Lets try your Understanding

Exercises

Figure 1 show the structure of the human eye.

Figure 1

a)      Label the structure of the eye with the following words: 
·         retina 
·         lens 
·         blind spot
·         yellow spot
·         pupil 
·         iris                     

b)      State the function of 
·         cornea 
·         ciliary muscles 
·         aqueous humour 
·         sclera

c)      What is a blind spot?

Figure 2 shows the cross-section of the human ear.

Figure 2

a)      Label the structure of the ear: 
1.      ______________________ 
2.      ______________________ 
3.      ______________________ 
4.      ______________________ 
5.      ______________________ 
6.      ______________________

b)      State the function of the

·         semicircular canals

·         Eustachian tube

·         cochlea

Figure 3 shows the structure of the human skin.

Figure 3

a)      Label the structure of the ear: 
1.      ______________________ 
2.      ______________________ 
3.      ______________________ 
4.      ______________________ 
5.      ______________________ 
6.      ______________________ 
7.      ______________________ 
8.      ______________________ 
9.      ______________________ 
10.  ______________________ 
11.  ______________________

*Remember to try first before you refer to the notes given.
  Check your answer from the notes given in front.

Sense of Sight

The structure of eyes   

Structure of eyes	Function
Suspensory ligament	- holds the lens in its position
Ciliary muscles (ciliary body)	- change the thickness of the lens
Iris	- controls the amount of light entering the eye
Pupil	- the central opening formed by the iris - allows light rays to enter the eye
Cornea	- helps to focus light rays onto the retina
Aqueous humour	- a transparent liquid which fills the space between the     lens and the cornea - maintains the shape of the eye and helps to refract     light rays
Lens	- bends and focuses light rays onto the retina
Blind spot	- the region of the retina that lacks receptors - the part of the retina that is not sensitive to light
Choroid	- contains a lot of blood vessels and black pigments  - blood vessels provide nutrients and oxygen to the eye  - the black pigments absorb light and prevent reflection     of light in the eye
Optic nerve	- connects the retina to the brain - sends impulses from the retina to the brain for     processing
Fovea (yellow spot)	- the part of retina that is most sensitive towards light
Retina	- formed by millions of light-sensitive cells  - responds to light rays - enables image formation  - sends impulses to the brain using the optic nerve
Sclera	- protects and maintains the shape of the eye
Vitreous humour	- a transparent jelly-like substance which fills the     space  between the lens and the retina - maintains the shape of the eye and helps to refract     light rays

Reason of blinking:

Video with task: How to take care our eyes 

After watching the video, discuss with your friend and list out 5 ways on how to take care our eyes.

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How we see things from PandaSnake

Sense of Hearing

The structure of ear

Parts of Ear	Function
Pinna	Collects sound waves
Ear canal	Directs sound waves to the eardrum
Ear drum	Vibrates when hit by sound waves
Ossicles	Make the vibrations of sound stronger
Cochlea	Contains fluid and receptors, changes sound vibration into impulses.
Auditory nerve	Carries impulses to brain
Balance canal (semicircular canal)	Contain fluid, helps us keep our balance
Eustachian tube	Keep air pressure equal on both sides of eardrum.

Watch this video to understand how we hear: Hearing Process

Summary of Hearing Process (click the picture to enlarge)

Sense of Taste

• The tongue is sensory organ that can detect sweet, bitter, sour and salty tastes.
• Other kinds of taste are the combinations of these four major tastes.
• Different areas of the tongue are sensitive to different types of tastes.
• Picture below show the parts of the tongue that respond to different types of tastes.

 

Without sense of smell, it will influence our appetite. We cannot fully enjoy the flavours of food and drinks.

Example: 

Sense of Smell

• Our nose is the sensory organ that enables us to smell.

Structure of Nose

• The sensory cells which respond to the stimulus of smell are located in the roof of the nasal cavity.
• These receptors are covered with the mucus, which dissolves airborne chemicals.
• When chemicals dissolve in the mucus, the sensory cells will send a message (nerve impulses) to the brain for identifying the kind of smell detected. 

Reason of Running Nose

Sense of Touch

• Our skin is sensory organ that can detect stimuli such as pain, pressure, touch, heat and cold.

Structure of the Human Skin

• Our skin consists of two main layers: Epidermis (outer layer) and Dermis (inner layer)
• There are 5 types of receptors in our skin. Can you identify them in the figure above?
• Each type of receptor is sensitive to a different stimulus.
• The skin at different body parts is not equally sensitive to stimuli. The skin of some body parts is more sensitive than that of other body part.
• Such difference is due to the different thickness of the epidermis and different numbers of receptors in the skin.

Watch the following video: Skin sensitivity

After watching the video, can you identify which parts of our body part have great sensitivity and less sensitivity? 

How sensitive are you? Try out this simple experiment.

What did you find?

On some parts of the body, such as the index finger is more sensitive. This means that the volunteer has more sensory receptors in that part of their body. Sensory receptors are specialised cells. They detect changes in the environment, called stimuli, and turn them into electrical impulses. In this case, the sensory receptors are detecting pressure. Sensory neurones - nerve cells - carry these electrical impulses to the spinal cord and brain.To be really sensitive, each sensory receptor must connect to a different nerve cell.

The Sensory Organs and their Function

• The skin, nose, tongue, ears and eyes are our sensory organs.
• They enable us to use our senses of touch, smell, taste, hearing and sight to detect changes in our environment.
• Our senses are our abilities to detect changes in our environment.
• The changes in our environments are called stimuli (singular: stimulus).
• Table below shows the connection between the five senses, the sensory organs and the stimuli.

Sensory Organs	Senses	Stimuli
Skin	Touch	Pain, Cold, cheat, Pressure
Nose	Smell	Chemicals
Tongue	Taste	Chemicals
Ear	Hearing	Sound
Eye	Sight	Light

• When a stimulus is detected by our sensory organs, a message is sent to the brain trough our nerves.
• The brain is the centre of control of our response.
• The brain interprets the message and tells our body how to respond to the stimulus.

Pathway from stimulus to response can be simplified as follow:

• The nerves that carry messages from the sensory organs to the brain are called sensory nerves.
•  The nerves that carry messages from the brain to the muscles are called motor nerves.
• Example: