the world through our sense

The World Through Our Senses

SENSORY ORGANS

Sensory Organs

They all contribute to us something special. And that is our senses.

Changes in the surrounding are called stimuli.

Each sensory organ has special structures that are very sensitive to stimuli.

These structures are called receptors.For example, our ears detect stimuli when we

hear something. The way the stimulus travels through our body is described below.

Sensory Organs

Stimulus > Receptors > Nerves > Brain > Nerves >Effectors

Sense of Touch

The skin is the sensory organ for touch

It is the largest organ in the bodyThe skin can detect changes in

temperatures, pain, touch and pressure.

The skin has special receptors to detect each of these stimuli.

The Sense of Touch

1. Slight pressure is detected by the Touch Receptor.

2. Pain Receptors detect the slightest pain as they lie very close to the surface of the skin.

3. Heat Receptors are sensitive to heat.4. The cold is detected by Cold Receptors.5. Pressure Receptors are only sensitive to

heavy pressure as they lie deep within the skin.

The Skin

The Nose

The Nose

Mucous in the nasal cavity lines warms and moistens the air before it enters the lungs.

The roof of the nasal cavity has many receptors and sensory cells to detect smell.

Chemicals released by food, perfume and flowers into the air are known as smells.

The Nose

The chemicals dissolve in the mucous lining and stimulate the sensory cells which in turn, send out nerve impulses to the brain which interpret them as a smell.

The TongueOur tongue is the sensory organ

for taste.

It can detect four basic tastes :• Salty• Sweet• Sour• Bitter

The Tongue

The Tongue

The chemicals of the food dissolve in our saliva as we chew. The dissolved chemicals then stimulate the taste receptors in our taste buds to produce nerve impulses, which are then sent to the brain where they will be identified as tastes.

The TongueOur sense of smell improves our sense of

taste. As we chew, some chemicals from the food dissolve in our saliva and stimulate the taste buds. But there are also some chemicals that move into our nasal passages. These chemicals stimulate the sensory cells in our nose.

Taste

The food is tasteless when you have a cold. Why?

It's because the smell from the food cannot reach the sensory cells in the nose.

This is because the passages in your nose are blocked.

Since you cannot smell it, food seems tasteless.

The Ear The ear is the sensory organ of sound. The sense of hearing is sensitive to

the sound stimuli. The human ear can be divided into

three main parts. These are known as the outer ear, the middle ear and the inner ear.

Every structure of the ear has their own functions and are very important.

The EarOuter Ear

StructureFunction/ExplanationPinnaMade of cartilage and skin and shaped like a funnel. It collects and directs sounds into the ear canal.Ear canalA long tube lined with hairs. It directs sounds to the eardrum.

The EarMiddle Ear

StructureFunction/Explanation

EardrumA thin membrane that seperates the outer ear from the

middle ear. It vibrates and transmits sound waves to the ossicles.

OssiclesMade up of three small bones which is the hammer, the anvil and the stirrup. It intensifies the vibrations of the

sound waves by 22 times before transmitting to the oval window.

Eustachian tubeA narrow tube that joins the middle ear to the throat

that balances the air pressure at both sides of the eardrum.

Oval windowAn oval-shaped, thin membrane between the middle

ear and the inner ear. It transmits sound vibrations from the middle ear to the inner ear.

The Ear Inner Ear

StructureFunction/ExplanationCochleaFilled with liquid and contains the ends of nerve cells. The vibration of the oval window causes this liquid to vibrate. The vibration is detected by the nerve cells and are then changed into impulses.Auditory nerveIt carries the impulses to the brain which then interprets the impulses as sound.Semicircular canalsFor body balance

How Do We Hear1. The pinna collects sound waves and

directs them along the ear canal to the ear drum.

2. When the sound waves hit the eardrum, it vibrates.

3. The ossicles amplify the vibrations about 20 times before transferring them to the oval window.

How DO We Hear?4. Vibrations of the oval window set up

waves which travel through the fluid in the cochlea.

