four basic tastes are found in different part of tongue.

6)   Central region of the tongue is least sensitive to tatse.

7)   Smell and appearance of food helps in the identification of the taste.

1.5| Sense of hearing

1)   Sensory organ for hearing is ear.

2)   Human ear can be divided into three parts : outer ear, middle ear and inner ear.

3) Outer ear : consists of the pinna (ear lobe) and ear canal

Middle ear : consists of the eardrum, ossicles, oval window and Eustachian tube.

Inner ear : consists of the cochlea, auditory nerve endings and semicircular canals.

4)   The different parts of the ear have various function.

5)   Sound waves that enter the pinna travel up the ear canal and cause the eardrum to vibrate. The eardrum  passes the vibrations to the ossicles, where they will be amplified and transmitted to the oval window. The oval window will in turn transfer the vibrations to the cochlea. The receptors in the cochlea will form impulses and the auditory nerves will pass the impulses to the brain where the sound is interpreted.

1.6| Sense of sight

1)    Eye is the sensory organ for sight.

2)   Eye consists of a ball which is slightly oblong in front.

3)   Eyelid is a layer of skin that protects the front part of the eye.

4)   There are three layers in the wall of the eye ball.

·         Sclera –protects and maintains the shape of the eyeball.

·      Choroid – middle layer which is dark that contains a large amount of blood vessels. It absorbs and prevents light from reflecting into the eyeball. It also supplies the eye with nutrients and oxygen.

·         Retina – innermost layer and contains the light receptors (cones and rods). It detect light and converts it to nerve impulses. The cones detect colours in bright light, the rods detect shades of grey in dim light.