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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

Relationship between stimuli and senses to sensory organs

Sensory organTypes of senseStimulus detectedSkinTouchTouch, pressure, pain, cold and heatNoseSmellChemical substancesTongueTasteChemicalsEarHearing and balanceSoundEyeSightLight

Sense of Touch

The skin is the sensory organ for touchIt 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 Slight pressure is detected by the Touch Receptor.Pain Receptors detect the slightest pain as they lie very close to the surface of the skin.Heat Receptors are sensitive to heat.The cold is detected by Cold Receptors.Pressure Receptors are only sensitive to heavy pressure as they lie deep within the skin.

The Skin

What are the factors that affect the sensitivity of skin?

The thickness of the skin

the number of receptor

Hots..Why blind people use their fingertips to read or determine the value of malaysian ringgit?Why the doctor give injection at the forearm or hip?

Sense of smell

The NoseNose help us to breath and act as sensory organ of smellTwo holes is called nostrilIt open into a hollow space called nasal cavityMucous lining the nasal cavityMucous 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 NoseThe 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.

Chemical substance receptor nerve

brain

The TongueOur tongue is the sensory organ for taste.Different areas of tounge are sensitive to different tastetongue is lined with taste bud which contain taste receptorIt 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 EarThe 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 Pinna Made of cartilage and skin and shaped like a funnel. It collects and directs sounds into the ear canal.

Ear canal A long tube lined with hairs. It directs sounds to the eardrum.

Middle Ear Eardrum A thin membrane that seperates the outer ear from the middle ear. It vibrates and transmits sound waves to the ossicles. Ossicles Made 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 tube A narrow tube that joins the middle ear to the throat that balances the air pressure at both sides of the eardrum. Oval window An oval-shaped, thin membrane between the middle ear and the inner ear. It transmits sound vibrations from the middle ear to the inner ear.

Inner Ear Cochlea Filled 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 nerve It carries the impulses to the brain which then interprets the impulses as sound. Semicircular canals For body balance

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 vibrates.The 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.The auditory canal 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 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 thats 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 SEELight rays travel from the object to the eye.

As the light pass through the eye, they are refracted (bent) by the cornea, aqueous humour, lens and the vitreous humour.

HOW DO WE SEEAn upside down image (picture) is formed on the retina.

The photoreceptors on the retina send nerve impulses along the optic nerve to the brain.

The brain interprets the impulses and allows us to see the object the right way up.

Short sightednessLong sightednessAstigmatism Eye defects

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

Short sightedness (Myopia) Distance vision blurry, near usually OK.Short-sighted focusShort-sighted correctionNormal focus

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

Long-sightedness(Hyperopia) Difficulty seeing clearly and comfortably up close.Long-sightedfocusLong-sightedcorrection

ASTIGMATISM

Astigmatism Irregular curvature of the eye (shaped more like a football than a basketball)

Light in different planes focuses at different pointsAB90180

OPTICAL ILLUSION

Optical illusionThe brain cannot correctly interprete impulse received from the eye

Blind spotA point on the retina that cannot detect any image due to the absence of photo receptors

Stereoscopic vision1. 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.

Monocular visionMonocular vision is a vision using only one eye. The advantage of monocular vision is having a wide vision field.Its disadvantage is that it cannot estimate distance accurately. Animal preys use monocular vision to detect predators coming from all direction.

A stimulus will stimulate receptors in sensory organ to produce electrical messages known as nerve impulses.These impulses are sent along the nerves to the brain.The brain receives the message and interprets it.Depending on the message it decides what to do.The brain sends out nerve impulses to the related effectors.Effectors are parts of the body that carry out responses.

*Everyone is born with two very important lenses the lenses of our eyes. Light enters the eye through a small round opening called the PUPIL. This is the black dot in the middle of your eye. Surrounding the pupil is a circle of muscle known as the IRIS. Colored chemicals in the iris give it various shades of brown, blue, or green. By altering the size of the pupil, the muscles of the iris control the amount of light that passes into the eyeball. Just behind the pupil is the lens. It is flexible like rubber, convex in shape, and small about the size of your little fingernail. Light, falling on the lens, is focused to form an image on a sort of screen at the back of the eye called the RETINA. As you move your eyes from distant to near objects, your lenses are pulled from a thin shape to a fatter one by muscles that are attached to them. In this way, whatever you look at can be brought into focus, even though the distance from the lens to the retina stays the same. *Astigmatism can be corrected by using cylindrical lens