5. Receptors in the cochlea are stimulated to produce nerve impulses.

6. The auditory canal nerve carries the impulses to the brain.

7. The brain interprets the impulses as sounds.

HOW DO We HEARThe pinna collects sound waves and directs

them along the ear canal to the ear drum.When the sound waves hit the eardrum, it

vibratesThe ossicles amplify the vibrations about 20

times before transferring them to the oval window.

Vibrations of the oval window set up waves which travel through the fluid in the cochlea

Receptors in the cochlea are stimulated to produce nerve impulses.

HoW Do We HEArVibrations of the oval window set up waves

which travel through the fluid in the cochlea

Receptors in the cochlea are stimulated to produce nerve impulses

The auditory nerve carries the impulses to the brain

The brain interprets the impulses as sounds.

Facts about SightMost people blink every 2-10 seconds.

Each time you blink, you shut your eyes for 0.3 seconds, which means your eyes are closed at least 30 minutes a day just from blinking.

If you only had one eye, everything would appear two-dimensional. (This does not work just by closing one eye.)

Facts about SightOwls can see a mouse moving over 150

feet away with light no brighter than a candle.

The reason cat's and dog's eyes glow at night is because of silver mirrors in the back of their eyes called the tapetum. This makes it easier for them to see at night.

An ostrich has eyes that are two inches across. Each eye weighs more than the brain.

Sense of SightSclera Protect and maintains the shape of the eyeball.

Choroid Absorbs light and prevents internal reflection of light. Supplies the eye with nutrients and oxygen.

Retina – Detects light and produces nerve impulses. Cones

Detect colours in bright light. Rods detect shades of grey in

Dim light

Sense of SightLensFocuses light onto the retina

Vitreous humourHelps in reflecting light, maintains the shape

of the eyeball.

Suspensory ligamentsHold the lens in its position

Sense of SightCiliary bodyContracts and relaxes to change the

thickness of thelens.ConjunctivaProtects the cornea

Aqueous humourHelps in refracting light, maintains the shape

of theeyeball.

Sense of SightCorneaRefracts light onto the retina

PupilControls the amount of light that’s

enters the eyes.

IrisControls the size of the pupil

Sense of SightYellow spotDetects light or any images that fall on it.

Blind spotIt is the spot where the optic nerve leaves

the eyeball

Optic nerveCarries nerve impulses from the retina to

the brain

HOW DO WE SEE

HOW DO WE SEE

HOW DO WE SEE1. LIGHT RAYS TRAVEL FROM THE

OBJECT TO THE EYE.

2. AS THE LIGHT PASS THROUGH THE EYE, THEY ARE REFRACTED (BENT) BY THE CORNEA, AQUEOUS HUMOUR, LENS AND THE VITREOUS HUMOUR.

HOW DO WE SEE3. AN UPSIDE DOWN IMAGE (PICTURE) IS

FORMED ON THE RETINA.

4. THE PHOTORECEPTORS ON THE RETINA SEND NERVE IMPULSES ALONG THE OPTIC NERVE TO THE BRAIN.

5. THE BRAIN INTERPRETS THE IMPULSES AND ALLOWS US TO SEE THE OBJECT THE RIGHT WAY UP.

Short- sightedness

SHORT SIGHTEDNESSA person can see near objects clearly but cannot focus on distance objects.

Light from distance object is focused in front of the retina, so the image become blur.

This is because the lens is too thick or eyeball too long

Short sightedness can be corrected using concave lens.

Short sightedness (Myopia)• Distance vision blurry, near usually OK.

Short-sighted focus

Short-sighted correction

Normal focus

Long-sightedness

LONG SIGHTEDNESSA long sighted person can see distant objects clearly but cannot focus on near objects.

Light from a near object converges to a point behind the retina, so the image is blur.

This is either because the lens is too thin or the eyeball is too short.

Long sightedness can be corrected using convex lens.

Long-sightedness(Hyperopia)

• Difficulty seeing clearly and comfortably up close.

Long-sightedfocus

Long-sightedcorrection

ASTIGMATISM

Astigmatism• Irregular curvature of the eye (shaped more like a football than a basketball)• Light in different planes focuses at different points

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B90

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