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Damia
Science Form 2 : The world
through Our Senses
Chapter 1
Sensory organs and their function :
The flow of impulses through the nerves
1. Stimuli travel from the sensory organs to brain through the spinal cord.
2. Responce is produced after the brain has interpreted the impulses.
Stimulus --> Sensory organ (receptor) --> Nerve --> Brain --> Nerve -->
Muscles (effector) --> Responce
Skin
1. The skin is the sensory organ of touch.
2.The skin respond to heat, cold, pressure, touch, pain stimuli.
Nose
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 mucous that is important to dissolve chemicals
4. Structure of human nose.
Tongue
1. The tongue is sensory organ related to the sense of taste.
2. They are four types of taste receptors on the tongue which are sensitive to sweet, bitter, sour and salty taste respactively.
Ear
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, eardrum
b) Middle ear; ossicles (hammer, anvil & stirrup), oval window and Eustachian tube.
c) Inner ear; cochlea, auditory nerve and semicircular canals.
Eye
1. The eye is the sensory organ of sight.
2. The image that is formed on the retina is real, inverted and smaller than the actual object.
Reflextion 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 reflectors
3. 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)
Eye Defects
A person with normal vision sees distant and close objects clearly. To maintain a clear image of the object on the retina, the thickness of one's eye lenses changes, in a process called accommodation.
However, for some people, clear vision is not achieved because of defects. Common vision defects are:
A person with normal vision sees distant and close objects clearly. To maintain a clear image of the object on the retina, the thickness of one's eye lenses changes, in a process called accommodation.
However, for some people, clear vision is not achieved because of defects. Common vision defects are:
- Short-sightedness (myopia)
- Long-sightedness (hypermetropia or hyperopia)
- Astigmatism
- Colour-blindness
- Lack of accommodation (presbyopia)
Limitation of sight
1. Optical illusion are caused by disturbances to the nerve impulses going to the brain.
2. The disturbances may caused by the object or condition around the object.
3. The brain cannot accurately interpret the information sent by the receptors in eye.
4. That’s why you will incorrectly interpret what you actually see.
Types of vision : Stereoscopic and monocular
Stereoscopic vision
- Stereoscopic vision is a vision involving both eyes
- This vision enables us to estimate distance accurately
- The stereoscopic field of vision in narrow
- Predators usually have stereoscopic vision
- Monocular vision is a vision involving only one eye. This makes it difficult to estimate distances accurately
- The monocular vision field of vision is wide
- Prey usually have monocular vision
Sound
1. Optical illusion are caused by disturbances to the nerve impulses going to the brain.
2. The disturbances may caused by the object or condition around the object.
3. The brain cannot accurately interpret the information sent by the receptors in eye.
4. That’s why you will incorrectly interpret what you actually see.
Stimulus and response in plant
The response by plants to stimuli is called tropism.