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Template : PT5; SENSE OF SIGHT
Monday, October 6, 2014 ? 0 Atashinchi ?
1. The sense of sight is the sense that can detect light stimulus.2. Structure of the human eye:
i. the sclera (outermost)
ii. the choroids (middle) and
iii. the retina (innermost)
3. Fucntion of eye;
MECHANISM OF LIGHT
1. The lens in the human eye is a transparent convex lens.
2. An inverted image is focused on the retina.
3. Light rays are refracted by the eye lens. The eye lens focuses the image
onto the retina by changing the thickness of the eye lens. The thickness of
the lens is changed by the ciliary muscles.
i. Focusing near objects
To focus near objects onto the retina, the ciliary muscles
contract. The eye lens become thicker.
ii. Focusing distant object.
To focus distant objects onto the retina, the ciliary muscles relax.
The eye lens becomes thinner.
4. light travels at a speed of ;
i. 300,000,000 meter/second (m/s) in the air.
ii. 225,000,000 m/s in water
iii. 200,000,000 m/s in glass
5.. Light travels in a straight lines.
REFRACTION OF LIGHT
1. Light can be reflected. (that means can change direction)
2. When the reflected light rays enter our eyes, we can see the object.
3. The image in a plane mirror is,
i. virtual (cannot be formed on a screen)
ii. upright
iii. laterally inverted
iv. the same size as the object
v. the same distance behind the mirror as the object is in mirror.
REFRACTION OF LIGHT
1. Refraction of light is the bending of light. This happens when light
travels from one transparent medium to another which is of a different
density.
2. The speed of light decrease when light enters a denser medium.
3. Light travels through media like air, water and glass.
VARIOUS DEFECT OF VISION
1.Two common vision defects are long-sightedness and short-sightedness.
2.Astigmatism is another vision defect.
i. Its caused by the cornea and the eye lens that are not evenly
curved.
ii. As a result, the image formed on the retina is distorted and not
clear (hazy/blurred).
iii. This defect can be overcome by wearing glasses with cylindrical
lenses or contact lens or by surgery.
4. Optical illusion.
i. Optical illusion occurs when the brain cannot interpret
impulses received properly.
5. Blind spot
i. The blind spot is a spot on the retina of the eye that cannot
detect light stimulus.
ii. The image of the object formed at the blind spot cannot be
seen by the eye because there are no light-sensitive cells
(photoreceptors) at the blind spot.
MONOCULAR AND STEREOSCOPIC VISION
1. The stereoscopic vision is vision using both eyes.
2. The overlapping area of the vision of both the left and right eyes is
called stereoscopic field
3. Advantages of stereoscopic vision.
a. See three-dimensional pictures of objects.
b. Enables more accurate estimation of distance and position.
c. Animal predators normally have stereoscopic vision so better
estimate the distance when getting to pounce on their prey.
4. Monocular vision is a vision using only one eye.
5. The advantage of monocular vision is having a wide vision field.
6. Its disadvantage is that it cannot estimate distance accurately.
7. Animal preys use monocular vision to detect predators coming from all
direction.
DEVICES TO OVERCOME LIMITATIONS
Microscope :To see minute objects such as microorganisms and bacteria.
Telescope :To see far-off objects such as stars and planets.
Binocular : To see tiny distant objects such as birds in the sky.
Magnifying: To magnify tiny objects to become glass larger than original.
PT4; limitations, stereophonic, reflection and absorbption
Monday, September 29, 2014 ? 0 Atashinchi ?
LIMITATION 1. We cannot hear all the sounds around us.
2. The range of frequencies of hearing in man is 20 Hz until 20 000 Hz.
3. Different people have different limitations of hearing.
4. For example, old people generally cannot hear as well as young people.
5. Our ear drum become less sensitive to sound as we grow older.
6. To overcome the limitations of hearing, we use
i. the stethoscope – enables doctor to detect the soft heartbeats of patients.
ii. hearing aids – collects sound signals before being sent to the middle ear.
iii. amplifier – boosts weak sound signals.
STEREOPHONIC HEARING
1. Stereophonic hearing is hearing using both ears.
2. The advantages of stereophonic hearing:
i. enables the direction of the source of hearing to be detected more accurately.
ii. This is because the ear nearer the source of sound receives sound louder and earlier than the other ear.
iii. Animals that have stereophonic sound can detect the presence of preys and predators more quickly.
Properties of sound
1. The transfer of sound requires a medium.2. sound can transferred through;
b. solids
c. liquids
d. gases
e. cannot be transferred through in vacuum.
3. Sound can be transferred fastest in solids and slowest in gases.
4. This is because the particles in solids and liquids are closer each other compared to the molecules in gases.
5. Vacuum is space that does not have any particles.
REFLECTION AND ABSORPTION OF SOUND
1. Sound can be reflected or absorbed by the surface of an object.
2. The sound reflected repeatedly from one surface is known as echo.
3. Surfaces that are smooth, even and hard are good sound reflectors and produce loud echo.
For examples, concrete, plank, metal and mirror
4. Surfaces that are rough, hollow and soft are good sound absorbers and produce weak echo.
For examples cloth, sponge, cork, rubber, carpet and cushion
THE WORLD THROUGH OUR SENSES PT4
? 0 Atashinchi ?
1. The ear is the sense organ that is sensitive to sound stimuli producedby vibrating object.
2. A human ear has three main part.
i. the outer ear, filled with air.
ii. The middle ear, filled with air.
iii. The inner ear, filled with liquid
OUTER EAR
(Pinna)
collects and directs sound waves into the ear canal.
(ear canal / auditory)
canal transmits sound waves to the eardrum.
(Eardrum)
vibrates and transmits sound waves to the ossicles.
MIDDLE EAR
(Ossicles)
intensify the vibrations of the sound waves by 22 times before transmitting to the oval
window.
(Eustachian tube)
balances the air pressure at both side of the
eardrum.
(Oval window) transmits sound vibrations from the middle
ear to the inner ear.
INNER EAR
(Cochlea)
transforms sound vibrations into impulses.
(Semicircular canals)
balance the body position.
(auditory nerves)
send messages to the brain which interprets the messages as sound.
THE WORLD THROUGH OUR SENSES PT3
? 0 Atashinchi ?
1. The tongue is the sensory organ for taste.2. The surface of the tongue has groups of cells known as taste buds
which are sensitive to taste.
3. There are four types of taste buds on the tongue sensitive to sweet ,
bitter, sour and salty.
4. The tongue detects taste in the following way:
Dissolved substance → taste receptors → message →brain → type of
taste
5. The sense of smell helps the sense of taste .This explains why food
dose not taste appetizing when we have a cold or flu because we
cannot smell effectively
THE WORLD THROUGH OUR SENSES PT2
? 0 Atashinchi ?
The nose is sensory organ for smell.2. Cells sensitive to smell (smell receptors) are found on the top of the
nasal cavity.
3. When we have a cold or flu, a lot of mucus is produce. The smell
receptors are surrounded by this thick layer of mucus and vary little of
chemical vapor gets to the smell receptors. Therefore, the smell
receptors do not get stimulated enough to effectively function as a
sensory organ of smell.
4. The sensitivity of the nose towards stimuli is influenced by the
following factors:
i. The strength of the smell. A stronger smell will be detected by the
nose easily compared with a weaker smell.
ii. The presence of mucus in the nose. A lot of mucus will reduce the
sensitivity of the nose.
The inside of the nasal cavity produce mucus
↓
The chemical vapor entering nose during breathing
dissolves in mucus. The dissolve chemicals
stimulates the smell receptor at the top of the nasal
cavity.
↓
The smell receptor then produce impulse which are
sent through the nerves to the brain
↓
The brain interprets / evaluates the smell
THE WORLD THROUGH OUR SENSES PT1
? 0 Atashinchi ?
The sense of touch is the sense that is sensitive towards the touchstimulus provided by specific objects.
2. Organ involve in the detection of touch stimulus is the skin.
3. Structure of human skin:
a) The skin divided into three layer epidermis, dermis, fat layer
(subcutaneous layer @ adipose layer @ fat layer)
b) Receptors are cell in our body that detected stimuli.
c) Our body have different types of receptors. These are:
i. pain receptor
ii. touch receptor
iii. heat receptor
iv. cold receptor
v. pressure receptor
d) The pain receptor is in the epidermis.
e) The touch, heat and cold receptors are in the dermis. The
pressure receptors are in the fat layer.
f) Each type of receptor can detect only one particular stimulus.
g) The part or our body contain receptor are called sensory organs
h) These receptor have nerves attached to them
The part of the body that have thin epidermis and many receptors
sensitive to touch are
a) lips
b) fingertips
c) behind the ears
d) armpit
e) the back of the neck
6. The part of the body that are not so sensitive to touch are the:
a) elbow
b) knee
c) palm of the hand and sole of the foot
d) buttocks/hip
THE WORLD THROUGH OUR SENSES
? 0 Atashinchi ?
1.Humans being have five main sensory organ, which are skin, nose,
tongue, ears and eyes.2. Sense detects stimuli, that is changes in surroundings (around us).
3. Five senses:
i. sight
ii. hearing
iii. touch
iv. taste
v . smell
4. Senses are part of the body called sensory organs.
5. Changes or object that can detect by our senses are called stimuli.
6. The ability of the sensory organs to detect stimuli is called senses.
7. All the sensory organs are complete with sensory receptors, that is the nerve endings that can detect stimuli.
8. Our sensory organs are used to detect stimuli (Singular: stimulus). A
stimulus is anything that causes a reaction in a living organism, e.g.
Pain, heat, sound, chemicals.
9. When a stimulus is detected, receptor cells in the sensory organ will be
triggered and generate impulses.
10. These impulses will be transmitted through the nerve and than to the
brain.
11. The brain will further process and interpret the impulse signals as
specific information than the organism has to respond to.
12. This information is than sent back to the sensory organ through the
nerve to provide responses
